05000456/LER-2007-003
| Telephone Number (Include Area Code/ | |
| Event date: | 10-24-2007 |
|---|---|
| Report date: | 12-21-2007 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| Initial Reporting | |
| 4562007003R00 - NRC Website | |
A. Plant Operating Conditions Before The Event:
Event Date: October 24, 2007� Event Time: 0917 Unit: 1 MODE: 3� Reactor Power: 0.0 percent Unit 1 Reactor Coolant System (RCS) [AB] Temperature: 350 degrees F. Pressure: 756 psig
B. Description of Event:
There were no additional structures, systems or components inoperable at the beginning of the event that contributed to the severity of the event.
On October 24, 2007, at 0917 hours0.0106 days <br />0.255 hours <br />0.00152 weeks <br />3.489185e-4 months <br /> Braidwood Unit 1 entered Mode 3 while returning to power from a refueling outage. A Mechanical Maintenance supervisor observed that insulation was installed on the five main steam [SB] header safety valves (MSSVs) for both the 1A and 1D main steam lines. Insulation was not installed on the MSSVs on the 1B and 1C main steam lines. Following a review by the safety valve program engineer, it was determined that the insulation posed an operability issue due to the potential impact on the MSSVs' setpoint.
Based on information f rom the MSSV manufacturer, and later confirmed through testing, the insulated MSSVs were considered inoperable since the temperature rise experienced by the MSSV springs would have been sufficient to reduce the setpoint below the -3% tolerance permitted by Technical Specification (TS) 3.7.1, Main Steam Safety Valves. On October 26, 2007, with Unit 1 in Mode 1, the MSSVs were considered operable following removal of the insulation.
The TS 3.7.1 Required Action for one or more steam generators with four or more inoperable MSSVs is to return to Mode 4 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. Based on a review of the sequence of events, it was determined that this requirement to be in Mode 4 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> was not met. This event is reportable under 10 CFR 50.73(a)(2)(i)(B), any operation or condition which was prohibited by the Technical Specifications. The event requires a written report to the NRC (Licensee Event Response) within sixty days.
C. Cause of Event
The cause of the installation of insulation and associated MSSV inoperability was the breakdown in the application of established engineering fundamentals in various parts of the Engineering Organization.
Elevated main steam isolation valve (MSIV) room temperatures have challenged MSIV accumulators and environmental qualification of various equipment in the MSIV rooms. To gain margin to temperature limits, a walkdown of the MSIV rooms identified several sections of hot pipe with the insulation missing, including the MSSVs. During the process of determining the proper insulation of the MSSVs, a number of opportunities to determine whether installing insulation would affect MSSV operability existed but failed to recognize the impact:
A discussion with the safety valve program engineer identified that safety valves are generally not insulated due to the potential impact on lift setpoint; a walkdown with the system engineer and the insulation contractor to explain where insulation likely needed to be installed resulted in the insulation contractor assumption that the entire MSSV was to be insulated; Design Engineering response to insulation questions was that the MSSV piping should be insulated according to design, leaving the question of MSSV insulation unanswered; and the design specifications specify insulation be installed on valves in lines that are insulated, but the specific design insulation requirements for the MSSVs were not confirmed.
� The causes of this event are human performance related. The common thread through the identified causal and contributing factors is the apparent breakdown in the application of engineering fundamentals in various parts of the Engineering Organization. The fundamentals included Technical Rigor, Configuration and Design Basis Control, Assertive Engineering, Communications, Issue Reporting and Resolution. Teamwork and Work Management.
D. Safety Consequences:
There were no safety consequences impacting plant or public safety as a result of this event. During the time the insulation was installed on the MSSVs. Unit 1 was in Mode 1 and there were no actual plant events or conditions that challenged or required the function of the MSSVs. The impact of the MSSV insulation was to reduce the setpoint below the TS tolerance of —3%. As the safety function of the MSSVs is to prevent overpressurization, this function was not challenged by the installation of insulation. The potential consequences, should the MSSV lift early during an event, would have been bounded by present UFSAR accident analyses. This is based on Unit 1 being at low power levels and RCS activity was significantly below the TS limits while the insulation was installed.
E. Corrective Actions:
Corrective actions include:
1. Removal of the insulation on the MSSVs on the 1A and 1D main steam lines to restore the MSSVs to the condition at the time of MSSV setpoint establishment.
2. Performance of trevitesting of three MSSVs that bounded limiting conditions to obtain quantitative data on the potential long term impact on spring free-length. Trevitesting results indicated the valves had acceptable lift setpoints and the MSSV springs were not subjected to temperatures that permanently affected valve operability.
3. Determination of the impact on MSSV operability through testing of a spare MSSV with insulation, mimicking the actual plant conditions. Testing determined that the insulation would lower the setpoint to below the —3% tolerance.
4. Training provided to all Engineering personnel to re-enforce importance of applying appropriate engineering fundamentals and the need to evaluate the impact of abnormal plant configurations.
Previous Occurrences:
There have been no similar Licensee Event Report events at Braidwood Station in the last three years.
G. Component Failure Data:
Manufacturer� Nomenclature� Model�Mfg. Part Number NiA� N/A� N/A N/A �