ML120620462
| ML120620462 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 04/25/2012 |
| From: | NRC/FSME |
| To: | Pacific Gas & Electric Co |
| John Hickman (301) 415-3017 | |
| Shared Package | |
| ML120620450 | List: |
| References | |
| TAC J00369 | |
| Download: ML120620462 (6) | |
Text
SAFETY EVALUATION BY OFFICE OF FEDERAL AND STATE MATERIALS AND ENVIRONMENTAL MANAGEMENT PROGRAMS RELATED TO REQUEST FOR ALTERNATE DISPOSAL APPROVAL FOR DISPOSAL OF HUMBOLDT BAY POWER PLANT WASTE AT THE US ECOLOGY IDAHO FACILITY PACIFIC GAS AND ELECTRIC COMPANY HUMBOLDT BAY POWER PLANT, UNIT 3 DOCKET NO. 50-133
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Background===
On June 7, 2011, Pacific Gas and Electric Company (PG&E) submitted a request for NRC authorization for the disposal of waste from the Humboldt Bay Power Plant (HBPP) at the U.S.
Ecology Idaho (USEI) facility in accordance with 10 CFR 20.2002 (ML11160A211). On January 9, 2012, PG&E submitted answers to the NRC staffs questions on the request as well as corrections made to the original submittal (ML120330349).
This request is similar to a request made by PG&E on April 1, 2010 (ML101170554, ML102290019) that was approved by the NRC on November 2, 2010 (ML102870344). The previous 20.2002 request consisted of 200,000 ft3 (5663 m3) of waste that was primarily from the non-nuclear Units 1 and 2. The current 20.2002 request is for 2,000,000 cubic feet (56,634 cubic meters) of hazardous waste, soil, and debris containing low-activity radioactive debris generated during the demolition of structures and remediation activities at Unit 3. The waste material includes soil, concrete, steel, insulation, roofing material, gravel, metal, wood, and other debris. The waste would be transported by truck from Humboldt Bay Power Plant in Eureka, CA to the USEI facility in Grand View, Idaho in the Owyhee Desert over a period of four years. The USEI facility is a Subtitle C Resource Conservation and Recovery Act (RCRA) hazardous waste disposal facility permitted by the State of Idaho.
The NRC typically approves 20.2002 requests that will result in a dose to a member of the public (including all exposure groups) that is no more than a few millirem/year (see SECY 0060, Attachment 1, and NUREG-1757, Vol. 1, Rev. 2, Section 15.12).
Source Term The waste included in the current disposal request contains fission and activation products from operations at Unit 3. The debris waste will be scabbled/cleaned and surveyed to verify that alpha contamination from transuranics is non-detectable. The projected concentrations of radionuclides in the waste are less than or equal to the concentrations in Table 1, and PG&E will ensure that the concentrations in each shipment are less than the projected values. The Table 1 concentrations are the same as the maximum concentrations assumed in the previous 20.2002 request for HBPP waste. During the disposal of that waste, data on the actual concentrations was collected, and actual concentrations were equal to approximately 10% of the projected values.
2 Table 1. Source Term Concentration of Radionuclides Radionuclide Maximum Concentration transported from HBPP to USEI pCi/g (Bq/g)
Cs-137 15 (0.555)
Co-60 5 (0.185)
Sr-90 1 (0.037)
H-3 100 (3.7)
C-14 1 (0.037)
Fe-55 1 (0.037)
Ni-63 10 (0.37)
Eu-152 1 (0.037)
Eu-154 1 (0.037)
Ag-108m 0.1 (0.0037)
Scenarios, Modeling, and Results PG&E supplied dose assessments for different possible exposure scenarios for various members of the public. These exposure scenarios include dose to the transportation and USEI workers, post-closure dose to the general public, and intruder scenarios. These dose assessments are similar to those provided by PG&E in the previously approved 20.2002 request.
Transportation and Worker Doses The worker scenarios considered in this 20.2002 request are the same as those evaluated in the previously approved request: a truck driver who transports the waste from HBPP to USEI, a surveyor, a stabilization cell worker, and the waste cell operator.
It is estimated that 11 trucks will be used to transport the waste in approximately 3367 shipments total, or 842 shipments per year. The distance for the trip from HBPP to USEI is approximately 659 miles (1061 km), and the trip is estimated to take 13.18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> based on an assumed speed of 50 mph (80 km/hr). The conveyances will be verified to be in compliance with Department of Transportation external loose surface contamination limits prior to shipping, so it is assumed that there is no internal dose to the driver or members of the public during shipment of the waste. The potential external dose to members of the public during transportation is bounded by the dose to the truck driver since the time of exposure is longer for the truck driver.
The dose to three different types of USEI workers was calculated by the licensee. These workers included a surveyor, a stabilization cell worker, and a cell operator. The surveyor surveys the waste when it is received at the site. The waste is then taken to the stabilization building for treatment of RCRA hazardous constituents. It is conservatively assumed in this analysis that all waste from HBPP will be stabilized, but some of the waste will likely not require treatment. The waste is stabilized by mixing it with stabilization agents in a steel lined concrete tank. The building where stabilization is done has a negative pressure system and the air is exhausted through HEPA filters. The excavator operator performing the stabilization work
3 wears a respirator and is in an enclosed cab. After the waste is stabilized, the excavator operator moves the waste from the stabilization tank to trucks for transport to disposal cell.
Once the waste is brought to the disposal cell, the bulldozer operator at the cell spreads and compacts the waste. The bulldozer operator wears a respirator and is in an enclosed cab. The dose to the haul truck driver on site was not specifically analyzed by PG&E because it is assumed that their doses would be much less than the dose to the drivers transporting the waste to the site because the exposure times for the haul truck drivers are much shorter.
Table 2 summarizes the job function scenario assumptions. The times assigned are the times for one person to perform each function one time. In this analysis, it is assumed that a specific number of workers per year will be available to carry out each of the job functions, and the total dose for the job function is divided equally among all workers within a job function group.
Table 2. Job Function Scenario Assumptions Job Function Number of Workers in Group Time (hrs)
Number of Repetitions per year Truck Driver 11 13.18 842 Survey Crews 4
0.08 842 Stabilization Cell Worker 6
0.75 337 Waste Cell Operator 2
0.25 337 The method and parameters used by PG&E to calculate the internal dose for the stabilization worker and the truck driver are the same as those used in the previously approved 20.2002 request. In this assessment, the internal dose to the stabilization worker from the inhalation of contaminated dust was calculated based on an assumed concentration of dust in the building of 0.23 mg/m3, an assumed inhalation rate of 1.2 m3/hr, the concentrations of radioactivity in Table 1, and the FGR 11 inhalation Dose Conversion Factors (DCFs). The stabilization worker internal dose was assumed to be the bounding inhalation dose for all other personnel. The workers in the stabilization building and disposal cells are required to wear respirators, but credit for this was not taken in the calculations of dose due to the inhalation of dust, so the actual inhalation dose would likely be smaller than what was calculated. The inhalation dose to the truck driver and surveyor was assumed to be zero because the waste is going to be transported in a strong-tight container that is verified to be in compliance with DOT external loose surface contamination limits.
The MicroShield 7.02 code was used to calculate the external doses for the workers. The parameters used to estimate the external dose were identical to those used in the previous HBPP 20.2002 request except for:
aluminum shielding was assumed for the truck driver and surveyor instead of iron to account for the potential future use of aluminum intermodal containers; the assumed distance between the IMC and the truck driver was reduced from 36ft, 3.2 in (11.05 m) to 33 ft, 4.5 in (10.2 m); and the shielding for the stabilization worker was removed in this request because the working angle does not always provide the worker with the full benefit of the shielding from steel floor.
4 All of the above changes result in a higher estimated external dose for the worker. The internal, external, and total doses estimated for the workers from the waste in this 20.2002 request are presented below in Table 3.
Table 3. Annual Dose per Person for Individual Job Function Job Function Internal Dose mrem/yr (mSv/yr)
External Dose mrem/yr (mSv/yr)
Total Dose mrem/yr (mSv/yr)
HBPP Truck Driver 0 (0) 7.13e-1 (7.13e-3) 7.13e-1 (7.13e-3)
Surveyor 0 (0) 1.41e-1 (1.41e-3) 1.41e-1 (1.41e-3)
Stabilization Worker 4.05e-5 (4.05e-7) 1.54e-1 (1.54e-3) 1.54e-1 (1.54e-3)
Cell Operator 4.05e-5 (4.05e-7) 9.58e-2 (9.58e-4) 9.59e-2 (9.59e-4)
NRC staff performed independent calculations of the external doses using MicroShield and obtained similar results to the licensee. In addition, NRC staff performed independent calculations of the internal dose and obtained similar results to the licensee.
Since the disposal of the waste included in the previous 20.2002 request for HBPP is still ongoing, there is some potential for the USEI workers to receive a dose both from the waste in the previous 20.2002 request and the current request during the same year. However, as seen in Table 4, even if the workers were to receive the total expected annual dose from both sets of waste during the same year, the cumulative dose would still be less than one mrem. Therefore, the results of the dose assessment for the USEI and transportation workers indicate that the dose to these individuals will be within the few millirem criteria.
Table 4 Potential Cumulative Dose from Previous and Current 20.2002 Requests Previous Request mrem/yr (mSv/yr)
Current Request mrem/yr (mSv/yr)
Total Dose mrem/yr (mSv/yr)
HBPP Truck Driver 2.29e-1 (2.29e-3) 7.13e-1 (7.13e-3) 9.42e-1 (9.42e-3)
Surveyor 4.54e-2 (4.54e-4) 1.41e-1 (1.41e-3) 1.86e-1 (1.86e-3)
Stabilization Worker 2.91e-2 (2.91e-4) 1.54e-1 (1.54e-3) 1.83e-1 (1.83e-3)
Cell Operator 6.15e-2 (6.15e-4) 9.59e-2 (9.59e-4) 1.57e-1 (1.57e-3)
Post-Closure Dose The post-closure dose to a member of the public at the USEI site was evaluated by PG&E using the RESRAD Version 6.5 code. This analysis used the resident farmer scenario and the pathways modeled included external gamma exposure, inhalation, and plant, meat, milk, drinking water, and soil ingestion. The parameter values used in this assessment were the same as those used in the previously approved HBPP 20.2002 request. The maximum dose calculated by the licensee using the RESRAD code was 4.90e-3 mrem/yr (4.90e-5 mSv/yr) at a time of 1000 years following closure of the facility. NRC staff performed independent RESRAD calculations and obtained similar results as the licensee.
The radionuclide concentrations used in the RESRAD model were based on the assumption that all of the waste is shipped to the USEI facility at the concentrations listed in Table 1. The waste is assumed to be spread evenly over the entire disposal cell, which has an area of approximately 88,221 m2, a depth of 33.6 m, and an assumed density of 1.5 g/cm3, which corresponds to a dilution factor of approximately 90. The assumption that all of the HBPP waste will have the concentrations listed in Table 1 is conservative since these values correspond to
5 the maximum concentration that will be in waste. However, the assumption that the waste will be diluted across the entire disposal cell is likely optimistic. The NRC staff performed a sensitivity analysis to determine the effect of this assumption on the calculated dose and determined that even if the waste is not diluted at all in the disposal cell the projected dose is still less than 1 mrem.
The peak dose to the member of the public from the waste in this 20.2002 request and from the previous HBPP request is from the groundwater dependent pathways. Therefore, there is some potential for the member of the public to receive the dose from both disposal requests.
However, the predicted doses in both disposal requests are much less than one millirem, so the combined dose would also be less than one millirem and is consistent with the few millirem criteria.
Inadvertent Intruder Dose PG&E calculated the potential dose to a post-closure intruder using the methods in NUREG-0782. The intruder scenario considered was the intruder construction scenario, which assumes that a house is constructed on the site in the future and that the waste is contacted during excavation of the basement and placement of utilities. Since the thickness of the cap is more than 3 meters, it is unlikely that the excavation for a house with a basement would be deep enough to result in intrusion into the waste, so the well driller construction scenario is more likely for the inadvertent intruder at this site. However, the dilution of the waste would be higher for the well driller scenario, so the dose from the well driller scenario is bounded by the intruder construction scenario. The parameter values used in the intruder assessment were the same as those assumed in the previously approved HBPP 20.2002 request. PG&E estimated the dose to the intruder to be 0.147 mrem/yr (1.47e-3 mSv/yr). The NRC staff reviewed these calculations and found that they were performed accurately. The NRC staff also performed an independent sensitivity analysis of the dose for the intruder resident farmer scenario. The results indicated that the dose to a receptor who drills a well through the waste and who lives and farms on soil containing the well cuttings would still be within the few millirem range.
The methodology used by PG&E to evaluate the dose from the intruder construction scenario considers the dose from the direct exposure to waste that has been brought to the surface, so an individual would only receive a cumulative dose from the waste in this request and the previous HBPP request if the individual intruded into both sets of waste during the same year, which is not a likely scenario. However, the intruder doses calculated in this 20.2002 request and the previous HBPP request were both small, so even in the unlikely event that an intruder was exposed to both, the dose would still be well within the few millirem range.
As a result of the calculations described above, the NRC staff finds that the potential dose to an inadvertent intruder is consistent with the few millirem per year criteria.
Conclusions PG&E requested that NRC approve alternate disposal, in accordance with 10 CFR 20.2002, for disposing of 2,000,000 ft3 (56,634 m3) of waste at the USEI Facility near Grand View, Idaho.
PG&E has provided an adequate description of the waste to be disposed of and the proposed manner and conditions of waste disposal. In addition, PG&E will verify that the maximum concentrations in the waste do not exceed the concentrations assumed in this assessment prior to shipment of the waste.
6 The potential doses associated with transportation, waste handling and disposal have been evaluated as a part of the review of this 10 CFR 20.2002 application. As described above, the NRC staff found that the projected doses to individual transportation and USEI workers have been appropriately estimated and are demonstrated to meet the NRCs alternate disposal criteria of contributing a dose of not more than a few millirem per year to any member of the public. Independent review of the post-closure and intruder scenarios confirmed that the maximum projected dose over a period of 1,000 years is also within a few millirem per year.
As described above, the potential cumulative dose from the waste in this disposal request plus the dose from the waste in the previous disposal request is also within a few millirem per year.
Based on the staffs analysis, the licensees request is authorized by law and will not endanger life or property or the common defense and security. Additionally, the proposed disposal is in the public interest in that it will conserve low-level radioactive waste disposal capacity and provides a more cost effective decommissioning. Therefore, to the extent that the material authorized for disposal in this 20.2002 authorization is otherwise licensable, the staff concludes that the material is exempt from further Atomic Energy Act and NRC licensing requirements.
Principal Contributor: Karen Pinkston, FSME