ML18227C740

Referring to Letter of 1/30/1976 Response to NRC Requested Analysis to Confirm Integrity of Main Steam Isolation Valves, Letter Advising MSIV Analysis Is Acceptable

ML18227C740
Person / Time
Site:	Turkey Point
Issue date:	08/02/1976
From:	Lear G Office of Nuclear Reactor Regulation
To:	Robert E. Uhrig Florida Power & Light Co
References
Download: ML18227C740 (7)

Text

DISTRIBUTION:

Dockets NRC PDR Local PDR ORB/33 Rdg KRGoller TJCarter Dockets Hos. 50-250 GLear and 50-251 CParrish DEiliott OELD OX&E(4)

Florida Power and Light Company TBAbernathy ATTN: Dr. Robert E. Uhrig JRBuchanan Vice President ACRS (16)

P. 0. Box 013100 VStello

?Kami, Florida 33101 File CTrammell Gentlemen:

By letter dated Nay 27, 1975, we requested an analysis which would confirm that the integrity of the main steam isolation valves (MSIV's) would be maintained under accident conditions at Turkey Point Nuclear Generating<,

Station Units Nos. 3 and 4. By letter dated January 30, 1976, you responded to our request. In your letter you described valve modifications which you stated would be completed during the fall of 1976 for Unit No. 3 and during the spring of 1977 for Unit No. 4.

Ve have completed our review of your submittal and have concluded that your NSIV analysis is acceptable and demonstrates that your proposed valve modifications will add assurance that the NSIV's and check valves will

.fulfill their design function.

Sincerely, George Lear, Chief Operating Reactors Branch 83 Division of Operating Reactors

Enclosure:

Safety Evaluation OR/ICE~ ORB83 SURNAMC W Ghee...................

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Form hKC 318 (RCT. 9.55) hECM 0240 Q V, 8, OOVCRNMCNT RRINTINO ORRICCI 1074 504 IVIII

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Florida Power & Light ompany cc:

Mr. Jack R. Newman, Esquire Lowenstein, Newman, Reis & Axelrad 1025 Connecticut Avenue, N. W.

Suite 1214 Washington, D. C. 20036 Environmental & Urban Affairs Library Florida International University Miami, Florida 33199

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~i t UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REGARDING THE INTEGRITY OF MAIN STEAM ISOLATION VALVES DURING ACCIDENT CONDITIONS FLORIDA POWER AND LIGHT COMPANY TURKEY POINT NUCLEAR GENERATING UNITS 3 AND 4 DOCKETS NOS. 50-250 AND 50-251 Introduction Adverse operating experience concerning main steam isolation valves (MSIVs) has been reported to the Office of Inspection and Enforcement (015E) following operational tests and spurious closures at. various pressurized water reactor (PWR) stations over an extended period of time. In an effort to gain a better understanding of these events, Information Request No. 74-2 was sent to all PWR stations by 015E.

The information thus obtained was used as input to a generic study conducted by the Office of Nuclear Reactor Regulation. During our review, we had the benefit of discussions with personnel representing various valve manufacturers and also with utility representatives whose facilities were affected.

Our concern was the ability of the swing-check type MSIVs to withstand the dynamic forces associated with rapid closure in the event of a steam line rupture. As a result of this generic study, it was determined that in some cases there may be a need to upgrade both the materials and the design of the larger swing-check MSIVs in order to prevent degradation during normal service and to assure performance of all design safety functions.

Therefore, on May 27, 1975 the Nuclear Regulatory Commission (NRC) requested a number of licensees of pressuriz,ed water reactors (PWR's) to supply summary information on the analyses or tests performed to confirm the ability of the main steam isolation valves (MSIV's) to withstand the forces associated with rapid closure under postulated steam line break conditions.

By letter dated January 30, 1976, Florida Power and Light Company (FPL) responded to our request. Our evaluation of FPL's response relative to the concerns of MSIV performance under postulated main steam line break conditions, follows.

Evaluation An MSIV is provided outside containment on each of the three steam generator main steam lines. Each MSIV consists of a swing disc valve with a pneumatic cyclinder holding the disc open against flow. Located downstream of each MSIV is a check valve whose purpose is to prevent reverse steam flow in the event of a line break between the MSIV and the steam generator.

In their analysis, FPL utilized a dynamic plasticity model to determine the structural response of the disc and valve body under worst case impact closure. As a result of this analysis FPL plans to modify both the MSIV's and the check valves. The rockshaft, tail links and seats of the MSIV's and check valves will be modified to limit disc deflections and to allow a more uniform transfer of kinetic energy from the disc to the valve body during impact. In addition, the pneumatic cylinder for the MSIV will be replaced with a cylinder of larger diameter.

FPL's initial analysis of the unmodified valves indicated that some permanent deformation of the valve components may occur. However, the deformation would not be great enough to cause the MSIV or check valves to lose their capability to perform their design function. FPL plans to modify the MSIV's and check valves in order to limit potential valve component deflection and strain. Our evaluation has determined that:the valve modifications will: (I) assure that the MSIV and check valves will perform satisfactorily under all accident conditions and (2) provide a significantly increased margin of safety.

Conclusion Based on our review, we have concluded that the analysis of the MSIV's and check valves is acceptable and that the valves satisfy General Design Criterion 4 of Appendix A of 10 CFR Part 50. Your proposed modifications will add assurance that the HSXV's and check valves will fulfilltheir design function.

August 2, 1976

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