A07141, Responds to Generic Ltr 88-05, Boric Acid Corrosion of Carbon Steel Reactor Pressure Boundary Components in PWR Plants. Source of RCS Leakage Determined by Insp to Be at Reactor Vessel Head O-Ring

Responds to Generic Ltr 88-05, Boric Acid Corrosion of Carbon Steel Reactor Pressure Boundary Components in PWR Plants. Source of RCS Leakage Determined by Insp to Be at Reactor Vessel Head O-Ring

ML20155C528
Person / Time
Site:	Millstone, Haddam Neck, 05000000
Issue date:	05/27/1988
From:	Mroczka E CONNECTICUT YANKEE ATOMIC POWER CO., NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
A07141, A7141, GL-88-05, GL-88-5, NUDOCS 8806140233
Download: ML20155C528 (6)

Text

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e a MEAST UTILITIES cene,.i Ore,ces . seioen street. Beri.n. connecticui l es i nu.ws u:w cwe P.O. BOX 270 m . m. .c.i . c"" H ARTFORD, CONNECTl";UT 061414270 k ' J $7eEd[,l((~ (203) 665-5000 May 27, 1988 Docket Nos. 50-213 50-336 50-423 A07141 Re: Generic letter 88-05 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Gentlemer:

Haddam Neck Plant Millstone Nuclear Power Station, Unit Nos. 2 and 3 Generic Letter 88-05 Boric Acid Corrosion of Carbon Steel Reactor Pressure Boundary Comoonents in PWR Plants On March 17, 1988, the NRC issued Generic Letter 88-05(I) requesting licensees to provide assurances that a program has been implemented to address the effects of reactor coolant leakage on external corrosion of pressure boundary components. The NRC requested pursuant to 10CFR50.54(f) a response within 60 days of receipt of the letter. Northeast Nuclear Energy Company (NNECO),

on behalf of Millstone Nuclear Power Station, Unit Nos. 2 and 3, and Connecticut Yankee Atomic Power Company (CYAPC0), on behalf of the Haddam Neck Plant, hereby submit our response to Generic Letter 88-05.

Millstone Unit Nos. 2 and 3 and the Haddam Neck Plant have had an aggressive ,

preventative maintenance program from the onset of their operation. Our j nuclear facilities have ,vograms in place that require specific action when i potential problems are identified. Although there is not one separate proce- I dure which addresses boric acid corrosion control specifically, there are  ;

procedures in place that provide detailed action plans for the determination '

of leakage, evaluation of the severity, and disposition of potential damage due to reactor coolant leakage on pressure-containing components. The proce-dures are discussed in Attachment 1 to this letter.

These methods and techniques were used during recent operations at Millstone Unit No. 2. Reactor coolant system unidentified leakage was approximately one-half the allowable Technical Specification limit. Detailed inspection of the visible surfaces of the reactor coolant system were conducted. When these (1) U.S. Nuclear Regulatory Commission letter to all Licensees of PWRs and all Applicants for Construction Permits for PWRs, "Boric Acid Corrosion of Carbon Steel Reactor Pressure Boundary Components in PWR Plants,"

dated March 17, 1988.

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U.S. Nuclear Regulatory Commission A07141/Page 2 May 27, 1988 inspections failed to identify a source of leakage, the reactor was shut down and detailed walkdowns of otherwise inaccessible areas were conducted. It was determined that the leakage was at the reactor vessel head 0-ring. Extensive, detailed examinations, including insulation removal from portions of the reactor coolant system, were conducted for all areas potentially affected by the leakage. All areas were cleaned to remove boric acid residue.

Nine reactor vessel studs and two small areas on the cold leg nozzles were found to be affected by the leakage. Nonconformance reports were generated and dispositioned for all identified damage. Since spares were available, nine reactor vessel studs were replaced. The removed studs are being cleaned and reworked and it is expected that seven to eight studs will be acceptable for reuse. Two areas on the cold leg nozzles were identified with unusual surface conditions. These areas were bright metal without the usual high-temperature corrosion film. After flapper wheel and wire brush cleaning, the '

surface condition of the affected area was .4milar to adjacent unaffected areas. Ultrasonic testing determined there was i a measurable wall loss.

In a May 6, 1988(2) letter, NNEC0 submitted Licensee Event Report (LER)

No. 88-008-00 to the Staff. This LER presents additional information on boric acid leakage concerns at Millstone Unit No. 2.

The above is used to illustrate the effectiveness of our programs to fdentify and control boric acid corrosion at our plants. NNECO and CYAPC0 believe that the programs implemented at Millstone Unit Nos. 2 and 3 and the Haddam Neck Plant provide adequate confidence that boric acid corrosion does not lead to degradation of the assurance that the reactor coolant pressure boundary will have an extremely low probability of abnormal leakage, rapidly propagating failure, or gross rupture.

We trust that this submittal adequately responds to Generic Letter No. 88-05 and the NRC Staff's 10CFR50.54(f) request for information.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY CONNECTICUT YANKEE ATOMIC POWER COMPANY j ET '. Mroczka (/ l Sen)iorVicePresident 1

(2) S. E. Scace letter to U.S. Nuclear Regulatory Commission, "Licensee Event Report No.88-008 00," dated May 6, 1988.

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U.S. Nuclear Regulatory Commission A07141/Page 3 May 27, 1988 Attachment cc: W. T. Russell, Region I Administrator D. H. Jaffe, NRC Project Manager, Millstone Unit No. 2 R. L. Ferguson, NRC Project Manager, Millstone Unit No. 3  ;

A. B. Wang, NRC Project Manager, Haddam Neck Plant W. J. Raymond, Senior Resident Inspector, Millstone Unit Nos. 1, 2, and 3 J. T. Shedlosky, Senior Resident Inspector, Haddam Neck Plant STATE OF CONNECTICUT)

) ss. Berlin COUNTY OF HARTFORD )

Then personally appeared before me, E. J. Mroczka, who bdng duly sworn, did state that he is Senior Vice President of Northeast Nuclear 'l;)rgy company and Connecticut Yankee Atomic Power Company, Licensees herein, tnat lie is author-ized to execute and file the foregoing information in the s - e ano on behalf of the Licensees herein, and that the statements contained in : Sid information are true and correct to the best of his knowledge and belief.

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c Attachment 1 Summary of Northeast Utilities Operated Pressurized Water Reactors Boric Acid Corrosion Mitigation Programs I

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Attachment 1 A07141/Page 1 May 27, 1988 Pressurized water reactors operated by Northeast Nuclear Energy Company and Connecticut Yankee Atomic Power Company do not have programs 1pecifically in place to address the concerns of Generic Letter 88-05. However, various procedures are utilized which, in practice, collectively serve to address the four points of Generic Letter 88-05. The following is a summary of how those issues are addressed at the Haddam Neck Plant and Millstone Unit Nos. 2 and 3.

1. A determination of the principal locations where leaks that are smaller than the allowable technical specification limit can cause degradation of the primary pressure boundary by boric acid corrosion. Particular consideration should be given to identifying those locations where conditions exist that could cause high concentrations of boric acid on pressure boundary surfaces.

Resoonse Leakage is most likely to occur at mechanical joints. Those joints with carbon or low-alloy steel fasteners have been identified. In addition, welded penetrations of the reactor coolant system are potential corrosion areas since most of the primary system components are carbon steel clad with a corrosion-resistant alloy. Exceptions to this situation are the primary piping at Haddam Neck and Millstone Unit No. 3, the surge line at Millstone Unit No. 2, and the reactor coolant pump casings at all three plants since these components are already made of boric acid corrosion-resistant stainless steel.

2. Procedures for locating small coolant leaks; i.e., leakage rates at less than technical specification limits. It is important to establish the potential path of the leaking coolant and the reactor pressure boundary components it is likely to contact. This information is important in determining the interaction between the leaking coolant and reactor coolant pressure boundary materials.

Resoonse Surveillance procedures have been developed to periodically inspect the points identified in No. I above. These inspections include identifica-tion of leakage, boric acid deposits, and corrosion. A determination of the path of leakage and the effects of leakage is made.

In addition, prior to start-up from a refueling outage, a reactor coolant system (RCS) in-service leak test is performed. Particular attention is paid to the above-mentioned mechanical joints for les!. age.

During plant operation, the RCS leak rate is monitored. Any sustained increase in unidentified RCS leak rate is investigated. This could include containment entry to inspect accessible areas. Unit experience is utilized in identifying likely sources for initial inspection. If the

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! May 27, 1988 l I source of leakage cannot be found and corrected, the unit is typically l

shut down for more complete inspections. In the case of Millstone Unit No. 3 we will continue to pursue alternatives with the Staff to facilitate prompt access to the containment. To date, the containment sub-atmospheric conditions required by Technical Specifications has  !

i hindered access to containment during operation. Self-contained l breathing apparatus is currently required to perform a containment entry, j We believe that some relaxation of the exieting Technical Specifications 1 can be achieved while maintaining assurat-:e that a design basis accident can be successfully mitigated.

l 3. Methods for conducting examinations. and performing engineering evalua-tions to establish the impact on the reactor coolant pressure boundary when leakage is located. This should include procedures to promptly l gather the necessary information for en engineering evahatton before the removal of evidence of leakage, such as boric acid crysul buildup.

t l Resoonse If leakage is identified as a result of the r. Love-mentioned procedures, the leakage is repaired and the affected corponents inspected for degra-dation. The inspection is documented in accordance with established approved plant procedures. If degradatien is identified, an engineering evaluation is performed to determine the need for and extent of correc- l tive actions. This is done for all affected parts and systems including,

, but not limited to, the pressure boridary, fasteners, supports, and/or l snobbers. Initial inspections are done visually.

4. Corrective actions to prevent recurrent.es of this type of corrosion.

. This should include any modifications to be introduced in the present i design or operating procedures of the plant that: (a) reduce the proba-

! bility of damage, and (b) entail the use of suitable corrosion-resistant l materials or the application of protective coatings / claddings. '

Resoonse All instances of RCS leakage are evaluated to determine root cause and appropriate long-term corrective actions. Tha infrequent o.cerrences of this problem at our units suggest that the methods used arr.: effective.

Stainless steel fasteners are used whenever the arflicatlon requirements permit. Similarly, protective coatings are utilized where the applica- 4 tion permits and a resistant, durable coating system can be identified, l

I for Millstone Unit No. 3, snubber boots have beeii added to iniprove the  !

reliability of snubbers that could be subjected to boric acid fouling. l l

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