ML20072C639

Interim Deficiency Rept Re Potential post-accident Errors in RCS wide-range Pressure Instruments.Potential Inaccuracies Do Not Constitute Significant Deficiency for Facility. Summary of Evaluation Encl

ML20072C639
Person / Time
Site:	Wolf Creek
Issue date:	03/01/1983
From:	Koester G KANSAS GAS & ELECTRIC CO.
To:	Seidle W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
10CFR-050.55E, 10CFR-50.55E, KMLNRC-83-018, KMLNRC-83-18, NUDOCS 8303080498
Download: ML20072C639 (6)

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> KANSAS GAS AND ELECTRIC COMPANY y THE ELECTFhC COMPANY

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OLENN L MOESTER vaca remosast asuctaan March 1, 1983 Mr. W.C. oeidle, Chief Reactor Projects Branch 2 U.S. Nuclear Reculatory Commission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76011 KMLNRC 83-018 Re: Docket No. STN 50-482 Ref: 1) Letter KMLNRC 82-211, dated June % 1982, from GLKoester, KG&E, to WCSeidle, NRC

2) Letter NS-EPR-2586, dated Oril 21, 1982 from EPRahe, Westinghouse, to RC'mYoung, NRC Subj: Interim 10CFR50.55(e) Report - Post Accident Instrument Errors

Dear Mr. Seidle:

Reference 1) provided an interim report on a 10CFR50.55(e) matter concerning the potential, post-accident errors in the reactor coolant system wide range pressure instruments. Westinghouse reported this matter to the NRC on a generic basis in Reference 2) and the NRC disseminated the subject in IE Information Notice No. 82-11.

Westinghouse determined that the post-accident accuracy of the wide range pressure instruments may not meet functional requirements.

Kansas Gas and Electric Company has reviewed this matter with Westinghouse and has determined that, for most functions dependent on wide range instruments, the potential inaccuracies do not constitute a significant deficiency for the Wolf Creek Generating Station. A summary of the evaluation that leads to this conclusion is provided in the attached report. The effects of the potential inaccuracies on the reactor vessel level instrumentation system and core cooling monitor system are still being evaluated. The status of that evaluation will be reported to you on or before July 1, 1983.

In the interim, please direct any questions on this matter to me or to Mr. Otto Maynard of my staff.

8303080498 830301 Yours very truly, PDR ADOCK 05000482

'. g GLK: b Attach cc: RCDeYoung, w/a TVandel/SSchum, w/a 201 N. Market - WicNta, Kansas - Mail Address: PO. Box 208 I Wichita, Kansas 67201 - Telephone: Area Code (316) 261-6451

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THE EFFECT OF POTENTIAL i

i POST-ACCIDENT ERRORS IN U:E O

WIDE RANGE REACTOR COOLANT SYSTEM PRESSURE INSTRUMENTS

[ ON THE SNUPPS PLANTS I

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' I 5ttachment KMLNRC 83-018 Introduction In early April 1982, Westinghouse informed SNUPPS of a potential signifi-cant deficiency, as defined by'10CFR 50.55(e), for the SNUPPS plants concerning the potential, post-accident inaccuracy of the reactor

- coolant system ~(RCS) wide range pressure instrument. This Westinghouse determination was based on a review of the results of equipment qualifi-cation testing and of design / operational requirements.placed on the instrument. Westinghouse also recognized that due to the complexity of the' issue and plant-specific differences, the issue may affect individ-ual plants differently. Tne SNUPPS plants (Callaway and Wolf Creek) are identical insofar as this issue affecting, or being affected by, olant design and operation. Therefore the SNUPPS Utilities jointly reviewed this matter. The review include'd Westinghouse and the architect /

engineer for SNUPPS, Bechtel Power Corporation.

4 Normal Plant Operations and Evolutions In a normal plant environment, the RCS wide range pressure instrument has an indication accuracy of + 90 psi (3% of span) and a trip and actuatian accuracy of + 63 psi-(2.1% of span). During plant operation, the' instrumentation is'~used to monitor RCS pressure outside of the

, narrow range pressurizer pressure measurement. The indication accuracy l provided is acceptable for this function. '

i For initiation of Residual Heat Removal System (RHRS) operation, the

( instrumentation provides an open permissive signal to the RHRS isolation L valves. The system pressure requirements are based on precluding over '

pressurization of the RHRS and yet maintaining a sufficient RCS pressui-to maintain the required differential pressure on the #1 Reactor Coolant l

Pump seals. The actual allowance in the SNUPPS design is + 117 psi.

Therefore the j; 90 psi indication and j; 63 psi trip accuracies are acceptable.

l l The RCS wide range pressure transmitter provides an input signal to the l overpressure mitigation system (OMS). in the SNUPPS design. Analyses of the OMS have shown that the + 63 psi trip accuracy is acceptable.

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Attachment

. KMLNRC 83-018 Page Two Abnormal / Accident Conditions 4

In the worst case accident environment, the RCS wide range pressure instrument accuracies are + 390 psi (13% of span) for irdication and

+ 363 psi (12.1% of span) Tor trip and actuation. These values assume a

+ 10% sensor environmental allowance based on the environenntal testing described above and also reflect normal sensor and sign _. processing allowances for calibration accuracy, drift, comparator setting, tempera-ture'effect, indicator accuracy, and indicator readability. During accident conditions the RCS wide range pressure signal is relied upon in '

several of the emergency response guidelines developed by the Westing-

, house Owners' Group and provides an input to the Reactor Vessel Level Instrumentation System (RVLIS) and the Core Cooling Monitor System

(CCMS).

1 The emergency operating procedures for the SNUPPS plants have not been completed. However, they will be based on Westinghouse Owners' Group

Emergency Response Guidelines (ERG). ERGS E-1 (Loss of Reactor Coolant) and E-2 (Loss of Seconoary Coolant) use RCS pressure for the operator evaluation of safety injection (SI) termination. The purpose of the

evaluation is to minimize the number of demands on the pressurizer power-

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operated relief valves and yet maintain subcooling following a small LOCA or steam system break.. Westinghouse has determi,ned that an accuracy of

+325 psi'is required for this function and thuskis not met by the + 390 L accuracy of the RCS wide range pressure instrument. However, narrow rang.e t pressure instrumentation has a post-accident accuracy of about + 144 psi

,' - and its range (1700 to 2500 psig) includes the SI termination v'aTue (RCS

' pressure greater than 2000 psig). Use of the narrow range instrument for l this post-accident function has the advantage that the operator uses the same instrument that is used during normal plant operation and that is most familiar to h'im. If, during the finalization of the emergency operating procedures for the SNUPPS plants, (a) the accuracy require-ment for the SI termination function is not reduced, or (b) the accuracy of the wide range pressure instrument is not improved, the procedures will specify use of the narrow range instrument for SI termination; and equip-ment qualification documentation will show that the required accuracy is met. -

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Attachment' XMLNRC 83-018 Page Three ERG E-2 also uses wide range pressure for SI termination to minimize reactor vessel thermal shock while maintaining subcooling. The accuracy

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requirement for this function is j; 520 psi and the post-accident accu-racies are acceptable.

ERG E-3 (Steam Generato'r Tube Rupture) uses the RCS wide range pressure instrument for a variety of functions. However the ERG requires only that a pressure increase be read. A specific accuracy is not required.

In addition, the tube rupture accident would not result in a harsh postaccident environment that could cause the large inaccuracies.

ERG E-0 (Reactor Trip or Safety Injection) requires that the operators evaluate the need to trip the reactor coolant pumps. This step ensures that pumps are kept running for accident conditions in which decay heat removal via the steam generators is preferred. For SNUPPS, the allowed instrumentation accuracy is about j; 530 osi. Therefore the wide range RCS pressure instrument meets this requirement.

The-CCMS compares core outlet thermocouple temperatures and hot and cold leg RTD temperatures based on the lowest of three pressure signals.

One of the three pressure signals for each of the redundant portions of the.CCMS is the RCS wide range pressure. The effect of the uncertainty of the wide range pressure signal is still under evaluation.

The RVLIS measures the differential pressure between the bottom and top

, of the reactor-vessel. To provide accuracy for level measurement, temperature of the impulse lines, RCS temperature, and RCS wide range pressure are used to compensate the differential pressure transmitter

. outputs for differences in system and reference leg density. The effect l .of the wide range' pressure instrument accuracy for RVLIS is also still under evaluation.

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r Attachment KMLNRC 83-o18 Page Four As described in the SNUPPS FSAR Appendix 5.4A, the SNUPPS plants are designed to attain a cold shutdown condition using only safety-grade equipment. Part of the safety-grade cold shutdobin scenario is the use of the RHRS. The post-accident- accuracies of the RCS wide range pressure transmitter are greater than + 117 psi. However, the SNUPPS design and licensing commitments do not 17equire that the RHRS be initiated in a normal mode following a design basis accident. For a postulated accident scenario in which the RHRS is eventually used in its normal cooling mode, other pressure instruments can be used to insure the safe initi-ation of the RHRS. Specific instruments.available for this purpose are the third RCS wide range channel, for which the pressure transmitter is located on one of the RVLIS lines outside containment, and RCS pressure ,

instruments in the nuclear sampling system. Therefore, post-accident accuracies of, the instrument in question do not apply to RHRS initiation.

Conclusions There are no concerns about RCS pressure measurement during normal

- plant environmental conditions. Several of the guidelines that will be used as a basis for the operating procedures call for operator use of RCS wide range pressure. In all cases, either the required accuracy meets the demonstra.ted accuracy or a more accurate instrument will be used.

The RCS wide range pressure instrumcnt provides an input to other instru-mentation systems that may be used in a post-accident situation. In these cases, the safety effects of the wide range pressure transmitter inaccuracies are currently under evaluation.

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