ML13316A243
| ML13316A243 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/04/1997 |
| From: | Rainsberry J SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9712100063 | |
| Download: ML13316A243 (3) | |
Text
SOUTHERN CALIFORNIA E.L. Rainsberry EDISONManager, Plant Licensing An EDISON INTERNATIONAL" Company December 4, 1997 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 Fuel Storage Building San Onofre Nuclear Generating Station Unit 1
References:
- 1. July 15, 1997 letter from J. L. Rainsberry (SCE) to NRC Document Control Desk,
Subject:
Fuel Storage Building Waterproof Membrane
- 2. August 16, 1996 letter from Gregory T. Gibson (SCE to Louis Carson (NRC),
Subject:
Unit 1 Spent Fuel Pool Information
- 3. June 10, 1988 letter from M. 0. Medford (SCE) to NRC Document Control Desk,
Subject:
Spent Fuel Transshipment By letter dated July 15, 1997 (Reference 1), Southern California Edison (SCE) provided the Nuclear Regulatory Commission (NRC) a list of references on the docket regarding the Unit 1 Fuel Storage Building waterproof membrane. In that letter, SCE committed to reevaluate the condition of the waterproof membrane. This letter forwards the results of the engineering evaluation performed.
Engineering Evaluation The "Nob-lock" waterproof membrane is a 40 mil thick sheet lining that was supplied by Ameron Protective Linings, formerly known as Amercoat. The lining material is poly-vinyl chloride, and the sheets are joined together using hot air welding. Due to a concern regarding the condition of the waterproof membrane and the spent fuel pool stainless steel liner, the chemical analysis of water in the spent fuel pool leak detection well was reviewed.
The chemical signature of water samples from the spent fuel pool leak detection well continues to be different from the chemical signature of the San Onofre Nuclear Generating Station P. O. Box 128 San Clemente, CA 92674-0128 714-368-7420 9712100063 971204 E
PDR ADOCK 05000206 P
Document Control Desk
-2 spent fuel pool water. The differences indicate that other processes, either chemical and/or physical, are influencing the water chemistry in the leak detection well.
Recent chemical analyses of the water samples from the spent fuel pool leak detection well continue to show a lower tritium activity
(~ 1E-02 pCi/ml) than the tritium activity in the spent fuel pool water
(~ 3E-02 pCi/ml). Also, the concentrations of boron and radioactivity in the leak detection well water are lower than in the spent fuel pool water.
One of the possible physical processes that may be influencing the leak detection well water chemistry is dilution from in-leakage of groundwater.
However, chemical parameters such as pH and conductivity of the leak detection well are higher than those in the nearby groundwater, indicating that other processes are occurring. If groundwater infiltration is a cause of the dilution, then the waterproof membrane may not be completely leaktight.
Therefore, conservatively, the water level in the spent fuel pool leak detection well will continue to be monitored and kept below the low groundwater elevation to prevent leakage from the leak collection system to the environment. The spent fuel pool leak detection well is drained when its water level reaches Elevation 2.5 feet.
In Reference 2, "plateout" was mentioned as another possible explanation for the differences in chemical signatures. The term "plateout" is clarified to mean that chemical reactions or physical retardation of some fraction of the spent fuel pool water coming in contact with the concrete foundation may be occurring. However, the chemical data does not demonstrate with any degree of certainty what physical and/or chemical processes are responsible for the differences in chemical signatures between the water in the spent fuel pool leak detection well and the spent fuel pool itself.
The waterproof membrane was credited as a secondary water barrier in the event of a postulated 100 ton cask drop in the cask laydown area of the spent fuel pool.
The accident scenario of a cask drop was described in Reference 3. The cask drop does not perforate the spent fuel pool stainless steel liner, but the concrete basemat may develop stress cracks due to the impact force of the cask. This meant that there would be an increase in the possibility of water in the leak chase system leaking out into the soil through the potential concrete stress cracks if the waterproof membrane did not exist.
Therefore, the waterproof membrane was considered to be a secondary water barri.er for a postulated accident during spent fuel transshipment. During construction of the Fuel Storage Building, the waterproof membrane prevented groundwater from coming in contact with the concrete. Under normal circumstances, the waterproof membrane is not being relied on to prevent leakage into the soil.
Document Control Desk
-3 The NRC will be informed prior to commencing any future shipment of spent fuel from the Unit 1 spent fuel pool using the transshipment process. Spent fuel transshipment from Unit 1 is not currently planned in the near future.
Conclusion Ongoing chemical analyses and leakage rate data indicate the condition of the waterproof membrane has not changed significantly. The water level in the spent fuel pool leak detection well will continue to be monitored, and this well will be drained when the water level reaches Elevation 2.5 feet. The waterproof membrane was credited as a secondary leaktight barrier for transshipment.
No transshipment of spent fuel will be allowed until the transhipment process has been reevaluated and the NRC has been informed.
If you have any questions or need additional information on this subject, please let me know.
Sincerely, cc:
E. W. Merschoff, Regional Administrator, NRC Region IV K. E. Perkins, Jr., Director, Walnut Creek Field Office, NRC J. A. Sloan, NRC Senior Resident Inspector, San Onofre Units 2 & 3 M. B. Fields, NRC Project Manager, San Onofre Units 2 and 3 M. K. Webb, NRC Project Manager, San Onofre Unit 1 Louis Carson, Regional Project Inspector, San Onofre Unit 1 S. S. Bajwa, Section Chief, Decommissioning Section