05000317/LER-2002-004
| Calvert Cliffs Nuclear Power Plant, Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 3172002004R01 - NRC Website | |
I. DESCRIPTION OF EVENT
Post-Accident Monitoring (PAM) System from fulfilling its safety function. Specifically, loose cable connectors for Containment Area Radiation High Range Indicators 1(2)-R15317A(B) could have caused the channels to fail during a seismic event. The cause of the loose cable connectors was the loss of pin retention springs in the connectors due to time and normal use. The pin retention springs are required for the operability of each channel. Corrective maintenance performed on each channel indicated that retention springs were missing from all four channels.
The affected channels remained in service, but would not have been operable from the time of discovery until completion of the post-maintenance testing after the corrective maintenance.
The first indication of problems with containment high range radiation monitor connections was traced back to April 14, 2000, when an alarm condition on 1-RI-5317B was received with no apparent cause. Troubleshooting indicated that the problem was related to loose cables or connectors. Discovery of this condition occurred on April 14, 2000 and ended on February 16, 2002 (Unit 1) and April 11, 2002 (Unit 2). The duration for Unit 1 ended earlier due to entry into Mode 4 for refueling on February 16, 2002. Analysis indicated that during this period the channels should have been declared out-of-service and the appropriate Technical Specification Limiting Condition for Operation (LCO) should have been entered, but was not.
This reportable condition was discovered on August 27, 2002, during a review of the causal analyses performed on the instrument connections. No other structures, systems, or components were inoperable during this condition that contributed to or influenced the event.
II. CAUSE OF EVENT
The inoperability of the Unit 1 and 2 containment area high range radiation indicators was caused by a loss of the pin retention springs within the connectors, which are required to maintain circuit continuity during a seismic event. The loss, over time, of the pin retention springs was caused by inadequate preventive maintenance, inconsistent use of the proper extraction tool, and a failure to recognize the connector retention springs as a critical component for operability.
III. ANALYSIS OF EVENT
A Technical Specification LCO requires PAM indication channels to be operable while in Modes 1, 2, and 3. During the time period from April 14, 2000 through February 16, 2002 (Unit 1) and April 11, 2002 (Unit 2), the Unit 1 and 2 containment area radiation high range indication should have been declared out-of-service and the associated Technical Specification LCO entered, while each Unit was in the applicable modes. This condition required submittal of a report to the Nuclear Regulatory Commission within 14 days, in accordance with Technical Specifications, outlining alternate monitoring methods, the cause of the inoperability, plans, and schedule for restoring the instrumentation channels of the function to operable status. The failure to submit this report placed both Units in a condition prohibited by Technical Specifications 21 days after first identifying the condition on April 14, 2000. The inoperability of both channels of Unit 1 and 2 containment area high range instrumentation resulted in the loss of the safety function for those indications.
The subject event describes a condition prohibited by the plant's Technical Specifications, which existed for a time longer than permitted by the Technical Specification LCO. Therefore, this event is reportable, per 10 CFR 50.73(a)(2)(i)(B), as a condition which was prohibited by the plant's Technical Specifications.
The PAM instrumentation ensures, per the Technical Specification Bases, the operability of Regulatory Guide 1.97 Type A variables. This allows the Control Room operating staff to:
- perform the diagnosis specified in the emergency operating procedures, or - take the specified, preplanned, manually-controlled actions, for which no automatic control is provided, that are required for safety systems to accomplish their safety functions.
This condition, therefore, is also reportable, per 10 CFR 50.73(a)(2)(v)(D), as a condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
This condition was also found to cause two independent channels (in both units) in a single system to become inoperable in excess of the Technical Specification LCO allowed completion time. The safety function of the PAM System is to mitigate the consequences of an accident, therefore, 10 CFR 50.73(a)(2)(vii) reporting criteria were also met.
There were no actual safety consequences as a result of this condition. The containment area radiation high range indication does not impact core damage frequency or large early release assessments. The system is required for mitigation of accidents and, therefore does not contribute to the probability of any specific event. The containment area radiation monitors provide similar indication at a lower operating range and were operable throughout the duration of this condition.
IV. CORRECTIVE ACTIONS
A. The connectors were promptly replaced upon determination of cause.
B. Maintenance procedures were revised to add requirements to perform checks of connector integrity prior to reconnection of the affected instrumentation. A requirement was also added to ensure the use of the proper extraction tool when disconnecting. An additional procedure revision alerts craft personnel to the significance of the specific connectors on operability of the equipment.
C. The subject connectors are now checked for integrity at each Refueling Outage based on the procedure revisions implemented as a result of this event.
V. ADDITIONAL INFORMATION
A. Component Identification Component Containment Area Radiation High Range Monitor
B. Previous Occurrences
IEEE 803 IEEE 805 EIIS Function System ID
RI IP
No other previous similar events have occurred within the past three years.