ML20077K436
| ML20077K436 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 01/05/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20077K412 | List: |
| References | |
| NUDOCS 9501100338 | |
| Download: ML20077K436 (4) | |
Text
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UNITED STATES.
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NUCLEAR REGULATORY COMMISSION l
WASHINGTON. D.C. 20086-0001 f
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j SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION f
RELATED TO AMENDMENT NOS. 77 AND 78 TO FACILITY OPERATING LICENSE NPF-68 I
AND AMEN 0 MENT NOS. 56 AND 57 TO FACILITY OPERATING LICENSE NPF-81
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V0GTLE ELECTRIC GENERATING PLANT. UNITS 1 AND 2 l
i DOCKET NOS. 50-424 AND 50-425 j
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1.0 INTRODUCTION
By letter dated September 13, 1994, as supplemented by letter dated December 6,1994, Georgia Power Company, et al. (the licensee) proposed license amendments to change the Technical Specifications (TS) for Vogtle Electric Generating Plant (Vogtle), Units 1 and 2.
The proposed changes would replace the Containment Systems TS 3.6.2.2 for the Spray Additive System with 1
a new Emergency Core Cooling System (ECCS) TS 3.5.5 for the ECCS Recirculation Fluid pH Control System. This action is to support a planned plant modification which would eliminate the containment spray additive system for Units 1 and 2.
The proposed plant modifications will be made in two phases. During Phase I, the Unit 2 Spray Additive System will be replaced by the ECCS Recirculation Fluid pH Control System.
This is planned to be accomplished during the Unit 2 Cycle.4 refueling (2R4) outage scheduled to begin in February 1995. At that' time, the TS regarding the Spray Additive System will be applicable to Unit 1 only. During Phase II, the Unit 1 Spray Additive System will be replaced by i
the ECCS Recirculation Fluid pH Control System. The replacement work on Unit I will be completed during the Unit 1 Cycle.6 refueling (IR6) outage which is scheduled to begin in the spring of 1996. The license amendments for both Units 1 and 2 are being issued at this time, with Unit 1 pH control system TS to be implemented prior to startup following the IR6 refueling outige, and Unit 2 pH control system TS to be implemented prior to startup following the 2R4 refueling outage. The December 6,1994, letter provided clarifying information that did not change the initial proposed no significant hazards consideration.
2.0 LY6LUATION The containment spray system (CSS) is an engineered safety features system that functions to reduce reactor containment building pressure and temperature and the quantity of airborne fission products in the containment atmosphere during the initial injection and subsequent recirculation phases after a loss 9501100338 950105 PDR ADOCK 00000424 P
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I - of coolant accident (LOCA).
In the original design, liquid sodium hydroxide (NaOH) is added to the containment spray water to increase the pH in order to enhance absorption of the airborne fission product iodine, retain the iodine in the containment sump solution, minimize hydrogen production,: and inhibit stress corrosion cracking of austenitic stainless steel components During the LOCA injection phase, the licenset. has proposed to operate the containment spray system with a boric acid (2400 to 2600 ppm) solution from the refueling water storage tank (RWST), which has a pH of approximately 4.5.
Recent results, documented in Revision 2 of the Standard Review Plan (SRP),
i Section 6.5.2, " Containment Spray As A Fission Product Cleanup. System"'
addressing iodine removal, demonstrate that a low pH value would not affect the removal rate of the elemental and particulate iodine from the post-LOCA containment atmosphere.
r These rates are determined by the first-order removal coefficients which, for elemental iodine removal by spray water and deposition on the containment i
walls, are independent of pH and therefore are not affected by elimination of the pH controlling additive. The same applies to the removal coefficients for particulate iodine which is controlled by the hydrodynamic characteristics of the spray.
During the recirculation spray phase, coolant from the sump will contain dissolved iodine removed from the containment atmosphere during the injection phase.
In a radiation erwironment this iodine could be desorbed from the water and released to the containment atmosphere if the pH of the sump solution is too low.
Sins:e the long-term pH of the ECCS solution should be no
-less than 7.0, a chemical additive must be utilized to raise the pH of the solution in the containment building sump.
1 The licensee has proposed to control the pH above a level of 7.5 by the addition of the ECCS recirculation fluid pH control system..This is a passive system which consists of crystalline trisodium phosphate (TSP) stored in three baskets located in the containment sump area with a total minimum TSP loading of approximately 11,484 pounds (220 ft ).
The stainless steel baskets are '
designed to Seismic Category I standards and would be anchored to the filler slab at an elevation of 171 ft - 9 inches.
In accordance with the proposed ECCS recirculation fluid pH control system TS, the licensee has proposed to verify during each refueling outage that the:
(a) three storage baskets are in place, (b) have maintained thgir integrity, and (c) are f111ed with a total 3
of between 11,484 pounds (220 ft ) and 14,612 pounds (260 ft ) of TSP.
The licensee plans to selectively leave in place or remove the components associated with the spray additive system. The blank orifice plates installed to isolate the spray additive system will meet ASME Section III Class 3 requirements. The piping and components isolated will not be maintained as ASME Section III components, however, they will be maintained as Seismic Category 1, since they remain connected to the piping downstream. The level and flow indicators and hand switches associated with these components will be removed from the main control board and replaced with cover plates.
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., The sump water must also be maintained -in the alkaline condition in order to minimize corrosion of metallic surfaces. Chloride-induced stress corrosion cracking of austenitic stainless steel components is considerably reduced if the pH of the solution is maintained above 7.
During the injection phase, the TSP will begin to dissolve and the pH of the ECCS sump solution will be raised from 4.5 into the range of 7.5 to 10.5.
The surfaces sprayed during the-injection will be resprayed during the recirculation phase with a high pH solution.
Control of the sump pH is also required to minimize hydrogen' generation by corrosion of aluminum and zinc on galvanized surfaces and in the organic coatings on containment surfaces._ The proposed change will affect the pH'by introducing an initial pH of 4.5 (borated water spray) followed by a pH range of 7.5 to 10.5 using TSP. The proposed lowering of the pH for the spray will have no significant effect on the corrosion of aluminum as long as the pH remains above 4.5.
The corrosion of zinc and zinc-based paints will produce hydrogen. However, the results of NRC-sponsored studies performed by Sandia National Laboratory demenstrate that with a controlled pH the corrosion rate will be low and no significant amounts of hydrogen would be produced. The operating conditions proposed by the licensee would preclude any unfavorable conditions.
TSP is being used in similar passive systems at several operating nuclear power plants. The proposed pH levels have been determined to have no significant effect on the removal of elemental and particulate iodine from the post-LOCA containment atmosphere. Also, the potential for stress corrosion and hydrogen generation has been evaluated and dismissed as credible threats to the plant components by study of the pH levels. The staff has reviewed the proposed changes and finds the proposed TS changes acceptable, j
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Georgia State official was notified of the proposed issuance of the amendments. The State official 1
had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendments change requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendments involve no significant increase in the amounts, and iio significant change in the types, of any effluents that may be released offsite, and that there is no i
significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments involve no'significant hazards consideration, and there has been no public comment on such finding (59 FR 53840). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
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5.0 CONCLUSION
The Comission has concluded, based on the considerations discussed abcve, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Comission's regulations, and (3) the issuance of the amendments will not be inimical to the comon defense and security or to the health and safety of the public.
Principal t oributor:
J. Zimerman Date:
January 5, 1995 t)its.