ML20237D644

Responds to Util Comments on NRC 980531 SE Re Implementation of ATWS Rule.Based on Info & W Analysis for 50% Reactor Power,Nrc Finds Util Current Setpoint of 40% Turbine Load Acceptable & Determined That No Further Actions Required

ML20237D644
Person / Time
Site:	Beaver Valley
Issue date:	08/25/1998
From:	Brinkman D NRC (Affiliation Not Assigned)
To:	Cross J DUQUESNE LIGHT CO.
References
TAC-MA0715, TAC-MA0716, TAC-MA715, TAC-MA716, NUDOCS 9808270103
Download: ML20237D644 (4)

Text

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cm M 2 p""%k M 39 f/2-p UNITED STATES g j NUCLEAR REGUI.ATORY COMMISSION e $ WASHINGTON, D.C. 20066 4 001

% 4j o August 25, 1998 Mr. J. E. Cross President-Generation Group Duquesne Light Company Post Office Box 4 Shippingport, PA 15077

SUBJECT:

RESPONSE TO DUQUESNE LIGHT COMPANY'S COMMENTS ON NRC'S SAFETY EVALUATION REGARDING IMPLEMENTA flON OF THE ANTICIPATED

, TRANSIENT WITHOUT SCRAM (ATWS) RULE AT BEAVER VALLEY POWER STATION, UNIT NOS.1 AND 2 (BVPS-1 AND BVPS-2) (TAC NOS. MA0715 AND MA0718)

Dear Mr. Cross:

By [[letter::L-97-065, Discusses Inconsistency Between NRC SER Supplied to Util on Implementation of ATWS Rule & Design of ATWS AMSAC Submitted by Util,Per 10CFR50.62|letter dated January 5,1998]], as supplemented July 9 and August 4,1998, Duquesne Light Company (DLC) identified an inconsistency between the NRC Safety Evaluation (SE) regarding the implementation of the ATWS Rule and the design of the ATWS Mitigating System Actuation Circuitry (AMSAC) at BVPS-1 and BVPS-2. DLC indicated that whereas the NRC SE stated that the C-20 AMSAC permissive is set at 40% reactor power, the AMSAC Design, WCAP 10858-P-A, Revision 1, directed that the C-20 permissive setpoint for arming the AMSAC system be set at a nominal value of 40% turbine load. In its letters, DLC discussed Westinghouse Tecnical Bulletin ESBU-TB-08 which was issued by Westinghouse to inform plants of this problem. The Technical Bulletin indicated that, due to differences between turbine power and reactor thermal power, the AMSAC C-20 setpoint may be set non-conservatively on Westinghouse PWRs using the AMSAC designs identified in the WCAP. DLC indicated that a recent re-evaluation (discussed in the Technical Bulletin) was conducted with an initial condition of 50% reactor power with no subsequent AMSAC actuation. This analysis demonstrated that the amount of reactor coolant system (RCS) voiding is less than previously predicted at 100%

power with AMSAC and that RCS inventory remaining at 10 minutes into the transient is well above that needed to ensure that the core remained covered. DLC stated, "[t]hus Westinghouse concluded, since there exists 30% margin in thermal power in the initial power conditions i between the C-20 permissive setpoint condition and when AMSAC is needed to preclude exceeding a peak RCS pressure of 3200 psig during this limiting ATWS event, the existing 30%

power margin is considered acceptable for basing the C-20 permissive on turbine power as indicated in WCAP-10858-P-A." DLC agreed with this statement and requested that the NRC l staff amend the NRC SE to acknowledge that the BVPS-1 and BVPS-2 AMSAC design for the l C-20 permissive is acceptable based on a nominal setpoint of 40% turbine load.

The NRC staff has reviewed DLC's letters, Westinghouse Technical Bulletin NSD-TB 97-08, WCAP-10858-P-A, Revision 1, NUREG-0460 Volumes 1 through 4, and other ATWG related documents. In the WCAP, Westinghouse stated that'AMSAC is not required to actuate at or below 70% power to limit peak pressure in the unlikely event of a loss of normal feedwater ATWS event. However, in orcer to limit the amount of RCS voiding..., the C-20 power level ,

should be reduced to 40% power." In the Technical Bulletin, Westinghouse stated that at j thermal powers of 40% and below, no boiling is predicted to occur within the 600 second time i duration of the original ATWS analysis. Hence the specification of a C-20 AMSAC interlock  !

permissive corresponding to 40% power conservatively eliminated any potential concems associated with the initiation of boiling in the RCS when AMSAC is r,ot armed. This is conalstent 9808270103 990825 l l PDR ADOCK 05000334 n, pD P pop -

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J. Cross with an NRC staff position in NUREG-0460 that "...the system transient code, LOFTRAN, is an inappropriate code to predict system behavior after the formation of voids in the primary loop."

Additionally, the Westinghouse technical Bulletin informed recipients that the basis for the interlock permissive setpoint of 40% was originally determined using reactor power and that the difference between reactor and turbine power at part-power condition could make the setpoint of 40% turbine power non-conservative.

Based on the above discussion, the NRC staff finds that the conclusion in the NRC SE dated May 31,1988, that the C-20 setpoint should be 40% reactor power was based on the safety analysis at the time which demonstrated acceptable voiding levels at 40% reactor power. This is confirmed in the Westinghouse Technical Bulletin as discussed above.

As was discussed in DLC's [[letter::L-97-065, Discusses Inconsistency Between NRC SER Supplied to Util on Implementation of ATWS Rule & Design of ATWS AMSAC Submitted by Util,Per 10CFR50.62|January 5,1998 letter]] and Technical Bulletin NSD-TB-97-08, Westinghouse investigated the consequences of the limiting ATWS transients in which a loss of feedwater occurs for an initial condition of 50% reactor power with no subsequent AMSAC actuation. Westinghouse concluded that for these conditions, the amount of RCS voiding is still less than that previously predicted at 100% power with AMSAC and the RCS inventory remaining at 10 minutes into the transient is well above that needed to ensure that the core remains covered. Hence, no core damage 60e to RCS boiling is anticipated to occur without AMSAC at or below 50% reactor power. In addition, DLC's review of the data from recent startups and shutdowns at BVPS-1 and BVPS-2 indicated that the discrepancy at 40% reactor power between reactor power and turbine load has been a maximum of approximately 6 percent. Therefore, at 40% turbine load (the C-20 setpoint), the reactor power should still be below 50%. Based on this information and the Westinghouse analysis for 50% reactor power, the NRC staff finds DLC's current setpoint of 40% turbine load acceptable and has determined that no further actions are required.

Sincerely,

/s/

Donald S. Brinkman, Senior Project Manager Project Directorate 1-2 Division of Reactor Projects - 1/11 Office of Nuclear Reactor Regulation Docket Nos. 50-334 and 50-412 cc: See next page DISTRIBUTION Docket File MShuaibi PUBLIO TCollins ,

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J. Cross with an NRC staff position in NUREG-0460 that "...the system transient code, LOFTRAN, is an inappropriate code to predict system behavior after the formation of voids in the primary loop."

Additionally, the Westinghouse technical Bulletin informed recipients that the basis for the interlock permissive setpoint of 40% was originally determined using reactor power and that the difference between reactor and tuit>ine power at part-power condition could make the setpoint of 40% turbine power non-conservative.

Based on the above discussion, the NRC staff finds that the conclusion in the NRC SE dated May 31,1988, that the C-20 setpoint should be 40% reactor power was based on the safety analysis at the time which demonstrated acceptaole voiding levels at 40% reactor power. This is confirmed in the Westinghouse Technical Bulletin as discussed above.

As was discussed in DLC's [[letter::L-97-065, Discusses Inconsistency Between NRC SER Supplied to Util on Implementation of ATWS Rule & Design of ATWS AMSAC Submitted by Util,Per 10CFR50.62|January 5,1998 letter]] and Technical Bulletin NSD-TB-97-08, Westinghouse investigated the consequences of the limiting ATWS transients in which a loss of feedwater occurs wr an initial condition of 50% reactor power with no subsequent AMSAC actuation. Westinghouse concluded that for these conditions, the amount of RCS voiding is still less than that previously predicted at 100% power with AMSAC and the RCS inventory remaining at 10 minutes into the transient is well above that needed to ensure that the core remains covered. Hence, no core damage due to RCS boiling is anticipated to occur without AMSAC at or below 50% reactor power, in addition, DLC's review of the data from recent startups and shutdowns at BVPS-1 and BVPS-2 indicated that the discrepancy at 40% reactor power between reactor power and turbine load has been a maximum of approximately 6 percent. Therefore, at 40% turt>ine load (the C-20 setpoint), the reactor power should still be below SC 4. Based on this information and the Westinghouse analysis for 50% reactor power, the NRC steff finds DLC's I current setpoint of 40% turbine load acceptable and has determined that no further actions are (

required.

Sincerely, 1

M h.

Donald S. Brinkman, Senior Project Manager W

i Project Directorate 1-2 Division of Reactor Projects - 1/II Office of Nuclear Reactor Regulation Docket Nos. 50-334 and 50-412 e cc: See next page

J. E. Cross Beaver Valley Power Station, Units 1 & 2 Duquesne Light Company cc:

Jay E. Silberg, Esquire Gureau of Radiation Protection Shaw, Pittman, Potts & Trowbridge Pennsylvania Department of 2300 N Street, NW.

Environmental Resources Washington, DC 20037 ATTN: Michael P. Murphy Post Office Box 2063 Director-Safety and Licensing Harrisburg, PA 17120 Department (BV-A)

Duquesne Light Company _ Mayor of the Borough of Beaver Valley Power Station Shippingport PO Box 4 Post Office Box 3 Shippingport, PA 15077 Shippingport, PA 15077 Commissioner Roy M. Smith Regional Administrator, Region i West Virginia Departrnent of Labor U.S. Nuclear Regulatory Commission Building 3, Room 319 475 Allendale Road I Capitol Complex King of Prussia, PA 19406 Charleston, WVA 25305 Resident inspector  !

Director, Utilities Department U.S. Nuclear Regulatory Commission '

Public Utilities Commission Post Office Box 298 j 180 East Broad Street Shippingport, PA 15077 Columbus, OH 43266-0573 Director, Pennsylvania Emergency Duquesr.e Light Company Management Agency Beaver Valley Power Station Post Office Box 3321 PO Box 4 Harrisburg, PA 17105-3321 Shippingport, PA 15077 ATTN: S. C. Jain, Senior Vice President Ohio EPA-DERR Nuclear Services (BV-A)

ATTN: Zack A. Clayton Post Office Box 1049 Mr. J. A. Huitz, Manager Columbus, OH 43266-0149 Projects & Support Services First Energy Dr. Judith Johnsrud 76 South Main Street National Energy Committee Akron, OH 44308 Sierra Club 433 Orlando Avenue State College, PA 16803 l Duquesne Light Company Beaver Valley Power Station PO Box 4 Shippingport, PA 15077 ATTN: R. D. Brandt, Divisio1 Vice President, Nuclear Operatioqs I and Plant Manager (BV-SO3B-7) 11