05000306/LER-2011-001, Regarding Shield Building Inoperable Due to Maintenance Activity
| ML111110544 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 04/20/2011 |
| From: | Schimmel M Northern States Power Co, Xcel Energy |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| L-PI-11-029 LER 11-001-00 | |
| Download: ML111110544 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 3062011001R00 - NRC Website | |
text
a Xcel Energy*
April 20, 201 1 L-PI-11-029 10 CFR 50.73 U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie lsland Nuclear Generating Plant Unit 2 Docket: 50-306 License No.: DPR-60 LER 50-3061201 1-001 -00, Unit 2 Shield Building Inoperable Due to Maintenance Activity Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, herewith encloses Licensee Event Report (LER) 50-3061201 1-001-00.
Improper control of Unit 2 Shield Building doors (Doors 172 and 173) during planned maintenance resulted in an unplanned Limiting Condition for Operation entry and a Loss of Safety Function for the Shield Building system.
Summary of Commitments This letter contains no new commitments and no changes to existing commitments.
Mark Schimmel Site Vice President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:
Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant (PINGP), USNRC Resident Inspector, PINGP, USNRC Department of Commerce, State of Minnesota 171 7 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1 121
ENCLOSURE LICENSEE EVENT REPORT 50-3061201 "1001-00 3 Pages Follow
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SUBMISSION DATE ABSTRACT (Limlt to 1400 spaces, i e, approximately 15 single-spaced typewntten lines)
While Unit 2 was operating at 100% power, improper control of Unit 2 Shield Building access doors (Doors 172 and 173) during planned maintenance resulted in an unplanned Limiting Condition for Operation (LCO) entry and a Loss of Safety Function (LOSF) for the Shield Building system. During the maintenance work, the doors were simultaneously opened several times, for approximately ten seconds each time, resulting in a LOSF. This was reportable per 10 CFR 50.73(a)(2)(v)(C) as a condition that could have prevented the fulfillment of the safety function that was needed to control the release of radioactive material.
The causal evaluation determined that Planning did not identify within the Work Order (WO) the latent impact of the LOSF when two Shield Building access doors were to be simultaneously opened.
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Prairie Island Nuclear Generating Plant Un~t 2
EVENT DESCRIPTION
On February 19, 201 1, at approximately 08:OO CST with Unit 2 in Mode l a n d operating at lQOo/a 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 Q8:00 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 3.6.1 0, 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 LC0 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 I, 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 Ells System Code: BD
SAFETY SIGNIFICANCE
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, LC0 Condition A, was exited at 08: 15 CST on February 19, 201 1.
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 PlNGP involving doors and inoperability was identified in the last three years.
LER 50-28212010-003-01, Postulated Flooding of Battery Rooms Due To Inadequate Battery Room Door Threshold Seals, was submitted March 31, 201 1. This LER described a condition where the battery rooms were declared inoperable due to potential flooding.