05000282/LER-2010-001, For Prairie Island, Unit 1, Regarding Unanalyzed Condition Due to Postulated High Energy Line Break on Cooling Water System

For Prairie Island, Unit 1, Regarding Unanalyzed Condition Due to Postulated High Energy Line Break on Cooling Water System

ML101230471
Person / Time
Site:	Prairie Island
Issue date:	05/03/2010
From:	Schimmel M Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-10-043 LER 10-001-00
Download: ML101230471 (6)

LER-2010-001, For Prairie Island, Unit 1, Regarding Unanalyzed Condition Due to Postulated High Energy Line Break on Cooling Water System

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
2822010001R00 - NRC Website

text

@ Xcel Energye May 3, 2010 L-PI-10-043 10 CFR 50.73 U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 License Nos. DPR-42 and DPR-60 LER 50-28212010-001-00, Unanalvzed Condition Due to Postulated High Energv Line Break On Cooling Water Svstem Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, herewith encloses Licensee Event Report (LER) 50-2821201 0-001-00.

The causal evaluation for the reported condition is in progress. A supplement to the LER will provide additional information from the casual evaluation.

Summary of Commitments This letter contains no new commitments and no changes to existing commitments.

Mark A. Schimmel Site Vice President, Prairie lsland Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:

Administrator, Region Ill, USNRC Project Manager, Prairie Island, USNRC Resident Inspector, Prairie Island, 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 50-2821201 0-001-00 4 Pages Follow

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION i92oo0'~

LICENSEE EVENT REPORT (LER)

(See reverse for required number of digitslcharacters for each block)

1. FACILITY NAME Prairie Island Nuclear Generating Plant Unit 1 APPROVED BY OMB NO. 3150-0104 EXPIRES: 08/31/2010 Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the Records and FOWPrivacy Service Branch (l-5 F52), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e-mail to infocollects@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0066), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

2. DOCKET NUMBER 05000282

4. TITLE Unanalyzed Condition Due to Postulated High Energy Line Break On Cooling Water System

3. PAGE 1 of4

5. EVENT DATE

' FACILITY NAME

' DOCKET NUMBER 20.2203(a)(3)(i) 50,73(a)(2)(i)(C) 50,73(a)(2)(vii) 20.2203(a)(3)(ii) 50,73(a)(2)(ii)(A) 50,73(a)(2)(viii)(A) 20.2203(a)(I) 20.2203(a)(4) a 50,73(a)(2)(ii)(B) 50,73(a)(2)(viii)(B) 20.2203(a)(2)(i) 50.36(c)(l)(i)(A) 50,73(a)(2)(iii) 50,73(a)(2)(ix)(A) 20.2203(a)(2)(ii) 50,36(c)(l)(ii)(A) 50,73(a)(2)(iv)(A) 50.73(a)(2)(x) 20.2203(a)(2)(iii) 50.36(~)(2) 50.73(a)(2)(v)(A) 73.71 (a)(4) 20.2203(a)(2)(iv) 50,46(a)(3)(ii) 50,73(a)(2)(v)(B) 73.71 (a)(5) 20.2203(a)(2)(v) 50.73(a)(2)(i)(A) 50.73(a)(2)(v)(C) 20.2203(a)(2)(vi) 50.73(a)(2)(i)(B) 651.388.1 121 x7350 On March 5, 2010, Prairie Island Nuclear Generating Plant (PINGP) Unit 1 and Unit 2 were at 100%

power. PINGP staff determined that in the event of a postulated high energy line break (HELB) event with a concurrent loss of offsite power (LOOP) and a single active failure of a cooling water (CL) pump without a corresponding safety injection (SI) signal, the CL system might not provide sufficient water to required cooling loads until after the turbine building cooling loads were isolated.

The condition was determined to be reportable while investigating licensing conditions associated with a HELB. Procedural changes have been made to ensure that the current configuration of two OPERABLE and one additional FUNCTIONAL safeguards cooling water pumps is maintained. The casual evaluation is in progress and the results will be provided in a supplemental LER.

I NRC FORM 366 (9-2007)

MONTH DAY YEAR

6. LER NUMBER YEAR

7. REPORT DATE

8. OTHER FACILITIES INVOLVED MONTH SEQUENTIAL NUMBER FACILITY NAME Prairie Island Unit REV NO DOCKET NUMBER 05000306 DAY YEAR

EVENT DESCRIPTION LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION (9-2007)

CONTINUATION SHEET The Prairie Island Nuclear Generating Plant's (PINGP) Cooling Water (CL) system1 consists of a shared system common to both units. The CL system provides a heat sink for the removal of process and operating heat from safety related components during a Design Basis Accident (DBA) or transient. The CL system consists of a common CL pump discharge header for the five CL (2 nonsafeguards, 2 safeguards, and 1 that can be designated as safeguards or nonsafeguards) pumps that direct flow into two separate, 100% capacity, CL headers. Each header then supplies loops in the Turbine Building (TB) and Auxiliary Building (AB) and containments for the two units. Normally, three safeguards pumps were maintained available.

A high energy line break (HELB) can cause consequential failure of adjacent piping such as cooling water lines. For a postulated HELB event, any consequential failures due to the HELB must be assumed along with a loss of offsite power (LOOP) and the most-limiting single failure. The most-l~miting single failure for a HELB event is dependent on the system or component being evaluated.

3. PAGE 2 o f 4 For evaluations of the CL system, the most-limiting single failure would be the failure that most challenges the ability of the system to perform its mitigating functions. Given that the CL system is typically not required to change state (i.e., split headers, isolate loads, etc.) in a HELB event due to the lack of a safety injection2 (SI) signal, the most limiting single-failure for the system would be the failure that results in the least flow to the required mitigating equipment.

6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2010 -

001

- 00 I.

FACILITY NAME Prairie Island Nuclear Generating Plant Unit 1 Most required components in the CL system are arranged in parallel such that a failure of one component will not adversely affect the flow in the system. The remaining active components required to operate in a HELB event are the safeguards CL pumps. If only two safeguards CL pumps were available and the single failure assumed is the failure of one of the pumps to start, both supply headers would be supplied by a single safeguards CL pump. This condition has been previously evaluated to be acceptable with no break in the supply header; however, there is not expected to be sufficient margin available to show that a single CL pump can supply both headers and the flow through the broken pipe due to the HELB event. Therefore, the failure of one safeguards CL pump to start is expected to be the most-limiting single failure.

2. DOCKET NUMBER 05000282 PINGP staff has been in the process of evaluating the potential effects of a postulated HELB event.

On March 5, 2010, Unit 1 and Unit 2 were at 100% power. It was determined that there was a previous period in the last three years during which only two safeguards CL pumps were OPERABLE for a period greater than seven days. During this timeframe, the postulated HELB licensing basis scenario would have resulted in the potential for a single CL pump to attempt supplying all normal loads on both trains of the CL system plus the flow through the break location. This was beyond the analyzed conditions for the CL system and determined to be reportable.

Ells System Code. BI Ells System Code. BP

EVENT ANALYSIS LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION (9-2007)

CONTINUATION SHEET For the postulated HELB event (which includes a LOOP, with two safeguards CL pumps available, no SI signal and the most-limiting single failure), the most limiting single-failure for the system would be the failure of one of the safeguards CL pumps to start or operate. During this condition, the CL system might not provide sufficient water to required safety-related cooling loads until after the turbine building cooling loads were isolated. This event is being reported under 10 CFR 50.73(a)(2)(ii)(B) as an unanalyzed condition.

NUREG-1 022, "Event Reporting Guidelines 10 CFR 50.72 and 50.7311, Revision 2, page 54, regarding the reporting of safety system functional failures states, "In determining the reportability of an event or condition that affects a system, it is not necessary to assume an additional random single failure in that system." Considering that an additional single failure does not need to be assumed for the reporting of a safety system functional failure, the additional failure of one safeguards CL pump does not need to be assumed. The two safeguards CL pump capacity would have been available and adequate to supply system loads during a HELB event. Therefore, this event does not represent a safety system functional failure for Unit 1 or Unit 2.

3. PAGE 3 o f 4

SAFETY SIGNIFICANCE

6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2010 -

001

- 00 I. FACILITY NAME Prairie Island Nuclear Generating Plant Unit 1 This condition resulted in a potential for a postulated HELB to cause a break in a CL line. This LER is not associated with an event resulting in an actual HELB in any portion of the plant. There were no actual consequences to the health and safety of the public as a result of this condition.

2. DOCKET NUMBER 05000282 CAUSE AND CORRECTIVE ACTION The causal evaluation for the reported condition is in progress. Northern States Power Company, a Minnesota corporation (NSPM), will provide a supplement to this LER once the casual evaluation has been completed.

Corrective actions have been implemented that revised procedures to ensure that the current configuration of two OPERABLE and one additional FUNCTIONAL safeguards cooling water pumps IS maintained.

PREVIOUS SIMILAR EVENTS LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMlsslON (9-2007)

CONTINUATION SHEET LER 2-08-01 for PINGP, Unit 2 regarding an "Unanalyzed Condition Due to Both Trains of Component Cooling Susceptible to a Postulated High Energy Line Break" was submitted on January 19, 2009. This LER described a condition where both trains of the component cooling3 water system were susceptible to a single failure caused by a postulated HELB in the turbine building.

1. FACILITY NAME Pra~r~e Island Nuclear Generating Plant Unit 1 LER 1-09-06 for PINGP, Units 1 and 2, regarding an "Unanalyzed Condition Due to Potential Safety System Susceptibility to Turbine Building Flooding Due to a Postulated High Energy Line Break, Supplement 1" was submitted April 8, 2010. This LER described a condition where the operability of the Unit 1 Emergency Diesel en era tors^ may not be assured during a HELB event.

Ells System Code CC

" Ells System Code EK

2. DOCKET NUMBER 05000282

6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2010 -

001

- 00

3. PAGE 4 of 4