05000306/LER-2011-001
| Prairie Island Nuclear Generating Plant Unit 2 | |
| Event date: | 02-19-2011 |
|---|---|
| Report date: | 04-20-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material |
| 3062011001R00 - NRC Website | |
power, electricians used a Work Order (WO) to perform maintenance on Doors 172 and 173. Doors 172 and 173 are part of the Unit 2 Shield Building' access opening (maintenance access). As part of the troubleshooting process, both doors were simultaneously opened several times for approximately ten seconds each time between 08:00 and 08:15 CST.
At approximately 10:15 CST, the Shift Supervisor reviewed the troubleshooting process and the Technical Specifications (TS) Basis for section 3.6.10. The Shift Supervisor realized that TS 3.6.10, Limiting Condition for Operation (LCO), Condition A should have been entered during the time that Doors 172 and 173 were simultaneously opened. The Shift Manager was informed and he directed the Shift Supervisor to enter TS 3.6.10, LCO, Condition A, as an unplanned LCO for the duration of the work activity.
EVENT ANALYSIS
At the Prairie Island Nuclear Generating Plant (PINGP), the Unit 2 Shield Building is a concrete structure that surrounds the steel Containment vessel. Between the Containment vessel and the Shield Building inner wall is an annular space that collects a portion of the containment leakage that may occur following a design basis accident (DBA). The Shield Building provides the means for collecting and filtering containment fission product leakage following a DBA.
Following a DBA the Shield Building Ventilation System (SBVS) establishes a negative pressure in the annulus between the Shield Building and the steel containment vessel. The Shield Building is required to be operable to ensure retention of containment leakage and proper operation of the SBVS. This operability is required when Unit 2 is in Modes 1, 2, 3, and 4.
The Shield Building is operable when:
a. At least one door in each access opening is closed including when the access opening is being used for normal transit entry and exit; and b. The Shield Building equipment opening is closed.
Before scheduling the WO to be performed while Unit 2 was in Mode 1, planners did not adequately write the WO instructions for the potential Loss of Safety Function (LOSF) when both access doors were opened simultaneously. During the WO activity described above, Doors 172 and 173 were simultaneously opened for short periods of time. While both doors were opened, operability of the Shield Building was compromised and the safety function of the Shield Building was not assured.
The condition described above represents a Safety System Functional Failure reportable under 10 CFR 50.73(a)(2)(v)(C).
1 ENS System Code: BD U.S NUCLEAR REGULATORY COMMISSION A loss of safety function did occur however the short periods of time that both doors were opened limited the safety risk. A DBA did not occur while both access doors were simultaneously opened for maintenance. Therefore this event had no nuclear, radiological, industrial, or environmental impact and did not affect the health and safety of the public.
CAUSE
The causal evaluation determined that Planning did not identify within the Work Order (WO) the latent impact of the LOSF when two Shield Building ventilation doors were to be opened simultaneously.
CORRECTIVE ACTION
- The Shield Building functionality was restored when the worker's troubleshooting efforts stopped, the work was suspended, and both Unit 2 Shield Building access doors were closed. TS 3.6.10, LCO Condition A, was exited at 08:15 CST on February 19, 2011.
- The preventive maintenance procedure for the door repair work was revised to explicitly state that the two doors associated with an access can only be simultaneously opened in Modes 5 or 6.
- A Plant Impact Statement checklist was created to increase the rigor of planning. The checklist is required to be performed as part of the work order planning process. A line will be added to the checklist to review the loss of safety function concerns.
- The Outage Scope Change Request Scope Control form will be revised to ensure that the outage screening team determines if the proposed work can be done online (Mode 1). The form will be revised to require the Online Manager (or designee) approval that the work can be performed online.
PREVIOUS SIMILAR EVENTS
A LER search was conducted and one similar LER event at PINGP involving doors and inoperability was identified in the last three years.
Door Threshold Seals, was submitted March 31, 2011. This LER described a condition where the battery rooms were declared inoperable due to potential flooding.