E.10.0 EX SITU/IN SITU COMBINATION 2 ALTERNATIVE
The Ex Situ/In Situ Combination 2 alternative is a combination of the Ex Situ Intermediate Separations alternative and the In Situ Fill and Cap alternative. The Ex Situ/In Situ Combination 2 alternative would involve ex situ treatment and disposal of some waste and in situ treatment of the remaining waste like Ex Situ/In Situ Combination 1, except that there would be retrieval from fewer tanks. This section analyzes and compares the construction, operation, and transportation risks associated with this alternative.
E.10.1 CONSTRUCTION ACCIDENTS
The construction activities associated with the Ex Situ/In Situ Combination 2 alternative are discussed in Appendix B of the EIS. It should be noted there are no radiological or chemical consequences associated with construction accidents. Occupational injuries, illnesses, and fatalities resulting from potential construction accidents are calculated as follows.
The number of construction personnel to support the Ex Situ/In Situ Combination 2 alternative was estimated at an average of 1.79E+04 person-years (Jacobs 1996).
The following total recordable injuries and illnesses, lost workday cases, and fatalities were calculated using the incidence rates from Table E.1.2.1:
Total Recordable Cases = (1.79E+04 person-years) · (9.75E+00 incidences/100 person-years) = 1.74E+03
Lost Workday Cases = (1.79E+04 person-years) · (2.45E+00 incidences/100 person-years) = 4.38E+02
Fatalities = (1.79E+04 person-years) · (3.20E-03 fatalities/100 person-years) =5.72E-01
E.10.2 TRANSPORTATION ACCIDENTS
Transportation activities associated with this alternative are:
- Transporting residual SST waste to vitrification facility;
- Transporting earthen material from onsite borrow sites to fill tank voids;
- Transporting earthen material from onsite borrow sites for Hanford Barrier;
- Transporting construction material to the Hanford Site; and
- Employees commuting to work each day.
E.10.2.1 Radiological Consequences
The methodology for determining radiological consequences from accidents while transporting residual SST waste to the vitrification facility was previously discussed in Section E.6.2.1.
The receptor dose and LCF risk resulting from the accident analysis for retrieval of SST residuals is presented in Table E.10.2.1 for the integrated population and Table E.10.2.2 for the MEI worker and MEI general public.
Table E.10.2.1 Integrated Radiological Impact from Retrieval Transport Accidents
Table E.10.2.2 Maximally-Exposed Individual Radiological Impact from Retrieval Transport Accidents
There would be no LCFs resulting from an accident while transporting retrieved waste onsite.
E.10.2.2 Chemical Exposure
The same chemicals would be transported to the Hanford Site by truck and rail as in the Ex Situ Intermediate Separations alternative. Therefore, the chemical exposure resulting from an accident would be the same as that shown in Table E.6.2.4 for Ex Situ Intermediate Separations alternative.
However, there would be 70 percent fewer shipments, which equates to a 70 percent reduction in the probability of an accident.
The general public exposure to anhydrous ammonia would exceed the ratio of exposure to ERPG-3 by 1.24E+01 and sodium hydroxide would exceed the ratio of exposure to ERPG-1 by 2.45E+00 for corrosive/irritant chemicals. Consequently, this exposure to the MEI general public could potentially result in lethal effects.
E.10.2.3 Occupational Injuries and Fatalities
Truck and Rail Transportation
Injuries and fatalities resulting from direct impact of transportation accidents are analyzed in this subsection. Rail and truck transportation activities to transport material and supplies to the Site for this alternative represents 70 percent of retrieval, 70 percent of vitrification plant construction, and 60 percent of vitrification operations of the data values in the Ex Situ/In Situ Combination 1 alternative. Closure represents 16 percent of the closure data values in the extensive retrieval engineering data package (WHC 1995j) plus 84 percent of the closure data values for In Situ Fill and Cap in the in situ vitrification engineering data package (WHC 1995f). The results are summarized in Table E.10.2.3.
The number of injuries and fatalities were calculated by multiplying the total distance traveled in each zone shown in Table E.10.2.4 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.
The expected injuries and fatalities resulting from transportation accidents associated with the ExSitu/In Situ Combination 2 alternative are summarized in Table E.10.2.5.
Employee Traffic
In addition to transporting materials and supplies to and from the Hanford Site by truck and rail, 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 5.36+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). From the information listed previously the total employee vehicle distance was calculated as follows:
(5.36E+04 person-years) · (260 days/year) · (140 km/day) · (1/1.35 passengers per vehicle) = 1.45E+09 km (9.02E+8 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 = (1.45E+09 km) · (7.1E-07 injuries/km) = 1.03E+03
Fatalities = (1.45E+09 km) · (8.98E-09 fatalities/km) =1.30E+01
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 and rail transport and employee vehicle accidents. The results are summarized in Table E.10.2.6.
E.10.3 OPERATION ACCIDENTS
The radiological and chemical operation accidents for the Ex Situ/In Situ Combination 2 alternative are the same as the Ex Situ Intermediate Separations alternative and the In Situ Fill and Cap alternative. The radiological cancer risk and the chemical exposure would be bound by the Ex Situ Intermediate Separations alternative presented in Section E.6.3 and are summarized as follows.
E.10.3.1 Routine Operation - Mispositioned Jumper Accident - Tank Waste Transfers
The dominant routine operations accident during tank waste transfers is the mispositioned jumper accident previously discussed in the No Action alternative in Section E.2.2.1 and are 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 Ex Situ/In Situ Combination 2 alternative was based on 16 years of operations; therefore, the probability was calculated to be 1.8E-01.
Radiological Consequences - The radiological consequences presented in Table E.2.2.2 are reproduced in Table E.10.3.1.
Table E.10.3.1 Dose Consequence from Mispositioned Jumper
Radiological Cancer Risk - The LCFs calculated in Section E.2.2.1.4 are the same for the Ex Situ/In Situ Combination 2 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.10.3.2. The bounding scenario calculations show that all 10 workers would potentially receive a fatal dose and assumably die directly after the exposure if the accident occurred. There would be approximately seven LCFs from the noninvolved worker population and two from the general public. The nominal scenario calculations show there would be no LCFs.
Table E.10.3.2 Latent Cancer Fatality Risk from Mispositioned Jumper
Chemical Consequences
Potential acute hazards associated with a mispositioned jumper are identical to those 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 chemicals, bounding conditions) for the No Action alternative.
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 1.0, 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 3.00E+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 1.75E-01.
E.10.3.2 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 is summarized as follows:
Source-Term - The source-term resulting from the fire 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 25 years of operation was therefore estimated to be 1.8E01.
Radiological Consequences - The radiological consequences presented in Table E.2.2.8 are reproduced in Table E.10.3.3.
Table E.10.3.3 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.10.3.4.
Table E.10.3.4 Latent Cancer Fatality Risk from Hydrogen Deflagration in Waste Storage Tank
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 2 LCFs to the general public if the accident occurred. The nominal scenario calculations show there would be no LCFs.
Chemical Consequences
Potential acute hazards associated with a hydrogen burn in a waste storage tank are identical to those 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.
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.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 100 m (330 ft) from the source area. The nearest 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 100 m (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 m (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 1.80E-01.
E.10.3.3 Retrieval - Loss of Filtration Accident
The dominant retrieval operations accident is the loss of filtration accident previously discussed in the Ex Situ Intermediate Separations alternative in Section E.6.3.3 and is summarized as follows.
Source-Term - The source-term resulting from the airborne release in Section E.6.3.3.1 was calculated to be 2.5E-01 L (6.6E-02 gal).
Probability - The frequency of a loss of filtration in section E.6.3.3.2 was 8.8E-06 per year. The Ex Situ/In Situ Combination 2 retrieval activity was based on 25 years of operations; therefore, the probability was calculated to be 2.2E-04.
Radiological Consequences - The radiological consequences presented in Section 6.3.3.3 are reproduced in Table E.10.3.5.
Table E.10.3.5 Dose Consequence from Loss of Filtration
Radiological Cancer Risk - The LCFs and the LCF point estimate risk were calculated for the receptors and are presented in Table E.10.3.6.
Table E.10.3.6 Latent Cancer Fatality Risk from Loss of Filtration
In the bounding scenario all 10 workers would potentially receive a fatal dose and assumably die directly after the exposure if the accident occurred. The calculations also show there would be less than one LCF attributed to the exposure to the noninvolved workers and the general public if the accident occurred. The nominal scenario calculations show there would be no LCFs.
Chemical Consequences
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.6.3.8 and E.6.3.9 for the nominal and bounding toxic effects, respectively, and Tables E.6.3.10 and E.6.3.11 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.
Under nominal conditions (Table E.6.3.8), the cumulative acute hazard ratio for the MEI worker was less than 1.0 for all ERPGs, indicating that no adverse acute health effects would be expected. For the MEI noninvolved worker, the cumulative acute hazard ratio was 1.84E+00 for ERPG-1, indicating that only mild, transient, acute health effects would be expected. No acute health effects were predicted for the MEI general public under nominal conditions.
Under bounding conditions (Table E.6.3.9), the cumulative acute hazard ratio for the MEI noninvolved worker was 7.27E+01 for ERPG-3, indicating the potential for irreversible health effects that could be life threatening. This acute hazard ratio is primarily attributable to:
- Uranium (approximately 48 percent of the total hazard ratio);
- Oxalate (approximately 24 percent of the total hazard ratio);
- Mercury (approximately 13 percent of the total hazard ratio); and
- TOC (approximately 7 percent of the total hazard ratio).
As discussed previously, this is a hypothetical receptor located 100 m (330 ft) from the source. The cumulative acute hazard ratio for the nearest noninvolved worker population (335 workers) located 290 m (950 ft) from the source was 5.40E+00 for ERPG-2, indicating that reversible acute health effects would be expected. No acute health impacts were predicted for the MEI general public.
Corrosive/Irritant Impact from Loss of Filtration
Under nominal conditions (Table E.6.3.10), the cumulative acute hazard ratio for the MEI worker was 2.11E+00 for ERPG-2, indicating that reversible corrosive/irritant effects would be expected. For the MEI noninvolved worker, the cumulative acute hazard ratio for ERPG-3 was 1.72E+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 3.02E+00, indicating that only mild, transient irritant effects would be expected. No acute health impacts were predicted for the MEI general public under nominal conditions.
Under bounding conditions (Table E.6.3.11), the cumulative acute hazard ratio for the MEI noninvolved worker was 2.47E+01 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 82 percent of the total hazard ratio); and
- Calcium (approximately 9 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 4.38E+00 for ERPG-1, indicating that only mild, transient irritant 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 loss of filtration event in a waste storage tank is 2.20E-04.
E.10.3.4 Pretreatment - Seismic Induced Line Break in Vault
The dominant pretreatment operations accident is the seismic-induced line break in vault accident previously discussed in the Ex Situ Intermediate Separations alternative in Section E.6.3.4 and is summarized as follows:
Source-Term - The source-term resulting from the airborne release in Section E.6.3.4.1 was calculated to be 7.3E-02 L (1.9E-02 gal).
Probability - The annual exceedance frequency of the seismic event in Section E.6.3.4.2 was 6.5E-04 per year. The Ex Situ/In Situ Combination 2 alternative was based on 25 years of operations; therefore, the probability was calculated to be 1.6E-02.
Radiological Consequences - The radiological consequences presented in Section 6.3.4.3 are reproduced in Table E.10.3.7.
Table E.10.3.7 Dose Consequence from Seismic Induced Line Break in Vault
Radiological Cancer Risk - The LCFs and the LCF point estimate risk were calculated for the receptors and presented in Table E.10.3.8. The calculations show there would be no LCFs attributable to this exposure if the accident occurs for the bounding and nominal scenarios.
Table E.10.3.8 Latent Cancer Fatality Risk from Seismic-Induced Line Break in Vault
Chemical Consequences
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.6.3.14 and E.6.3.15 for the nominal and bounding toxic effects, respectively, and Tables E.6.3.16 and E.6.3.17 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.
Toxic Impact from Chemical Exposure
Under nominal conditions (Table E.6.3.14), the cumulative acute hazard ratios for the MEI worker, MEI noninvolved worker, and MEI general public were less than 1.0, indicating that no adverse acute health effects would be expected for these three receptors. Under bounding conditions (Table E.6.3.15), the cumulative acute hazard ratios for the MEI worker, MEI noninvolved worker and MEI general public were less than 1.0, indicating that no adverse acute health effects would be expected for these three receptors.
Corrosive/Irritant Impact from Chemical Exposure
Under nominal conditions (Table E.6.3.16), the cumulative acute hazard ratios for the MEI worker, MEI noninvolved worker, and MEI general public were less than 1.0, indicating that no adverse acute health effects would be expected for these three receptors. Under bounding conditions (Table E.6.3.17), the cumulative acute hazard ratios for the MEI worker, MEI noninvolved worker, and MEI general public were less than 1.0, indicating that no adverse acute health effects would be expected for these three receptors.
Under both nominal and bounding conditions, the probability of a pretreatment spray release is 1.63E-02 .
E.10.3.5 Treatment (Ex Situ Vitrification) - Canister of Vitrified High-Level Waste Inadvertently Drops and Ruptures
The dominant immobilization operations accident is the "canister of vitrified HLW inadvertently drops and ruptures" accident previously discussed in the Ex Situ Intermediate Separations alternative in Section E.6.3.5 and is summarized as follows:
Source-Term - The source-term resulting from the airborne release in Section E.6.3.5.1 was calculated to be 2.5E-06 g (8.8E-08 oz).
Probability - The frequency of the accident in Section E.6.3.5.2 was 6.0E-01 per year. The Ex Situ/In Situ Combination 2 alternative was based on 25 years of operations; therefore, the probability was calculated to be 1.0E+00.
Radiological Consequences - The radiological consequences presented in Section 6.3.5.3 are reproduced in Table E.10.3.9.
Table E.10.3.9 Dose Consequence from Breached Canister
Radiological Cancer Risk - The LCFs and the LCF point estimate risk were calculated for the receptors and presented in Table E.10.3.10. The calculations show there would be no LCFs attributable to this exposure if the accident occurs for the bounding and nominal scenarios.
Table E.10.3.10 Latent Cancer Fatality Risk from Breached Canister
Chemical Consequences - No chemical consequences were evaluated (Shire et al. 1995 and Jacobs 1996) because the release would be through two-stage HEPA filters that would reduce the source-term well below the cumulative ratio of exposure to ERPG-1 values for toxic or corrosive/irritant chemicals.
E.10.3.6 Treatment - In Situ Fill and Cap
The dominant treatment operations accident is the tank deflagration accident resulting in a tank dome collapse previously discussed in the In Situ Fill and Cap alternative in Section E.4.3.3 and is summarized as follows:
Source-Term - The source-term resulting from the airborne release in Section E.4.3.3.1 was calculated to be 7.5 L (2.0 gal).
Probability - The probability of a tank dome collapse in Section E.4.3.3.2 was assumed to be 1.0E-04.
Radiological Consequences - The radiological consequences presented in Section 4.3.3.3 are reproduced in Table E.10.3.11.
Table E.10.3.11 Dose Consequence from Tank Dome Collapse Due to Deflagration
Radiological Cancer Risk - All 10 workers and the MEI noninvolved worker would potentially receive a lethal dose. The LCFs and the LCF point estimate risk were calculated for the receptors and presented in Table E.10.3.12.
Table E.10.3.12 Latent Cancer Fatality Risk from Tank Dome Collapse Due to Deflagration
In addition to all 10 workers dying from a lethal dose, the calculations show there would be eleven LCFs attributed to the exposure to the noninvolved workers and two LCFs attributed to the general public if the accident occurred. The nominal scenario calculations show there would be no LCFs.
E.10.3.6.1 Chemical Consequences of Tank Dome Collapse
The chemical exposure to the receptors from the postulated accident was identical to that 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 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.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.
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.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 2.65E+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 1.00E-04.
E.10.3.7 Beyond Design Basis Accident
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.10.3.7.1 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 (660 gal) for each tank. It was postulated that the fall of the dome and overburden generated an air movement sufficient to suspend a fraction 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) + (5.0 L) + (2.4 L) = 7.4 L (2.0 gal).
E.10.3.7.2 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 25 years of operation was therefore estimated to be 3.5E-03.
E.10.3.7.3 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.10.3.13.
Table E.10.3.13 Dose Consequence from Seismic Event
E.10.3.7.4 Radiological Cancer Risk from a Beyond Design Basis Earthquake
The LCFs and LCF point estimate risk are presented in Table E.10.3.14.
Table E.10.3.14 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.10.3.7.5 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.2.2.18 (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, 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 away) were 2.15E+03 and 7.80 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, 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 3.50E-03.
E.10.3.8 Occupation Injuries, Illnesses, and Fatalities from Operations
The number of operation personnel to support the Ex Situ/In Situ Combination 2 alternative was estimated at an average of 3.58E+04 person-years (Jacobs 1996).
The total recordable injuries and illnesses, lost workday cases, and fatalities were calculated as follows:
Total Recordable Cases = (3.58E+04 person-years) · (2.2E+00 incidences/100 person-years) = 7.87E+02
Lost Workday Cases = (3.58E+04 person-years) · (1.1E+00 incidences/100 person-years) = 3.93E+02
Fatalities = (3.58E+04 person-years) · (3.20E-03 fatalities/100 person-years) = 1.14E+00
E.10.4 POST-REMEDIATION ACCIDENT
E.10.4.1 Deflagration in Storage Tank
The tanks that have had 99 percent of their waste removed and filled with gravel do not pose a credible risk. However, the tanks that have been saltwell pumped and filled with gravel may. 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. An explosion that could breach the dome, displace 2 m (7 ft) of overburden, and displace an additional 5 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 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 continqe 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.
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 upon 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
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.
E.10.4.2 Seismic Induced Rupture of Stabilized Tanks
As discussed in Section E.4.4.2, displacement on a fault that would increase exposure to the waste after remediation is considered to be incredible. The tanks would most likely crack, allowing increased infiltration to the groundwater.
E.10.5 SUMMARY OF ACCIDENTS
The potential consequences from nonradiological and nonchemical accidents that include occupational and transportation impacts are summarized in Table E.10.5.1. The LCFs associated with representative accidents for each component of the alternative are summarized in Table E.10.5.2 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.10.5.3. The chemical hazard is expressed as an exceedance of the ERPG threshold values.
Table E.10.5.1 Summary of Potential Nonradiological/Nonchemical Accident Consequences
Table E.10.5.2 Summary of Potential Radiological Accident Consequences
Table E.10.5.3 Chemical Exposures Resulting from Potential Operations and Transportation Accidents
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