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5.12 ACCIDENTS

This section compares the risks resulting from potential accidents associated with the alternatives. Accidents are unplanned events or a sequence of events that would cause undesirable consequences. This analysis addresses the following:

• Occupational risks, including the nonradiological/nontoxicological injuries, illnesses, and fatalities from construction, operation, or transportation accidents common to the workplace such as falls, cuts, and operator-machine impacts. The risk associated with an accident was defined as the product of the probability of an accident occurring and the consequence of the accident; and
• Radiological and toxicological risks associated with transportation and operations. The risks associated with a toxicological or radiological release were expressed as the probability or the number of latent cancer fatalities given the occurrence and consequences of an accident.

The results of the analyses are summarized in the following sections. More detailed information concerning the methodology, supporting data, and assumptions for the basis of the analysis is contained in Volume Four, Appendix E. Appendix E also contains a latent cancer fatality point estimate risk evaluation. The point estimate risk accounted for the probability of the accident occurring. The probability was factored into the latent cancer fatality risk.

Nonradiological occupational and transportation accidents would largely be a function of the number of person-years of labor required to complete the total activities for each alternative. The more person-years of labor, the more injuries, illnesses, and fatalities. For the tank waste alternatives, the alternative that was estimated to have the greatest number of injuries, illnesses, and fatalities was Long-Term Management, and the alternative with the least number was In Situ Fill and Cap. Onsite Disposal would have the highest number of injuries, illnesses, and fatalities among the capsule alternatives, with the Overpack and Ship and Vitrify with Tank Waste alternatives having the lowest.

For radiological and chemical exposures resulting from accidents during remediation, the greatest risk to workers and the public would be associated with a flammable gas deflagration in a waste storage tank. The alternative that would allow the waste to remain unstabilized over the longest period of time would pose the greatest risk. Therefore, the No Action (Tank Waste) and Long-Term Management alternatives would have the highest risk. The lowest risk would come from In Situ Fill and Cap.

For radiological and chemical exposure resulting from accidents after remediation, the greatest risk to the general population would be associated with the No Action and Long-Term Management tank waste alternatives in which the tanks would not have been stabilized with gravel.

In Volume Five, Appendix K an analysis is presented regarding uncertainties associated with the accident analyses for the tank waste alternatives. For the operation accidents, uncertainties were associated with the inventory of waste in the tanks and the atmospheric conditions that would transport the waste released as a result of an accident. Because of this uncertainty, a 100-percent composite inventory was developed for tank farm accidents. This composite incorporated estimates of the historical tank contents, the results from prior individual tank analyses, and the results of recent tank characterization programs. This composite provided a bounding tank waste inventory for the accident analysis. A less conservative approach was 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. Reduction factors were applied to account for extracted plutonium, uranium, cesium, and strontium. This nominal radiological inventory is shown in Volume Four, Section E.1.0. Because the tank waste inventory has not yet been well characterized, bounding and nominal radiological and toxicological consequences were presented in the analysis to provide a risk range.

Atmospheric conditions would influence the dispersion in air of contaminants to potential receptors. To provide a bounding case for analysis in the EIS, very unlikely atmospheric conditions were used (99.5 percentile). To assess the effect of using the bounding atmospheric conditions, the uncertainties analysis compared the results of bounding case atmospheric conditions to typical atmospheric conditions (50th percentile).

There would also be uncertainties associated with the analysis of consequences of an accident involving the transportation of vitrified HLW to the potential geologic repository under certain tank waste alternatives. The potential consequences would be influenced by the percent for the HLW by weight that would be mixed in the glass. The baseline analysis in the EIS assumed a 20 percent waste loading ; however, a waste loading of as little as 15 percent and as much as 40 percent could occur. Uncertainties associated with waste loading are discussed further in Volume Two, Section B.8.0. To address this uncertainty , the impacts from a transportation accident involving the baseline waste loading were compared to an accident involving vitrified glass with a 15 percent waste loading and with a 40 percent waste loading (see Volume Four, Section E.16).

In addition to the uncertainties associated with the accident analysis, a number of important assumptions influenced the results presented in this section. These assumptions included the following :

• The offsite general public population for operation accidents was based on census data from the 1990 census. While it is unlikely that the general public population would be constant throughout the operation phase of each alternative, the use of the 1990 census provided a uniform basis for comparison of impact among the alternatives.
• The onsite worker population for operation accidents was based on the Hanford Site work force in 1995. In the future, the Site work force would likely decline , resulting in proportionately lesser impacts than are presented in the EIS. However, use of the existing worker population provided a bounding impact analysis in terms of total impacts and also provided a basis for uniform comparison of impacts among the alternatives.
• For nonradiological occupational construction, operation, and transportation accidents, it was assumed that injuries, illnesses, and fatalities would occur at rates similar to historical rates for each activity.
• It was assumed that there would be no evacuation of Hanford Site personnel in the event of an accident. Emergency planning and evacuation programs are in place at the Hanford Site to mitigate potential consequences resulting from an accident.
• For transportation of HLW to a potential geologic repository the accident scenarios were based on transportation of the waste from the Hanford Site to Yucca Mountain, Nevada by rail.

5.12.1 Comparison of Consequences from Nonradiological Occupational and Transportation Accidents

The number of total recordable cases (injuries and illnesses requiring medical care), lost workday cases (an injury or illness resulting in an employee missing work), and fatalities resulting from construction and operations for each alternative was based on the projected number of employees associated with the activity, multiplied by historical incidence rates. The incidence rates for total recordable and lost workday cases were based on Hanford Site construction statistics. Fatality incidence rates for all DOE sites were used. A comparison of the accident consequences is presented in Table 5.12.1.

Table 5.12.1 also presents consequences of transportation accidents, based on a comparison of the number of injuries and fatalities resulting from the direct impact of traffic accidents. The traffic scenarios analyzed included employee traffic to and from work, and transportation of building materials and other miscellaneous materials to support the alternatives. The incidence rates for injuries and fatalities were based on U.S. Department of Transportation statistics, Washington State Highway accident reports, and Hanford Site statistics.

The calculations for the tank waste alternatives showed the greatest nonradiological and nontoxicological risk would result from the Long-Term Management alternative. This is because of the large number of person-years that would be required to support 100 years of operations and the two retanking campaigns. The In Situ Fill and Cap alternative would have the lowest risk due to the reduced number of person-years required to support 12 years of construction and operation.

The calculations for the capsule alternatives showed the greatest nonradiological and nontoxicological risk would result from the Onsite Disposal alternative because it would require the greatest number of person-years among all of the capsule alternatives. The Overpack and Ship and the Vitrify with Tank Waste alternatives would have the lowest risk.

5.12.2 Comparison of Potential Consequences from Radiological Accidents

Risk is the product of the chance, or probability, of an accident occurring during an operation and the consequences of the accident if it were to occur. An event that was certain to occur would have a probability of 1 (a 100 percent certainty). If an accident was expected to happen once every 100 years, the frequency of occurrence would be 0.01 per year (1 occurrence divided by 100 years = 0.01 occurrences per year). If the operation was scheduled to continue for 20 years, the probability of the accident would be 0.2 (0.01 occurrences per year multiplied by 20 years of operation).

Table 5.12.1 Comparison of Potential Nonradiological/Nontoxicological Accident Consequences

Once the probability and the consequences (for radiation effects, measured in terms of the number of latent cancer fatalities caused by the radiation exposure) of an accident are known, the risk can be determined. The risk is the product of the probability of occurrence times the number of latent cancer fatalities or, in this scenario, a risk of 0.01 latent cancer fatalities . This risk expresses the expected number of latent cancer fatalities, taking account of both the chance that an accident might occur and the estimated consequences if it does occur.

Each phase of the various operations associated with the alternatives was assessed for potential accidents. The spectrum of accidents associated with each alternative is identified in Volume Four, Appendix E, from which dominant accident scenarios were selected for further analysis to determine the latent cancer fatality risk. Dominant accidents were selected through a screening process that involved multiplying the consequence of each accident by the probability of the accident.

5.12.2.1 Tank Waste Alternatives Accident Scenarios

Table 5.12.2 presents the accident scenarios postulated for each tank waste alternative. Table 5.12.3 presents the accident scenarios postulated for each capsule alternative.

5.12.2.2 Summary of Results

Table 5.12.4 compares the latent cancer fatality risk resulting from bounding accident scenarios of each alternative. Details of the risk calculation methodology are presented in Volume Four, Appendix E.

Table 5.12.2 Tank Waste Alternatives Accident Scenarios

Table 5.12.3 Capsule Alternatives Accident Scenarios

The values presented in Table 5.12.4 for the population receptors showed the total number of cancer fatalities resulting from radiological exposure. For the maximally-exposed individual, the table value is the probability that the individual would die as a result of the exposure assuming that the accident occurred.

The calculations for the tank waste alternatives showed the greatest radiological impact during remediation would result from an accident associated with the In Situ Vitrification alternative, in which all 10 workers potentially could die from a lethal radiological dose. From the same accident, 36 noninvolved workers and 5 individuals from the general public potentially could die from latent cancers. The accident could occur during in situ vitrification, if a double-ended break occurred in the off-gas line between the off-gas hood and the off-gas facility, resulting in an unfiltered release directly to the environment. The initiating event was postulated to be an earthquake.

The other alternatives would have the same radiological impact resulting from a flammable gas deflagration in a waste storage tank. The overall risk (factoring in the probability of occurrence) would be lowest for In Situ Fill and Cap, which would require the least amount of time to stabilize the waste.

Table 5.12.4 Comparison of Radiological Consequences Resulting from Potential Operations and Transportation Accidents

The post-remediation accidents with the greatest radiological and chemical risk would result from an accident associated with the No Action (Tank Waste) and Long-Term Management alternatives, in which 42 fatalities could be expected within the population living at that time (beyond the institutional control period) on the Hanford Site and 4 latent cancer fatalities could be expected within the population living off the Hanford Site. The accident could occur after the 100 years of institutional control, when the tanks have exceeded the design life and could collapse. The initiating event was postulated to be an earthquake. The tanks would be stabilized for all the other alternatives and there would be no airborne releases of waste from an earthquake.

A common accident to all capsule alternatives would be crushed capsules caused by an earthquake. It was postulated that the water could be drained from the pool cell storage and capsules crushed at WESF from structural failure because of an earthquake. The workers were assumed to have died as a direct result of the building collapsing on them. Latent cancer fatalities resulting from the exposure to the nonworkers and general public would be unlikely. No other accidents were identified that could result in radiological latent-cancer fatalities for the capsule alternatives.

Beyond design basis accidents (accidents with an annual frequency of happening between 1.0E-06 and 1.0E-07 or below the site-specific designated return frequency for natural events ) were also analyzed in Volume Four, Appendix E for radiological and chemical consequences. The bounding beyond design basis accident, common to all tank waste alternatives, was a seismic event resulting in tank dome collapse. Exposure from this accident potentially could result in all the workers receiving a lethal dose and 11 noninvolved workers and 2 individuals from the general public dying from potential latent cancers.

5.12.3 Comparison of Consequences from Potential Toxicological Accidents

The chemical exposures for the accidents listed in Table 5.12.2 were calculated for each alternative. The chemical exposures to the maximally-exposed individual in each of the worker, noninvolved worker, and general public receptor groups were compared to the following guidelines.

The American Industrial Hygiene Agency Emergency Response Planning Guidelines (ERPGs) were used as the primary criteria. For those chemicals lacking published American Industrial Hygiene Agency ERPGs, Hanford Site-specific ERPGs were used as published in the Toxicological Evaluation of Tank Waste Chemicals, Hanford Environmental Health Foundation Industrial Hygiene Assessments (Dentler 1995). These tank farm-specific ERPGs were developed by the Hanford Environmental Health Foundation for the purpose of evaluating health hazards associated with chemicals in the tank farms for accidental releases.

Cumulative hazard indices were calculated for each maximally-exposed individual receptor and for each ERPG screening level (i.e., ERPG-1, ERPG-2, and ERPG-3). A cumulative (concentrations of chemicals with similar hazard effects were added) hazard index greater than 1.0 indicated that the acute hazard guidelines for a group of chemicals would be exceeded and the chemical group could pose a potential acute health impact. Chemicals were subdivided based on acute health impacts into toxic chemicals or corrosive/irritant chemicals.

Table 5.12.5 summarizes the comparison of chemical exposures to their respective ERPGs for operational activities. The same methodology was applied to transportation accidents involving the transport of chemicals to the Hanford Site as summarized in Table 5.12.5 . An integrated worker/public population was used as the receptor for the transportation accident scenarios that included both onsite and offsite receptors.

Table 5.12.5 Comparison of Chemical Exposures Resulting From Potential Operations and Transportation Accidents

Table 5.12.5 Comparison of Chemical Exposures Resulting From Potential Operations and Transportation Accidents (cont'd)

The general public and nominal worker population exposure to toxic or corrosive/irritant chemicals resulting from potential accidents during operations would not exceed the cumulative ratio of exposure to ERPG-3 concentration value for any of the tank waste alternatives. The only such exposure potentially could occur as a result of a transportation accident when chemicals are being transported to the Hanford Site in support of the Ex Situ Intermediate Separations, Ex Situ No Separations, Ex Situ Extensive Separations, Ex Situ/In Situ Combination 1 and 2 , and Phased Implementation alternatives.

A flammable gas deflagration in a waste storage tank would have the highest chemical impacts for all the alternatives. In the event of this accident, emergency planning and evacuation plans are in place at the Hanford Site to mitigate potential consequences. Consequently, these noninvolved workers would not likely be exposed to air concentrations that would result in significant health effects. Failure to evacuate could result in noninvolved worker exposure downwind from the plume source that could exceed the cumulative ratio of exposure to ERPG-3 concentration value. The potential exists for workers to exceed ERPG-3; however, the workers would have received a potentially lethal radiological dose from the accident. There would be no irreversible health effects to the general public.

The cesium and strontium capsule alternatives would not exceed the cumulative ratio of exposure to any ERPG concentration values for the general public, noninvolved worker, or worker.

5.12.4 Vitrified HLW Transport to the Potential Geologic Repository

Under the ex situ tank waste treatment alternatives the HLW streams would be vitrified or calcined and eventually shipped to a geologic repository assumed to be located 2,140 km (1,330 mi) offsite by a dedicated train of 10 railcars per train. The nonradiological and radiological transportation impacts associated with this activity are evaluated in this section.

The expected injuries and fatalities resulting from transportation accidents associated with each ex situ stabilization alternative are summarized in Table 5.12.6. Fatalities resulting from trauma caused by transportation accidents would be directly proportional to the number of miles driven. The Ex Situ No Separations alternative would have the highest number of shipments and therefore the most fatalities. The Ex Situ Extensive Separations alternative would have the least fatalities.

Table 5.12.6 Injuries and Fatalities from Rail Transportation Accidents

Radiological exposures resulting from routine exposures and accidents while the waste is in transit were analyzed using RADTRAN 4 (Neuhauser-Kanipe 1992). For routine risk, the key variable in the code was the dose rate from the vehicle package. The radioactive shipments in this analysis were assumed to be less than the regulatory maximum dose rate of 10 mrem per hour at 1 m (Jacobs 1996). For accidents, the population doses calculated by RADTRAN 4 were dependent on the accident probability, release quantities, atmospheric dispersion parameters, population distribution parameters, human uptake, and dosimetry models (Jacobs 1996).

The routine exposures were addressed as onsite population latent cancer fatality risk and offsite population latent cancer fatality risk. The analysis addressed radiological accident impacts as both integrated population latent cancer risk (i.e., accident frequencies time consequences integrated over the entire shipping campaign) and urban population latent cancer fatality risk. The routine and accident latent cancer fatality risks resulting from transporting vitrified or calcined HLW to a potential geologic repository are presented in Table 5.12.7 for each of the ex situ treatment alternatives. The radiological impacts from both routine exposure and accidents would be directly proportional to the number of trips made to the repository. The Ex Situ No Separations alternative would have the highest number of trips made to the repository. The Ex Situ No Separations alternative would have the highest number of shipments and therefore the highest latent cancer fatality risk. The Ex Situ Extensive Separations alternative would have the lowest latent cancer fatality risk.

Table 5.12.7 Latent Cancer Fatality Risk from Routine and Accident Radiological Exposures While Shipping Vitrified or Calcined High-Level Waste By Rail to a Proposed Geologic Repository

A main uncertainty associated with calculating the radiological doses resulting from transporting HLW to a potential geologic repository would be the location of the repository. The analysis was based on the assumption that the waste would be transported to Yucca Mountain should that site be shown to be acceptable and approved as a potential geologic repository. If Yucca Mountain should not be approved the latent cancer fatality risks could increase or decrease depending on the distance and population pathways of the alternative site.