ML20086H968
| ML20086H968 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 12/06/1991 |
| From: | Kovach T COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9112100215 | |
| Download: ML20086H968 (4) | |
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!)ocembnr 6,1991 U. S. lluclear 'Aegulatory Commission Attn: Document Control Desk Washington, DC 20555
Subject:
Braldwood Station Units 1 and 2 Byron Station Units 1 and 2 Response to One Lovel IV Violation Inspection Report Nos. 50-454/91021; 50 455/91021; 50 456/91020 and 50-457/91018 NRC Decket Nos. 50 454; 50-455; 50 456 and 50-457
Reference:
W. D. Shafer Letter to Cordell Reed dated November 8,1991 transmitting NRC Inspection Report 50-454;91021; 50-455/91021; 50 450/91020 and 50 457/91018 Enclosed is Commonwealth Edison Company's response to the subject Notico of Violation (NOV). The NOV cited one severity LovelIV Violation. The violation was for having all four channols of the Overtemperature delta Temperature trip of the Reactor Protection System inoperable nt the same time. The violation response is provided in Attachment A.
Attachment B provides a discussion of a disciopancy that was identified in the Overtemperature delta Temperature Axial Flux Difference penalty.
thnm to Deniso Saccomando, Complianco Engineer at (708) 51S. this lettor, please rotor If your staff has any questions or comments concernin 7285.
Very truly yours l.f. r/
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T'. J. lear Licensing Manager Kovach Nuc TJK/sjs Attachments cc:
A. Bert Davis, Regional Administrator Alli S. G. Dupont, NRC Senior Resident inspector - Sraide,md W. J. Kropp, NRC Senior Resident inspector - Byron R.M. Pulslier, Braldwood Project Manaoer - NRR A.H. Hsia, Byron Project Manager - NRh c
1 ZNLD/13G9/1 l
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1 ATTACllMENT A RESPONSE TO NOTICE OF VIOLATION INSPECTION REPORT 454191021; 455/91021 456/91020;457/91010 VIOLATION:
Byron Units 1 and 2 and Braldwood Units 1 and 2 Technical Specification 3.3.1 requires, as a minimum, three of four Overtemperature delta Temperature trip channels to be operable in Modes 1 and 2. Power operation may continue provided an inoperable channel is placed in the tripped condition within 0 houts and the Minimum Channels operable requirement is met.
Byron Units 1 and 2 and Braidwood Units 1 and 2 Technical Specification 3.0.3 requires that when a Limiting Condition for Operation is not met, except as provided in the associated action requirement, within 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> action shall be initiated to place the unit in a mode in which the specification does not apply: at least mode 3 within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.
Contra to the above, on July 19,1991, all four Overtemperature delta Temperature tri channels were found to be inoperable since February 1985 at Byron t, January 198 at Byron Unit 2, May 1987 at Braidwood Unit 1, and March,1988 at Braidwood Unit 2. During th9se periods, the units operated in modes 1 and 2 without 3 lacing the Inoperable channois.n the tripped condillon and the units were not placed n mode 3 as required.
RESPONSE
Commonweab Edison Com 3any (CECol acknowledges the violation as stated above. CECO believes the tool cause of th s event was inadequate procedural guidance when the channels were initially scaled. The Precautions, Limliations 4,d Setpoint (PLS) manual provided by Westinghouse along with the Westinghouse 7300 Tra ning Manual, Byron /Braldwood Technical Specifications and scaling manuals from other stations contained the information used for scaling the Overtemperature delta Temperature (OTdT) setpoint. The average temperature (T Avg) in 3ut to the OTdT setpoint requires a certain overallloop gain, The gain should have 3een distributed between the lead / lag card and the summing amplifier. However, the PLS implied that the majorRy of the in aut gain should be placed on the lead / lag card. This error resulted in the loop reaching ts maximum output value when the input indicated that T Av0 was equal to 597 degrees F. Therefore, the OTdT reactor trip function was invalid when the T-Avg input was greater than 597 degrees F.
A review of this event for Part 21 considerations determined that the NRC has previously been informed of the issue and has issued NRC Information Notice 91052 describing this event. Also, Westinghouse has indicated that it will be issuing a Technical Bulletin on this event.
CECO's review of this event cetermined that there had been no negative impact on the health and safety of the public.
ZNLD/1369/2
' CORRECTIVE ACTION TAKEN AND RESULTS ACHIEVED:
T he Overtemperature delta Temperature (OTdT) loop channels were rescaled on the units at both Byron and Braldwood. This was accomplished by adjusting the Lead / Lag gain to 0.7447 from 1.4954 and replacing the existing 50 K ohm input resistors with 24.9 K ohm resistors. These changes restored the trip setpoint range to O to 150 percent as assumed by accident analys s.
An assessment for potential scallnq deficiencies in similar Reactor Protection and Engineered Safeguard Feature channels was pedormed at both Braidwood and Byron. Specifically, due to the features of the loop circuitry, the Overpower Delta T emperature and Steam Line Pressure instrument loops were examined. Neither of these functions were limited by the Instrument scaling.
The calibration procedures at both Braidwood and Byron were reviewed to determine if deficiencies existed in the program associated with scaling. The Test Report Packages used during loop calibration specify the engineering units (voltage values) for each loop module. The engineering units were derived based on process requirements provided by Westinghouse via the PLS manual. No other defic encies in the scaling process were identified during this review.
CECO's Corporate Nuclear Fuel Services (NFS) Department is currently performing analyses concoming the safety significance of the OTdT scaling deficiency.
i he only translent which requires reanalysis is the Rod Withdrawal at Power (RWAP) event. NFS is performing this analysis with the OTdT protection function modeled with deficient T. Avg cornpensation. Some best estimate assumptions will be factored into the analysis since this is a safety significance analysis and not a IMensing analysis.
The analysis report willinclude an evaluation of the non-affected event, and the analysis of the RWAP event. This analysis is expected to be completed by February 28,1992.
CORRECTIVE ACTION TAKEN TO AVOID FURTHER VIOLATION:
Braidwood Administrative Procedure, BwAP 5001 ' Station Process Control Scaling," and Byron Admin!stration Procedure, BAP 500 6, " Byron Station Process Control System Scaling," will be revised to include a statement Indicating that special consideration should be given to cards with multiple inputs and/or gains greater than 1.0 and that all input / output combinations must be considered for loops with multiple cards. These procedure changes are e,,pected to be completed by February 28, t 992.
CECO recognizes that reliance on the PLS contributed to this event. In order to minimize this reliance, CECO's Nuclear Engineering Department has determined that information on instrument scaling and setroints should be consolidated, maintained, and controlled in station procedures and other CECO documents. CECO is initiating an evaluation of scaling practices at Byron and Braidwood Station. The results of this evaluation will determine if additional review of the scaling methodology is necessary.
This evaluation is expected to be completed by January 31,1992.
DATE OF FULL COMPLlANCE:
The Overtemperature delta Temperature loop channels have been rescaled at both Braidwood and Byron. Full compliance was achieved in August,- 1991.
ZNLD/1369/3
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d ATTACHMENT D An issue similar in nature to the cited violation was reviewed with the NRC Senior Resident inspector at Braldwood Station. It was decided that a discussion of the issue would be appropriate in conjunction with the violation response of Attachment A. The issue involves a previously documented discrepancy in the Axial Flux Difference (dl) perially applied to the Overtemperature delta Temperature (OTdT) setpoint, The Westinghouse accident analysis has assumed a maximum axial flux difforence of 35% which would result in a maximum penalty to the OTdT setpoint of 50% The Byton/Braidwood Technical Sp1cification includes a formula to calculato the di penalty to the OTdT set aolnt based upv the axlal flux differenen. As a result, the dl
,enalty to the OTdT netpo nt should W be Nited te 50% Previously, the 3yron/Braldwood Test Report Packages scalco the GTdT setpoint such that it truncated the di penalty above 50% Rerut!), ti < Tost Report Packages wore changed to remove the truncation of the d! ne";rty. Discussions with Westinghouse indicated there was no safety significanco td Mis event since there is no <
- edible accident that would rely on a di pennity of o' eater than 50% to initiate a teactor trip.
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