05000263/LER-2011-007
| Monticello Nuclear Generating Plant | |
| Event date: | 9-29-2011 |
|---|---|
| Report date: | 02-28-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor |
| LER closed by | |
| IR 05000263/2011005 (1 February 2012) | |
| 2632011007R01 - NRC Website | |
Generators (EDG) [DG] with the single largest post-accident load, did not satisfy the TS surveillance requirement. This condition resulted in both EDGs being declared inoperable as TS Limiting Condition for Operation (LCO) 3.8.1, "AC Sources - Operating," was not met. At 1900 hours0.022 days <br />0.528 hours <br />0.00314 weeks <br />7.2295e-4 months <br /> CDT, Condition F, the shutdown portion of the actions was entered.
Consequently, at approximately 2220 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.4471e-4 months <br /> CDT, on September 29, 2011, a teleconference was initiated between U.S. Nuclear Regulatory Commission (NRC) Region III, NRC headquarters staff, and MNGP personnel. MNGP presented its bases for a one-time extension of the Completion Time of Specification 3.8A, Condition F.1 from 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> to 5 days. Enforcement discretion was requested to provide sufficient time to develop and perform a new surveillance test procedure meeting SR 3.8.1.7. At 2358 hours0.0273 days <br />0.655 hours <br />0.0039 weeks <br />8.97219e-4 months <br /> CDT, the NRC verbally granted the request for enforcement discretion.
EVENT ANALYSIS
This condition is being reported in accordance with 10 CFR 50.73(a)(2)(v)(A),(B),(C) and (D) -- Event or Condition that Could Have Prevented Fulfillment of a Safety Function and 10 CFR 50.73(a)(2)(vii) Common Cause Inoperability of Independent Trains or Channels.
SR 3.8.1.7 verifies that each EDG rejects a load greater than or equal to its associated single largest post-accident load, and following load rejection, the frequency is performed SR 3.8.1.7 by tripping the Core Spray pump motor while loaded onto the associated EDG, with the pump flow rate set to approximately 3000 gpm. The test deficiency identified that the flow rate at which the Core Spray pump motor was tripped is not the flow rate expected at run-out or near run-out conditions - corresponding to the trip of the largest single post accident load. Consequently, the frequency response of the EDG had not been fully demonstrated in accordance with SR 3.8.1.7.
A new surveillance test procedure was developed to perform an EDG load rejection with an EDG loaded to the grid simulating the load associated with the single largest post-accident load.
On October 2, 2011, 12 EDG was tested in accordance with the new surveillance test procedure, and determined to meet SR 3.8.1.7. The 12 EDG was declared Operable at 2101 hours0.0243 days <br />0.584 hours <br />0.00347 weeks <br />7.994305e-4 months <br /> CDT and the enforcement discretion period exited. On October 3, 2011, at 11:58 p.m. TS LCO 3.8.1 was met after the 11 EDG was declared operable following successful surveillance testing.
To support the request for enforcement discretion, MNGP completed a bounding risk assessment for the extension of TS 3.8.1, Condition F, from 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> to 5 days. The assessment determined that there was not a significant increase in risk for the five day period. To mitigate risk, MNGP committed to implement a series of compensatory actions for the duration of the enforcement discretion period.
In the written confirmation of enforcement discretion, the NRC concurred that there was no adverse impact on public health and safety as a result of this event.
MNGP was able to demonstrate that both EDGs were operable before the end of the enforcement discretion period. As a result of the successful completion of the new surveillance test procedure, MNGP concluded that the EDGs were capable of performing their safety function throughout the period from implementation of Improved Standard Technical Specifications (ITS) until the present and this event did not involve a Safety System Functional Failure.
CAUSE
The cause of the event was an inadequate surveillance test procedure resulting from a failure to fully reflect the changes enacted through the implementation of ITS in 2006. This was a new surveillance requirement for MNGP that did not exist within the previous MNGP custom TS. The surveillance requirement was not correctly translated into an adequate test to meet SR 3.8.1.7 and hence was not correctly implemented as part of the ITS implementation process.
CORRECTIVE ACTION
Procedures were created to simulate the loss of the largest post accident load by paralleling the engine with the offsite power source and opening the diesel output breaker to verify engine response.
OSP-EDG-0535-11, "11 Emergency Diesel Generator Load Rejection Test" and OSP-EDG-0535-12, "12 Emergency Diesel Generator Load Rejection Test" were created to satisfy the surveillance requirement.
PREVIOUS SIMILAR EVENTS
There have been no similar licensee event reports in the last three years.
ADDITIONAL INFORMATION
The request for Notice of Enforcement Discretion (NOED) submitted by MNGP is ADAMS accession number ML112760776.
The written response from the NRC formally granting the NOED is ADAMS accession number ML11278A176.