05000245/LER-1981-025, Forwards LER 81-025/01T-0.Detailed Event Analysis Encl

Forwards LER 81-025/01T-0.Detailed Event Analysis Encl

ML20031C967
Person / Time
Site:	Millstone
Issue date:	09/30/1981
From:	Mroczka E NORTHEAST NUCLEAR ENERGY CO.
To:	Haynes R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML20031C969	List: 05000245/LER-1981-025, Forwards LER 81-025/01T-0.Detailed Event Analysis Encl 05000245/LER-1981-025-01, /01T-0:810915,both Reactor Recirculation Pumps Tripped.Caused by Voltage Fluctuation in 125 volt-dc Electrical Sys,Resulting in Spurious Isolation of ATWS Sys.Installation of Annunciator Is Being Evaluated
References
MP-1-1896, NUDOCS 8110090168
Download: ML20031C967 (3)

LER-1981-025, Forwards LER 81-025/01T-0.Detailed Event Analysis Encl

Event date:
Report date:
2451981025R00 - NRC Website

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Reference:

Facility Operating License No. DPR-21 j

Docket No. 50-245

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Reportable Occurrence R0-81-25/1T

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Dear Mr. hayaes:

This ietter forwards the Licensee Event Report for Reportable Occurrence R0-81-25/1T required to be submitted within 14 days pursuant to the requirements of the Millstone Unit 1 Technical Specifications, Section 6.9.1.8.b.

An additional three copies of the report are enclosed.

Yours truly, NORTHEAST NUCLEAR ENERGY COMPANY y

E J. Mroczkd Station Superintendent Millstone Nuclear Power Station EJM/TST:jf

Attachment:

LER R0-81-25/1T cc:

Director, Office of Inspection and Enforcement, Washington, D.C. (30)

Q Director, Office of Management Information and Program Control, T

Washington, D. C. (3)

U. S. Nuclear Regulatory Commission, c/o Document Management Branch, Washington, D. C.

20555 8110090168 810930 PDR ADOCK 05000245 S

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ATTACHMENT TO LER 81-25/1T NOR1HEAST NUCLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION - UNIT 1 PROVISIONAL LICENSE NUMBER DPR-21 DOCKET NUMBER 50-245 Identification of Occurrence Operation in a manner less conservative than the least conservative aspect of the limiting condition established in technical specifications occurred when both reactor recirculation pumps tripped.

Conditions Prior to Occurrence The Unit was operating in the startup mode with reactor power less than one (1) percent of rated and reactor pressure at 450 psig.

Description of Occurrence On September 15, 1981, at 1042 hours0.0121 days <br />0.289 hours <br />0.00172 weeks <br />3.96481e-4 months <br />, both reactor recirculation pumps tripped. Technical Specification 3.6.H.4 requires operation with forced circulation (at least one recirculation pump) when the mode switch is in the startup/ hot standby or run mode. Operation without forced circulation is not permitted and necessitates reactor shutdown.

Subsequent to the event, the Main Steam Isolation Valves were closed to perform turbine testing.

Tha resulting pressure increase in combination with insertion of colder water due to recirculation pump trip resulted in a higher moderator density and an IRM hi-hi neutron flux scram occurring at 1057 hours0.0122 days <br />0.294 hours <br />0.00175 weeks <br />4.021885e-4 months <br />.

Apparent Cause of Occurrence Voltage fluctuation in the 125VDC electrical system resulted in spurious isolation of the ATWS (Anticipated Transient Without Scram) system.

Upon re-energizing ATWS System the electronics caused automatic trip of both recirculation pumps.

Since the pumps were operating at minimum speed at the time of the event, pump coastdown and natural circulation maintained recirculation flow. With no significant change in the differential pressure across the recirculation pumps and no annunciated alarm for recirculation pump trip, the control room personnel were not immediately alerted to the event.

Analysis of Occurrence Forced recirculation flow is required to provide mixing of feedwater entering the reactor vessel to mitigate the consequences of rapid changes in reactor moderator density and to eliminate the potential for high local reactor vessel stresses due to thermal stratification of reactor coolant.

Although natural circulation flow provides some mixing, analysis has shown that forced circulation is required to maintain the parameters within acceptable limits at high power levels.

The effects of no forced circulation for the occurrence in question was analyzed with respect to fuel and reactor vessel thermal effects

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0 and were found to be negligible due to low reactor power level and the short amount of time at which there was no forced circulation before the reactor scram occurred.

Corrective Action

To prevent a reoccurrence installation of an annunciator off the recirculation pump field breaker is being evaluated. This will alert control room personnel of recirculation pump trip.

Additionally to pievent ATWS System initiation during automatic reset after a voltage fluctuation, the ATWS System inverter has been set to manual.

This will cause all safety functions initiated by RPT/ API (recircualtion pump trip / alternate rod insertion) to lock in automatically and only be reset by