ML19319B063
| ML19319B063 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 12/04/2019 |
| From: | John Hickman Division of Decommissioning, Uranium Recovery and Waste Programs |
| To: | Halpin E Pacific Gas & Electric Co |
| J HICKMAN DUWP | |
| References | |
| Download: ML19319B063 (3) | |
Text
SAFETY EVALUATION BY OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS RELATED TO FINAL STATUS SURVEYS FOR THE RELAY BUILDING AND THE MEPPS ISLAND BUILDING FACILITY OPERATING LICENSE NO. DPR-7 PACIFIC GAS AND ELECTRIC COMPANY HUMBOLDT BAY POWER PLANT UNIT 3 DOCKET NO. 50-133
1.0 INTRODUCTION
The U.S. Nuclear Regulatory Commission (NRC) staff reviewed Final Status Survey Reports (FSSRs) for the Relay Building (Survey Units RLY01-01 and RL Y01-02) and the MEPPS Island Building (Survey Units MEPPS01-01 and MEPPS01-02), as provided by letter on May 22, 2019 Agencywide Documents Access and Management System (ADAMS) Accession Number ML19143A046). The licensees Final Status Survey (FSS) design criteria, implementation of the Data Quality Objectives (DQO) process, and survey approach/methods were reviewed, and final results were assessed against the licensees approved release criteria.
2.0 EVALUATION The survey units designated as RLY01-01, RLY01-02, MEPPS01-01 and MEPPS01-02 were classified by the licensee as MARSSIM Class 3 units. The licensee describes Survey Units RLY01-01 and RL Y01-02 as the interior and exterior surfaces respectively of the Relay Building and is bounded by Survey Unit OOL10-18 to the north, on the west by Survey Unit OOL10-06, and on the east by Survey Unit NFGA-WST. The licensee describes Survey Units MEPPS01-01 and MEPPS01-02 as the interior and exterior surfaces respectively of the Mobile Emergency Power Plant Station (MEPPS) Island Building which was formerly known as the MEPPS Control Building which is bounded by survey unit OOL10-04 to the east, on the south by Survey Unit OOL10-06, and on the north and east by Survey Unit NFGA-WST. Survey Units RLY01-01 and RL Y01-02 are 84 m2 and 86 m2, respectively, and Survey Units MEPPS01-01 and MEPPS01-02 are 110 m2 and 121 m2, respectively. These areas are consistent with MARSSIM guidance on Class 3 structure survey areas (i.e., no size limit).
The licensees LTP requires 1-10 percent of areal scan coverage for Class 3 Survey Units. For Survey Units RLY01-01 and RLY01-02, the scan survey design criteria were as follows: 100 percent of accessible Survey Unit floors and interior walls to 8 feet, 100 percent scanning of the accessible roof and the area in the immediate proximity to the ventilation system, and 1-2 percent of the balance of the survey unit. For Survey Units MEPPS01-01 and MEPPS01-02, the scan survey design criteria were as follows: 100 percent of accessible Survey Unit floors and interior walls to 6 feet, 10-50 percent scanning of accessible roof areas within reach by personnel on ladders, 100 percent of accessible ventilation and the area in immediate proximity to the ventilation system, and 1-10 percent of the balance of the survey unit. This scan coverage is consistent with MARSSIM recommendations for judgmental scan coverage in Class 3 areas.
Enclosure
The licensees DQO process was utilized to design the FSS and to develop a gross activity Derived Concentration Guideline Level (DCGLGA) for both beta/gamma and alpha contamination measurements. The beta/gamma-gross activity DCGL was based on Cs-137 and Co-60 weighted at 94 percent and 6 percent, respectively. The alpha-gross activity DCGL was conservatively based on Am-241, since Am-241 was determined to be the most limiting prevalent alpha emitter at HBPP in the March 18, 2014 technical support document, Gross Activity DCGL in Support of Final Status Survey at HBPP. The licensees beta/gamma DCGLGA was set at 40,600 dpm/100 cm2, and the alpha DCGLGA was set at 3,000 dpm/100 cm2.
Investigation levels for direct measurements were set at >50 percent of the DCGLGA (i.e.,
>20,300 dpm/100 cm2 beta/gamma and >1,500 dpm/100 cm2 alpha). The investigation level for scan measurements was designated as a discernable and reproducible audible indication of activity above background.
The licensee calculated the required number of discrete measurements as 14, per Section 5.3.3 of the HBPP LTP, and the licensees survey design included 15 direct measurements for beta/gamma and for alpha in the Relay Building and MEPPS Island Building Survey Units.
A total of 15 smear measurements were also taken in each Survey Unit at the location of the direct measurements in order to assess removable radioactivity. In addition to the planned direct measurements, In-Situ Object Counting System (ISOCS) measurements were taken in some areas to address accessibility or safety concerns, and biased media samples (e.g.,
soil/debris or slurry) were also taken in the Relay and MEPPS Island Buildings. Both easy-to-detect and hard-to-detect radionuclides were measured as a part of the media sample analyses, which included alpha and gamma spectroscopy, gas proportional counting, and liquid scintillation depending on the radionuclide and the measurement method.
The licensees survey results indicated that direct measurements for all of the Relay and MEPPS building Survey Units were at a small fraction of the DCGL. The removable activity measurements (smears) were all well below the applicable DCGLs. Scanning measurements were mostly not discernable from background, and measurements discernable above background resulted in further investigation. Scan results above background on wall areas of Survey Units RLY01-01 and RLY01-02 were confirmed to be from Naturally Occurring Radioactive Material (NORM) using the Inspector 1000 instrument coupled with a sodium iodide (NaI) detector. ISOCS measurements which were utilized to measure Relay Building vaults and electrical trenches indicated that Cs-137 was detected at a small fraction of the DCGL. There were no audible indications above background noted during the scan surveys of the MEPPS01-01 and MEPPS01-02 Survey Units, and the ISOCS measurements of MEPPS01-02 roof surfaces did not identify plant-derived gamma-emitting radionuclides. All of the media samples collected during the Relay Building FSS and Vault Characterization survey tested positive for either Cs-137 and/or Co-60 at less than investigation levels, with no other plant-derived nuclides identified. There were no HTD radionuclides detected above method detection levels from any of the three media samples collected during the Relay Building Vault Characterization Survey. A biased media sample collected of the organic material within a section of rain gutter attached to the roof was taken during the MEPPS exterior FSS. The sample indicated Cs-137 levels slightly above 50 percent of the soil DCGL for Cs-137, and an investigation was performed including two additional samples from the area. The investigation determined that the activity was localized in the vegetation/organic material inside the gutter, and ratios of Cs-134 to Cs-137 were used to conclude the Cs-137 was due to fallout from the Fukushima Reactor accident. There were insufficient amounts of material to perform HTD analyses on these media samples.
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The licensee calculated a number of statistical evaluations using the survey results, and also indicated that since all result values were less than the alpha gross activity, beta/gamma gross activity, or Cs-137 DCGL, the Sign Test was passed by inspection. The licensee additionally notes that the maximum hypothetical dose, from all sources, including groundwater, to a future resident farmer was determined to be less than 0.53 mrem/yr for RLY01-01, 0.50 mrem/yr for RLY01-02, 0.41 mrem/yr for MEPPS01-01, and 0.41 mrem/yr for MEPPS01-02, and that these values are the TEDE based on the average concentration of the beta total surface activity measurements used for non-parametric statistical sampling. These TEDE values are considerably less than the limit of 25 mrem/yr from 10 CFR 20.1402, and would indicate that the radiological criteria for unrestricted use have been met.
3.0 CONCLUSION
NRC staff concludes that the licensees survey and analyses for these survey units provide reasonable assurance of compliance with the unrestricted release criteria of 10 CFR 20.1402.
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