ML20034H849
| ML20034H849 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 03/18/1993 |
| From: | Schuster T COMMONWEALTH EDISON CO. |
| To: | Murley T NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation |
| References | |
| REF-PT21-93 NUDOCS 9303220156 | |
| Download: ML20034H849 (5) | |
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Ccmmonw3cith Edison I
f 1400 Opus Place
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s Downers Grove, tilinois 60515 March 18,1993 l
l Dr. Thomas E. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Document Control Desk l
Subject:
Commonwealth Edison Company Minimum Temperature for Criticality Analysis 10 CFR Part 21 Notification
Dear Dr. Murley:
The purpose of this letter is to notify the NRC Staff of concerns by Commonwealth Edison Company (CECO) regarding a minimum temperature for j
criticality analysis supplied to CECO by Westinghouse Electric Corporation. This analysis utilized potentially non-conservative temperature assumptions to evaluate j
uncertainties associated with the Zion Units 1 and 2 reactor protection system.
The temperature utilized in the analysis is not consistent with the minimum temperature for criticality allowed by the Zion Units 1 and 2 Technical Snedfications. Provided as an attachment to this letter is CECO's notification in U.
sance with the requirements of 10 CFR 21, Section 21.
As stated in the attached corrective actions, CECO has performed an evaluation to determine an appropriate alternative minimum temperature for i
criticality. Administrative controls have been instituted to ensure the reactor coolant system average temperature is above this value prior to achieving criticality, and to maintain it above this value whenever the reactor is critical.
In addition, CECO will update th? Zion Station Technical Specifications and UFSAR as described in the attached corrective actions, ss:cah/1 i
g/I annnno.
l 9303220156 930318 PDR ADDCK 05000295 S
PDR g
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Dr. Murley March 18,1993 i
If there are any questions regarding this notification, please direct them to Stephen F. Stimac at (708) 663-7275.
t Respectfully,
/M 1
Terence K. Schuster Licensing Operations Director f
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Attachment:
10 CFR 21 Notification l
cc:
A. Bert Davis, Regional Administrator - Rlli C.Y. Shiraki, Project Manager - NRR J.D. Smith, Senior Resident inspector - Zion t
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l Page 1 of 3 10 CFR Part 21 Report l
Minimum Temperature for Criticality Analysis Acolicability This notification is submitted in accordance with the requirements of 10 CFR i
Part 21, Section 21.21(a)(1).
I hientification of Facility and Component This notification concerns setpoint methodology and the selection of limiting core parameters for various design basis transients which can occur at zero power or low power at a nuclear power plant.
Identificalion of Comoonent Manufacturer /Supp_ lier WCAP 12582, " Westinghouse Setpoint Methodology for Protection Systems, Zion Units 1 and 2, EAGLE 21 Version," August,1991, Power Range Nuclear instrumentation Reactor Trip, Low Setpoint l
Westinghouse Electric Corporation Energy Systems P.O. Box 355 Pittsburgh, PA 15230-0355 Tel. (412)374-5282 Nature of Defect The safety analysis performed for Zion Nuclear Station assumed potentially non-conservative initial conditions for various design basis transients. Zion's I
Technical Specification 3.2.1.C 2.b requires that the reactor coolant system average temperature be at least 500 F prior to achieving criticality. The licensing basis analysis performed by Westinghouse assumes that the reactor is near the nominal no-load operating temperature, 547 F. _ For temperatures below 530 F, the Pawer Range Nuclear Instrumentation Low Setpoint Reactor trip is outside of i
its analyzed range. The response of the Power Range channel may be adversely
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effected by the increased density of the coolant at lower temperatures. Core i
Physics parameters and power distribution analysis are also potentially affected by the lower temperatures, ss:cah/3 1
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1 Page 2 of 3 l
10 CFR Part 21 Report Minimum Temperature for Criticality Analysis Nature of Defect (continued)
The setpoint study assumed that while critical, operators would control reactor no-load temperature to within 4 F of the nominal 547 F value. The technical specification allows for a temperature deviation of up to 47 F below the nominal value.
Safety Sionificance For low power transients which rely on the Power Range Nuclear instrumentation Low Setpoint for reactor protection, a reduction in the assumed initial reactor coolant system average temperature may potentially result in a reactor trip occurring at a higher core power than previously assumed. This is due to the increased shielding of the excore detector due to the increased density of the moderator in the downcomer of the reactor. These transients include Rod Control Cluster Assembly (RCCA) Bank Withdrawal from Subcritical and RCCA Ejection. Other transients rely on the power Range Nuclear Instrumentation Trip Low Setpoints as a backup only.
For initial core temperatures at or above 530 F, CECO has concluded that sufficient margin exists in the current safety analysis limit to ensure acceptable analysis results. CECO has not concluded whether a DNB ratio below the current licensing basis limit could result from a design basis transient with an initial temperature below 530 F. Since CECO does not plan on operating below 530 F and due to the significant expense of re-analyzing setpoint and core conditions at this reduced temperature, no such analysis has been planned.
Time of Discovery Commonwealth Edison Company, first determined that the defect in the analysis could potentially adversely affect licensirig basis and that the defect could be reportable per 10CFR21 on January 12,1993.
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Page 3 of 3 10 CFR Part 21 Report Minimum Tempcrature for Criticality Analysis 3
Number and Location of All Defective Componenta Zion Station Units 1 and 2 are the only Commonwealth Edison units which have a minimum temperature for criticality limit below the analyzed range of uncertainties of reactor protection instrumentation. Commonwealth Edison has notified Westinghouse Electric Company and asked them to notify other potentially affected plants.
Corrective Actions:
Zion Station has instituted administrative controls to ensure that the reactor coolant system average temperature is above 530 F prior to achieving criticality, and to ensure appropriate actions, consistent with those specified in the Westinghouse Standardized Technical Specifications (NUREG 0542), are taken if the temperature falls below 530 F whenever critical. A license amendment to i
revise the Zion minimum Temperature for Criticality requirements will be submitted by July 30,1993. UFSAR revisions will be provided with the 1994 update.
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Contacts Questions pertaining to this notification should be addressed to:
j Linda M. Taylor Engineering and Construction Regulatory Assurance l
i Commonwealth Edison Company 1400 Opus Place, Suite 500
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Downers Grove, Illinois 60515 (708) 663-6641 4
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