ML20064L056
Text
UNITED STATES 8,
i NUCLEAR REGULATORY COMMISSION AE0D/E132
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q WASHINGT ON, D. C. 20555
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DEC 231981 Sh' W.d6 MEMORANDUM FOR:
Richard C. DeYoung, Director Office of Inspection and Enforcement FROM:
Carlyle Michelson, Director Office for Analysis and Evaluation of Operational Data
SUBJECT:
. ABNORMAL WEAR ENC 0UNTERED ON ALOYC0 SWING CHECK YALVES INSTALLED IN THE LPSI SYSTEM AT THE PALISADES NUCLEAR PLANT It was reported in LER 81-037 that on September 9,1961, during required modifications of the LPSI s'ystem at the Palisades Plant, two of the four LPSI swing check valves were found to have internal damage. The disc nut, disc nut washer and the disc nut pin were missing and severe wear to the valve body, clapper arm, disc clapper am shaft and clapper arm support had occurred in both valves. The dises were still attached to their clapper arms and the valves were operational, however, valve seat and disc sealing surfaces were damaged and the valves might have been leaking excessively.
The abnormal wear of the check valves was discovered during modifications of the LPSI piping to add leak testing capability as required by NRC order, dated April 20; 1981,- for Event V valve Configurations. This order required the Ticensee to perfom periodic leak-testing of check valves that fonn the interface between a high pressure system connected to the reactor coolant system (RCS) and a low pressure system whose piping leads outside containment.
Event Y is identified in WASH-1400 as a sequence of events leading to a core melt that is initiated by the failure of two in-series check valves to function as a pressure isolation barrier between a high pressure system connected to the RCS and a lower pressure system extending beyond containment. This failure causes an overpres-surization and rupture of the low-pressure system, which results in a LOCA that bypasses containment.
At Palisades, the ALOYC0 check valves form the boundary between the LPSI and HPSI systems.
Failure of these check valves could cause overpres-surization of the LPSI from the HPSI system and the loss of some HPSI flow following a small break LOCA.
The partial loss of HPSI flow to the RCS and the accompanying damage to the LPSI system were not postulated in A l+ +
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Richard C. DeYoung the small break LOCA analysis. As a result, a failure of this type may be an unreviewed safety question.
The NRC order caused the licensee to make the first inspection of these valves in about ten years of power operation.
It was subsequently discovered that the remaining two LPSI check valves had also failed in a similar fashion. The four LPSI check valves at Palisades were manufactured by Alloy Steel Products Com-pany (ALOYCO), circa 1968.
They are six inch swing type check valves with weld. ends for attachment to Sch.120 piping.
All four valves were mounted vertically with the flow direction upward.
The swing check valves are of in-line configuration with a ballooned or expanded area in the valve body for movement of the flapper-type disc (see Figure 1).
The disc is substantially larger than the pipe or nominal valve I.D.
If the disc should become separated fraca the clapper arm, the disc would be trapped within the expanded portion of the valve body. This could lead to reduced LPSI flow, or with some small probability, the complete
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blockage of the line during a LOCA or during shutdown cooling.
Operation of the swing check valve in the direction of flow (nonnal operation) results in the threaded shaft on the back of the valve disc striking the valve
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body as it opens to the full flow position.
(The valve body is the ultimate 1imiter of disc opening.)
In full flow operation, it is presumed the disc will generate sufficient turbulence to cause it to chatter against the valve body.
At Palisades these valves, which are used for extended periods of operation during shutdown cooling, exhibited about one-half of an inch of wear (greater than the height of the disc nut) of the threaded portion of the disc shaft.
However, although the disc nuts had been worn away, none of the discs had separated from their clapper ann because of the " peening" of the shaft to a larger diameter.
From a generic consideration, the design of ALOYC0 swing check valves is different from swing check valves of some other manufacturcrs. Other designs have removed the possibility of threaded portions of the internals from acting as the striking surface by providing an alternate raised sur-face on the valve disc to contact the valve. body upon full flow conditibns (see Figure 2).
ALOYC0 swing check valves can be found from two inch to twelve inch pipe size at Palisades.
Palisades is replacing the four ALOYC0 check valves in the LPSI system with valves of another manufacturer.
The Event V order was issued because of the unsatisfactory perfonnance of in-series check valves.
At Davis-Besse, the valve internals were found disassembled, and at Sequoyah, the check valves jammed open against the valve over-travel limiters.
Considering the associate risk postulated from an Event V accident, the possible generic design problem of the ALOYC0 swing check valves, and their possible wide, spread use in the nuclear
A DEC 231881 Richard C. DeYoung.
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industry, we recommend that I&E issue an Infonnation Notice to infonn the licensees of some of the problems with ALOYC0 swing check valves.
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Carlyle Michelson, Director
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Office for Analysis and Evaluation of Operational Data cc:
H. Denton, NRR T. Wambach, NRR-T. t!ovak, NRR E. Jordan, IE.
R. Baer, IE B. Jorgenson, Region III O
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FIGURE 2.
Cross Section of aJypical_ Swing Check Valve (Powell). Showing The Fully Open and Closed Positions of the Flapper Disc O
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