05000263/LER-2009-001

LER-2009-001, Containment Overpressure Not Ensured in the Appendix R Analysis

Docket Number
Event date:	04-02-2009
Report date:	12-22-2010
Reporting criterion:	10 CFR 50.73(a)(2)(ii)
2632009001R02 - NRC Website

On April 2, 2009, the plant was shutdown and in Mode 5 for a refueling outage. During the review of calculations to respond to a request for additional information from the NRC in support of the station's Extended Power Uprate license amendment, station personnel discovered that although the plant credits Containment Overpressure (COP), the Appendix R analysis does not ensure Containment Overpressure is maintained. For certain design basis accident scenarios, COP is required in order to ensure adequate net positive suction head (NPSH) is available for vessel injection and suppression pool cooling pumps. The station procedure for performing a shutdown from outside the control room did not contain any steps to require operators to ensure adequate NPSH was maintained. Although this issue was discovered in April 2009, the issue has existed since design basis accident reanalysis in 2002.

Depending on initial conditions, a fire in the cable spreading room or control room, with or without a fire induced loss of off site power, could cause two in-series valves to spuriously open leading to venting of containment. Venting of containment during this scenario could result in the loss of required NPSH for the 12 Core Spray (CS) [BM] and the 12 Residual Heat Removal (RHR) [BO] pumps [P]. With no operator action, inadequate NPSH could prevent vessel injection and or suppression pool cooling.

EVENT ANALYSIS

The event was reportable under 10 CFR 50.73(a)(2)(ii) Degraded or Unanalyzed Condition. Since the issue was for past operability, there was no 10 CFR 50.72 report for this event.

The event is not considered a safety system functional failure since all required safety related systems would have been available to perform their safety functions.

SAFETY SIGNIFICANCE

There was no impact to the health and safety of the public; and the risk significance is less than the red threshold requirements for 10 CFR 50.48.

Monticello maintains administrative controls for the introduction of combustible materials and ignition sources to limit the probability and severity of a fire. Fire detection equipment or continuous manning is provided in the affected areas for rapid detection. Fire extinguishers and hose stations are in place and fire brigade response is expected to be rapid and successful for any fire in the affected areas.

These prevention, detection and suppression measures limit the frequency of fire induced loss of required COP to a very small value.

A Significance Determination Process evaluation was performed per the guidance of NRC Inspection Manual Chapter 0609, Appendix F, Fire Protection Significance Determination Process. In summary, this analysis determined that the change in Core Damage Frequency attributable to this event is less than the red risk threshold. Accordingly enforcement discretion via the provisions of Interim Enforcement Policy Regarding Enforcement Discretion for Certain Fire Protection Issues (10 CFR 50.48) is warranted.

Cause

Fire protection engineering personnel either did not review or were unaware/did not internalize that COP was required for an Appendix R fire and that the Appendix R analysis might require revision to ensure COP was maintained. Although the calculation procedure in 2002 required a fire protection review for the potential to affect the fire protection analysis, the requirements were not clear enough to ensure the personnel performing the calculation revision obtained a fire protection review.

Corrective Action The calculation process has been revised since 2002. Specifically, completion of a Fire Protection Program checklist is now required by the fleet calculation procedure. Therefore, the process has already been revised to prevent this type of error, and no further action is required to prevent recurrence.

Remediation of these conditions will be coincident with MNGP's Regulatory Guide 1.189 project. The Regulatory Guide 1.189 project will either evaluate the non-compliant manual actions as acceptable or the non-compliant manual actions will be corrected via physical changes to the plant.

Procedure CA-C has been revised to provide guidance to maintain the required NPSH for the CS and RHR pumps.

Until this issue is resolved, compensatory measures will be used to ensure the ability to safely shut down is maintained. Existing transient combustible material control procedures for the Control Room (CR) and Cable Spreading Room (CSR) are adequate and use will be continued. Additional/new compensatory measures will include:

- No hot work in the CR or CSR without shift manager approval. If hot work is required, Shift Manager (SM) and work supervisor must walk down the job and ensure adequate compensatory measures are taken.

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