ML20137Z760

Provides Addl Info Re Backfit Issue 4, Steam Generator Level Control & Protection, Per SER (NUREG-1057).Addl Info & 850509 Transcript of Backfit Appeal Meeting Provide Justification for Closure of Issue

ML20137Z760
Person / Time
Site:	Beaver Valley
Issue date:	03/10/1986
From:	Carey J DUQUESNE LIGHT CO.
To:	Harold Denton, Tam P Office of Nuclear Reactor Regulation
References
RTR-NUREG-1057 1NRC-6-21, 2NRC-6-021, 2NRC-6-21, GL-84-08, GL-84-8, TAC-62881, NUDOCS 8603130112
Download: ML20137Z760 (2)

Text

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," $ arch 1 198 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: Mr. Peter Tam, Project Manager Division of PWR Licensing - A Office of Nuclear Reactor Regulations S UBJECT: Beaver Valley Power Station - Unit No. 2 Docket No. 50-412 Steam Generator Level Control Backfit

REFERENCE:

a) NUREG/CR-4326, dated August,1985, "Ef fects of Control System Failures on Transients and Accidents at a 3-Loop Westinghouse Pressurized Water Reactor, b) Transcript of Beaver Valley - Unit 2 Backfit Appeal Meeting on Steam Generator Water Level Channel Instrumentation Issue on May 9, 1985.

Gentl emen:

Additional information has come to our attention regarding Backfit Issue No. 4, " Steam Generator Level Control and Protection" in Table 1.3 of the Beaver Valley rawer Station Unit No. 2 (BV-2) Safety Evaluation Report, NUREG-1057. Rderence (a) documents an evaluation of the effects of non-safety grioe centrol system failures on a typical 3-loop Westinghouse pres-surized wai.er reactor plant. One of the sequences that the report evaluates is " Failures that result in excessive feedwater flow rates with subsequent failure of the steam generator high water level trip". This is explicitly the event that was the subject of Reference (b).

Reference (a) documents that the median probabil ity for such an event is 5.4 E-8 per reactor year. Duquesne Light notes that this extramely remote value of occurrence is significantly lower than either the general probability for an ATWS event or the proposed Safety Goal probability value.

It also substantiates the Duquesne Light cla im in Reference (b) that "the probability of this event occurring is quite remote".

Reference (a) also evaluated the use of a two out of four high steam generator water level trip logic system which was suggested by the NRC Staff as a precise method to resolve this BV-2 Backfit issue. Although a 4 channel system would decrease some of the identiflad failure mode probabill-ties which could lead to steam generator overfill, Reference (a) concludes 8603130112 860310 l PDR ADOCK 05000412 Opl E PDR U  ;

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o Mr. Harold R. Denton, Director Steam Generator Level Control Backfit Page 2 "With an additional independent failure included in the sequence fault tree for the paths that utt11ze the level instrument failures to inhibit the MFW pump trip, the sequence top event probability would decrease, however, those f aul t tree paths that inhibit the trip by fail ures in the trip circuitry would be unchanged and would dominate the calculation to hold the probability (for the overall event) near the original value". Thus adding a fourth steam generator high water level channel to the BV-2 trip logic would result in an insignificant decrease in the already extremely remote probability of the subject event occurring.

Reference (a) also suggests that "it may be judged reasonable to assume operator action is less than 10 minutes" during startup or shutdown evol utic1s . This further supports Duquesne Light's claim in Reference (b) that operators would take corrective action much sooner than the Staff speci-fled guidance of 10 minutes for overfill events at low power.

Generic Letter 84-08 allows a backfit if it is necessary to achieve an acceptable level of safety and the new backfit rule requires that there must be a " substantial increase in the overall protection of the public health and safety". Neither of these criteria is met by the information in Reference (a). Therefore, Duquesne Light believes that this new information developed independently for the NRC coupled with the past argunents discussed in Reference (b) provides justification for the immediate closure of Backfit Item No. 4'in Table 1.3 in the BV-2 Safety Evaluation Report (SER). Duquesne Light requests that the next supplement to the BVPS-2 SER close this issue.

Please inform us of yc'Jr concurrence.

DUQUESNE LIGHT COMPANY e'_ M; By __J(sot >Carey ~

Vice President RWF/ sip NR/STM/ GEN cc: Mr. P. Tam, Project Manager Mr. G. Walton, NRC Senior Resident t ispector Mr. V. Stello, Acting Executive Director for Operations

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