ML20206P400
| ML20206P400 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/11/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20206P394 | List: |
| References | |
| TAC-60722, TAC-60723, NUDOCS 8608270201 | |
| Download: ML20206P400 (5) | |
Text
,
f *%g UNITED STATES
- j NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 i
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 51 TO NPF-10 AND AMENDMENT N0. 40 TO NPF-15 SOUTHERN CALIFORNIA EDISON COMPANY, ET AL C0CKET N05. 50-361 AND 50-362 1.0 IhTRODUCTION Southern California Edison Company (SCE), on behalf of itself and the other licenses, San Diego Gas and Electric Company, The City of Riverside California, and The City of Anaheim, California, has submitted several applications for license amendments for San Onofre Nuclear Generating Station, Units 2 and 3.
One such request, Proposed Change PCN-210, is evaluated herein. This change would revise Technical Specifications (TS) 3.6.2.2 and 4.6.2.2.
The proposed change would delete the existing requirement for the sodium hydroxide containment spray chemica1 additive tank and add a new requirement for trisodium phosphate post-accident sump 1
pH control. The licensees stated that a new analysis utilizing recent changes in NRC methodology, combined with knowledge gained from recent I.
studies on the behavior of iodine in the post-LOCA environment demon-strated that the deletion of the spray additive system and replacement with a sump pH control system does not significantly change the calculated offsite thyroid does. The pH control system provides satis-a factory retention of iodine in the sump water. It also provides sufficient pH control to minimize chloride induced stress corrosion cracking of austenitic stainless steel components and prevents hydrogen generation from the corrosion of galvanized surfaces and surfaces coated i
with zinc-based paints. The staff's evaluation of the proposed change is given below.
2.0 SAFETY EVALUATION A.
System Modifications By letters dated February 7, March 10 and May 9, 1986, the licensees provided information on the capabilities of the modified containment spray system and demonstrated that this modified system would meet applicable criteria.
The original containment spray system included a chemical additive tank containing 1456 gallons of 40 to 44 w/o sodium hydroxide solution. The main purpose of this additive system was to ensure that in the event of a LOCA, a sufficient amount of sodium hydroxide would be added to the containment spray to raise its pH to between 8 and 9 during the initial phase of the spray. The effects of the 8608270201 860811 PDR ADOCK 0500 1
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increased pH levels were to increase iodine removal capability of the spray and to improve iodine retention in the sump. An additional function of the sodium hydroxide additive was to control pH in the sump during the long term recirculation phase in order to minimize the potential for chloride induced stress corrosion cracking of austenitic stainless steel components in essential shutdown systems and to prevent generation of hydrogen from corrosion of galvanized surfaces and surfaces coated with zinc-based paints in contact with the water. However, this sodium hydroxide additive system proved to be very burdensome and its maintenance required considerable effort on the part of plant personnel. The licensees decided, therefore, to abandon it in favor of a system where pH control of the sump water was accomplished by addition of trisodium phosphate.
In its letter of March 10, 1986, the licensees provided an analysis demon-strating that the proposed changes will not significantly impact the original plant licensing design basis. The analysis includes detennination of offsite thyroid doses for the modified system, iodine retention, and corrosion effects of the sump water.
(1) Offsite Thyroid Doses The offsite thyroid doses were calculated using the Westinghouse TITAN computer code. Most of the input data to the code were taken from the FSAR for San Onofre 2 and 3, the Standard Revicw Plan and Regulatory Guide 1.109.
In the calculations, several conservative assumptions were maca including no credit for removal of elemental iodine by the containment spray. With these assumptions the licensees determined that the 0-2 hour thyroid dose at the exclusion area boundary was about 11 percent lower and the 0-30 day thyroid dose at the low population zone was six percent higher than the corresponding values determined previously for the containment spray system with sodium hydroxide additive. However, in both cases the doses were well below the 10 CFR 100 acceptance limits.
(2) pH Control of Sump Water In the modified system, the pH of the sump water will be controlled after an accident (LOCA) by dissolved trisodium phosphate. A minimum of 15,400 lbs. of hydrated trisodium phosphate will be placed in racks in the containment sump. These racks will be suitably located in the sump to assure that the containment spray and safety injection water will dissolve most of the salt and form a solution with uniform concentration. The amount of trisodium phosphate in the racks will be periodically verified by visual inspection. The licensee calculated that with this amount of trisodium phosphate, a pH in the range of 7 to 7.5 could be maintained in the spray water. This pH range assures that the sump water will possess sufficient alkalinity to prevent chloride
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induced stress corrosion cracking of austenitic steel, and at the same time will be low enough not to cause corrosion of aluminum.
Also, this pH will assure that corrosion of galvanizsd surfaces and surfaces painted with zinc-based paints will be minimized, and the information of hydrogen in the containment will be impeded, The alkalinity of the sump water will also cause retention of iodine i
absorbed by the water.
Further, the change from sodium hydroxide to trisodium phosphate will not affect the equipment exposed to the sump solution since the new environment will be more benign than the envircnment to which this equipment was exposed during its qualifi-cation tests. We have reviewed the above information presented by the licensee and find that it provides sufficient basis for acceptance of the proposed system modifications.
B.
Technical Specification Change The licensees have proposed revised technical specifications which reflect the above system modifications.
In technical specfication 3.6.2.2 the previcus requirement for a sodium hydroxide spray additive tank was deleted and a new requirement for a minimum of 15,400 lbs of hydrated
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trisodium phosphate in the containment sump was added. This requirement applies to plant operating modes 1, 2 and 3.
In addition, the surveillance requirements of technical specification 4.6.2.2 were revised to include periodic visual inspection of the racks containing the trisodium phosphate l
and solubility analysis to assure that under post-accident conditions enough trisodium phosphate will be dissolved to produce a pH of greater than or equal to 7.
We have reviewed these proposed revised technical t
specifications and find that they adequately control operation of the modified containment spray and sump pH control system.
C.
Sumary of Safety Evaluation Based on the considerations discussed above, we conclude that the modifi-i cations to the San Onofre Units 2 and 3 post-accident fission product control system proposed by the licensees meet the requirements of General Design Criterion (GDC) 41 for providing a satisfactory means of post-LOCA containment atmosphe.re cleanup. We further conclude that the proposed l
revised technical specifications for surveillance of the trisodium phosphate meet the requirements of GDC 42 for inspection of the containment atmosphere cleanup systems. We, therefore, find the proposed deletion of the sodium hydroxide containment spray chemical additive tank and addition of a trisodium phosphate pH control system to be acceptable, as are the proposed technical specifications.
3.0 CONTACT WITH STATE OFFICIAL The NRC staff has advised the Chief of the Radiological Health Branch, State Department of Health Services, State of California, of the proposed determination of no significant hazards consideration. No comments were received.
o 4.0 ENVIR0l; MENTAL CONSIDERATION These amendments involve changes in the installation or use of facility components located within the restricted area. The staff has determined that the amendments involve no significant increase in the amounts of any effluents that may be released offsite and that there is no significant increase in individual or cumnulative occupation radiation exposure. The Commission has previously issued proposed findings that the amendments involve no significar,t hazards consideration, and there has been no public j
comment on such findings. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR Sec. 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environ-mental assessment need to be prepared in connection with the issuance of these amendments.
E.0 CONCLUSION The Staff has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of the amendments will not be inimical to the common defense and securitylor to the health and safety 1
of the public. We, therefore, conclude that the proposed changes are acceptable, and are hereby incorporated into the San Onofre 2 and 3 2
Technical Specification!..
Dated: August 11, 1986 i
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ISSUANCE OF AMENDMENT N0. 51 TO FACILITY OPERATING LICEd '
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