UNITED24 - Make a charitable donation in support of Ukraine!

Weapons of Mass Destruction (WMD)

E.1.0 INTRODUCTION AND METHODOLOGY

This appendix describes the current safety concerns associated with the tank waste and analyzes the potential accidents and associated potential health effects that could occur under the alternatives included in this Tank Waste Remediation System (TWRS) Environmental Impact Statement (EIS).

Current Tank Safety Issues

The 177 underground storage tanks and approximately 60 active and inactive miscellaneous underground storage tanks (MUST) included in the TWRS contain a wide variety of waste that has numerous safety concerns associated within their current condition. The principal safety issues associated with maintaining an adequate margin of safety for tank farm operations include flammable gas, noxious vapor, organic solvent, organic complexant, ferrocyanide, high-heat, criticality, and tank structural integrity. An accelerated safety analysis (ASA) is currently being developed that will more completely define the current hazards, provide a thorough accident analysis, and develop associated operational safety requirements (controls) that, when implemented, will provide an adequate safety margin for tank farm operations. A summary and status of the TWRS Safety Program, including current hazards and accident analysis, safety issues in progress, and the approach for their resolution is found in a document entitled TWRS Safety Basis (Lipke et al. 1995). The text from that document is presented nearly verbatim in the remaining paragraphs of Section E.1.0.

Historically, the Hanford Waste Tank Safety Program focused on resolving specific safety issues that were identified from a variety of sources. These issues include flammable gas, noxious vapor, organic solvent, organic complexant, ferrocyanide, high-heat, criticality, and tank structural integrity. The approach to evaluating waste tank safety concerns included developing a safety basis by applying safety analysis methodology. The TWRS ASA will provide the necessary documentation to define the safety margin for conducting safe tank farm operations.

The results from the ASA will demonstrate that the waste tanks can be safely managed with the appropriate controls as specified in the Interim Operational Safety Requirements (IOSRs). Continued characterization by sampling of the waste will be used to 1) further confirm the models of waste behavior used in the safety analysis; 2) reduce the uncertainty associated with the calculations; and 3) confirm the conservatism of the source-term data used in the analysis. This additional characterization information will provide the basis for confirming, reducing, or eliminating controls presently in place through the IOSRs.

Safety Issues

Several tank farm safety issues have been previously identified and progress has been made to resolve and close these safety issues with the appropriate documentation and/or controls. The major safety issues are related to the potential for flammable-gas generation, storage, and release, organic solvent combustion reactions, exothermic ferrocyanide-nitrate reactions, deflagration associated with organic complexants, criticality, high-heat generating waste, and tank structural integrity. Identifying and making progress toward resolving of these safety issues helped focus attention on the fact that the original safety basis for the Hanford Site waste tanks was lacking and that specific controls needed to be implemented to ensure that the health and safety of the public, workers, and environment were being adequately protected. Resolution of the remaining safety issues requires gathering information from laboratory energetics and waste degradation studies, assessing of existing sample data, evaluating historical data, and using various waste tank models to predict waste thermal behavior.

Safety Analysis

Developing the safe operating margin for the tanks system required integrating the current evolution of characterization data and understanding the safety issues to conservatively develop the safety basis for continued waste storage. An Interim Safety Basis (ISB) document was issued in November 1993 to establish the authorization basis for the tank farm facilities as part of implementing the U.S. Department of Energy (DOE) Order 5480.23, Nuclear Safety Analysis Reports. The ISB provided the basis for interim operations and controls until an upgraded Safety Analysis Report (SAR) for the tank farm facilities is completed.

Because of the importance of the safety issues associated with the Hanford Site waste tanks, a strategy was developed in mid fiscal year (FY) 1993 to accelerate the hazards and accident analyses for the waste tanks. Developing a full SAR that addressed each of the topics specified by the DOE order would follow, based on the completed hazards and accident analyses.

Application of Data to Determine Source-terms - Because of the variability of waste in the waste tanks, conservative assumptions were used to develop an upper bound for safe operations. Radiological and toxicological source-terms were developed from a combination of theoretical models, recent characterization sampling, and historical sample data. Existing data were evaluated from all sources to determine representative and bounding source-term concentrations for radioactive isotopes and hazardous chemical species. Data from further waste characterization efforts will result in reducing the conservatism in the source-terms used in the ASA analysis.

Development of Safety Envelope - The safety analysis as documented in a SAR for a nuclear facility is intended to define an operating margin or envelope including necessary controls to ensure that the facility can be operated, maintained, shut down, and decommissioned safely in compliance with applicable laws and regulations. The ASA documents the hazards and accident analysis information that will be used in the upgraded Hanford Site tank farm SAR. The ASA systematically identifies facility hazards, selects accident scenarios, and evaluates credible accident scenarios analyzed for potential consequences. When the ASA is approved, the results of the hazards and accident analyses, in combination with the IOSRs, will define the facility's safety envelope. Selecting safety class equipment and performing unreviewed safety question (USQ) determinations will be based on this safety envelope. Results presented in the ASA indicate that the tank farms can be safely maintained within acceptable bounds using appropriate design features and controls.

The hazards analysis validated that the selection of accidents analyzed in the ASA was an appropriate spectrum of bounding and representation events, which are known as evaluation basis accidents (EBAs). The hazard evaluation process also provides a thorough qualitative evaluation of the spectrum of potential accidents involving identified hazards.

The hazards analysis considered a comprehensive range of potential process-related hazards as well as those hazards associated with internal and external events for all 177 waste tanks. The hazards analysis forms the basis for understanding facility worker protection, environmental protection, selecting or confirming potential EBAs to be further developed and quantified, and determining the facility hazard classification.

The analysis results of the selected EBAs provided the basis for developing controls needed for protecting the public and co-located workers. The unmitigated consequences and associated likelihood of the EBAs were compared to the Hanford Site management and operating contractor's risk acceptance guidelines. If the unmitigated consequences and likelihoods exceeded the risk acceptance guidelines, appropriate design features, safety systems, structures and components (SSCs), or administrative controls were identified to reduce the consequence or frequency of the accidents to acceptable levels.

Each EBA was described in the following order:

  • Accident scenario;
  • Accident frequency;
  • Radiological source-term and unmitigated consequences;
  • Toxicological source-term and unmitigated consequences;
  • Mitigated or prevented radiological consequences;
  • Mitigated or prevented toxicological consequences; and
  • SSCs, design features, or controls required to meet risk acceptance guidelines.

Table E.1.0.1 provides a list of the EBAs that were analyzed in the ASA and for which radiological and toxicological consequences were determined.

Table E.1.0.1 List of Evaluation Basis Accidents Analyzed in Accelerated Safety Analysis

A primary purpose of the accident analysis is to identify whether SSCs, design features, or controls are required for preventing or mitigating postulated accidents. By including this information in the evaluation basis accidents documentation, safety functions that required consideration for the IOSRs were easily identified. The IOSRs included the definition of acceptable conditions, safe boundaries, basis thereof, and management or administrative controls required to ensure safe operation of the tank farms.

Operational Controls

The accident analysis of the ASA calculated the consequences for unmitigated accidents and identified a range for the accident sequence event frequencies. For each accident sequence, if the consequence and frequency were outside of the risk acceptance guidelines, additional physical and/or administrative controls were established that would either prevent the postulated accident or reduce the calculated consequences or likelihood of the accident. The controls will be incorporated into the IOSRs (technical safety requirements when the SAR is completed) for the facility.

An example of the controls are those used for tanks containing flammable gases. The unmitigated consequences and associated likelihood of a flammable gas deflagration with a tank dome collapse were above the risk acceptance guidelines. Therefore, controls were developed to prevent a gas deflagration. The controls specifically addressed flammable gases accumulating within the tank vapor space, monitoring vapor space flammability concentrations, limiting or preventing ignition sources, and minimizing intrusive activities to reduce hazard exposure.

Safety Relationship with Characterization

The objective of safe waste storage and disposal requires that the waste tank characterization strategy be structured to provide priority support to addressing tank farm safety issues in the most efficient manner.

The Safety Program and characterization approach for resolving priority safety issues related to flammable gas, noxious vapor, organic solvent, organic complexant, ferrocyanide, high-heat generating waste, criticality, and tank structural integrity has been influenced by the progress made to date. The progress includes 1) completing safety analyses for flammable gas, ferrocyanide, criticality, organic solvent (tank 241-C-103), and sludge dry out; 2) successfully mitigating tank 241-SY-101 safety issues; 3) demonstrating actual and simulated waste energetics; 4) demonstrating waste degradation (aging resulting in lower energy products) in laboratory experiments and limited waste sampling for ferrocyanide and organics; 5) completing laboratory tests to define conditions required for condensed phase propagating reactions, and 6) developing an increased understanding of safety-related information that can be obtained from tank headspace sampling.

Safety Issues

The characterization approach for the safety issues continues to evolve as the parameters affecting safe storage and their relationship are better understood. In general, characterization demands are lessened as safety issues become better understood. This section reviews the current safety issues to ensure safe storage and examines the direction of future efforts.

The high-level waste (HLW) tank subcriticality safety assessment concluded that the waste in the Hanford Site waste tanks is in a form that is favorable to maintaining a large margin of subcriticality because of the small quantities of fissile material and the large amounts of neutron-absorbing materials.

The Characterization Program will continue to provide appropriate confirmatory sample data (e.g., fissile material, absorber content, and alkalinity information) as waste samples are obtained for other reasons.

High-heat tanks have been identified through temperature monitoring coupled with thermal analyses. However, only one tank, tank 241-C-106, has demonstrated any substantial high-heat load. This tank is scheduled for retrieval in late 1996. In the meantime, a chiller is being procured for this tank to mitigate potential risk that may be associated with leaks that might result from accelerated corrosion because of the increased temperature.

Waste tank structural integrity evaluations are being completed for all waste tanks. Structural and seismic evaluations are being completed, and the tank life expectancy is being determined for each tank.

Flammable Gases. Flammable gas species (mainly hydrogen and ammonia) are produced at low rates by radiochemical and thermochemical degradation reactions in waste. Vapor from organic solvents may also contribute to headspace flammability. While a mixture of gases may contain flammable constituents, a flammability hazard exists only if a minimum flammability concentration can be retained within the tank headspace (i.e., enough to exceed the minimum fuel concentration known as the lower flammability limit [LFL]). Otherwise, the gases will be dissipated to the atmosphere at concentrations too low to represent a flammability hazard.

For a flammable gas to ignite and burn, it must be mixed with an oxidizer (usually oxygen) and be provided sufficient energy to initiate the chemical reactions. A sufficiently dilute mixture of flammable gas (i.e., a concentration below the LFL) and oxidizer will not burn. The National Fire Protection Association recommends that processes be controlled so that flammable gas concentrations are less than 25 percent of the LFL. DOE requires that Hanford Site waste tanks be operated within National Fire Protection Association guidelines; therefore, management efforts must ensure that flammable gas levels are maintained below 25 percent of the LFL.

The flammable gas hazard can be classified according to the mode by which the flammable gases are released from the waste. For a steady-state gas release, gases are released at approximately the rate at which they are formed, and the concern is an accumulation of flammable gases in the tank headspace (i.e., a steady-state flammability hazard). For a limited number of tanks, gases are released episodically at comparatively high rates. For these episodic releases, flammable gas concentrations could and have exceeded 25 percent of the LFL for brief time periods. The LFL has been exceeded several times by tank 241-SY-101 (more than 100 percent of the LFL has been attained on occasion) and at least once by tank 241-AN-105. Forty-seven Hanford Site waste tanks are on a flammable gas Watchlist because the waste in these tanks is believed to have the potential to retain hydrogen gas until appreciable quantities are released. Monitors have been installed on these tanks and access controls have been imposed to minimize the potential hazard.

Steady-State Release of Flammable Gases. All double-shell tanks (DSTs) are actively ventilated, and air exchange is rapid enough (except during an episodic release) to keep steady-state bulk hydrogen concentrations in the headspace well below 25 percent of the LFL. However, most single-shell tanks (SSTs) are passively ventilated and only exchange air with the environment by relatively slow barometric pressure changes and instrument air purges. Therefore, potential accumulation of flammable gases in the headspace and risers of all SSTs has been explored.

Preliminary studies have examined the accumulation of flammable gases in the headspace and risers of SSTs that are not on the flammable gas Watchlist. A more detailed study on flammable gas accumulation is currently being developed. However, calculations performed thus far show that gas production and release rates from thermochemical and radiochemical processes are modest and that passive ventilation alone will keep the headspace well below 25 percent of the LFL. The contribution to the flammable gas mixture from organic solvent vapor is low because the bulk of organic solvent remaining in any tank would likely have a low vapor pressure. Sampling data from tank 241-C-103, which contains a floating organic layer, support this conclusion. Vapors from the organic solvent amount to less than 5 percent of the LFL.

Episodic Release of Flammable Gases. The ability of waste to retain large amounts of gas depends on its physical properties and chemical/radiological composition. The waste retains gases that increase the waste volume (slurry growth) until the gases escape. Slurry gas is only present in tank headspace at high concentrations when it is released by the waste; therefore, the most direct way to characterize gas may be to sample the waste directly.

The amount of gas retained in the waste will be estimated from analyzing the tank operational data. Tank monitoring data include changes in surface level (resulting from gas release events and changes in atmospheric pressure) and axial waste temperature profiles. New, more accurate level gages and instrument trees (that measure temperature) are being installed in Hanford Site waste tanks. In addition, standard hydrogen monitoring systems (SHMS) are also being installed on all flammable gas Watchlist tanks.

Near-Term Characterization of Flammable Gas. Sampling and/or continuous monitoring is being used to confirm that flammable gas does not accumulate in the SSTs. Headspace sampling results from 30 SSTs (none of which are on the flammable gas Watchlist) indicate that flammability in the headspace and risers is well below 25 percent of the LFL. Headspace sampling of passively ventilated SSTs for flammable gases will continue until all are sampled. None of these tanks are expected to contain steady-state flammable gas concentrations above 25 percent of the LFL. However, if concentrations greater than 25 percent of the LFL are measured for non-Watchlist tanks, then these tanks would become candidates for continuous gas monitoring and potential mitigation.

The headspace of tanks that are suspected of having waste that releases flammable gases episodically will be continuously monitored for flammable gases. SHMS have been designed, built, and installed on all flammable gas Watchlist tanks. SHMS contain instrumentation that support an online hydrogen detector and a gas grab sampler.

Future Characterization of Flammable Gases. Two techniques that are being developed to directly characterize waste for retained gas are 1) a void meter to measure the volume fraction of the gas phase in the waste, and 2) a retained gas sampling system to extract a waste sample from a tank so that the waste can be analyzed (gas can exist as a distinct phase in the waste, and it can also be absorbed on solid or dissolved in aqueous liquid phases). In the near future ammonia monitoring capability will be added to the SHMS. Another system is being developed for in situ measurement of physical properties (density, viscosity, shear strength) that are critical to evaluating stored gas. Development of these systems is underway.

Noxious Vapors

Several health and safety issues are related to noxious vapors that may be present in some of the HLW tanks at the Hanford Site. A tank-by-tank sampling approach is being pursued to resolve headspace issues dealing with flammability and noxious vapors. Vapor sampling will be conducted on all tanks in the Tank Farm Complex.

Modeling and vapor data from tank 241-C-103 indicate that the tank head space is well mixed except during an episodic gas release. To verify that the headspace is well mixed, additional headspace sampling at different vertical and horizontal locations will be conducted in selected tanks.

If any compounds are detected inside a tank dome with toxicological properties that exceed their respective trigger points, Westinghouse Hanford Company (WHC) Industrial Hygiene is advised that gases with toxicological concern are present in the tank headspace. The trigger point has been defined as 50 percent of the appropriate Consensus Exposure Standard (CES) concentration for all analyses of interest. A CES, which is generally defined as the most stringent of known regulatory or recommended toxicological values for the occupational setting, includes the threshold limit value, permissible exposure limit, recommended exposure limit, and biological exposure limit.

The data required to assess toxicity include 1) identifying chemical compounds in the tank headspace of concern for worker health and safety or toxicological importance; 2) estimating the concentrations of these toxicologically substantial compounds in the headspace; and 3) understanding the toxicological effects of these compounds and the CES for each constituent of concern.

Organic Solvents

Various separation processes involving organic solvents have been used at the Hanford Site. These organic solvents were inadvertently and/or purposely sent to the underground storage tanks, and subsequent waste transfer operations distributed organic solvents among several of the 177 HLW tanks. The potential hazards associated with organic solvent are 1) contributing to headspace flammability (as discussed previously); 2) igniting an organic solvent pool; and 3) igniting an organic solvent that is entrained in waste solids.

Currently, one tank (241-C-103) is known to contain an organic solvent pool. Additional tanks that may contain an organic solvent pool will be identified through continued vapor sampling of the tank headspace. Analyses have shown that solvent pool fires are difficult to initiate. Waste that may contain entrained organic solvent will also be identified through vapor sampling of the tank headspace. These analyses have been integrated into the noxious vapor sampling campaign. If vapor sampling suggests the presence of organic solvent, liquid grab samples and/or near-surface samples will be obtained to better quantify the potential for an organic solvent fire.

Fuel-Nitrate (Condensed-Phase) Reactions

Organic complexants and ferrocyanide were sent to the tanks. These compounds have the potential to act as a fuel when combined with an oxidizer. Nitrate salts have also precipitated in the tanks and are potential oxidizer sources. For the organic complexant (nonvolatile materials) and ferrocyanide safety issues, the approach to safety characterization is based on the fact that propagating reactions cannot occur if either the fuel, oxidizer, or potential initiators (e.g., temperature or energy) are controlled. Because specific limits of fuel, oxidizer, and initiators must be satisfied for a propagating chemical reaction to occur, waste can be stored safely if the conditions for the reaction are not possible. Therefore, the approach for obtaining characterization information is to obtain data that would confirm that one of the conditions of fuel or oxidizer is not present in sufficient quantities or that initiators are absent or can be controlled.

An important parameter in controlling propagating reactions is an inhibitor such as moisture. In sufficient quantity, moisture will prevent propagating reactions by 1) behaving as an inert diluent (lowering the effective fuel concentration); 2) preventing initiation of a propagating reaction (the energy from most credible initiators would be absorbed by the sensible and latent heat of the moisture before the waste reached the critical initiation temperature); and 3) providing a large heat sink that inhibits propagation (for a reaction to propagate, enough energy must be supplied to overcome the sensible and latent heat of the moisture present).

Fuel and Moisture Criteria - Experiments have shown that moisture can prevent condensed-phase propagating reactions. Tube propagation tests on waste simulants have shown that propagating reactions cannot occur in waste simulants containing more than 20 weight percent moisture. Sufficient moisture content can ensure that a propagating reaction will not occur, regardless of the fuel-oxidizer concentration. For example, if adequate moisture can be confirmed through monitoring, analysis, or sampling, then it can be concluded that condensed-phase exothermic reactions will not occur, thus ensuring interim safety waste storage.

The minimum required fuel concentration has been determined using a contact temperature ignition model. A necessary (but not sufficient) condition for a condensed-phased propagating chemical reaction is that the fuel concentration be greater than 4.5 weight percent total organic carbon (TOC), based on sodium acetate as fuel, or 1,200 joule/gram (J/g) on an energy equivalent basis. For fuel concentrations between 1,200 and 2,100 J/g, the waste moisture content required to prevent a propagating reaction varies linearly from 0 to 20 weight percent. Above 20 weight percent moisture, the fuel-moisture linear relationship no longer holds because the mixture become a continuous liquid phase, effectively preventing propagating reactions. Note that the TOC criteria depends on the chemical concentration of the waste. Table E.1.0.2 summarizes the criteria for safe storage.

Table E.1.0.2 Safe Storage Criteria

Parameters Affecting Fuel Concentration - Waste tank operations have affected fuel concentration in the tanks. Experiments on waste simulants have shown that the high-energy organic complexants (i.e., the organic salts that could support a propagating reaction) are highly soluble in the tank supernatant solutions. Subsequent pumping of the tank liquid might have removed most of the organic complexant fuels.

Ferrocyanide waste stored in Hanford Site tanks has been exposed to caustic solutions and radiation for nearly 40 years. Long-term degradation (aging) of ferrocyanide is known to have occurred through chemical and radiolytic processes in the waste. Analyses of core samples taken from six of the 18 ferrocyanide tanks reveal fuel values about an order of magnitude less than the original flowsheet concentrations. These remaining fuel values are well below the concentration of concern. Experimental work at Georgia Tech and Pacific Northwest National Laboratory (PNL) has demonstrated that complexants and other organics degrade under radiation and/or chemical oxidation conditions found in tanks. In addition, analysis of the original tank 241-SY-101 core sample complexant waste demonstrated extensive chemical degradation products.

Near-Term Characterization of the Condensed Phase - Current characterization efforts are focused on testing tank waste samples to confirm that the criteria shown in Table E.1.0.2 are conservative for actual waste. That is, if the waste meets the energy (fuel value), TOC, or moisture criterion, then the waste will not support a propagating reaction. Waste from selected tanks will be tested for reaction propagation in the same type of adiabatic calorimeter (the reactive system screening tool) that was used to develop the criteria.

Near-term sampling efforts are also focused on confirming degradation of ferrocyanide and organic complexant waste. Full-depth core samples from ferrocyanide tanks will be analyzed for fuel, nickel (a signature analyte of the sodium nickel ferrocyanide scavenging campaign), and total cyanide to confirm ferrocyanide aging. Full-depth core samples for organic complexant tanks will be analyzed for organic species to confirm that organic complexants have degraded to less energetic species.

In addition, liquid and solid samples from organic complexant tanks will be analyzed to confirm the laboratory demonstration that high-energy organic complexants are soluble.

Reaction Ignition

Credible Ignition Sources - If the waste has a sufficiently high fuel and low moisture content, a propagating reaction could be initiated if an energy source raised the temperature of the waste to the reaction initiation temperature. The potential for tank farm equipment and operations to initiate propagating reactions has been evaluated and is summarized in Table E.1.0.3. In this evaluation, all credible initiators would be located near the waste surface, with the exception of rotary-core drilling incidents and lightning.

Table E.1.0.3 Summary of Operation Evaluation

Although rotary-core drilling incidents and lightning strikes cannot be deemed incredible initiating events, the risk can be mitigated with controls. The rotary-core driller is designed with safety interlocks that limit increases in drill bit temperature. Ignition from lightning strikes can be prevented by appropriate grounding. The need to further ground the SSTs is being studied because of their unique construction.

The TWRS Safety Program is currently establishing the requirements for analytical data to confirm the models used in the safety analysis and the conservatism of the source-term. This additional characterization information will provide the basis for conforming, adjusting, or eliminating controls at Hanford Site waste tanks to ensure adequate protection of the workers, public, and the environment.

Criticality

Based on new information available to DOE, regarding nuclear criticality safety concerns during retrieval, transfer, and storage actions since the issuance of the Final Safe Interim Storage EIS, DOE has decided to defer a decision on the construction and operation of a retrieval system in tank 241-SY-102. Through an ongoing safety evaluation process, DOE recently revisited its operational assumptions regarding the potential for the occurrence of a nuclear criticality event during waste storage and transfers. Changes to the Tank Farm Authorization Basis for Criticality that were approved in September 1995 were rescinded by DOE in October 1995, pending the outcome of a criticality safety evaluation process outlined for the Defense Nuclear Facility Safety Board on November 8, 1995. Until these criticality safety evaluations are completed, the Hanford Site will operate under the historic limits, which maintain reasonable insurance of subcritical conditions during tank farm storage and transfer operations. Of the actions evaluated in the Final Safe Interim Storage EIS, only the retrieval of solids from tank 241-SY-102 was affected by the technical uncertainties regarding criticality. Based on the quantities of plutonium in tank 241-SY-102 sludge, retrieval of the solids falls within the scope of the criticality safety issues that will be evaluated over the next few months. As a result, a decision on retrieval of solids from tank 241-SY-102 was deferred in the Safe Interim Storage EIS Record of Decision. Also, pending the outcome of the technical initiative to resolve the tank waste criticality safety issue, transfers of waste (primarily saltwell liquid) through tank 241-SY-102 will be limited to noncomplexed waste. Tank 241-SY-101 mixer pump operations, interim operations of the existing cross-site transfer system, operation of the replacement cross-site transfer system, saltwell liquid retrievals, and 200 West Area facility waste generation all would occur within the applicable criticality limits and would be subcritical.

The remainder of this document analyzes potential accidents and the related consequences that could occur from implementing the alternatives addressed in this EIS.

Risk from Remediation Accidents

Accidents are unplanned events or a sequence of events that cause undesirable consequences. The risk associated with an accident is defined as the product of the probability of an accident occurring and the consequences of the accident. This includes nonradiological injuries, illnesses, and fatalities from construction, operations, or transportation accidents. Risk is also defined as the probability or the number of latent cancer fatalities (LCFs) from radiological or toxicological releases, given the occurrence and consequences of an accident. This analysis considers both types of risk.

An analysis was performed to determine the nonradiological and nontoxicological risks from construction, operations, and transportation. These are called occupational risks and include personal injuries, illnesses, and fatalities common to the work place such as falls, cuts, and operator-machine impacts.

An analysis was also performed to determine the potential for radiological and toxicological impacts. The results of the analyses are summarized in the following subsections. More detailed information concerning the methodology, supporting data, and assumptions for the basis of the analysis is contained in this appendix.

The alternatives, as described in Volume Two, Appendix B, include the following:

Tank Waste

  • No Action alternative
  • Long-Term Management alternative
  • In Situ Fill and Cap alternative
  • In Situ Vitrification alternative
  • Ex Situ Intermediate Separations alternative
  • Ex Situ No Separations alternative
  • Ex Situ Extensive Separations alternative
  • Ex Situ/In Situ Combination 1 and 2 alternatives
  • Phased Implementation

Cesium (Cs) and Strontium (Sr) Capsules

  • No Action alternative
  • Onsite Disposal alternative
  • Overpack and Ship alternative
  • Vitrify with Tank Waste alternative

E.1.1 RADIOLOGICAL LATENT CANCER FATALITY RISK AND CHEMICAL EXPOSURE

The methodology used to identify and quantify the radiological cancer risks, chemical exposures, occupational injuries, illnesses and fatalities, and transportation risks from postulated accidents are discussed in this section. The radiological LCF risk and chemical exposure to humans from accidents was performed using the following steps:

  • Identify the spectrum of potential accidents associated with each alternative (Section E.1.1.1, Accident Identification);
  • Select the dominant (highest potential risk) accidents for risk analysis (Section E.1.1.2, Accident Scenario Selection);
  • Determine the radiological and chemical inventories potentially released in the accidents (Section E.1.1.3, Source-term and Direct Exposure);
  • Calculate the probability of occurrence of the potential accident (Section E.1.1.4, Probabilities);
  • Determine the location of the worker, noninvolved worker, and general public (receptors) relative to the point of release of the waste material (Section E.1.1.5, Receptor Locations);
  • Determine the radiological dose and chemical exposure to the worker, noninvolved worker, and general public at the location of the receptor (Section E.1.1.6, Radiological Dose and Chemical Exposure Assessment); and
  • Calculate the LCF risk and compare the chemical exposure to concentration limits (Section E.1.1.7, Risk Development).

The following subsections discuss these steps in detail.

E.1.1.1 Accident Identification

A hazard is an inherent physical or chemical characteristic that has the potential for causing harm. The potential release of high-level radioactive waste to the environment from the tank farms and processing facilities that are included in the various alternatives is of concern to DOE, Hanford Site workers, and the public. Initiating events that could result in such a release include natural phenomena, human error, component failure, and spontaneous reactions.

Accidents are unplanned events or a sequence of events that result in undesirable consequences. The first step in the analysis was to identify the spectrum of potential accidents associated with construction, transportation, and operation activities involved in each TWRS EIS alternative. Construction activities include potential occupational accidents. Transportation activities include potential radiological, toxicological, and occupational accidents. Operation activities include potential radiological, toxicological, and occupational accidents.

The compilation of potential accident scenarios for tank farms, waste transfer facilities, pretreatment facilities, and processing facilities for each alternative is contained in the accident data package (Shire et al. 1995). This accident data package was prepared specifically to support the TWRS EIS. The spectrum of potential accidents identified in the data package are summarized in Table E.1.1.1.

Table E.1.1.1 Summary of Potential Tank Waste Accidents

Each alternative was divided into six components as applicable: continued operations (C), retrieval (R), pretreatment (separations of HLW from low-activity waste [LAW]) (P), treatment or immobilization (I), transportation (T), and disposal (D). A determination was then made whether each potential accident could occur during each component for each alternative. Not all alternatives involve every component. For example, there is no treatment component for the No Action tank waste alternative. In addition, not every potential accident can occur in a particular component for every alternative. For instance a dropped canister filled with vitrified HLW could only happen during treatment in the Ex Situ Vitrification alternatives. In Table E.1.1.1, an "x" indicates that the accident is applicable to the component for the identified alternative.

Each potential accident in Table E.1.1.1 is coded with a multi-digit number corresponding to the subsection in which it was found in the accident data package (Shire et al. 1995 and Jacobs 1996). A more detailed description of these accidents is provided in the referenced sections in the data package.

E.1.1.2 Accident Scenario Selection

After the potential accidents were identified, accidents with highest risks for each general waste-handling activity were screened and analyzed in further detail.

Screening for the highest risk accidents involved listing all the potential accidents from Table E.1.1.1 on an accident screening table. Table E.1.1.2 is an example of a screening table. The table identifies the broad range of potential accidents and assigns calculated or estimated risk (frequency of the event times the consequences) of each accident. The potential hazards were grouped according to the mode of operation and subdivided further according to the activity within this mode. The risk shown in the last column is the product of the annual frequency of the event happening and the severity(consequences) of the accident. The values used in the annual frequency and severity columns are qualitative as defined in Tables E.1.1.3 and E.1.1.4. For the frequency of the event, factor values of 4 (anticipated); 3 (unlikely); 2 (extremely unlikely); and 1 (beyond design basis) were assigned. For the severity of the events, factor values of 4 (high); 3 (moderate); 2 (low); and 1 (no) were assigned. The factor values used for the frequency of the event and the severity of the event are numbers used only for the purpose of screening. Where the risk values for more than one event in the same category are the same, the rationale for choosing the scenario to be evaluated was based on the accident with the highest severity. It should be noted that accident scenarios with the worst radiological consequences would also result in the worst chemical exposures.

Table E.1.1.2 Example Accident Screening Table

Table E.1.1.3 Frequency Category Definition

Table E.1.1.4 Qualitative Accident Severity Levels

Beyond design basis accidents were also analyzed for each alternative. For this analysis, beyond design basis accidents are accidents with a frequency range of 1.0E-06 to 1.0E-07 per year (design basis accidents are greater than 1.0E-06 per year) for operator external accidents or below the Site-specific designated return frequency for natural events. This does not mean that the facilities have been designed to this accident frequency range. Accidents with frequencies less than 1.0E-07 (less than one in10million) per year were not examined because of their extremely low probability of occurrence.

When an alternative has been selected for remediation of the Hanford tank waste, if accidents associated with the alternative exceed the acceptable limits of risk, mitigation measures may be required to reduce the level of risk.

The types of accidents selected for evaluation in the TWRS EIS are consistent with the types of accidents currently being developed for the TWRS Final Safety Analysis Report (FSAR). The FSAR is comprehensive and detailed evaluation of the potential accidents that could occur within TWRS and will be used to establish safe operating methods. The preliminary FSAR is scheduled to be issued in the fall of 1996. Because the accident analyses for the FSAR are at different stages of development and review, they are subject to change at this time. The three worst-case scenarios being developed in the TWRS FSAR that were evaluated as bounding design basis accidents in the TWRS EIS are:

  • Spray leak in a valve pit during waste transfer;
  • Flammable gas deflagration in a waste storage tank; and
  • Organic nitrate fire in a waste storage tank.

The spray leak in a valve pit was identified in the screening analysis as the accident with the highest risk during waste tank transfer for the continued operations component.

The flammable gas deflagration in a waste storage tank was identified as having a higher risk than an organic nitrate fire in a storage waste tank during continued operations; therefore, the flammable gas deflagration was selected for further evaluation to determine the radiological and toxicological risks.

The beyond design basis accident evaluated in the TWRS EIS is a seismic event resulting in the collapse of a SST dome. The TWRS FSAR is currently developing a beyond design basis earthquake scenario that would result in tank failure.

The consequences presented in the Final EIS are based on National Environmental Policies Act (NEPA) guidance that calls for an integrated risk assessment based on a "reasonably foreseeable" accidents that could occur over the lifetime of the operation. The consequences presented in the FSAR result from worst-case scenarios based on extreme parameters. The worst-case scenarios are used to determine the hazard classification and the safety classification and are not considered to be "reasonably foreseeable" scenarios and therefore inappropriate for an EIS. To develop an integrated risk for the EIS based on the worst-case scenarios would result in unrealistic and undefendable risk values.

E.1.1.3 Source-term and Direct Exposure

For this analysis the source-term is the respirable fraction of inventory from which the receptor dose is calculated. It is based on the inventory that could potentially be released to the environment from an accident, referred to as material at risk (MAR), multiplied by the applicable reduction factors listed in the following text. Use of the reduction factors is dependent on the nature of the accident (i.e., energy of accident at impact, waste form, and effectiveness of mitigating barriers such as high-efficiency particulate air [HEPA] filter).

Damage ratio (DR) - The fraction of the MAR impacted by the event.

Airborne release fraction (ARF) - The fraction of released material made airborne by the event at the point of origin.

Airborne release rate (ARR) - The fractional ARR of material resulting from the accident at the point of origin. ARR is converted to ARF by integrating over the time available for release.

Leak path factor (LPF) - The fraction that escapes the confinement boundary by design, natural causes, or degradation caused by the event.

Respirable fraction (RF) - The fraction of airborne droplets or particulate matter with individual particle aerodynamic equivalent diameter less than or equal to 10 micrometers (m) (3.9 E-04 inches [in.]).

Exposure also may result from direct exposure to radiation. Direct exposure is the direct gamma radiation dose rate to a receptor.

It should be noted that the ingestion and groundshine pathways were not included for remediation accidents because of the corrective action that would be taken by DOE to remediate the release from the accident. Corrective actions would be taken that would include 1) restricting access to the impacted area; 2) evacuating offsite populations within the area of impact; and 3) remediating contaminant deposition to levels that ensure protection of human health before access to the area would be allowed.

Under all accident scenarios, most of the deposition would occur near the tank farms and extend at diminishing levels to the Site boundary in the direction of the prevailing wind at the time of the accident. Deposition would also occur at much lower levels offsite, with the highest levels closest to the Site boundary and diminishing levels out to a 80 kilometers (km) (50-mile [mi]) radius of the Site where no depositions at levels that would impact human health or the environment would occur. In addition to the direct impacts to human health resulting from inhalation, if an accident were to occur there would be additional impacts that would potentially occur based on the magnitude of the accident. These impacts could include:

  • Restrictions on access to sites sacred to Tribal Nations impacted by depositions on the Hanford Site during remediation of the depositions;
  • Temporary disturbance to ecological, biological, and cultural resources impacted by depositions and the resulting remediation of the depositions; and
  • Economic impacts associated with the cost of the remediation of depositions and the dislocation of populations within the area of impact.

All of the accident scenarios during remediation have small offsite consequences or the probability of the event is extremely unlikely. Therefore, a detailed analysis of environmental, socioeconomic, and cultural impacts from these accidents, in accordance with NEPA guidance (DOE 1993d), have not been performed. However, a relative comparison among the alternatives of the impacts of these potential accidents is possible based on the human health impacts addressed previously. In most cases, the greater the impact to human health, the greater the environmental, socioeconomic, and cultural impact that would result from the accident.

Post-remediation accidents that take place after the 100-year institutional control period assume no corrective action and include the added risk from groundshine, ingestion, and deposition.

E.1.1.3.1 Inventory

The tank waste inventory for the SSTs, DSTs, and MUSTs is presented in Appendix A, Section A.2.1, Tables A.2.1.1, A.2.1.2, and A.2.1.3 of this EIS. The Cs and Sr capsule inventory at the Waste Encapsulation Storage Facility (WESF) are presented in Table A.2.2.1. However, for developing tank farm accidents, a 100 percent inventory bounding composite was developed. This composite incorporates historical tank contents estimates, the results from prior individual tank analyses, and the results of recent tank characterization programs (Shire et al. 1995 and Jacobs 1996). This composite was developed because engineering information was not sufficiently mature to determine which tanks would have their inventory mixed during retrieval and transfer. This could be thought of as a single tank containing the highest activity concentration for each nuclide found in the sample data. This maximum sample activity composite grouping means the highest radioactivity concentration for each radionuclide is combined to define a hypothetical "highest concentration" inventory used to bound the accidents. For process facility accidents a 90 percent composite was assumed.

A less conservative approach was also used to estimate the inventory of radioactive materials contained in the fuel from the single-pass reactors and N Reactor and sent to the tank farms. Total radionuclide inventories were calculated based on the complete operating history of all of the Hanford Site production reactors. Reduction factors were then applied to the total inventories to account for plutonium (Pu) and uranium (U) extracted from the waste sent to the tanks. Reduction factors also were applied to Cs and Sr, which also were extracted from the waste. The 11 radionuclides that contribute to over 99 percent of the total dose as reported in the supporting document for developing the unit liter doses (ULDs) (WHC 1996c) are shown in Table E.1.1.5 with the total activity of each nuclide.

Table E.1.1.5 Tank Inventory Based On Reactor Products

Because the tank waste inventory has not yet been well characterized, bounding and nominal radiological and toxicological consequences are presented in the analysis to provide a risk range.

E.1.1.4 Probabilities

The probabilities of radiological and toxicological accidents occurring were taken from the accident data package (Shire et al. 1995 and Jacobs 1996). The accident probability data package was prepared specifically to support the TWRS EIS. The accident initiator frequencies were established using currently accepted sources of occurrence frequency such as natural phenomena statistics for the Hanford Site, recent analysis of the initiators, or industry-accepted frequencies.

The probabilities have conservatively not taken into account 1) the frequency of time the wind blows in the direction of the presumed receptor location (the wind is always assumed to blow towards the receptor); 2) the likelihood the receptor would be at the presumed receptor location for the duration of the plume passage; 3) the likelihood that the source-term (composite inventory) would be released. It is assumed that the composite inventory would always be released; and 4) emergency planning and evacuation programs are in place at the Hanford Site to mitigate potential consequences resulting from an accident. In the event of an accident, the Emergency Control Center is responsible for determining the correct plan of action in accordance with the Emergency Management Procedures (WHC 1996a). For example, if the appropriate plan of action is to take cover, individuals are notified by announcements over the public address system to go inside building(s). The ventilation system is turned off to prevent unfiltered air, with contaminants, from entering the buildings. If the appropriate plan of action is to evacuate the Site, an orderly evacuation with designated meeting places is conducted. It has been demonstrated that evacuation can be conducted in less than an hour (Sutton 1996).

Accidents with annual frequencies greater than 1.0E-06 were considered to be within design basis accidents. Beyond design basis accidents have an annual frequency range from 1.0E-06 to 1.0E-07. Accidents with annual frequencies less than 1.0E-07 were not examined.

E.1.1.5 Receptor Locations

The radiological dose to a receptor depends on the location of the receptor relative to the point of release of the radioactive material. Doses for a maximally-exposed individual (MEI) and population dose were computed for each receptor (worker, noninvolved worker, and general public). Workers are those involved in the proposed action and are in the work place performing work at the facility. Noninvolved workers are onsite workers but not involved in the proposed action. The general public are those located off the Hanford Site. The MEI for each of these three receptor categories is a single individual that is assumed to receive the highest exposure in the category. The location of each receptor is discussed in the following text.

Worker Population and Maximally-Exposed Individual Worker - The worker population and MEI worker are those individuals directly involved in implementing the alternatives. They are assumed to be in the center of a 10 m (33.0 foot [ft]) radius hemisphere where the airborne released material has spread instantaneously and uniformly and would expose a typical size crew of 10 people.

Noninvolved Worker Population - The noninvolved worker population was based on the Site employment and was assumed to extend from 100m (330 ft) out to the Hanford Site boundary. The Hanford Site specific population was obtained from the Hanford Site phone directory and increased by 10 percent to account for uncertainties. No reduction was applied for multiple work shifts or absences. All employees were assumed to be present. For accidents at the tank farms, the noninvolved worker population would be 1,835. For accidents at the vitrification facilities, the population would be 5,500.

Maximally-Exposed Individual Noninvolved Worker - The MEI noninvolved worker was assumed to be located at 100m (330 ft) from the release point in the direction that produces the highest dose. This distance was used rather than the actual nearest building location, because new construction or movement of trailers and relocateable buildings can change the actual nearest building locations.

General Public Population - The offsite population distribution from the Hanford Site boundary to a distance of 80 km (50 mi) was taken from the GENII computer code (Napier et al. 1988). The offsite population would be 114,734.

Maximally-Exposed Individual General Public - The MEI general public was assumed to be located at the Hanford Site boundary ( Volume 1, Figure 1.0.1) in the direction that produces the highest dose. An adjusted Site boundary that excludes areas likely to be released by DOE in the near future was used in the analysis. The Site boundary for the EIS was defined as follows:

  • N. Columbia River - 0.4 km (0.25 mi) south of the south river bank.
  • E. Columbia River - 0.4 km (0.25 mi) west of the west river bank.
  • S. A line running west from the Columbia River, just north of the Washington Public Power Supply System (Supply System) leased area, through the Wye Barricade to Highway 240.
  • W. Highway 240 and Highway 24.

E.1.1.6 Radiological Dose and Chemical Exposure Assessment

The computer code GXQ was used to calculate the dispersion of potential radiological releases into the atmosphere referred to as the atmospheric dispersion coefficient (Chi/Q). GXQ has been verified and benchmarked against the GENII computer code. The calculations use the most recent available meteorological joint frequency data based on the nine-year (1983 through 1991) average data from the Hanford Site meteorology tower in the 200 Area (Schreckhise 1993). The method for computing Chi/Q is based on Nuclear Regulatory Commission (NRC) Regulatory Guide 1.145 (NRC 1982). All accident-induced releases were assumed to be ground level releases, and plume meander was factored into the GXQ model. Plume rise, building wake, and dry deposition were not used. The receptor was assumed to be located at the plume centerline (i.e., at the location of peak concentration). For the bounding scenarios, the greater of the 99.5 percent maximum sector or 95 percent overall Site Chi/Q values were used.

Doses for atmospheric releases were computed with the GENII code, which has been verified and validated. The doses from radioactivity deposited inside the body were computed using weighting factors for various body organs and the results summed to calculate a committed effective dose equivalent (CEDE). The computer code was used to calculate the inhalation dose for a 70-year dose commitment period.

The radiological dose [D (Sv)] for the noninvolved worker and general public receptors were calculated using the straight-line Gaussian dispersion model as shown in the following equation:

D (Sv) = [Q (L)] · [Chi/Q (s/m3)] · [R (m3/s)] · [ULD (Sv/L)]

Where:
Q = Liters of respirable waste released from the accident
Chi/Q = Time integrated atmospheric dispersion coefficient calculated by GXQ code
R = Typical acute breathing rate of 3.3E-04 cubic meter per second (m3/s) (1.2E-02 cubic feet per second (ft3/s) (ICRP 1975)
ULD = CEDE per unit liter inhaled.

The liters of respirable waste released (Q) is the source-term as defined in Section E.1.1.3. The Chi/Q is generated by the GXQ computer code (Section E.1.1.5.3). The breathing rate (R) is the typical acute (light activity) breathing rate. The ULD was generated by the GENII computer code for composite source-terms and the values are given in terms of CEDE per unit liter of waste inhaled at the receptor location.

The radiological dose [D (Sv)] for the worker receptor was calculated using the following equation:

D (Sv) = [Q (L)] · [BR (m3/s)] · [t (s)] · [2/3r3]-1 · [ULD (Sv/L)]

Where:
Q = Liters of respirable tank waste released
t = Duration of worker exposure
BR = Typical acute breathing rate, 3.3E-04 m3/s (1.2E-02 ft3/s)
r = Assumed 10 m ( 33ft) radius from point of release for distribution of source activity
ULD = CEDE per unit liter inhaled.

Peak concentrations, C (mg/m3), for a continuous release of solid or liquid chemical materials were calculated using the following equation:

C (mg/m3) = [Q (mg/s)] · [Chi/Q (s/m3)]

Where:
Q = Chemical material release rate
Chi/Q = Continuous release atmospheric dispersion coefficient.

The volume of respirable material released (Q) is the source-term and the Chi/Q was generated by GXQ computer code.

For instantaneous or short duration releases of chemicals, the maximum puff Chi/Q was used. The following equation was used to calculate the peak concentration:

C (mg/m3) = Q (mg) · Chi/Q (1/m3)

Where:
Q = Toxic material released
Chi/Q = Puff release atmospheric dispersion coefficient.

E.1.1.7 Risk Development

Radiological risk. The likelihood that a dose of radiation would result in a fatal cancer at some future time is known as LCF and is calculated by multiplying the calculated dose (radiation effective man [rem]) by a risk factor, or dose-to-risk conversion factors. Conversion factors are predictions of health effects from radiation exposure. The dose-to-risk conversion factors used for estimating cancer deaths from low doses of radiological exposure and from high doses were taken from Recommendations of the International Commissions on Radiological Protection (ICRP 1991). They are summarized as follows:

  • Onsite (worker and noninvolved worker) - 4.0E-04 LCF/person-rem or 400 cancer fatalities per million person-rem for low doses (less than 20 rem) and 8.0E-04 LCF/rem or 800 cancer fatalities for million person-rem for doses greater or equal to 20 rem.
  • Offsite (general public) - 5.0E-04 LCF/person-rem or 500 cancer fatalities per million person rem for low doses (less than 20 rem) and 1.0E-03 LCF/rem or 1,000 cancer fatalities per million person-rem for high doses greater or equal to 20 rem. The difference in the onsite and offsite conversion factors is attributable to the presence of children offsite.

Multiplying the dose by the conversion factor shows the risk only if the accident takes place. Because the probability of the accident also needs to be factored into the evaluation, the radiological LCF risk is the product of the receptor dose, the dose-to-risk conversion factor, and the probability of the accident.

The quantitative estimate for the population receptors is the number of fatal cancers resulting from the radiological exposure. For the MEI receptors it is the probability the individual will die from cancer as a result of the exposure.

Other biological effects may result from radiological exposures. Somatic effects that occur early as a result of receiving a large dose in a short period of time (acute exposure) include vomiting, nausea, and diarrhea from a dose of 25 rem up to 220 rem. Deaths begin to occur beyond 220 rem with up to 100 percent deaths from doses between 500 to 750 rem.

Chemical risk - Potential acute hazards associated with exposure to concentrations of postulated accidental chemical releases were evaluated using a screening-level approach for the MEI worker, MEI noninvolved worker, and the MEI general public. This screening-level assessment involved direct comparison of calculated exposure point concentrations of chemicals to a set of site-specific (i.e., Hanford Site-specific) air concentration screening criteria, known as emergency response planning guidelines (ERPGs).

ERPGs, as developed by the American Industrial Hygiene Association (AIHA), are specific levels of chemical contaminants in air designed to be protective of acute adverse health impacts for the general population. ERPGs are defined in the following text.

ERPG-1 - The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing other than mild transient adverse effects or perceiving a clearly defined objectionable odor.

ERPG-2 - The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair their ability to take protective action.

ERPG-3 - The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing life-threatening health effects.

For the accident scenarios evaluated, AIHA ERPGs were used as the primary criteria. For those chemicals lacking published AIHA ERPGs, Hanford Site-specific ERPGs were used as published in the Toxicological Evaluation of Tank Waste Chemicals, Hanford Environmental Health Foundation (HEHF) Industrial Hygiene Assessments (Dentler 1995). These tank farm-specific ERPGs were developed by HEHF for the purpose of evaluating health hazards associated with chemicals in the tank farms from accidental releases.

Chemicals were subdivided based on acute health impacts into toxic chemicals or corrosive/irritant chemicals. Given the lack of quantitative data and large number of target organs affected by a chemical from acute exposure, chemicals within each group were conservatively assumed to be additive. Cumulative hazards or the Acute Hazard Index for the toxic and corrosive/irritant chemical classes were evaluated as follows:

Cumulative Hazard (Acute Hazard Index) = C1/E1 + C2/E2 + ... +Ci/Ei

Where
Ci = Calculated airborne exposure point concentration for the ith chemical, (mg/m3)
Ei = The ERPG for the ith chemical (mg/m3)

Cumulative hazard indices were estimated for each MEI receptor and for each ERPG screening level (e.g., ERPG-1, ERPG-2, and ERPG-3). A cumulative hazard index greater than 1.0 (unity) indicates that the acute hazard guidelines for a mixture of chemicals has been exceeded and the chemical mixture may pose a potential acute health impact.

For accident scenarios involving the waste storage tanks (e.g., mispositioned jumper resulting in spray release, loss of tank ventilation filtration, and dome collapse, and hydrogen deflagration in storage tanks), the upper-bound, maximum receptor population that could be potentially impacted by an ERPG exceedance is:

  • 10 workers (involved);
  • 335 noninvolved workers at 290 m (950 ft);
  • 1,500 noninvolved workers at 1,780 m (5,840 ft) ;
  • 1 MEI noninvolved worker at 100m (330 ft); and
  • 114,734 general public receptors.

For accident scenarios involving the vitrification plant (e.g., pretreatment line break in ventilated vault and canister of vitrified HLW inadvertently dropped), the upper-bound, maximum population that could be potentially impacted by an ERPG exceedance is:

  • 10 workers (involved);
  • 1,500 noninvolved workers at 1,050 m (3,340 ft);
  • 1,000 noninvolved workers at 20,500 m (12.7 mi);
  • 3,000 noninvolved workers at 30,500 m (19.0 mi);
  • 1 MEI noninvolved worker at 100m (330 ft); and
  • 114,734 general public receptors.

For any of the above receptor populations, a cumulative acute hazard index greater than 1.0 would be expected to result in the following ERPG-specific effects:

  • ERPG-1 exceedance could result in mild transient effects such as minor irritation or objectionable odor perception;
  • ERPG-2 exceedance could result in reversible adverse effects such as nausea, vomiting or bronchitis; and
  • ERPG-3 exceedance could result in lethal exposures for some or all of the exposed population.

A calculated acute hazard index greater than 1.0 for an ERPG level (ERPG exceedance) is conservatively assumed to impact the entire receptor population.

Potential carcinogenic health effects from chemical exposure were not evaluated for these accident scenarios. Exposure to chemicals from accidental releases was assumed to occur only once, with a maximum duration of 24 hours. All of the carcinogenic chemicals have been shown to produce a carcinogenic response only after administering high doses for a lifetime of exposure. None of these carcinogenic chemicals have been shown to produce a carcinogenic response from an acute exposure. Consequently, a single acute dose can not be evaluated using cancer slope factors derived from chronic or lifetime studies.

E.1.2 OCCUPATIONAL INJURIES, ILLNESSES, AND FATALITIES

Total recordable cases, lost workday cases, and fatalities resulting from construction and operations were calculated by the following equations:

Total recordable cases = (occupational incidence rate) · (manpower required to complete the alternative)

Lost workday cases = (occupational incidence rate) · (manpower required to complete the alternative)

Fatalities = (occupational fatality rate) · (manpower required to complete the alternative).

The injuries, illnesses, and fatalities rates used in the analysis are incidence rates taken from the occupational injuries summary report (DOE 1994j). The total recordable case (injuries and illnesses requiring medical care) and lost workday case (an injury or illness resulting in an employee missing work) rates are specific to the Hanford Site from 1988 through 1992. The fatality rate is the average for all DOE sites from 1988 through 1992 (the report does not distinguish between construction fatalities and operation fatalities). These incidence rates are summarized in Table E.1.2.1.

Table E.1.2.1 DOE and Contractor Incidence Rates

E.1.3 TRANSPORTATION FATALITIES AND INJURIES

Truck and Rail Transport Accidents

The rates of transportation accidents are assumed comparable to that of average truck and rail transport in the United States. Unit-risk factors were developed based on statistics compiled by the U.S. Department of Transportation (Rao et al. 1982). These unit-risk factors are summarized in Table E.1.3.1.

Table E.1.3.1 Unit-Risk Factors for Fatalities and Injuries for Truck and Rail

The number of injuries and fatalities was calculated by multiplying the total distance traveled in each population zone by the appropriate risk factors shown in Table E.1.3.1. The distance traveled in each population zone was calculated by applying the fractions of travel from NUREG-0170 (NRC 1977). The values are 5 percent of the travel in urban, 5 percent of the travel in suburban, and 90 percent of the travel in rural areas. For this analysis the Hanford Site (onsite) is considered to be a suburban zone.

Employee Commuting Accidents

To calculate the expected number of injuries and fatalities resulting from vehicle accidents for employees commuting to and from work, the following injury/fatality rates were taken from the 1993 Washington State Highway Accident Report (WSDT 1993):

  • 7.14E-07 injuries/km; and
  • 8.98E-09 fatalities/km.

There were 18 recorded injuries and no fatalities at the Hanford Site for both 1993 and 1994. The estimated average vehicle distance driven was 3.46E+07 km (2.15E+07 mi). The injury rate for 1993 and 1994 is therefore calculated at 5.20E-07 injuries/km, which is comparable to the Washington State injury rates listed previously.

E.1. 4 UNCERTAINTY

The uncertainties in calculating the radiological doses and the toxicological exposures resulting from operation accidents include the tank inventory concentration and the atmospheric dispersion once the source-term is in the air. To demonstrate these uncertainties, a sample accident scenario is presented in Volume 5, Appendix K.

The accident initiator frequencies were established using currently accepted sources of occurrence frequency such as natural phenomena statistics for the Hanford Site or recent analysis of the initiators from safety assessment reports. The frequency of these accidents is presented as estimates and is provided as an aid in screening accident scenarios. Differences in frequencies are significant only when orders of magnitude are present. An accident scenario with a frequency of 1E-06 and one with a frequency of 5E-05 should not be considered significantly different in frequency.

The nonradiological injuries and fatalities resulting from construction and operation accidents were based on incidence rates taken from the occupational injuries summary report (DOE 1994j). The transportation injuries and fatalities from trucks and train were based on incidence rates taken from statistics compiled by the U.S. Department of Transportation (Rao et al. 1982). Injuries and fatalities resulting from employee vehicle accidents were based on incidence rates taken from the Washington State Highway Accident Report (WSDT 1993). Because these are widely accepted incidence rates, there was no attempt to evaluate the uncertainties.



NEWSLETTER
Join the GlobalSecurity.org mailing list