05000263/LER-2013-001, E SRV Low-Low Set Tailpipe Dp Root Valve Found Closed

E SRV Low-Low Set Tailpipe Dp Root Valve Found Closed

ML13158A270
Person / Time
Site:	Monticello
Issue date:	06/07/2013
From:	Schimmel M Northern States Power Co, Xcel Energy
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
L-MT-13-054 LER 13-001-00
Download: ML13158A270 (4)

LER-2013-001, E SRV Low-Low Set Tailpipe Dp Root Valve Found Closed

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded 10 CFR 50.73(a)(2)(viii)(A) 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition 10 CFR 50.73(a)(2)(viii)(B) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(ix)(A) 10 CFR 50.73(a)(2)(iv)(A), System Actuation 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)(v)(B), Loss of Safety Function - Remove Residual Heat 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)(i)(8) 10 CFR 50.73(a)(2)(ii)(8)
2632013001R00 - NRC Website

text

Xcel Energy@

June 07,2013 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket 50-263 Renewed Facility Operating License No. DPR-22 Monticello Nuclear Generating Plant 2807 W County Road 75 Monticello, MN 55362 L -MT 054 10 CFR 50.73 LER 2013-001 liE SRV Low-Low Set Tailpipe dP Root Valve Found Closed" A Licensee Event Report (LER) for this occurrence is attached.

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

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

Regional Administrator, Region III, USNRC Project Manager, Monticello Nuclear Generating Plant, USNRC Resident Inspector, Monticello Nuclear Generating Plant, USNRC

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104 EXPIRES 10/31/2013 (10-2010)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. PAGE Monticello Nuclear Generating Plant 05000 - 263 1 OF 3

4. TITLE E SRV Low-Low Set Tail Jipe dP Root Valve Found Closed

5. EVENT DATE

6. LER NUMBER

7. REPORT DATE

8. OTHER FACILITIES INVOLVED YEAR I SEQUENTIAL I REV FACILITY NAME DOCKET NUMBER MONTH DAY YEAR NUMBER NO MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 04 12 13 2013 - 001 - 00 06 07 2013

9. OPERATING MODE

11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR §: (Check all that apply)

D 20.2201(b)

D 20.2203(a)(3)(i)

D 50.73(a)(2)(i)(C)

D 50.73(a)(2)(vii)

N D 20.2201 (d)

D 20.2203(a)(3)(ii)

D 50.73(a)(2)(ii)(A)

D 50.73(a)(2)(viii)(A)

D 20.2203(a)(1)

D 20.2203(a)(4)

[SJ 50.73(a)(2)(ii)(B)

D 50.73(a)(2)(viii)(B)

D 20.2203(a)(2)(i)

D 50.36(c)(1)(i)(A)

D 50.73(a)(2)(iii)

D 50.73(a)(2)(ix)(A)

10. POWER LEVEL D 20.2203(a)(2)(ii)

D 50.36(c)(1)(ii)(A)

D 50.73(a)(2)(iv)(A)

D 50.73(a)(2)(x)

D 20.2203(a)(2)(iii)

D 50.36(c)(2)

D 50.73(a)(2)(v)(A)

D 73.71(a)(4) 0%

D 20.2203(a)(2)(iv)

D 50.46(a)(3)(ii)

D 50.73(a)(2)(v)(B)

D 73.71 (a)(5)

D 20.2203(a)(2)(v)

D 50.73(a)(2)(i)(A)

D 50.73(a)(2)(v)(C)

D OTHER Specify in Abstract below or in D 20.2203(a)(2)(vi)

[SJ 50.73(a)(2)(i)(B)

D 50.73(a)(2)(v)(D)

EVENT DESCRIPTION

When the condition was discovered, the Monticello Nuclear Generating Plant [MNGP] was in a refueling outage and defueled.

On April 12, 2013 at 2200, during investigation into the inability to complete a Safety Relief Valve (SRV) discharge line excess flow check valve test, a relief valve discharge monitoring instrument valve [RTV],

MS-44-28, was discovered to have been inappropriately closed. The closed valve isolated two differential pressure switches [POlS] that impact operation of E Low-Low Set (LLS) Valve [RV]. The valve found closed was returned to its normal open position.

EVENT ANALYSIS

This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(8), Operation or Condition Prohibited by Technical Specifications and 10 CFR 50.73(a)(2)(ii)(8), Unanalyzed Condition. This event was not considered a safety system functional failure.

SAFETY SIGNIFICANCE

The function of the SRV LLS System is to minimize the possibility of a SRV reopening while an elevated water leg is in its discharge line. The elevated water leg occurs after an SRV closes. The condensing steam in the SRV discharge line creates a vacuum which draws Torus water into the discharge line. If an SRV reopens while an elevated water leg is in the discharge line, the resulting water thrust load on primary containment could exceed its design strength. The system also reduces subsequent SRV actuations during plant transients and improves overall SRV performance.

The discovered condition would not have prevented E SRV from opening for LLS or on mechanical setpoint.

The purpose of the signal from the instruments associated with valve MS-44-28 is to provide a 10 second interlock following actuation of the E SRV, before the E SRV can be opened again. The maximum expected discharge line water leg clearing time is 5.75 seconds.

The LLS protective function is fully automatic and requires no operator action. The LLS SRVs have lower opening setpoints than the mechanical setpoints. These lower setpoints are for electrical/pneumatic actuation. In the worst case transients, two LLS SRVs are required. The third is provided for redundancy. The Hand G SRVs were not affected by the isolated pressure switches and would have been capable of functioning as designed. The E SRV actuates at 1072 psig for LLS. As this is the highest set point for an SRV in the LLS sequence, it is less likely that E SRV would be required to actuate. Additionally, the Automatic Depressurization System is completely independent of LLS and was available to depressurize the Reactor.

CAUSE

Following the 2011 Refueling Outage, the E SRV tailpipe temperatures were elevated. On June 25, 2011, the E SRV main stage body valve and SRV pilot assembly were replaced. Per procedural restoration step, valve MS-44-28 was closed. This closure step was performed as part of a restoration activity to reinstall a vent cap.

A procedure change had been made in 2005, including venting steps, which did not reflect differences in tailpipe configurations on the SRVs.

CORRECTIVE ACTION

3. PAGE 3 OF 3 The immediate corrective action was to restore the valve MS-44-2B to open. The long-term corrective action is to revise the procedure to incorporate the difference in SRV tailpipe vent cap configuration.

PREVIOUS SIMILAR EVENTS

There were no previous similar licensee event reports in the past three years.

ADDITIONAL INFORMATION

Energy industry identification system (EllS) codes are identified in the text within brackets [xx].