05000261/LER-1981-001, Updated LER 81-001/01T-1:on 810109,turbine Runback & Automatic Rod Withdrawal Block Protection Defeated W/Power Range Channel N41 Being Out of Svc.Caused by Improper Rod Drop Analysis.Administrative Controls Revised

Updated LER 81-001/01T-1:on 810109,turbine Runback & Automatic Rod Withdrawal Block Protection Defeated W/Power Range Channel N41 Being Out of Svc.Caused by Improper Rod Drop Analysis.Administrative Controls Revised

ML20066K959
Person / Time
Site:	Robinson
Issue date:	11/17/1982
From:	Cox H CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20066K946	List: 05000261/LER-1981-001, Updated LER 81-001/01T-1:on 810109,turbine Runback & Automatic Rod Withdrawal Block Protection Defeated W/Power Range Channel N41 Being Out of Svc.Caused by Improper Rod Drop Analysis.Administrative Controls Revised
References
LER-81-001-01T, LER-81-1-1T, NUDOCS 8211290703
Download: ML20066K959 (2)

LER-1981-001, Updated LER 81-001/01T-1:on 810109,turbine Runback & Automatic Rod Withdrawal Block Protection Defeated W/Power Range Channel N41 Being Out of Svc.Caused by Improper Rod Drop Analysis.Administrative Controls Revised

Event date:
Report date:
2611981001R00 - NRC Website

text

NRC FORM 366

" UPDATE REPORT - PREVIOUS REPORT DATE 1/23/81" u.S. NUCLEAR REGULATORY COMMISSION (7-77 F LICENSEE EVENT REPORT 0

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8 60 61 DOCK ET NUMBER 68 69 EVENT DATE 74 75 REPORT DATE 80 EVENT DESCRIPTION AND PROB ABLE CONSEQUENCES h l o l 2 l l0n January 9,1981, with the unit at 100% power, it was determined that operation with l g o,3, lthe RPI System input to the turbine runback and auto rod withdrawal defeated and power l

, o g,, [ range channel N41 input out of service is contrary to the assumptions in the safety l

, o g g analysis prepared during the fuel reload safety evaluation.

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g lnot sensing a dropped rod is small since three of the power range detectors were l

l o l, l [ ope rab le. 'Ihis occurrence is reportable pursuant to Technical Specifications l

.9.2.a(6).

No adverse consequences resulted from the above condition.

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6 SUPPLEMENTAL INFORMATION FOR LICENSEE EVENT UPDATE REPORT 81-001, REVISION 1 I.

Cause Description and Analysis, On January 7,1981, the Power Range Channel N41 was taken out of service.

Previous to this, the Rod Position Indication System (RPI) input to the turbine runback system and auto rod withdrawal circuit had been defeated due to spurious rod drop indications in an effort to prevent unnecessary thermal cycles to Reactor Coolant System (RCS) components. On January 9, 1981, it was determined, by a review of the H. B. Robinson, Unit No. 2 FSAR and Fuel Reload Safety Evaluation, that both of these documents assume that turbine runback and auto rod withdrawal defeat occur follow-ing a control rod drop.

These systems are actuated by any one RPI bottom signal or a rapid flux decrease on any one power range channel.

By having N41 inoperable, a few rods located in the core region nearest N41 might not be detected by the other three power range detectors if they were to drop.

Based on this review, therefore, the event was identified as reportabic pursuant to Technical Specification 6.9.2.a.6.

Since an RCCA drop event did not occur during this time, no adverse consequences resulted from the above situation.

II.

Corrective Action

All atfected systems were immediately returned to service when it was determined that having both inputs to the turbine runback and auto rod withdrawal systems defeated may be contrary to the FSAR and fuel reload

safety analysis

III. Correct ive Action To Prevent Recurrence A review of this issue has been completed, and an analysis has been performed by the fuel supplier.

On the basis of this analysis, it has i

been concluded that even without the turbine runback and automatic rod withdrawal block protection systems, H. B. Robinson, Unit No. 2 will have acceptable thermal margin with respect to a dropped rod transient.

The results of this analysis also envelope the current reduced temper-nture and power operation.

Following this event, administrative controis were implemented to ensure that both turbine runback and auto rod withdrawal block initiating circuits are not defeated at power levels greater than 70%.

Based on the analysis described above, the administrative controls governing the RPI and power range nuclear instrumentation inputs to be the tudi tne runback and automatic rod withdrawal block circuits will be revised to delete the requirement to reduce power to 70%.

In general, this action will be taken when instrument problems in the rod position indication system cause false rod bottom signals leading to needless turbine 1.nbacks, or when a power range NIS channel fails or is taken out of service for maintenance and/or testing.

The intent of the remaining controls will be to minimize the time these inputs are blocked. Normal operation will continue to be with the runback initiating circuits in place. No further action is considered necessary.