NUREG-0152, Comments on Pressure Interlocks on Valves Interfacing Between Low Pressure ECCS & Reactor Pressure Vessel. Redundant Protection Against Overpressurization of Low Pressure Sys Should Be Provided,Per NUREG-0152

Comments on Pressure Interlocks on Valves Interfacing Between Low Pressure ECCS & Reactor Pressure Vessel. Redundant Protection Against Overpressurization of Low Pressure Sys Should Be Provided,Per NUREG-0152

ML20033B203
Person / Time
Site:	LaSalle
Issue date:	11/05/1981
From:	Tedesco R Office of Nuclear Reactor Regulation
To:	Delgeorge L COMMONWEALTH EDISON CO.
References
RTR-NUREG-0152, RTR-NUREG-152 NUDOCS 8112010027
Download: ML20033B203 (3)

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Subject:

Pressure Interlocks on Valves Interfacing Between Low Pressure Energency Core Cooling Systems and the Reactor Pressure Vessel at La Salle In recent telephone conversations with your personnel, we indicated that in our review of the La Salle Technical Specifications, we noted that the pemissive-for opening valves which interface between the low pressure emergency core cooling (ECC) systens and the reactor vessel is based upon a pressure differential across each valve. The la Salle design would allow valve opening whenever the pressure differential is less than 729 psi. Since the low pressure ECC punps develop a head of about 300 psi, this rieans that the injection valves can open while the reactor vessel is at oprating pressure. The low pressure systems 'are not designed for reactor operating pressure on the pump side of the injection valve and could be overpressurized.

Section 6.3 of the Standard Review Plan states:

"The design of emergency core cooling systen low pressure injection lines is reviewed to confirm that the isolation provisions at thE interface with the reactor coolant system are adequate. The number and type of valves used to form the interfac?s between low pressure portions of the emergency core cooling systens and the reactor coolant system must provide adequate assur-ance the emergency core cooling systems will not be subjected to a pressure greater than the design pressure. This may be accomplished by any of the following provisions:

1.

One or more check valves in series with a nomally closed motor-operated valve. The motor-operated valve is to be opened upon receipt of a safety injection signal once the reactor coolant pressure had decreased below the energency core cooling system design pressure.

2.

Three check valves in series.

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OFFICIAL RECORD COPY useo: mi-us.us NRC FORM 318 (10-80} NRCM 024o

Mr. Louis 0. De1 George 3.

Two check valves in series, provided that there are des!gn pro-visions to permit periodic testing of the check valves for leak-tinhtness and the testing is perfomed at least annually."

The La Salle design consists of a testable check valve in series with a normally closed rotor operated valve. On a high drywell pressure signal or a low-loy-low (Level 1) water level signal, the low pressure ECC system pumps are signaled to start. The injection valves are also signaled to open but require that the differential pressure pernissive is first satisfied. For a small break event, the punp will quickly develop a head sufficient to satisfy the pemissive, even though the reactor vessel pressure can still be at ersentially operating pressure. A single failure of the check valve would then result in a loss-of-coolant accident outside containment. Check valve failures in lines interfacing between high and lou pressure systems have been reported at several operatinc reactors (see LERs 50-255-81-37, 50-327/80150, 50-272-80-76/03L and PH0-50-346-111-80-185). Based on these data, we must expect additional check valve failures in the future.

It is our position therefore that redundant protection against overpressurization of the low pressure ECC systens be provided. He note that this same position was published in Section 7.3.2.3 of HUREG-0152 " Safety Evaluation Report related to the preliminary design of the GESSAR-238 Huc1 car Steam Supply System Standard Design," March 1977. This may be satisfied at La Salle by nodifying the current design such that the motor operated valves which interface between the low

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pressure ECC systens and the reactor coolant system are interlocked to prevent opening unless the reactor vessel pressure is lower than the design pressure of the ECC systen involved. Alternatively, this aise may be satisfied by either of the other two positions in SRP Section 6.3.

Therefore, we will require that a design change be impler.ented and incorporated prior to start up after the first refueling outage. Prior to start up, an additional inspection should be performed on all low and high pressure interface check valves to ascertain their isolation function.

Please respond within 15 days of receipt of this letter to our position on this itea.

If there any further questions in this regard, please contact A. Bournia, Licensing Project Manager, (301) 492-8196.

Sincerely, Original signed by gobert L Tedesoo Robert L. Tedesco, Assistant Director for Licensing Division of Licensing cc:

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.Mr. Louis 0. De! George DirectqIbof. Nuclear Licensing Commonwealth Edison Company P. O. Box 767

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Philip P. Steptoe, Esquire

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Suite 4200-One First National Plaza Chicago, Illinois 60603 Dean Hansell, Esquire

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Assistant Attorney General 188 West Randolph Street Suite 2315 Chicago, Illinois 60601 Roger Walker, Resident Inspector LaSalle NPS, U.S.N.R.C.-

P. O. Box 224 Marseilles, Illinois 61364

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