ML20205L092

Part 21 Rept Re Throttling Requirements & Capabilities of HPI Valves Supplied to Bellefonte,Units 1 & 2 & Washington Nuclear Project.Utils Notified & B&W Suggested Listed Options for Resolving Concern

ML20205L092
Person / Time
Site:	Columbia, Bellefonte, 05000000
Issue date:	03/21/1986
From:	Taylor J BABCOCK & WILCOX CO.
To:	Taylor J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
REF-PT21-86, REF-PT21-86-220-000, REF-QA-99900400 JHT-86-042, JHT-86-42, PT21-86-220, PT21-86-220-000, NUDOCS 8604030039
Download: ML20205L092 (3)

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$ddg u Babcock & Wilcox Noci.ar ro.., owon a McDermott cornpany 3315 ord forest Road

-h u3"I March 21, 1986 P.O. Box 10935 Lynchburg. V A 24506 0935

'M. JHT/86-042 P gef (804) 385 2000 g 3W Mr. James M. Taylor, Director Office of Inspection and Enforcement United States Nuclear Regulatory Commission Washington, DC 20555

Dear Mr. Taylor:

Babcock & Wilcox is hereby informing you of an issue which has-been under investigation pursuant to the requirements of 10CFR21. We have not, however, made a determination as to the safety significance of this issue or of its reportability under that regulation.

The issue involves the throttling requirements 'and capabilities of the High Pressure Injection (HPI) valves supplied to Bellefonte Units 1 and 2 of Tennessee Valley Authority (TVA) and to Washington Nuclear Project-Unit 1 (WNP-1) of Washington Public Power Supply System (WPPSS). The valves were manufactured by the Anchor-Darling Valve Company.

Nature of the Issue The HPI valves were originally purchased to a specification based on their intended safety function, which was to open to a pre-throttled position and remain in this position for the duration of the accident while HPI is in use. As a result of the TMI-2 accident, small break LOCA analyses, and development of Anticipated Transient Operating Guidelines (ATOG), guidelines have been developed that impose more severe throttling requirements on these valves. Since the valves were not originally designed for a continuous throttling service, an element of risk exists in using these valves for that purpose.

The probability of an event occurring that requires long-term HPI valve throttling-is low. For example, one of the events requir-ing HPI throttling is a total loss of feedwater. The calculated probability of a total failure of feedwater for the design life of the plant is roughly 6x10 4 for the Bellsfonte Units and 3x10-4 for the WNP-1 unit. Total failure for this purpose is defined as failure to provide full flow from one pump to one steam generator in 20 minutes, allowing for some operator action. The other scenarios that may result in long-term HPI throttling are tube ruptures and small break LOCAs and, for tube ruptures, only 8604030039 860321 +

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if.other complications occur as well'. Other scenarios,.such as overcooling, would only require throttling of HPI for-short durations to cover the transition back to normal makeup and letdown control.

B&W provided the valve vendor, Anchor-Darling, Lwith a typical

. valve. performance curve to obtain.an indication of the capability of the-HPI valves to perform throttling service.' Anchor-Darling has stated that, in their opinion, the HPI valves could throttle to this curve without sustaining major damage or loss of operability. While this is an engineering judgment and the curve may not represent the ." worst case", the curve does impose a substantial pressure drop across the valve for a 20-hour time frame. Twenty hours should be sufficient for the rare cases requiring extended HPI throttling.

Resolution B&W has notified TVA and WPPSS of this issue and has suggested three options for resolving the concern. These options are described below.

-1. Pursue cualification for throttlina service:

This~ option is directed at obtaining the maximum possible confidence that the HPI valves can perform long-term throttling with a minimum risk of valve failure. Two paths are available:

(a) Perform qualification tests on the existing valves.

(b) Pursue acquisition of new, qualified valves.

2. Develon cuidance for steoned flow control:

This option involves the use of ' "on-of f" HPI flow. control

! instead of prolonged throttling. Essentially, the flow l is reduced by the closure of valves and securing of pumps in

! a stepped sequence. . Pursuing this option does not increase I the confidence level in the throttling capability of the HPI l

valves but rather provides an alternate control method'which i avoids any need for throttling. The resulting operator

, actions would be a periodic step change in'HPI flow to achieve a " staircase" RC pressure reduction.

l 3. Limited HPI throttlina:

1 This option involves a combination of using the present l valves and stepped flow control. One of two of the present

< valves would be throttled (without additional qualifica-l tion). If indications-of the onset of valve failure were.

detected, the operator would revert to stepped flow control.

3 Status In response to B&W's notification, TVA has advised that further review of the issue will he necessary and that, due to the delay in the.Bellefonte construction schedule, they will not make a decision on which option to pursue until July 1987. This will allow approximately 24 months to resolve this issue prior to the resolution need date.

WPPSS has responded with a request for additional information with respect to the valve ' design in order to evaluate B&W's suggested options. B&W is now in the process of developing the information requested. It is to be noted that the WNP-1 Unit is currently in an extendel construction delay.

B&W will perform further evaluations to resolve this. issue in accordance with the construction schedule requirements of the Bellefonte and WNP-1 Units. If, upon completion of these evaluations, a determination is made that a reportable condition exists under 10CFR21, B&W will notify the NRC as appropriate.

If you have any questions, please call me (804-385-2817) or D. Mars (804-385-2852).

Very truly yours,

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. H. Tay19 r, Manager Licensing services JHT/fw cc: J. A. Raulston Chief Nuclear Engineer Tennessee Valley Authority G. K. Dyekman Manager, Design Engineering, WNP-1 Washington Public Power Supply System 1