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Significance:
Feb 01, 2008
Identified By: Self-Revealing
Item Type: FIN Finding
Inadequate Maintenance Procedure for the 2A Main Transformer
A self-revealing finding was identified for an inadequate maintenance procedure regarding electrical connections associated with the Unit 2A Main Transformer bushings. The procedure was not clear as to the appropriate method to prepare the surface for an aluminum bushing terminal and did not provide adequate information on torque requirements and the use of anti-oxidant grease. This resulted in the failure of the bushing connection and a Unit 2 reactor scram on February 1, 2008. Exelon entered this issue into the corrective action program (CAP), performed repairs, and revised the procedure to reflect the appropriate information to successfully assemble the connection.
The issue is more that minor because it is associated with procedure quality attribute of the Initiating Events cornerstone and affected the objective to limit the likelihood of those events that upset plant stability and challenge critical safety functions during power operations. The inspectors evaluated the finding using Phase 1 of IMC 0609, Appendix A, “Significance Determination of Reactor Inspection Findings for At-Power Situations.” This finding was determined to be of very low safety significance (Green) because it did not contribute to both the likelihood of a reactor trip and the likelihood that mitigation equipment or functions would be unavailable. (Section 1R12)
Inspection Report# : 2008002 (pdf)
Significance: Nov 09, 2007
Identified By: NRC
Item Type: NCV NonCited Violation
Required Voltage for Load Tap Changer Motor
The team identified a non-cited violation (NCV) of 10 CFR 50, Appendix B, Criterion
III, Design Control. Specifically, the licensee did not ensure the automatic load tap changer
(LTC) controls and motor for the 101 and 201 safeguards, 10 station auxiliary, and 20
regulating transformers had adequate voltage to operate during design basis events. As a
result of a new voltage study, Exelon performed modifications to change the load tap changers
response time in 2006 and credited the LTCs for offsite power source operability. The team
questioned whether there was sufficient voltage supplied to the LTC motor to prevent it from
stalling during the worst case degraded voltage conditions of the transient. In response, the
licensee performed a number of calculations, revised existing calculations and received
additional information from the LTC vendor to demonstrate that sufficient voltage was available
during the worst case degraded voltage levels. The team reviewed and agreed with the
conclusion.
The finding was more than minor because it is associated with the design control attribute of
the Mitigating Systems Cornerstone and affected the cornerstone objective of ensuring the
availability, reliability, and capability of systems that respond to initiating events to prevent
undesirable consequences. In accordance with IMC 0609, Appendix A, “Significance
Determination of Reactor Inspection Findings for At-Power Situations,” the team conducted a
Phase 1 screening and determined the finding was of very low safety significance (Green)
because it was a design deficiency that did not result in a loss-of-offsite power operability. This
issue has a cross-cutting aspect in the area of Human Performance - Resources which requires
licensees to ensure that equipment is adequate to assure nuclear safety, specifically: complete,
accurate and up to date design documentation.
Inspection Report# : 2007007 (pdf)
Significance: Aug 09, 2007
Identified By: NRC
Item Type: NCV NonCited Violation
Inadequate Fire safe Shutdown Procedure for Securing HPCI
The team identified a finding of very low safety significance (Green) involving a
non-cited violation of the Limerick Generating Station operating license, in that the
procedure for shutting down the plant in response to a fire in the cable spreading room
was not consistent with the safe shutdown analysis. Specifically, impediments related to
the safe shutdown procedure would have prevented the operators from securing the
high pressure coolant injection (HPCI) system within the design time limit. Fire induced
cable failures in the cable spreading room could allow HPCI to overfill the reactor vessel
which would adversely affect the operation of the reactor core isolation cooling (RCIC)
system and the main steam relief valves (MSRVs).
This issue was more than minor because it affected the procedure quality attribute
associated with the mitigating systems cornerstone as related to the objective of
ensuring the reliability and availability of the RCIC system and MSRVs under postulated
fire scenarios. The finding was of very low safety significance based on a Phase 2
Significance Determination Process (SDP) evaluation performed in accordance with IMC
0609, Appendix F, “Fire Protection Significance Determination Process.”
Inspection Report# : 2007006 (pdf)
Significance: Jun 30, 2008
Identified By: NRC
Item Type: NCV NonCited Violation
Failure to Correct Adverse Condition Associated with Motor Operated Valves
The inspectors identified an NCV of Title 10 of the Code of Federal Regulation, Part 20 (10CFR50), Appendix B, Criterion XVI, Corrective Action, for not correcting a condition adverse to quality associated with safety-related motor operated valve motor control center auxiliary contact switches in a timely manner following the failure of the Unit 1 Core Spray Loop A test bypass primary containment isolation valve (HV-052-1F015A) to close on August 3, 2006. As a result, the Unit 2 RCIC turbine exhaust line vacuum breaker outboard primary containment isolation valve (HV-049-2F080) experienced a similar failure to close on June 4, 2008.
The finding was more than minor because it was associated with the structures, systems, and components and barrier containment performance attribute of the Barrier Integrity cornerstone and affected the objective to provide reasonable assurance that physical design barriers protect the public from radionuclide releases caused by accidents and events. The inspector assessed the finding using Phase 1 of IMC 0609, Appendix A, “Significance Determination Process for Reactor Inspection Findings for At-Power Situations” and determined the finding to be of very low safety significance (Green) because the finding did not represent an actual open pathway in the physical integrity of reactor containment. This finding has a cross-cutting aspect of Problem Identification and Resolution because Exelon did not take appropriate corrective actions to address safety issues and adverse trends in a timely manner, commensurate with the safety significance and complexity (P.1(d)). (Section 4OA2)
Inspection Report# : 2008003 (pdf)
Although the NRC is actively overseeing the Security cornerstone, the Commission has decided that certain findings pertaining to security cornerstone will not be publicly available to ensure that potentially useful information is not provided to a possible adversary. Therefore, the cover letters to security inspection reports may be viewed.
Last modified : August 29, 2008