United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9901220123


ABB

January 15, 1999

LD-99-002

U.S. Nuclear Regulatory Commission
Attn: Document Control Desk
Washington, D.C. 20555

Subject: Report of a Defect Pursuant to 10 CFR 21 Concerning Incorrect Modeling of a BWR Lower Plenum Volume in BISON

The purpose of this letter is to notify the Nuclear Regulatory Commission of a defect under 10 CFR 21, "Reporting of Defects and Noncompliance." The defect concerns the Operating Limit for the Minimum Critical Power Ratio (MCPR) in Boiling Water Reactors (BWRs) analyzed using the BISON fast transient analysis code. Specifically, the defect involves incorrect modeling of the reactor vessel lower plenum volume in the BISON code, which could lead to the establishment of non-conservative MCPR Operating Limits in plant technical specifications.

The Enclosure summarizes the evaluation performed by ABB Combustion Engineering (ABB-CE). If you have any questions, please feel free to contact me or Virgil Paggen of my staff at (860) 285-4700.

Very truly yours,

COMBUSTION ENGINEERING, INC.

Ian C. Rickard, Director
Nuclear Licensing

Enclosure: As stated
cc: M. A. Barnoski (ABB-CE)

ABB Combustion Engineering Nuclear Power
Combustion Engineering, Inc.

P.O. Box 500
2000 Day Hill Rd.
Windsor, CT 06095-0500
Telephone (860) 688-1911
Fax (860) 285-5203


Enclosure to LD-99-002
Page 1 of 2

ABB Combustion Engineering Nuclear Power
10 CFR 21 Report of a Defect or Failure to Comply

The following information is provided pursuant to the requirements set forth in 10 CFR 21.21(c)(4):

(i) Name and address of the individuals informing the Commission:

Ian C. Rickard, Director
Nuclear Licensing
Combustion Engineering, Inc.
2000 Day Hill Road
Windsor, CT 06095-0500

(ii) Identification of the facility, the activity, or the basic component supplied for such facility or such activity within the United States which fails to comply or contains a defect:
The activity for which this report is being filed is the establishment of non-conservative MCPR Operating Limits for the Washington Public Power Supply System Nuclear Project Unit 2(WNP-2) nuclear power plant during Cycles 12, 13, and 14 operation.
(iii) Identification of the firm constructing the facility or supplying the basic component which fails to comply or contains a defect:
Combustion Engineering, Inc.
2000 Day Hill Road
Windsor, CT 06095-0500
(iv) Nature of the defect or failure to comply and the safety hazard which is created or could be created by such defect or failure to comply:
The defect identified involves the incorrect modeling of the reactor vessel lower plenum volume in the BISON code. The defect caused the BISON code model to have a lower plenum volume approximately twice its proper size. This incorrect modeling has the potential to lead to calculation of non-conservative MCPR Operating Limits in some situations.
(v) The date on which the information of such defect or failure to comply was obtained:
ABB-CE determined that a defect in the BISON code existed on January 14, 1999.


Enclosure to LD-99-002
Page 2 of 2
(vi) In the case of a basic component which contains a defect or fails to comply, the number and location of all such components in use at, supplied for, or being supplied for one or more facilities or activities subject to the regulations in this part:
The BISON computer code is a proprietary ABB Atom AB program used by ABB-CE for performing BWR safety analyses for U.S. customers. The defect applies only to reload fuel assemblies currently in operation at WNP-2.
(vii) The corrective action which has been, is being, or will be taken; the name of the individual or organization responsible for the action; and the length of time that has been or will be taken to complete the action:
An evaluation of the defect has been performed by ABB-CE. The results of that evaluation show that there is no safety problem at WNP-2 for operation of the previous Cycles 12 and 13 and its current Cycle 14 operating state (Normal Scram Speed, Recirculation Pump Trip operable, and Turbine Bypass operable) prior to 5,000 MWd/MTU. That is, the established MCPR Operating Limits currently in the plant technical specifications for this operating state provide adequate protection. However, certain MCPR Operating Limits for other operating states prior to 5,000 MWd/MTU and all operating states after 5,000 MWd/MTU for WNP-2 Cycle 14 must be increased to accommodate the defect. The utility currently projects that WNP-2 will reach 5,000 MWd/MTU in early 1999. ABB-CE has notified the Washington Public Power Supply System of the necessary changes to the WNP-2 MCPR Operating Limits.
The BISON code model for WNP-2 has been revised to correct the error. All ABB-CE BWR fuel users have been notified of this condition.
(viii) Any advice related to the defect or failure to comply about the facility, activity, or basic component that has been, is being, or will be given to purchasers or licensees:
The Washington Public Power Supply System has been notified of the defect and has been provided with revised MCPR Operating Limits for WNP-2.


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