ML19270F956
| ML19270F956 | |
| Person / Time | |
|---|---|
| Site: | Washington Public Power Supply System |
| Issue date: | 03/09/1979 |
| From: | WASHINGTON PUBLIC POWER SUPPLY SYSTEM |
| To: | |
| Shared Package | |
| ML19270F948 | List: |
| References | |
| NUDOCS 7904090288 | |
| Download: ML19270F956 (2) | |
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APPErtDIX A WPPSS tluclear Projects flos. 1/4 Docket liumbers 50-460 and 50-513 Reportable Condition 10CFR50.55(e)
WKM Valve Overpressurization DESCRIPTION OF THE DEFICIEllCY The WKM Pow-R-Seal gate valve is a double sealing valve and as such requires special provision for pressure relief of fluids that may be trapped in the internal body cavities of the valve. When fluids trapped in the internal body cavity are heated due to increased temperatures of adjacent piping systems or of the environment, substantial pressure increases may result that could rupture the valve. When the valve is in the closed position, over-pressure relief is obtained by means of a relief valve installed in the segment, which relieves the fluid to the upstream side of the valve.
(flote:
the segment is a portion of the valve which, together with the valve gate, provides the required sealing function.) The reported concern is that when the valve is in the open position, there is no provision for pressure relief since the relief valve is not designed to function in this position.
The subject valves are used in the following applications in the B&W 205FA plant:
(a) 2 are 14" core flood tank isolation valves (CFV 1A and B)
(b) 2 are 4" make-up tank isolation valves (MUV 30 and 31)
(c) 2 are 12" in the low pressure injection line (DHV 1A and B)
(d) 4 are 12" in the decay heat letdown drop line (DHV 11A and B,.2A and B)
(e) 1 is a 2-1/2" pressurizer spray line isolation valve (RCV 11)
(f) 1 is a 4" pressurizer relief isolation valve (RCV 10)
CAUSE AND ANALYSIS The valve manufacturer had claimed until recently that pressure relief is provided when the valve is open because there is sufficient leakage between the mating surfaces of the segment and the gate to provide communication between the body and the valve conduit to prevent overpressurization.
In a meeting between B&W and the valve manufacturer on flovember 3,1978, the valve manu-facturer stated they could not guarantee that there was communication between the cavity and the conduit.
They therefore concluded that the potential to overpressurize did exist with the valve open.
DOS,C9DM $
M
APPENDIX A Page Two CAUSE AND ANALYSIS (Cont'd)
An analysis has not been performed to determine with certainty that over-pressurization of gate valves used as core flood isolation valves and on the low pressure injection line constitutes a significant deficiency.
Sufficient potential concern exists, however, to deem it reportable under the provisions of 10CFR50.55(c) for the WNP-1 and -4 units.
The basis for reportability is that, as defined by the regulation, there potentially is a "significant deficiency in the final design approval and released for construction," and that the deficiency, were it to remain uncorrected, could adversely affect safe operation of the plant.
SAFETY IMPLICATIONS As an example, two applications of the valves which are safety concerns are the core flood tank isolation valves and the low pressure injection line valves; both of these applications are in the ECCS.
The potential exists that, during or following a LOCA, the valve cavities could undergo a thermal transient and overpressurize.
An analysis has not been made to determine the degree to which the valve would be deformed or damaged when subjected to these thermal transients.
If valve body rupture were to take place, it could reduce the flow from the core flood tank or from the low pressure injection system in a non-conservative manner with respect to the safety analysis.
This occurrence therefore has the potential for adversely affecting safety of plant operations.
CCTRECTIVE ACTION All of the valves listed in the description of the deficiency will be modified by the manufacturer to ensure that overpressurization of the valve body cannot occur. A field change package has been prepared to authorize valve modification for the valves that have been shipped, and the manufacturer has agreed to modify the design on the remaining valves on order.
The modification requires that a 1/16" hold be drilled radially through the bottom of the gate. This 1/16" hole prevents the trapping of fluid in the valve body with the valve in the open position and a subsequent overpressuriza-tion of the valve body.