ML20037A151
| ML20037A151 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 03/19/2020 |
| From: | Bruce Watson Division of Decommissioning, Uranium Recovery and Waste Programs |
| To: | Fletcher D, Oestereicher M US Dept of the Navy |
| R CHANG | |
| Shared Package | |
| ML20037A149 | List: |
| References | |
| Download: ML20037A151 (4) | |
Text
Attachment:
U.S. Nuclear Regulatory Commission Staff Review of Southern California Edison Companys December 19, 2019, Letter Related to the Mesa Area Adjacent to San Onofre Nuclear Generating Station On December 19, 2019, Southern California Edison Company (SCE) submitted a request to the U.S. Nuclear Regulatory Commission (NRC) staff to respond to the U.S. Navy regarding the NRCs role with respect to the termination of SCEs leasehold interest in the Mesa area and its return to the control of the Department of the Navy (Navy).
NRC staff understands that certain minor radiological events took place in the Mesa area, mostly during the 1980s. Since the startup and operation of San Onofre Nuclear Generating Station (SONGS) Unit 1, the NRC has maintained resident inspectors full time at the site to provide oversight and inspections of plant operations. The resident inspectors were supplemented with a variety of technical experts, including health physics inspectors, that would have also reviewed these events. In response to SCEs December 19, 2019 letter, during early 2020, the NRC staff performed a review of documentation compiled by SCE for the areas outlined below for the Mesa area adjacent to the site. The documents provided by SCE are publicly available in NRCs Agencywide Documents Access and Management System (ADAMS) at accession number ML20034D837.
A summary of the areas reviewed by NRC staff are discussed below1:
Mesa Intersection Excavated soil adjacent to SONGS Unit 1 had been inappropriately transferred here in December 1980. Upon discovery, the contaminated material was removed and sent to a licensed burial facility. During a follow-up NRC inspection (available in ML20034D837),
Inspection Report 81-02, the NRC performed independent measurements and surface samples, and confirmed that all excavated material had been effectively removed.
Old Highway 101 Landfill Excavation at SONGS Unit 1 during October 1976 through 1977 were disposed of at the Old Highway 101 Landfill. An exposure rate survey was completed by the licensee in 1981 with measurement locations separated by 10 meters. Measurements were taken at a height of approximately 1 meter above the surface. Three soil samples were also taken. SCE states that their survey results indicate that the any fluctuations in the exposure rate appear to be due to naturally-occurring variability in the materials present, which is also consistent with findings at the STAR Yard and Ameron Laydown Area. NRC staff reviewed the survey results and sampling results and concurs with the SCEs conclusion that residual radioactivity levels are indistinguishable from background.
A minor item further considered was whether there may be sub-surface contamination in this area (>15 centimeters below the surface); however, NRC staff noted that inspectors were following the activities and assessments SCE was performing at the time and had no open items related to this area. It is also of note that the material placed here from SONGS Unit 1 was never identified as having residual radioactive contamination. As such, NRC staff find it highly unlikely any potential sub-surface residual radioactive contamination could be present at levels that could impact public health and safety.
1 The Mesa Drying Pad is not discussed because material on the drying pad has always been free of SONGS produced radionuclides.
Lower Mesa In 1981, a 1-inch pipe elbow contaminated with 0.14 microcuries of Cesium-137 within a tool storage box was identified, along with a forklift battery and metal filters. Additionally, in 1983, additional contaminated items were identified in the GRIP facility/Fabrication Shop and Mesa Training Facility. Items were brought back to the site, and the area was surveyed to confirm that there was no additional contamination remaining. Given the nature of the reported contamination (i.e., primarily non-transferrable), surveys conducted at the time to verify no residual radioactivity, and the fact that the area has been recontoured into ponds making additional surveys virtually meaningless (due to a combination of radioactive decay occurring over time and soil movement/mixing), NRC staff concurs with SCEs determination that it is unlikely residual radioactivity remains in this area which would be distinguishable from background.
Bechtel Warehouse In 1983, a contaminated welding stand and assorted other small equipment (e.g., hoses, and impact wrenches) were identified within the Bechtel Warehouse. These were returned to SONGS and the area was surveyed. This warehouse has been replaced with a new building.
Due to this, NRC staff concurs with SCEs conclusion that any residual radioactivity within this area is likely indistinguishable from background.
Paint/Sandblast Yard In 1983, three items (i.e., nylon sling, and two gate valves) were identified as contaminated in this area. These were returned to SONGS and the area was surveyed. These materials had no removeable contamination. This area has since been redeveloped such that additional surveys would not be expected to provide meaningful information due to the combination of radioactive decay with the passage of time and soil movement/mixing. Due to the nature of the reported contamination (i.e., not being transferrable) and the reasons cited previously, NRC staff concurs with SCEs conclusion that it would be unlikely that any residual radioactivity remains within this area.
Edison Building W-50 In 1983, seven items (i.e., tripod jack, pipe bender, roto hammer, electrical plug, two fire extinguishers, and a welding box) were identified in this building as having low-levels of contamination. These were returned to SONGS and the area was surveyed at the time. A survey was also performed in 2014 where 100% of the accessible floor was scanned and random smears were obtained from the walls and floors. Nothing above background radiation levels was identified. Due to this, NRC staff concurs with SCEs conclusion that any residual radioactivity in this area is indistinguishable from background.
Units 2 and 3 Laydown Areas In 1983 and 1984, over 60 contaminated items were discovered here. These were returned to SONGS and the area was surveyed at that time. A survey was also performed in 2014 where 40 static gamma flux measurements were obtained (scans are taken between the static measurement locations) and 20 soil samples were taken. Readings were within the range of normal background radiation and no residual radioactivity was detected in the samples. A drainage culvert through the area was also scanned and 6 soil samples taken. Again, readings were within the range of background and, with one exception, no plant derived radionuclides were identified in the samples. For the one sample with Cesium-137 identified, the levels were consistent with reference sample data, and environmental monitoring report data, which is believed to originate from fallout from past weapons testing and recent nuclear accidents such
at Fukushima. Due to this, NRC staff concurs with SCEs conclusion that any residual radioactivity within this area is indistinguishable from background.
STAR Yard and Ameron Laydown Area In 1983 and 1984, over 60 contaminated items were discovered at the Ameron Laydown area.
All items except for three aluminum pipes had non-detectable removeable contamination such that there was little risk of cross contamination of the Laydown area. These were returned to SONGS and the area was surveyed at the time. Additionally, at the STAR Yard, a contaminated pressure relief valve was identified in 1988; due to this, additional surveys were performed at the STAR Yard, which yielded the identification of additional contaminated items.
Likewise, these were returned to SONGS and the area was surveyed at the time.
In 2014 SCE resurveyed the STAR Yard and Ameron Laydown areas, which included three buildings encompassed by the land. The three buildings were subject to 100% floor scans with no radioactivity above background levels being detected. The land area was redefined into three survey units. In the land area where the largest number of contaminated items were discovered, 100% surface scanning of the soil was performed, along with 20 static surveys and soil samples. At the other two survey areas, a total of 40 static measurements (with scans between the static measurement locations) and twelve soil samples were taken. All readings were consistent with background radiation levels, except for an anomalous area north of Building G-20. Additional soil samples were taken for the area with anomalous readings (in the area north of Building G-20), and the mix of detected radionuclides is consistent with those naturally occurring in soil but at higher concentrations than the immediate surrounding area.
The licensee noted that the soil appeared to be ramp construction material brought into the area. The ramp construction materials had higher natural activity than the native soils in the area being investigated.
NRC staff reviewed the results of the 2014 surveys and sample results and since this ramp construction material appears to have higher naturally-occurring activity than the native soil, NRC staff concurs with SCEs conclusion that it would be unlikely that any residual radioactivity remains within this area that is distinguishable from background.
Mesa Salvage Yard Three items with fixed contamination were identified in 1992 (e.g., a gasket and wheels). These were returned to SONGS and the area was surveyed at the time. In 2014, static measurements at 20 locations were performed along with scans between the static measurement locations.
Additionally, three soil samples were taken. Nothing above background radiation levels was identified. Due to this, NRC staff concurs with SCEs conclusion that it would be unlikely that any residual radioactivity remains within this area that is distinguishable from background.
Classroom 105, Building G-48 A damaged radioactive check source was identified in the 1993-1994 timeframe. The carpet was removed. In 2014, the floor was scanned with ten smears being taken in the classroom.
No radioactivity above background was detected. Due to this, NRC staff concurs with SCEs conclusion that it would be unlikely that any residual radioactivity remains within this area that is distinguishable from background.
HP Lab, Building E-50 In 2014 a floor vault was surveyed which may have kept radioactive sources. Smears were also taken of the floor vault. Additionally, the entire floor of the room was scanned. No activity was identified above background levels. Due to this, NRC staff concurs with SCEs conclusion that it
would be unlikely that any residual radioactivity remains within this area that is distinguishable from background.
Mesa Paint Shop In 2001, a pair of pliers was identified with fixed contamination. The pliers were returned to the SONGS site. The surrounding area was scanned with no contamination being identified. Due to this, NRC staff concurs with SCEs conclusion that it would be unlikely that any residual radioactivity remains within this area that is distinguishable from background.
Sheet Metal Shop, Building G-40 In 2003, a sealed 55-gallon drum was brought from the Star Yard and opened in the Sheet Metal Shop. A contaminated air hose was identified within the drum. The hose had fixed contamination. Subsequent surveys of the drum and Sheet Metal Shop indicated no contamination and the hose was returned to SONGS. Due to this, NRC staff concurs with SCEs conclusion that it would be unlikely that any residual radioactivity remains within this area that is distinguishable from background.
Conclusion Prior to seeking termination of its lease agreement with the Navy, SCE performed a radiological survey of the Mesa area in 2014 that showed the residual radioactivity was below the regulatory limits set forth in NRC regulation 10 CFR 20.1402. NRC staff reviewed the actions taken at locations in the Mesa where radiological items were discovered. NRC staff concurs with SCEs conclusion that that it would be unlikely that any residual radioactivity remains within the Mesa area that could be distinguished from background based on a review of events and surveys compiled by SCE. The NRC staff affirmed that the Mesa area surveys showed that nothing exceeded the 25 mrem/yr regulatory limit in 10 CFR 20.1402 in our letter dated December 1, 2015.
Further, in 2016 SCE performed a bounding dose assessment for the areas they surveyed based on the level of detection of the instruments used to conduct their 2014 surveys at the Mesa property. SCE reported that the upper bound dose for a member of the public living in this area was 0.8 millirem per year above background. This dose assessment assumes that material is in place at the detection limits of the instruments used in the survey even though no residual radioactive contamination was identified. NRC staff also examined the potential impact of contamination which may be below the surface. Upon further NRC staff review, this issue was eventually considered to be of negligible importance because NRC inspectors were aware of SCEs activities addressing off-site contamination at the time and did not identify any safety issues pertaining to the locations of concern. As such, NRC staff consider it unlikely that any residual radioactive material posing a potential health and safety concern could be present in sub-surface soil, or that would significantly impact SCEs dose assessment. Therefore, NRC staff have no comments on the dose assessment performed by SCE.
Based on a review of the actions taken after contamination was identified and the follow-on surveys completed (in certain instances), from the information provided, the NRC staff have reasonable assurance that the areas in the Mesa area were remediated to levels indistinguishable from natural background.