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**UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555-0001**

August 18, 1998

**Addressees**

All holders of operating licenses for nuclear power reactors, except those licensees that have permanently ceased operationsand have certified that fuel has been permanently removed from the reactor vessel.

**Purpose**

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to a rupture of a firewater system valve, due to a water hammer, in a fire main vertical riser at Washington Nuclear Project Unit 2 (WNP-2) thatflooded two emergency core cooling system (ECCS) equipment rooms. It is expected that recipients will review theinformation for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However,suggestions contained in this information notice are not NRC requirements; therefore, no specific action or writtenresponse is required.

**Description of Circumstances**

On June 17, 1998, WNP-2 was in Mode 4 (cold shutdown) and preparations were underway for a plant startup. Atapproximately 1:45 p.m., multiple fire alarms were received in the control room coincident with three main fire pumpsautomatically starting and several loud water hammer noises being heard throughout the plant. The water hammer caused afire protection isolation valve (FP-V-29D) to rupture in the fire protection system riser in the northeast stairwell of thereactor building. Water from the stairwell entered residual heat removal (RHR) pump room C through a watertight doorthat had not been adequately secured and began rapidly flooding the room. A reactor drains system valve (FDR-V-609)located in a line connecting the sumps of the RHR C and low-pressure core spray (LPCS) pump rooms failed to close asdesigned and allowed water to flow into the LPCS pump room. The flood water completely submerged the RHR C pumpand motor and the Division II keepfill pump, which serves RHR B and C and is also located in the room. Water in theLPCS pump room rose to a level just below the pump motor and also completely submerged the minimum flow valve andthe Division I keepfill pump, which serves both the LPCS and RHR A trains.

To isolate the flooding, plant operators secured the fire pumps, which impaired the normal fire suppression capability of thestation. On the basis of these events, the plant operators declared a notification of unusual event (NOUE) and activated theplant emergency response organization. As a compensatory measure for the loss of the normal fire suppression capability,the nearby Hanford fire department dispatched emergency equipment to the site. Subsequently, the plant staff placed thefire suppression system in an alternate configuration, which was less susceptible to water hammer and terminated theunusual event.

**Discussion**

This information notice requires no specific action or written response. However, licensees are expected to review theinformation provided to determine whether similar system vulnerabilities exist at their facilities. Additionally, recipientsare reminded that they are required by 10 CFR 50.65 to take industry-wide operating experience (including the informationpresented in NRC information notices) into consideration, where practical, when setting goals and performing periodicevaluations. If you have any questions about the information in this notice, please contact one of the technical contactslisted below or the appropriate Office of Nuclear Reactor Regulation (NRR) Project Manager.

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