ML19257A308

Submits Deficiency Rept Re Nonconservatism Found in Error Analysis Assumptions Used to Determine Accuracy of Nuclear Instrumentation Reactor Rate Trip Circuitry.Solution Minimizes Power Overshoot for Rod Drop Events

ML19257A308
Person / Time
Site:	North Anna
Issue date:	12/11/1979
From:	Brown S VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
References
REF-PT21-79-181-000 NUDOCS 8001030703
Download: ML19257A308 (2)

Text

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-" za December 11, 1979 Mr. James P. O'Reilly, Director Serial No. 1117 Office of Inspection & Enforcement PSE&C/JCHjr:mac: wang U.S. Nuclear Regulatory Commission Region II Docket No. 50-339 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303

Dear Mr. O'Reilly:

On December 7,1979 a report was made under the provisions of 10CFR50.55(e) concerning the Nuclear Instrumentation Reactor Rate Trip Circuit.

In accordance with the reporting requirements of 10CFR21, the following information is submitted:

A. Name and address of reporting individual:

Mr. E. A. Baum, Executive Manager Licensing and Quality Assurance Virginia Electric and Power Company P. O. Box 26666 Richmond, Virginia 23261 B. Facility, activity and/or component affected:

North Anna Power Station, Unit 2 '

Nuclear Instrumentation Reactor Rate Trip Circuit C. Name of firm constructing the facility or supplying the component, activity or service:

Westinghouse Electric Corporation P. O. Box 355 Pittsburgh, Pennsylvania 15230 D. Description of defect, deficiency, or failure to comply:

A nonconservatism has been found in the error analysis assumptions used to determine the accuracy of the Nuclear Instrumentation Reactor Rate Trip Circuitry. The present allowance for instrument inaccuracy

- in the power range negative rate trip is 0.5%. This allowance was determined assuming that all circuitry inaccuracies preceding the rate trip differentiator cancel. Further analysis reveals that errors associated with precision, (hysterisis, repeatability, etc.)

of this upstream circuitry may not be entirely eliminated by the differentiator circuit. When these potential additional errors are factored into the analysis, a reactor trip may not occur in some () A y90 cases previously assumed.

E. Date of determination of reportability: 1667 300

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December 7, 1979 { h 801)D(13 0 hbw vigr em,

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. F. Similar components, activities, or services: '

North Anna Unit 1 G. Corrective action which has been, is being or will be taken, the individual responsible and the length of time to complete the action:

We will implement the following procedural solution prior to operation of the unit:

Manual Rod Control 0-100% Power: No change from current rod insertion limit.

(i.e., Technical Specification 3.1.3.6, North Anna 2)

Automatic Rod Control 0 to 90% Power: No change from current rod insertion limit.

(i.e., Technical Specification 3.1.3.6, North Anna 2) 90 to 100% Power: D bank greater than 215 steps.

The benefit of this solution is that it will minimize a power overshoot for rod drop events and preclude potential DNBR limit violations. We are also continuing our review of this problem for possible implementation of long term solutions which may be more desirable.

H. Other information:

None Any information not available at this time will be submitted in a follow-up letter as a 30-day report.

Should you require further information, please contact this office.

Very truly yours Yk lIl n s d'~ Sam C. Brown, Jr.

Senior Vice President - Power Station Engineering and Construction cc: Director, Office of Inspection and Enforcement (3)

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1667 301