E.4.0 IN SITU FILL AND CAP ALTERNATIVE
Under this alternative, all excess liquid from the DSTs would be evaporated at the 242-A Evaporator. The tanks would then be backfilled with gravel and a Hanford Barrier would be constructed over the tanks. The waste in the MUSTs would be grouted in situ.
E.4.1 CONSTRUCTION ACCIDENTS
Although construction activities are limited for the In Situ Fill and Cap alternative, the potential exists for accidents. The construction activities are discussed in Appendix B of the EIS.
The number of construction personnel was estimated at 7.25E+02 person-years (Jacobs 1996). The number of total recordable injuries and illnesses, lost workday cases, and fatalities were calculated using the incidence rates from Table E.1.2.1 as follows.
Total Recordable Cases = (7.25E+02 person-years) · (9.75E+00 incidences/100 person-years) = 7.07E+01
Lost Workday Cases = (7.25E+02 person-years) · (2.45E+00 incidences/100 person-years) = 1.78E+01
Fatalities = (7.25E+02 person-years) · (3.20E-03 fatalities/100 person-years) = 2.32E-02
E.4.2 TRANSPORTATION ACCIDENTS
Transporting activities associated with this alternative include:
- Transporting construction material from offsite for the waste transfer system upgrade (W-314);
- Transporting cement from offsite to grout MUSTs;
- Transporting sand and gravel from the Pit 30 borrow site to grout MUSTs;
- Transporting earthen material from onsite borrow sites for the Hanford Barrier; and
- Employees commuting to work each day.
E.4.2.1 Radiological Cancer Risk
All operations would be conducted within established operating parameters for the tanks and would not involve transporting radioactive materials by container. Therefore, there would be no radiological cancer risks from transportation.
E.4.2.2 Chemical Exposure
Because there would be very limited transportation of toxic materials (e.g., lubricants for routine operations), it is extremely unlikely there would be any accidents resulting in chemical exposures. Therefore, transportation accidents involving chemical exposures were not quantified.
E.4.2.3 Occupational Injuries and Fatalities
Truck Transport Accidents
Injuries and fatalities resulting from direct impact of transportation accidents are analyzed in this subsection. Truck transportation activities to transport materials and supplies to the Hanford Site for this alternative were estimated (Jacobs 1996) and are summarized in Table E.4.2.1.
Table E.4.2.1 Summary of Transportation Activities for the In Situ Fill and Cap Alternative
The number of injuries and fatalities were calculated by multiplying the total distance traveled in each zone shown in Table E.4.2.2 by the appropriate unit risk factors shown in Table E.1.3.1. The distance traveled in the population zones were calculated using the methodology previously discussed in Section E.1.3.
Table E.4.2.2 Distance Traveled in Population Zones for the In Situ Fill and Cap Alternative
The expected injuries and fatalities resulting from transportation accidents associated with the In Situ Fill and Cap alternative are summarized in Table E.4.2.3.
Employee Traffic
In addition to transporting materials and supplies to and from the Hanford Site by truck, site workers and other personnel required to perform the various activities would be driving to the site in their vehicles. The total person-years to perform the activities was estimated at 2.61E+04 (Jacobs 1996). Each person was assumed to work 260 days of the year. The round-trip distance traveled to work from the Tri-Cities area was estimated at 140 km (87 mi) with an estimated 1.35 passengers per vehicle (DOE 1994a). The total employee vehicle distance was therefore calculated as follows:
(2.61E+04 person-years) · (260 days/year) · (140 km/day) · (1/1.35) = 7.05E+08 km (4.37E+08 mi)
To calculate the expected number of injuries and fatalities resulting from vehicle accidents, the injury/fatality rates discussed in Section E.1.3 were used. The expected number of injuries and fatalities resulting from employee vehicle accidents were calculated as follows:
Injuries = (7.05E+08 km) · (7.14E-07 injuries/km) = 5.03E+02
Fatalities = (7.05E+08 km) · (8.98E-09 fatalities/km) = 6.33E+00
Cumulative Transportation Injuries and Fatalities
The cumulative nonradiological and nontoxicological injuries and fatalities incurred as a direct result of traffic accident impacts are the sum of the truck transport and employee vehicle accidents. The results are summarized in Table E.4.2.4.
E.4.3 OPERATION ACCIDENTS
The potential exists for accidents resulting from operation activities. The operations are discussed in Appendix B.
This analysis separates and analyzes operations according to the following modes of operation:
- Continued operations - These operations have been previously discussed in No Action alternative; and
- Treatment - After excess liquid has been removed from the tank waste the tanks are filled with gravel.
The dominant accident scenarios analyzed in the following subsections were selected from the Accident Screening Table (Table E.4.3.1). The accidents listed in Table E.4.3.1 were taken from the Accident Analysis Data Package (Shire et al. 1995 and Jacobs 1996). The methodology of screening was previously discussed in Section 1.1.2.
Table E.4.3.1 Accident Screening Table for the In Situ Fill and Cap Alternative
E.4.3.1 Continued Operation Accident - Tank Waste Transfers
The dominant continued operations accident during tank waste transfers is the mispositioned jumper accident previously discussed in the No Action alternative (Section E.2.2.1) and summarized as follows:
Source-term - The source-term resulting from a spray release in Section E.2.2.1.1 was calculated to be 52 L (14 gal).
Probability - The frequency of a mispositioned jumper in Section E.2.2.1.2 was 1.1E-02 per year. The In Situ Fill and Cap alternative was based on 1 2 years of operations. Therefore, the probability was calculated to be 1.3E-01.
Radiological Consequences - The radiological consequences presented in Table E.2.2.2 were reproduced in Table E.4.3.2.
Table E.4.3.2 Dose Consequence from Mispositioned Jumper
Radiological Cancer Risk - The LCFs calculated in Section E.2.2.1.4 are the same for the In Situ Fill and Cap alternative however, the LCF risk (point estimate) is not the same due to the difference in probabilities. The LCFs and the LCF risk are calculated in Table E.4.3.3. The bounding scenario calculations show all 10 workers would potentially receive fatal dose and would assumably die directly after the exposure if the accident occurred. Approximately seven noninvolved workers would receive fatal cancers, and two LCFs would be incurred to the general public. The nominal scenario calculations show there would be no LCFs.
Table E.4.3.3 Latent Cancer Fatality Risk from Mispositioned Jumper
Chemical Consequences
Potential acute hazards associated with a mispositioned jumper accident are summarized in Tables E.2.2.4 (toxic chemicals, nominal conditions), E.2.2.5 (toxic chemicals, bounding conditions), E.2.2.6 (corrosive/irritant chemicals, nominal conditions) and E.2.2.7 (corrosive/irritant bounding conditions) for the No Action alternatives.
Toxic Impact from Chemical Exposure
Under nominal conditions (Table E.2.2.4), the cumulative acute hazard ratios for the MEI worker, MEI noninvolved worker, and MEI general public were less than 1.0E+00, indicating that no adverse acute health effects would be expected for these three receptors. Under bounding conditions (Table E.2.2.5), the MEI worker was not evaluated because death would occur from exposure to radionuclides. The cumulative acute hazard ratio for the MEI noninvolved worker was 5.36E+00 for ERPG-2, indicating that reversible acute health effects would be expected. This acute hazard ratio was primarily attributable to mercury (approximately 89 percent of the overall hazard ratio). No adverse acute health effects were predicted for the MEI general public under bounding conditions.
Corrosive/Irritant Impact from Chemical Exposure
Under nominal conditions (Table E.2.2.6), the cumulative acute hazard ratio for the MEI worker was 2.70E+00 for ERPG-3, indicating the potential for irreversible health effects that could be life threatening. This acute hazard ratio was almost entirely attributable to sodium assumed to be equivalent to sodium hydroxide in corrosive/irritant effects. For the MEI noninvolved worker, the cumulative acute hazard ratio for ERPG-1 was 3.0E+00, indicating that only mild, reversible irritant effects would be expected. No acute health impacts were predicted for the MEI general public under nominal conditions. Under bounding conditions (Table E.2.2.7), the MEI worker was not evaluated because death would occur from exposure to radionuclides. For the MEI noninvolved worker, the cumulative acute hazard ratio for ERPG-1 was 4.36E+00, indicating that only mild, reversible irritant effects would be expected. No acute health impacts were predicted for the MEI general public under bounding conditions.
Under both nominal and bounding conditions, the probability of a mispositioned jumper is 1.32E-01.
E.4.3.2 Continued Operations Accident - Waste Storage Tanks
The dominant accident is a hydrogen deflagration in a waste storage tank previously discussed in the No Action alternative in Section E.2.2.2.1 and summarized as follows:
Source-term - The source-term resulting from a hydrogen deflagration in Section E.2.2.2.1 was calculated to be 2.4 L (0.6 gal).
Probability - The frequency of the hydrogen deflagration in a waste storage tank in Section E.2.2.2.2 was estimated to be 7.2E-03 per year. The probability of the scenario based on 12 years of operation was therefore estimated to be 8.6E-02.
Radiological Consequences - The radiological consequences presented in Table E.2.2.8 are reproduced in Table E.4.3.4.
Table E.4.3.4 Dose Consequence from Hydrogen Deflagration in Waste Storage Tank
Radiological Cancer Risk - The LCFs calculated in Section E.2.2.2.4 are reproduced in Table E.4.3.5.
Table E.4.3.5 Latent Cancer Fatality Risk from Hydrogen Deflagration in Waste Storage Tank
Chemical Consequences
Potential acute hazards associated with a hydrogen deflagration in a waste storage tank are summarized in Tables E.2.2.10 (toxic chemicals, nominal conditions), E.2.2.11 (toxic chemicals, bounding conditions), E.2.2.12 (corrosive/irritant chemicals, nominal conditions) and E.2.2.13 (corrosive/irritant chemicals bounding conditions) for the No Action alternative. Chemical impacts were not evaluated for the MEI worker since all workers would receive a lethal radiation dose, as discussed previously.
In the bounding scenario all 10 workers, would potentially receive a fatal dose and would assumably die directly after the exposure. There would also be 10 LCFs attributed to the exposure to the noninvolved workers and two LCFs to the general public if the accident occurred. The nominal scenario calculations show there would be no LCFs.
Toxic Impact from Chemical Exposure
Under nominal conditions (Table E.2.2.10), the cumulative acute hazard ratio for the MEI worker was 1.57E+00 for ERPG-2, indicating that reversible, acute health effects would be expected. This acute hazard ratio was primarily attributable to TOC (approximately 87 percent of the overall ERPG-2 ratio). The TOC is assumed to be equivalent in toxicity to tributylphosphate, which is the most acutely toxic constituent of the organic analytes identified. Tributylphosphate was used as a surrogate because an inventory of the various chemicals that make up the TOC class is not available. For the MEI noninvolved worker, the cumulative acute hazard ratio for ERPG-3 was 9.38E+00, indicating the potential for irreversible health effects that could be life-threatening. This acute hazard ratio was also primarily attributable to TOC (approximately 90 percent of the overall ERPG-3 ratio) However, the MEI noninvolved worker is a hypothetical worker assumed to be located 100m (330 ft) from the source area. The first anticipated noninvolved worker population is located 290 m (950 ft) from the source area and had no cumulative acute hazard ratios greater than 1.0 for any of the ERPGs, indicating that no acute health effects would be expected for the nearest noninvolved worker population. Likewise, no acute health effects were predicted for the MEI general public under nominal conditions.
Under bounding conditions (Table E.2.2.11), the cumulative acute hazard ratio for the MEI noninvolved worker was 4.54E+02 for ERPG-3, indicating the potential for irreversible health effects that could be life threatening. This acute hazard ratio is primarily attributable to:
- Oxalate (approximately 37 percent of the total hazard ratio);
- Beryllium (approximately 13 percent of the total hazard ratio);
- Cadmium (approximately 14 percent of the total hazard ratio);
- Uranium (approximately 12 percent of the total hazard ratio); and
- TOC (approximately 8 percent of the total hazard ratio).
As discussed previously, this is a hypothetical receptor located 100m (330 ft) from the source. The cumulative acute hazard ratio for the nearest noninvolved worker population located 290 m (950 ft) from the source was 1.65E+00 for ERPG-3, indicating the potential for irreversible health effects that could be life threatening for 335 workers. This hazard ratio was attributable to the same toxic chemicals listed above. This exceedance of the ERPG-3 criterion for the nearest noninvolved worker population would not be expected to result in irreversible health effects or place these workers in a life-threatening situation for the following reasons.
- ERPG-3 is defined as a concentration in which a receptor can be exposed for 1 hour without irreversible health effects. Because the Hanford Site has an in-place emergency response plan designed to evacuate workers within 1 hour of an accident, workers would be expected to evacuate their location and move to an area where potential exposures would be well below ERPG-3. Therefore, this worker population would not be exposed to airborne concentrations that would be either life threatening or result in irreversible health effects.
- The estimated air concentrations of chemicals as a result of this accident were based on very conservative meteorology, which results in movement of a plume directly toward the worker population at a relatively slow rate with minimal wind dispersion. If less conservative meteorological parameters were used, wind dispersion would cause the estimated air concentrations of chemicals to be substantially less, and the ERPG-3 criterion would not be exceeded.
- Only the bounding toxic chemical evaluation exceeded ERPG-3, while the nominal evaluation was well below 1.00E+00 for ERPG-3, suggesting that the noninvolved worker population would not receive an exposure that would result in any permanent health effects.
The next nearest noninvolved worker population is located 1,780 (5,840 ft) from the source and contains 1,500 workers. The cumulative acute hazard ratio was less than 1.0 for all ERPGs, indicating that no acute health effects would be expected for this population of workers. No acute health impacts were predicted for the MEI general public.
Corrosive/Irritant Impact from Chemical Exposure
Under nominal conditions (Table E.2.2.12), the cumulative acute hazard ratio for the MEI worker was 3.82E+00 for ERPG-3, indicating the potential for irreversible corrosive/irritant effects that could be life-threatening. For the MEI noninvolved worker, the cumulative acute hazard ratio for ERPG-3 was 7.89E+01 and would indicate irreversible corrosive/irritant effects that could be life threatening for this hypothetical receptor. This hazard ratio was primarily attributable to sodium, which was assumed to be equivalent to sodium hydroxide in corrosive/irritant effects. For the nearest noninvolved worker population (290 m [950 ft]) composed of 335 workers, the cumulative acute hazard ratio for ERPG-1 was 1.38E+01, indicating that only mild reversible effects would be expected. No acute health impacts were predicted for the MEI general public under nominal conditions.
Under bounding conditions (Table E.2.2.13), the cumulative acute hazard ratio for the MEI noninvolved worker was 1.91E+02 for ERPG-3, indicating irreversible health effects that could be life threatening for this hypothetical receptor. This hazard ratio was primarily attributable to :
- Sodium as sodium hydroxide (approximately 75 percent of the total hazard ratio);
- Chromium (approximately 14 percent of the total hazard ratio); and
- Calcium (approximately 6 percent of the total hazard ratio).
For the nearest noninvolved worker population (290 m [950 ft]) composed of 335 workers, the cumulative acute hazard ratio was 1.74E+00 for ERPG-2, indicating that reversible acute effects would be expected. No acute health impacts were predicted for the MEI general public under nominal conditions.
Under both nominal and bounding conditions, the probability of a hydrogen deflagration event in a waste storage tank is 8.64E-02.
E.4.3. 3 Treatment Accident
The treatment accidents identified in the accident engineering data package (Shire et al. 1995 and Jacobs 1996) are summarized in Table E.4.3.1. The rock slinger ignites gas plume in tank accident, which would lead to a partial tank dome collapse, was identified as the dominant accident.
E.4.3. 3 .1 Scenario and Source-Term Development for Deflagration In Tank During Fill and Cap
It was postulated that hydrogen deflagration could occur while filling the tank with gravel using a rock slinger. A spark from the gravel ignites a hydrogen gas plume, which is suddenly released from the solids or salt cake causing the tank to overpressurize. This in turn causes the HEPA filters to blow out (in the case of DST) or the dome to collapse (in the case of SST). The impact of the postulated accident would result in an airborne release of radionuclides and chemical constituents in the tank.
For this event to occur, the following conditions must exist.
- Flammable gases must be generated from the waste;
- The concentration of the flammable gas must exceed the lower flammability limit;
- There must be an ignition source; and
- The deflagration would have to generate enough energy to blow out the HEPA filters or collapse the tank dome.
Generation of Flammable Gas
All 177 waste tanks produce flammable gases at the molecular level such as hydrogen, ammonia, and methane due to radiolysis and organic degradation. The generation of flammable gas has been demonstrated in all the tanks and has resulted in 25 tanks being included on the Watchlist for hydrogen buildup. These 25 tanks include 19 SSTs and 6 DSTs.
Gas Concentration
Gases that are constantly being released into the headspace, and subsequently removed from the tank through the tank ventilation system, are unable to reach the lower flammability limits and do not pose a potential hydrogen deflagration event. Active ventilation systems can be engineered to provide removal of flammable gases and prevent gas concentrations from reaching 25 percent of the LFL.
Of concern are conditions in which the gas is not readily released from the waste leading to retention of substantial volumes of gas in the waste matrix. These trapped pockets of gas could be triggered into an instant release by pressure from the fill material on the tank waste. This would result in a gas plume in the head space. Studies made on the flammable gas Watchlist tanks (LANL 1995) have shown the potential for concentrations of hydrogen in these gas pockets to exceed the LFL. The composition of the mixture is important. If the mixture is hydrogen and air, it takes a relatively small ignition source (0.01 mJ - equivalent to pieces of fabric rubbing together or stray radio waves) to ignite the mixture.
Ignition of Gas
As the gravel is thrown into the tank by the rock slinger, it has the potential to create a spark by striking against metal inside the tank or against the gravel in the tank. The spark could ignite the sudden release of a plume of gas if hydrogen concentration exceeds the LFL. The probability of these events occurring at the same instant is low. At this time, it cannot be ruled out that the hydrogen concentration in the gas plume will exceed the LFL. The time it would take for the plume to diffuse and drop the hydrogen concentration to below the LFL by dilution from the ventilation system depends on the size and concentration of the plume, which cannot be accurately estimated at this time. Therefore, it may be assumed that the plume occurs and ignites.
The probability of the plume igniting could be reduced substantially by using wet sand or soil and possibly grout as fill instead of gravel.
Loss of Containment
The pressure necessary to cause failure in a SST varies from 76 kPa (11 psi) for a 3,800,000-L (1,000,000-gal) tank to 97 kPa (14 psi) for a 1,900,000-L (500,000-gal) tank (Julyk 1994). The pressure necessary to cause failure in a DST is 410 kPa (60 psi) because it has a steel liner. The pressure generated by the ignited plume is dependent on the plume size, head space, heat transfer, and ventilation. A plume of flammable gas (16 m3 [570 ft3]) sufficiently concentrated, if ignited, will cause an overpressure of 100 kPa (15 psi), which is more than enough to collapse the dome of a SST (Fox-Stepnewski 1994). For the DST, 100 kPa (15 psi) may not breach the dome but would blow out the HEPA filters. These potential overpressures do not take into account the 42-in. risers that penetrate the tank dome, which would absorb some of the pressure from a deflagration.
Additional saltwell pumping of the SSTs is expected to reduce the probability of hydrogen burps by removing liquids, which tend to trap gases in the saltcake. Additional saltwell pumping also would be expected to remove organic materials, such as complexants, which degrade to form flammable gases. The risk of a plume burn could also be reduced by filling the 25 Watchlist tanks last. It has been shown in tank waste that hydrogen generation rates drop by about one-half every 15 years. By waiting approximately 15 years to fill the 25 Watchlist tanks, the hydrogen generation rate of these tanks would drop by about 50 percent.
Source-term for SST Dome Collapse
It was conservatively assumed that all radiological and chemical contaminants in the headspace are available for release. The collapse of a portion of the dome and overburden compresses the vapor in the headspace as it descends, enhancing the vapor release rate by sudden pressure difference. Assuming a respirable concentration of contaminants in the headspace of 100 mg/m3, a liquid SpG of 1.5, and a headspace volume of 1,000 m3, the potential source-term contribution from the headspace release was calculated as follows:
(100 mg/m3) · (1 g/L 1,000 mg) · (1 L/1,000 g) · (1,000 m3) · (1/1.5) = 1.8E-02 L (1.8E-02 gal).
It was assumed that gravel fill takes place after saltwell pumping that has reduced the liquid in the SSTs to less than 0.5 percent. It was conservatively assumed the surface was dry and crumbly and the MAR was 2,500 L (660 gal). It was postulated that the fall of the objects generated a substantial air movement to suspend a fraction the MAR.
Assuming the respirable release fraction to be 2.0E-03, the potential source-term contribution from entrainment was calculated as follows:
(2,500 L) · (2.0E-03) = 5.0 L (1.3 gal).
It was postulated that prevailing winds resuspend a respirable fraction of the MAR (2,500 L [660 gal]). A respirable release fraction of 4.0E-05/hr for 24 hours was assumed. The potential source-term contribution from resuspension was calculated as follows:
(2,500 L) · (4.0E-05/hr) · (24 hr) = 2.4 L (0.6 gal).
The combined source-term of the potential SST accident is calculated as follows:
(0.07 L) + (5.0 L) + (2.4 L) = 7.5 L (2.0 gal).
Source-term for the DSTs
For the DSTs, a consequence analysis was performed (LANL 1995) based on a dome space loading of 0.39 L (0.10 gal) in the vapor space plus 3.30 L (0.87 gal) entrained by the deflagration. It was assumed that the HEPA filter was destroyed by the pressure pulse generated by the ignited gases. The amount of material on the filter was assumed to be 0.45 L (0.12 gal). Therefore, the amount of inventory released from the tank would be 4.14 L (1.09 gal). The bounding source-term or respirable amount released from a DST and made airborne was 2.0 L (0.5 gal) for tank 241-SY-101 (LANL 1995).
E.4.3. 3 .2 Probability of the Event
The probability of a plume burn is assumed to be a likely event due to the gas pockets that exist in the waste and the available ignition source. However, the magnitude of the deflagration is uncertain. It is more likely that the gas burn would be small and would not have sufficient energy to blow out the HEPA filters or breach the tank. It is therefore assumed to be an extremely unlikely event, and for the purpose of this analysis, a probability of 1E-04 is used to calculate the point estimates.
E.4.3. 3 .3 Radiological Consequence for Tank Dome Collapse
The tank dome collapse would be bounding so the radiological dose to the receptors was calculated from the source-term for the SST by the GENII computer code (Napier et al. 1988) using the methodology previously discussed in Section E.1.1.6. The results (Shire et al. 1995 and Jacobs 1996) are summarized in Table E.4.3. 6 .
Table E.4.3.6 Dose Consequence for Tank Dome Collapse Due to Deflagration
E.4.3. 3 .4 Radiological Cancer Risk for Tank Dome Collapse
All 10 workers and the MEI noninvolved worker potentially would receive a lethal dose. The LCFs and LCF point estimate risk were calculated for the receptors and presented in Table E.4.3. 7 .
Table E.4.3.7 Latent Cancer Fatality Risk from Tank Dome Collapse Due to Deflagration
In the bounding scenario all 10 workers would die from a lethal dose . T he calculations show there would be 11 LCFs attributed to the exposure to the noninvolved workers and 2 LCFs to the general public if the accident occurred. In the nominal scenario there would be no LCF.
E.4.3. 3 .5 Chemical Consequences of Tank Dome Collapse
The chemical exposure to the receptors from the postulated accident was calculated in Appendix A of the accident data package (Shire et al. 1995 and Jacobs 1996) and summarized in the exposure column in Tables E.4.3.8 and E.4.3.9 for the nominal and bounding toxic effects, respectively, and Tables E.4.3.10 and E.4.3.11 for the nominal and bounding corrosive/irritant effects, respectively. The tables compare the concentration of postulated chemical releases to acute exposure criteria (ERPGs) discussed in Section 1.1.7.
Under bounding conditions, chemical impacts were not evaluated for the MEI worker because all workers would receive a lethal radiation dose, as discussed previously.
Toxic Impact from Chemical Exposure
Under nominal conditions (Table E.4.3.8), the cumulative acute hazard ratio for the MEI worker was 2.64E+00 for ERPG-1, indicating that only mild transient effects would be expected. For the MEI noninvolved worker, the cumulative acute health hazard was 2.59E+00 for ERPG-3, indicating the potential for irreversible health effects that could be life threatening. This acute hazard ratio was primarily attributable to TOC (approximately 84 percent of the total hazard ratio). The TOC is assumed to be equivalent in toxicity to tributylphosphate which is the most acutely toxic constituent of the organic analytes identified. Tributylphosphate was used as a surrogate because an inventory of the various chemicals that make up the TOC class is not available. The cumulative acute hazard ratio, for the nearest noninvolved worker population consisting of 335 workers located 290 m (950 ft) away, was less than 1.0 for all ERPGs, suggesting that no acute health effects would be expected.
Under bounding conditions (Table E.4.3.9), the cumulative hazard ratios for the MEI and nearest noninvolved worker (335 workers located 290 m [950 ft] away) were 2.15E+03 and 7.80E+00 for ERPG-3, respectively. These ratios were primarily attributable to:
- Uranium (approximately 47 percent of the total hazard ratio);
- Oxalate (approximately 24 percent of the total hazard ratio); and
- Mercury (approximately 13 percent of the total hazard ratio).
This exceedance of the ERPG-3 criterion for the nearest noninvolved worker population would not be expected to result in irreversible health effects or place these workers in a life-threatening situation for the following reasons.
- ERPG-3 is defined as a concentration in which a receptor can be exposed for 1 hour without irreversible health effects. Because the Hanford Site has an in-place emergency response plan designed to evacuate workers within 1 hour of an accident, workers would be expected to evacuate their location and move to an area where potential exposures would be well below ERPG-3. Therefore, this worker population would not be exposed to airborne concentrations that would be either life threatening or result in irreversible health effects.
- The estimated air concentrations of chemicals as a result of this accident were based on very conservative meteorology, which results in movement of a plume directly toward the worker population at a relatively slow rate with minimal wind dispersion. If less conservative meteorological parameters were used, wind dispersion would cause the estimated air concentrations of chemicals to be substantially less, and the ERPG-3 criterion would not be exceeded.
- Only the bounding toxic chemical evaluation exceeded ERPG-3, while the nominal evaluation was well below 1.00E+00 for ERPG-3, suggesting that the noninvolved worker population would not receive an exposure that would result in any permanent health effects.
The cumulative acute hazard ratio for the next nearest noninvolved worker population, composed of 1,500 people and located 1,780 (5,840 ft) away, was 2.15 for ERPG-2, indicating that reversible acute health effects would be expected. The cumulative acute hazard ratio for the MEI general public was 1.76E+00 for ERPG-2, indicating that reversible acute health effects would be expected.
Corrosive/Irritant Impact from Chemical Exposure
Under nominal conditions (Table E.4.3.10), the cumulative acute hazard ratios for the MEI worker, MEI noninvolved worker and nearest noninvolved worker (335 workers at 290 m [950 ft]) were 2.47E+01, 5.10E+02 and 1.85E+00, respectively for ERPG-3, indicating the potential for irreversible health effects that could be life threatening. These ratios were almost entirely attributable to sodium which was assumed to be equivalent to sodium hydroxide in corrosive/irritant effects. This exceedance of the ERPG-3 criterion for the nearest noninvolved worker population would not be expected to result in irreversible health effects or place these workers in a life-threatening situation for the following reasons.
- ERPG-3 is defined as a concentration in which a receptor can be exposed for 1 hour without irreversible health effects. Because the Hanford Site has an in-place emergency response plan designed to evacuate workers within 1 hour of an accident, workers would be expected to evacuate their location and move to an area where potential exposures would be well below ERPG-3. Therefore, this worker population would not be exposed to airborne concentrations that would be either life threatening or result in irreversible health effects.
- The estimated air concentrations of chemicals as a result of this accident were based on very conservative meteorology, which results in movement of a plume directly toward the worker population at a relatively slow rate with minimal wind dispersion. If less conservative meteorological parameters were used, wind dispersion would cause the estimated air concentrations of chemicals to be substantially less, and the ERPG-3 criterion would not be exceeded.
- Only the bounding toxic chemical evaluation exceeded ERPG-3, while the nominal evaluation was well below 1.00E+00 for ERPG-3, suggesting that the noninvolved worker population would not receive an exposure that would result in any permanent health effects.
For the next nearest noninvolved worker population (1,500 workers at 1,780 [5,840 ft]), the cumulative acute hazard ratio was 1.20 for ERPG-1, indicating that only mild irreversible irritant effects would be anticipated. For the MEI general public, the cumulative acute hazard ratio was less than 1.0 for all ERPGs and no acute health effects would be expected.
Under bounding conditions (Table E.4.3.11), the cumulative acute hazard ratios for the MEI noninvolved worker and nearest noninvolved worker (335 workers at 290 m [950 ft]) were 7.31E+02 and 2.65, respectively for ERPG-3, indicating the potential for irreversible health effects that could be life threatening. These acute hazard ratios were primarily attributable to:
- Sodium (approximately 83 percent of the total hazard ratio); and
- Calcium (approximately 10 percent of the total hazard ratio).
As discussed previously, this exceedance of the ERPG-3 criterion would not be expected to result in irreversible or life threatening health effects.
For the next nearest noninvolved worker and MEI general public, the cumulative acute hazard ratios were 1.74 and 1.42, respectively for ERPG-1, indicating that only mild, transient irritant effects would be expected.
Under both nominal and bounding conditions, the probability of a seismic event is 1.00E-04.
E.4.3.4 Beyond Design Basis Accidents
The beyond design basis accident is a seismic event resulting in the collapse of a SST. In the event of a 0.43 g earthquake, a SST could potentially collapse (LANL 1995). This event is not dependent on the remediation alternative but has the same annual frequency regardless of the alternative that is chosen. The length of time unremediated waste would remain in tanks that have not been backfilled would vary depending on the alternative and would affect the probability of the event. The probability of the event is the product of the annual frequency of the earthquake and the number of years the waste remains untreated in the unstabilized tanks.
At smaller annual frequencies, larger earthquakes could occur resulting in greater destruction and larger numbers of LCF to the onsite and offsite populations. In addition to population exposures from the collapsed SSTs, the impact to other Hanford Site facilities and operations would potentially add to the chemical and radiological risk. This would be a severe earthquake that would cause catastrophic structural damage in the Tri-Cities and the Hanford Site with expected extensive loss of life. There would be injuries and fatalities resulting from collapsed buildings and homes, fires, and traffic accidents. However, this section evaluates the radiological and chemical impacts resulting from the collapse of one SST.
E.4.3.4.1 Source-Term Development
It was conservatively assumed that the radiological and chemical contaminants in the headspace are available for release. The collapse of a portion of the dome and overburden compresses the vapor in the headspace as it descends, enhancing the vapor release rate by a sudden pressure difference. Assuming for each tank a respirable concentration of contaminants in the headspace of 100 mg/m3, a liquid SpG of 1.5, and a headspace volume of 1,000 m3 (Shire et al. 1995 and Jacobs 1996), the potential source-term contribution from the headspace release was calculated as follows:
(100 mg/m3) · (1 g/1,000 mg) · (1 L/1,000 g) · (1,000 m3) · (1/1.5) = 6.67E-02 L (1.8E-02 gal).
It was conservatively assumed that the liquids had been pumped from the tanks so that the tanks contained only solids and the MAR was 2,500 L for each tank. It was postulated that the fall of the dome and overburden generated an air movement sufficient to suspend a fraction of the MAR. Assuming the respirable release fraction to be 2.0E-03 (Shire et al. 1995 and Jacobs 1996), the potential source-term contribution was calculated as follows:
(2,500 L) · (2.0E-03) = 5.0 L (1.3 gal).
It was postulated that prevailing winds resuspend a respirable fraction of the MAR (2,500 L [660 gal]). A respirable release fraction of 4.0E-05/hr for 24 hours was assumed. The potential source-term contribution from resuspension was calculated as follows:
(2,500 L) · (4.0E-05/hr) · (24 hr) = 2.4 L (0.6 gal).
The combined source-term for the acute release is calculated as follows:
(6.67E-02 L) + (5.00E+00 L) + (2.4 L) = 7.4 L (2.0 gal).
E.4.3.4.2 Probability of a Beyond Design Basis Earthquake
This earthquake has a calculated annual exceedance frequency of approximately 1.40E-04 (WHC 1996b). The probability for this scenario based on 12 years of operation was therefore estimated to be 1.7E-03.
E.4.3.4.3 Radiological Consequences from a Beyond Design Basis Earthquake
The radiological dose to the receptors from the previous source-term was calculated by the GENII computer code (Napier et al. 1988) using the methodology previously discussed in Section E.1.1.6. The results are presented in Table E.4.3.12.
Table E.4.3.12 Dose Consequence from Seismic Event
E.4.3.4.4 Radiological Cancer Risk from a Beyond Design Basis Earthquake
The LCFs and LCF point estimate risk are presented in Table E.4.3.13.
Table E.4.3.13 Latent Cancer Fatality Risk from Seismic Event
In the bounding scenario, all 10 workers would potentially receive a fatal dose and assumably die directly after the exposure. There would also be 10 LCFs attributed to the exposure to the noninvolved workers and two LCFs to the general public if the accident occurred. The nominal scenario calculations show there would be no LCFs.
E.4.3.4.5 Chemical Consequences from a Beyond Design Basis Earthquake
Potential acute hazards associated with a beyond design basis earthquake are identical to those summarized in Tables E.2.2.16 (toxic chemicals, nominal conditions), E.2.2.17 (toxic chemicals, bounding conditions), E.2.2.18 (corrosive/irritant chemicals, nominal conditions) and E.2.2.19 (corrosive/irritant chemicals, bounding conditions) for the No Action alternative.
Under bounding conditions, chemical impacts were not evaluated for the MEI worker because all workers would receive a lethal radiation dose, as described previously.
Toxic Impact from Chemical Exposure
Under nominal conditions (Table E.2.2.16), the cumulative acute hazard ratio for the MEI worker was 2.64E+00 for ERPG-1, indicating that only mild transient effects would be expected. For the MEI noninvolved worker, the cumulative acute health hazard was 2.59E+00 for ERPG-3, indicating the potential for irreversible health effects that could be life threatening. This acute hazard ratio was primarily attributable to TOC (approximately 84 percent of the total hazard ratio). The TOC is assumed to be equivalent in toxicity to tributylphosphate, which is the most acutely toxic constituent of the organic analytes identified. Tributylphosphate was used as a surrogate because an inventory of the various chemicals that make up the TOC class is not available. The cumulative acute hazard ratio for the nearest noninvolved worker population consisting of 335 workers located 290 m (950 ft) away was less than 1.0 for all ERPGs, suggesting that no acute health effects would be expected.
Under bounding conditions (Table E.2.2.17), the cumulative hazard ratios for the MEI and nearest noninvolved worker (335 workers located 290 m [950 ft] away) were 2.15E+03 and 7.80E+00 for ERPG-3, respectively. These ratios were primarily attributable to:
- Uranium (approximately 47 percent of the total hazard ratio);
- Oxalate (approximately 24 percent of the total hazard ratio); and
- Mercury (approximately 13 percent of the total hazard ratio).
This exceedance of the ERPG-3 criterion for the nearest noninvolved worker population would not be expected to result in irreversible health effects or place these workers in a life-threatening situation for the following reasons.
- ERPG-3 is defined as a concentration in which a receptor can be exposed for 1 hour without irreversible health effects. Because the Hanford Site has an in-place emergency response plan designed to evacuate workers within 1 hour of an accident, workers would be expected to evacuate their location and move to an area where potential exposures would be well below ERPG-3. Therefore, this worker population would not be exposed to airborne concentrations that would be either life threatening or result in irreversible health effects.
- The estimated air concentrations of chemicals as a result of this accident were based on very conservative meteorology, which results in movement of a plume directly toward the worker population at a relatively slow rate with minimal wind dispersion. If less conservative meteorological parameters were used, wind dispersion would cause the estimated air concentrations of chemicals to be substantially less, and the ERPG-3 criterion would not be exceeded.
- Only the bounding toxic chemical evaluation exceeded ERPG-3, while the nominal evaluation was well below 1.00E+00 for ERPG-3, suggesting that the noninvolved worker population would not receive an exposure that would result in any permanent health effects.
The cumulative acute hazard ratio for the next nearest noninvolved worker population, composed of 1,500 people and located 1,780 m (5,840 ft) away, was 2.15E+00 for ERPG-2, indicating that reversible acute health effects would be expected. The cumulative acute hazard ratio for the MEI general public was 1.76E+00 for ERPG-2, indicating that reversible acute health effects would be expected.
Corrosive/Irritant Impact from Chemical Exposure
Under nominal conditions (Table E.2.2.18), the cumulative acute hazard ratios for the MEI worker, MEI noninvolved worker and nearest noninvolved worker (335 workers at 290 m [950 ft]) were 2.47E+01, 5.10E+02 and 1.85E+00, respectively, for ERPG-3, indicating the potential for irreversible health effects that could be life threatening. These ratios were almost entirely attributable to sodium, which was assumed to be equivalent to sodium hydroxide in corrosive/irritant effects. As discussed previously, this exceedance of the ERPG-3 criterion would not be expected to result in irreversible or life threatening health effects. For the next nearest noninvolved worker population, (1,500 workers at 1,780 m [5,840 ft]), the cumulative acute hazard ratio was 1.20E+00 for ERPG-1, indicating that only mild irreversible irritant effects would be anticipated. For the MEI general public, the cumulative acute hazard ratio was less than 1.0 for all ERPGs, and no acute health effects would be expected.
Under bounding conditions (Table E.2.2.19), the cumulative acute hazard ratios for the MEI noninvolved worker and nearest noninvolved worker (335 workers at 290 m [950 ft]) were 7.31E+02 and 2.65E+00, respectively for ERPG-3, indicating the potential for irreversible health effects that could be life threatening. These acute hazard ratios were primarily attributable to:
- Sodium (approximately 83 percent of the total hazard ratio); and
- Calcium (approximately 10 percent of the total hazard ratio).
As discussed previously, this exceedance of the ERPG-3 criterion would not be expected to result in irreversible or life threatening health effects.
For the next nearest noninvolved worker, and MEI general public, the cumulative acute hazard ratios were 1.74E+00 and 1.42E+00, respectively, for ERPG-1, indicating that only mild, transient irritant effects would be expected.
Under both nominal and bounding conditions, the probability of a seismic event is 1.68E-03.
E.4.3.5 Occupation Injuries, Illnesses, and Fatalities from Operations
The number of operation personnel to support the In Situ Fill and Cap alternative is summarized as follows:
- Continued operations - 2.39E+04 person-years; and
- Treatment operations - 1.51E+03 person-years.
Therefore, there would be a total of 2.54E+04 person-years for the In Situ Fill and Cap alternative. The total recordable injuries and illnesses lost workday cases and fatalities were calculated as follows:
Total Recordable Cases = (2.54E+04 person-years) · (2.2E+00 incidences/100 person-years) = 5.59E+02
Lost Workday Cases = (2.54E+04 person-years) · (1.1E+00 incidences/100 person-years) = 2.80E+02
Fatalities = (2.54E+04 person-years) · (3.2E-03 fatalities/100 person-years) = 8.13E-01
E.4.4 POST-REMEDIATION ACCIDENT
E.4.4.1 Deflagration in Storage Tank
After the tanks have been filled with gravel, the dome sealed off, and the Hanford Barrier placed over the tank farms, it was postulated that hydrogen builds up in the tank, reaches the LFL, and ignites. The probable sequence of events is that the tank would breach and possibly the asphalt layer in the Hanford Barrier would crack allowing an increased movement of the residual tank waste into the groundwater from increased infiltration. An explosion that could breach the dome, displace 23 m (7 ft) of overburden, and displace an additional 50 m (15 ft) of the Hanford Barrier, is considered to be incredible. For this event to occur, the following conditions must exist:
- Flammable gases must be generated from the waste;
- The concentration of the flammable gas must exceed the lower flammability limit;
- There must be an ignition source; and
- The deflagration would have to generate enough energy to breach the tank and crack the asphalt liner.
Generation of Flammable Gas
All 177 waste tanks produce flammable gases at the molecular level such as hydrogen, ammonia, and methane along with nitrous oxide (an oxidizer) due to radiolysis, organic degradation, and corrosion.
Gas Concentration
Gases generated from the residual tank waste would diffuse and accumulate in the voids within the gravel and the tank headspace created by the waste settling under the pressure of the fill. If the hydrogen is not allowed to escape from the tank through leaks or cracks in the tank, the hydrogen concentration will continue to increase as long as the potential for radiolysis, organic degradation, or corrosion exists.
It has been shown in tank waste that hydrogen generation rates may drop by approximately one-half every 15 years. Therefore, the gas concentration potential could be reduced by allowing the tanks to vent for 100 years (during institutional controls) through vent pipes passing up through the Hanford Barrier. The vents could then be sealed off. Allowing the tanks to vent for 100 years would reduce the probability of hydrogen reaching the LFL in the tank. Hydrogen gas concentration could be retarded by placing catalytic recombiners in the tank that would recombine hydrogen and oxygen. The buildup of hydrogen could be mitigated over the long-term by engineering permanent measures to allow the gas to escape into the atmosphere. This may include cutting small openings in the tanks domes and the asphalt layer within the Hanford Barrier.
Ignition of Gas
If the gas concentrations in the tank manage to exceed the LFL, the ignition sources are limited. Possible ignition sources would include a lightning strike, an earthquake, or heat produced by reactions taking place in the materials remaining in the tank. If the gas was ignited, the propagation of the burn through the gravel is dependent on the size of the voids in the gravel matrix. Flames will not propagate in a porous material if the pore size is less than a critical value.
Consequences of Deflagration
The probable sequence of events is that the tank would breach and possibly the asphalt layer in the Hanford Barrier would crack allowing an increased leaching of the residual tank waste into the groundwater.
Consequences of Gas Building Up Under the Asphalt Barrier
If the hydrogen gas generated in the tanks was able to permeate from the tank through leaks and cracks, it could potentially build up under the asphalt layer of the Hanford Barrier if the permeation rate through the asphalt is slower than the rate in which it reaches the asphalt. Because hydrogen is highly diffusible, it is extremely unlikely that this would be the case. However, if hydrogen did build up under the asphalt layer, the worst credible consequences would result in the asphalt cracking allowing an increased movement of the residual tank waste into the groundwater. This event could be mitigated by placing catalytic recombiners under the asphalt that would recombine hydrogen and oxygen or venting the asphalt layer.
E.4.4.2 Seismic Induced Rupture of Stabilized Tanks
An evaluation was performed to determine if displacement on a fault could increase exposure to the waste after remediation was completed. For this to occur, a capable fault (a fault on which displacement can occur) would have to intersect one or more tanks and cause displacement equal to the thickness of the soil cover on the tank and the Hanford Barrier, a total of 6.4 m (21 ft).
The seismicity of the area was studied extensively when the area was a potential candidate site for a potential geologic repository (Rockwell 1983). This report concludes that earthquakes in the central Columbia Plateau indicate the stress regime that exists today has been relatively unchanged for more than 14 million years, and no change of this stress regime is anticipated over the next 100,000 years. Deformation was in progress in the late Grande Ronde time (approximately 14.5 million years before present) and continued at an average low rate of uplift (vertical strain) from 14.5 to 10.5 million years before present as determined from the aerial and thickness distribution of basalt flows.
Strain appears to be concentrated in steeply dipping strata and on major structures. New first-order structures do not appear to have developed in the Quaternary, nor are they anticipated to develop in the next 10,000 to 100,000 years (Rockwell 1983).
Seismicity in the central Columbia Plateau is confined to a thin, 2.6-m (8.5-ft) crust and is characterized by temporally and spatially limited swarms of low magnitude (magnitude 3.5), shallow (0.6-m [2-ft]) earthquakes that may be characteristic of brittle deformation in basalt.
Earthquakes in the central Columbia Plateau presently are not associated with mapped geologic faults, nor in a manner that suggests the presence of unmapped faults. Swarms have occurred on the flanks of the Saddle Mountains, a first-order structure which is faulted, but the events do not correspond with mapped faults. However, swarms also have occurred elsewhere where there are no mapped geologic structures. Some small alignments are indicated by the migration of swarm events in the Saddle Mountains.
An average displacement rate of 0.03 to 0.06 mm/yr (0.0012 to 0.0024 in/yr) was calculated. While a fault model has been assumed, this estimate could represent the total deformation associated with a wider zone north and south of the crest of the Saddle Mountains structure.
Because the average deformation rate of the region is 0.06 mm/yr (0.0024 in./yr), there would be 0.6 m (2 ft) of deformation in 10,000 years. This is much less than the 6.4 m (21 ft) of cover over the tanks. Therefore, even if all displacement in the region were concentrated on one fault and that fault intersected a tank, there would be only 0.6 m (2 ft) of displacement over 10,000 years and therefore, waste would not be displaced to the surface. The tanks would most likely crack, allowing increased infiltration to the groundwater.
E.4.5 SUMMARY OF ACCIDENTS
The potential consequences from nonradiological and nonchemical accidents that include occupational and transportation impacts are summarized in Table E.4.5.1 The LCFs associated with representative accidents for each component of the alternative are summarized in Table E.4.5.2 along with the probability of the accident. The chemical hazards associated with representative accidents for each component of the alternative are summarized in Table E.4.5.3. The chemical hazard is expressed as exceedance of the ERPG threshold values.
Table E.4.5.1 Summary of Potential Nonradiological/Nonchemical Accident Consequences
Table E.4.5.2 Summary of Potential Radiological Accident Consequences
Table E.4.5.3 Chemical Exposures Resulting from Potential Operations and Transportation Accidents
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