ML19296A253

LER 78-088/03L-1 on 780731:during Power Reduction,Positive Moderator Temp Coefficient & Adjustment to Reactor Demand Station Resulted in Rapid Decrease in Coolant Sys Average Temp.Caused by Operator Error

ML19296A253
Person / Time
Site:	Davis Besse
Issue date:	08/28/1978
From:	Marley J TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19296A252	List: ML19296A250 ML19296A253
References
FOIA-79-98 LER-78-088-03L, LER-78-88-3L, NUDOCS 7903050314
Download: ML19296A253 (3)

Text

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EVENT DESCRIPTION AND PROB ABLE CONSEQUENCES hreactor power was being redu o 7 l On July 31, 1978 at 1830 hours0.0212 days <br />0.508 hours <br />0.00303 weeks <br />6.96315e-4 months <br />, g

The Reactor Operator was reducing reactor power by adjusting entry into containment.

gg g3; g j The combination of the positive moderator temperature o 4 l the reactor demand station. g to the reactor demand station caused a rapid decrease coefficient and the adjustment g 3 ; j in Tave.

All safety systems remained unaffected and were capable of performing their gg g y .;

(NP-33-78-102) designed functions if an incident had occurred.

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AKEN ' ACTIO ON PL A T l43N g lCl@lzlg g g 33 34 3d lz g M 3d di l42N lg 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h j cause of the occurrence was operator error in controlling the reactor l i l o l l The apparent l of j 1

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PHONE:

TOLEDO EDISON COMPANY DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION (

SUPPLEMENTAL INFORMATION FOR LER NP-33-78-102 DATE OF EVENT: July 31, 1978 FACILITY: Davis-Besse Unit 1 Reactor Coolant System Loop Temperature Decreased IDENTIFICATION OF OCCURRENCE:

Below Minimum Temperature For Criticality The unit was in Mode 2 with Power (HWT) = 0, and Conditions Prior to Occurrence: .

Load (MWE) = 0.

Description of Occurrence: On July 31, 1978 at 1830 hours0.0212 days <br />0.508 hours <br />0.00303 weeks <br />6.96315e-4 months <br />, reactor power was being reduced in preparation for entry into containment. The reduction in reactor power The subsequently reduced the Reactor Coolant System average temperature (Tave).

Reactor Operator was reducing reactor power per " Station Shutdown and Cooldown Pro-cedure", PP 1102.10, by adjusting the reactor demand station. The combination of the positive moderator temperature coefficient and the adjustment to the reactor demand station caused a rapid decrease in Tave. The downward trend of the Tave could not be stopped and turned around until Tave had decreased belos the minimum temperature for criticality, 525 F tc a minimum of 519 F.

Technical Specification 3.1.1.4 states that Tave shall not drop below 525 F. The action statement requires Tave to be restored to the 525 F limit within 15 minutes or the unit be in hot standby within the next 15 minutes. The Reactor Operators were successful in restoring Tave above 5250F within 10 minutes, thus complying with the action statement. .

Designation of Apparent Cause of Occurrence: The apparent cause of the occurrence I was operator error in controlling the reactor with a positive moderator temperature coefficient that resulted from the removal of the burnable poison rods.

Analysis of Occurrence:

There was no danger to the health and safety of the public or to unit personnel. Reactor Coolant System Tave was restored to above 525oF in t a =In:tes, and the unit continued its planned shutdown. All safety systems remained unaffected and were capable of performing their designed functions should an incident have occurred.

Corrective Action: Reactor Coolant System loop temperature (Tave) was restored to above 525 0 F in ten minutes, thus removing the unit from Technical Specification 3.1.1.4's action statement. Procedure modifications were made to PP 1102.10, Plant Shutdown and Cooldown and PP 1102.02, Plant Startup to add a note of caution for operation with a positive moderator temperature coefficient.(T-3100, T-3101).

LER #78-088