05000315/LER-2006-001

LER-2006-001, Plant Shutdown Required by Technical Specification Action 3.6.5.B.1

Docket Number
Event date:	07-30-2006
Report date:	09-27-2006
3152006001R00 - NRC Website

Conditions Prior to Event Unit 1 in Mode 1 at 100% power.

Description of Event

As a result of an NRC inspection finding, Indiana Michigan Power Company (I&M) had approved a revised methodology for calculating lower containment average air temperature on July 28, 2006. The new methodology calculated an average lower containment temperature that was higher than the previous method.

While unrelated to the revised methodology for calculating lower containment average temperature, in July 2006, Unit 1 lower containment high temperature alarms were being evaluated by Engineering personnel and troubleshooting efforts were not able to increase Non-Essential Service Water (NESW) cooling flow through the Containment Lower Ventilation Units (CLVs). A temporary modification (T-Mod) to add supplemental cooled water to the NESW header as it entered containment was developed; however, delays in completing the design and implementation prevented it from being fully functional prior to the TS required shutdown.

The average temperature in the Unit 1 lower containment volume was determined to exceed 120 degrees Fahrenheit using the revised methodology and Unit 1 was declared to have exceeded the Limiting Condition for Operation of Technical Specification (TS) 3.6.5.b and Condition A was entered as of 2026 hours0.0234 days <br />0.563 hours <br />0.00335 weeks <br />7.70893e-4 months <br /> on July 29, 2006.

Required Action A.1 for Condition A was to restore containment average air temperature to within limits with an 8­ hour completion time. At 0426 hours0.00493 days <br />0.118 hours <br />7.043651e-4 weeks <br />1.62093e-4 months <br /> on July 30, 2006, TS 3.6.5 Condition B was entered when the 8-hour completion time of Required Action A.1 for Condition A was not met. In accordance with normal plant operating procedures and TS 3.6.5, Condition B, Required Action B.1, Unit 1 was shut down and entered Mode 3 at 1014 hours0.0117 days <br />0.282 hours <br />0.00168 weeks <br />3.85827e-4 months <br /> on July 30, 2006.

Cause of Event

The causes of the Unit 1 shutdown were:

1. The containment cooling water system design did not support continued plant operation with sustained high cooling water (Lake Michigan) temperatures and potential for cooler fouling.

2. A failure by l&M Engineering personnel to recognize and communicate that an evaluation supporting past operability would not permit unit operation under some possible operating conditions during the summer (loss of operating margin). The failure to recognize this loss of operating margin resulted in a delay in communicating the impact of the lost margin to station management so compensatory actions could be developed at an earlier time.

Contributing causes were that actions that were initiated to reduce the average temperature were hindered because the CLVs were partially plugged with sediment and the supplemental cooling T-Mod installation had numerous delays that were not resolved in a timely manner.

Analysis of Event

During an NRC inspection in May 2006, the NRC inspectors identified a finding that the methodology for calculating lower containment average air temperature was non-conservative. A past operability calculation was completed in June 2006 using an appropriately conservative volume weighted methodology. This calculation showed that under recent worst case conditions, average temperature in lower containment did not exceed 119.7 degrees Fahrenheit with sustained lake temperatures of 79 degrees Fahrenheit in 2005, and thus a past operability concern was not present. The fact that containment temperatures may not remain below 120 degrees Fahrenheit when lake temperature exceeded 79 degrees Fahrenheit (permissible temperature was 85.8 degrees Fahrenheit) was not addressed.

In addition to the new average air temperature calculation methodology of lower containment, two of the four CLVs in Unit 1 had significant blockage that was identified prior to the 2006 summer season. Performance of on-line maintenance to clear the blockage in the CLVs prior to the 2006 summer season would have improved CLV performance.

A T-Mod to provide supplemental containment cooling was initiated two weeks prior to the TS required shutdown.

The effort to implement this T-Mod was significantly larger than originally understood. Numerous equipment problems were identified during the installation and testing of the T-Mod, and these problems either delayed its implementation or resulted in reduced performance of the T-Mod below what was expected.

This event had minimal nuclear safety impact on the plant. A Probabilistic Risk Assessment (PRA) was performed and determined there was no nuclear safety significance to this event. Unit 1 was shut down in a controlled fashion and manually tripped as part of the normal shutdown procedure at approximately 16.5 percent reactor power. All safety systems and plant equipment used in the shutdown functioned as designed. In that the shutdown was orderly, there was no significant probabilistic risk associated with this event.

Corrective Actions

Two of the four Unit 1 CLVs cooling coils were cleaned to remove sediment and debris.

The T-Mod for supplemental cooling was installed and used to reduce Unit 1 lower containment average air temperature to less than 120 degrees Fahrenheit.

Engineering procedures for calculations and modifications will be revised to provide explicit considerations related to identifying and managing operating and design margin.

The procedure for summer readiness will be revised to require installation of the supplemental containment cooling T-Mod during the summer months until such time that a design change is made that precludes the need for installation of the supplemental containment cooling T-Mod.

Analysis will be completed to determine when a CLV can be removed from service for cleaning, and maintenance activities to clean the CLVs will be generated when required.

Previous Similar Events

A review was conducted of station Condition Reports and LERs for the previous 3 years. No similar events were identified.