05000346/LER-1981-047-03, /03L-0:on 810816,steady State Quadrant Power Tilt Limit Was Exceeded Due to Large Difference in RCS Cold Leg Temp.Caused by Mismatch in Feedwater Flows to once-through Steam Generators.Plant Startup Procedure Modified

/03L-0:on 810816,steady State Quadrant Power Tilt Limit Was Exceeded Due to Large Difference in RCS Cold Leg Temp.Caused by Mismatch in Feedwater Flows to once-through Steam Generators.Plant Startup Procedure Modified

ML20010G665
Person / Time
Site:	Davis Besse
Issue date:	09/11/1981
From:	Jerrica Johnson TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20010G660	List: 05000346/LER-1981-047, Forwards LER 81-047/03L-0 05000346/LER-1981-047-03, /03L-0:on 810816,steady State Quadrant Power Tilt Limit Was Exceeded Due to Large Difference in RCS Cold Leg Temp.Caused by Mismatch in Feedwater Flows to once-through Steam Generators.Plant Startup Procedure Modified
References
LER-81-047-03L, LER-81-47-3L, NUDOCS 8109220374
Download: ML20010G665 (3)

LER-1981-047, /03L-0:on 810816,steady State Quadrant Power Tilt Limit Was Exceeded Due to Large Difference in RCS Cold Leg Temp.Caused by Mismatch in Feedwater Flows to once-through Steam Generators.Plant Startup Procedure Modified

Event date:
Report date:
3461981047R03 - NRC Website

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8 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES h I O I 21 l (M-33-81-55) on 8/16/81 at 1403 hours0.0162 days <br />0.39 hours <br />0.00232 weeks <br />5.338415e-4 months <br />, the steady state qttadrant power tilt limit way fbb TTl l exceeded due to a large difference in the Reactor Coolant System cold leg temperature. l The station j

ITTTl l The difference was caused by a mismatch in feedwater flow to the OTSGs.

l 10 I s l l entered the action statemerit of Technical Specification 3.2.4.a when the quadrant There was no danger to the health and safety of the l l0 ls l l power reached a maximum of +3.4.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-81-55 DATE OF EVENT: August 16, 1981 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:

Steady state quadrant power tilt limit exceeded due to a large difference in Reactor Coolant System (RCS) cold leg temperature Conditions Prior to Occurrence: The unit was in Mode 1 with Power (MWT) = 887 and Load (Gross MRE) = 240 Description of Occurrence: At 1403 hturs on August 16, 1981, the reactor operator was attempting to bring the Once Through Steam Generators (OTSG) off low level limits. As power was increased, feedwater flow to the 1-2 OTSG increased and it came off low level limits. Feedwater flow to the 1-1 OTSG, however, responded only slightly. The operators correctly diagnosed the problem as the delta T con-e troller and knew it would respond properly if the 1-1 OTSG could be taken off low j

level limits. The operators continued to increase power in order to bring the 1-1 OTSG off low level limits but the feedwater flow increase was not sufficient to bring the 1-1 OTSG off low level limits. The power increase further increased feedwater flow to the 1-2 OTSG.

The mismatch in feedwater flows and levels to the two steam generators caused a delta Tc of 15 F to occur and the delta T in turn caused a quadrant power tilt in c

the reactor core. The operators immediately took mant al control of the feedwater whea the station computer indicated quadrant control valves to correct the delta Te power tilt was increasing. While the operators were manually controlling the feed-water valves to correct the delta T and to stop the quadrant power tilt increase, c

t quadrant power tilt reached a maximum of +3.4 as measured by power range channels which placed the station in the action statement of Technical Specification 3.2.4.a.

Quadrant power tilt finally returned below its steady state limit of 1.96 by 1427 hours0.0165 days <br />0.396 hours <br />0.00236 weeks <br />5.429735e-4 months <br /> due to the operators manually controlling feedwater valves and delta Tc.

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Designation of Apparent Cause of Occurrence:

The quadrant power tilt was caused by the large difference in RCS cold leg temperatures created by the mismatch in feed-water flow to the OTSGs. This mismatch was due to the delta T controller changing e

I the feedwater demand ratio between the two loops.

The delta Tc controller has a calibrating integral circuit to correct for long i

j term changes in the OTSG when the delta T controller is in automatic.

If the e

delta Te controller is in manual or if either OTSG is en low level limit, the nor-l mal input is blocked and an artificial zero error input is fed to the integral pre-venting it from sensing an actual dif ference in cold leg temperatures. The output of the integral is blocked only if the delta Tc controller is in manual but another circuit in the delta T controller will drive the output of the integral to match the c

i manual output signal, i

LER #81-047

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TOLEDO EDISON COMPANY DAVIS-LESSE NUCLEAR POWER STATION UNIT ONE PAGE 2 SUPPLEMENTAL INFORMATION FOR LER NP-33-81-55 When the delta Tc controller was placed into automatic during the startup the manual signal had been changed earlier to significantly ratio feedwater to the 1-2 OTSG. This incorrect manual signal was blocked by placing the delta Te con-troller in automatic, but the integral had followed the manual signal and was still sending the incorrect signal to ratio feedwater to the 1-2 OTSC.

Initially, this had no effect due to low level limits controlling feedwater flow. When the operator tried to come off low level limits, only the level in the 1-2 OTSG in-creased while the 1-1 OTSG remained on low level limits. This caus ed the differ-ence in RCS cold leg temperatures and this error was blocked to the delta T con-e troller kr. the 1-1 OTSG still on low level limits.

The delta T controller manual output should have been set at 50% on the Bailey e

hand / auto station before placing the delta T controller in automatic. The Plant e

Startup Procedure PP 1102.02 is deficient since it does not specify the delta Te controller output when placing the feedwater loop demands and delta Tc controller in automatic.

Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel. The operators immediately took manual control of feedwater as soon as the quadrant power tilt started to increase as indicated by the station computer. During the transient only the steady state limit was exceeded, and the transient limit was not approached.

Corrective Action

The initial action of the operators was to manually control the feedwater valves to bring quadrant power tilt to within the steady state limit in l

twenty-four minutes. This is the action of Technical Specification 3.2.4.a.1.a.

Modification T-5701 was written to the Plant Startup Procedure PP 1102.02 to ensure that the delta T controller manual output is set at a 50% feedwater ratio before c

controller is placed in automatic.

the feedwater loop' demands or delta Te Failure Data: There have been no previous similar reports.

LER #81-047 L