ML19093A967

Letter Serial # 374 Dated 08/29/1977 Provided Information Regarding NPSH Available for Lead Safety Injection Pumps at Surry. Determined That Procedures Should Be Implemented to Throttle Valves in Lhsi Pump Discharge

ML19093A967
Person / Time
Site:	Surry
Issue date:	09/01/1977
From:	Stallings C Virginia Electric & Power Co (VEPCO)
To:	Case E Office of Nuclear Reactor Regulation
References
Download: ML19093A967 (4)

Text

RIOHMOND, VIROINI.A. 2 3 2 61 September 1, 1977 Fil~ ~y~

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Mr. Edson G. Case, Acting Director Serial No. 374A/082977 Nuclear Reactor Regulation PO&M/ALH:das U. S. Nuclear Regulatory Commission Docket Nos. 50-280 Washington, D.C. 20555 50-281 License Nos. DPR-32 Attention: Mr. Robert W. Reid, Chief DPR-37 Operating Reactors Branch 4

Dear Mr. Case:

Our letter serial number 374 dated August 29, 1977* provided information regarding NPSH available for the low head safety injection (LHSI) pumps at Surry. As a result of the analysis provided in our letter, it was determin-ed that procedures should be implemented to throttle valves in the LHSI pump discharge lines. This will assure that NPSH requirements are met during LOCA.

These procedures have been approved and implemented at Surry.

We have also developed an interim design change which will allow throttl-ing of the applicable LHSI discharge valves from the control room. The detail-ed description of this design change is presented in the attachment to this letter. The Station and System Nuclear Safety and Operating Committees have approved the modification, and we would appreciate your approval to implement this ;hange as soon as possible.

We are developing a long term modification which will assure adequate NPSH for the LHSI pumps without the need to throttle any valves. This modification will be submitted for your review and approval by November 22, 1977.

Very truly yours,

~- Jl/l. ~t~-f,~1/J C. M. Stallings Vice President-Power Supply and Production Operations

.cc: Mr. James P. O'Reilly

e ATTACHMENT DESIGN MODIFICATION TO LHSI DISCHARGE VALVES AT THE SURRY POWER STATION This modification will result in changes to the control circuitry for the LHSI discharge valves to the hot and cold legs. These circuit changes will al-low the operator to move the valves to some intermediate position so that LHSI flow can be throttled. This operation will t~ke place in the control room where the operator has full view of LHSI flow instrumentation.

The existing circuitry is designed to operate the valves through full travel only. This is accomplished by a set of "seal-in" contacts which prevent the in- .

terruption of power to the valve motor unless the full travel limit switches are actuated. In order to allow the operator to stop the valves in mid travel, these "seal in" contactors can be taken out of service. The operator would then be able to stop the valves at any position by releasing the control switch which will spring return to its normal position. If full opening or closing is required, the operator must hold the control switch in the desired position. Approximately 15 seconds is required to fully shut or open the valve. The attached sketch shows a typical LHSI discharge valve control circuit.

This method was chased for several reasons. Additional switches to permit valve throttling would require a modification to the control panel which should not be done with the plant in operation. Additional switches would provide another piece of hard-ware that could fail. Additional switches could cause confusion during emergency sit-uations that would result in improper valve operation. The removal of the "seal in" contactors is simple, quick and can be accomplished safely during plant operation.

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