ML20207T226

Summarizes 870313 Telcon W/Util Re 870213 Proposed Change to Tech Specs to Lower RWCU Sys Isolation Setpoint from Existing Reactor Vessel low-water Level Setpoint to lo-lo Water Level Setpoint

ML20207T226
Person / Time
Site:	Millstone
Issue date:	03/18/1987
From:	James Shea NRC
To:	NRC
References
NUDOCS 8703230324
Download: ML20207T226 (3)

Text

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k NUCLEAR REGULATORY COMMISSION WASHINGTON. D. C. 20555 g March 18, 1987 Docket No.: 50-245 LICENSEE: Northeast Nuclear Energy Company (NNECO)

FACILITY: Millstone Nuclear Power Station, Unit No. 1

SUBJECT:

TELEPHONE

SUMMARY

REGARDING REACTOR WATER CLEANUP SYSTEM ISOLATION SETPOINT CHANGES By letter dated February 13, 1987, NNEC0 proposed to change a Millstone Nuclear Power Station, Unit No.1 (Millstone 1) technical specification.

The change would lower the Reactor Water Cleanup (RWCU) system isolation setpoint from the existing reactor vessel low-water level setpoint to the low-low-water level setpoint. In response to an NRC telephone request for additional information, NNEC0 representatives stated by telephone on March 13, 1987 that:

based on operating experience the low reactor vessel water level signal that causes automatic isolation of the RWCU system could be lowered by four (4) feet without compromising core cooling.

This corresponds to the proposed change from the existing low water level setpoint to low-low water level setpoint. The change would enhance reactor safety to the extent that a larger drop in water level could be tolerated without isolation of the RWCU system.

This change would preserve the ability to remove water from the ves-sel by the RWCU system following a reactor scram. During such incidents, water level drops suddenly due to increased pressure and void collapse, but is followed by a rapidly increasing water level as the feedwater control system adjusts downward to the new reduced feedwater demand.

Removal of excess water from the reactor vessel via the RWCU system provides additional assurance that reactor vessel water level will not reach the automatic high-level reactor feedwater pump trip. In i other words, the RWCU system can be used to bleed excess water from the vessel to prevent an unnecessary feedwater pump trip and the risk that the pump could not be restarted in time to maintain sufficient w-ter level in the reactor vessel to assure core cooling. Such an un-necessary loss of RWCU system, when it has occurred at Millstone 1, has required the dedicated attention of a plant operator and con-siderable time to fully restore the RWCU system to normal operation.

normal reactor vessel water level is 512" above the bottom of the reactor vessel. The assumed largest accident pipe break (full pipe cross section) in the RWCU system outside containment would allow more water to escape from the vessel into the reactor building, i.e.,

82,000 pounds of pressurized 550* water with the RWCU setpoint re-duced to 434 inches, in contrast to 34,500 pounds for the current technical specification isolation setpoint of 482 inches, before automatic closure of the RWCU isolation valves. Changing the 8703230324 e7031s PDR P ADOCK 05000245 PDR

Telephone Summary (Millstone 1) setpoints as proposed would extend the time to automatically iso-late the RWCU system following the postulated maximum pipe break of the drywell containment by 19 seconds.

there are non-safety grade signals / alarms indicative of a RWCU pipe break outside of containment that could alert the control room operators to manually close the RWCU system isolation valves before auto closure on low-low reactor water level. signal.

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. Telephone Summary (Millstone 1) setpoints as proposed would extend the time to automatically iso-

. late the RWCU system following the postulated maximum pipe break of the drywell containment by 19 seconds.

• there are non-safety grade signals / alarms indicative of a RWCU pipe break outside of containment that could alert the control room operators to manually close the RWCU system isolation valves before auto closure on low-low reactor water level signal.

James J. Shea cc:

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