05000306/LER-2010-001, Regarding Unit 2 Turbine Trip During Reactor Shutdown Resulting in a Reactor Scram

From kanterella
(Redirected from 05000306/LER-2010-001)
Jump to navigation Jump to search
Regarding Unit 2 Turbine Trip During Reactor Shutdown Resulting in a Reactor Scram
ML101670053
Person / Time
Site: Prairie Island 
(DPR-060)
Issue date: 06/15/2010
From: Schimmel M
Northern States Power Co, Xcel Energy
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-10-055 LER 10-001-00
Download: ML101670053 (6)
v • d • e


LER-2010-001, Regarding Unit 2 Turbine Trip During Reactor Shutdown Resulting in a Reactor Scram
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)
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)(iv)(A), System Actuation
3062010001R00 - NRC Website
v • d • e

text

(2 Xcel Energ ym June 1 5, 2010 L-PI-10-055 10 CFR 50.73 U S Nuclear Regulatory Commission ATTN Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Unit 2 Docket 50-306 License No DPR-60 LER 50-30612010-001-00, Unit 2 Turbine Trip during Reactor Shutdown Resulting in a Reactor Scram Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, herewith encloses Licensee Event Report (LER) 50-3061201 0-001-00.

On April 16, 2010, the Prairie Island Nuclear Generating Plant's (PINGP) Unit 2 reactor down power began in preparation for Unit 2, Cycle 26 Refueling Outage (2R26). At approximately 13% power the turbine automatically tripped due to a greater than 2.5 inch Hg pressure differential between the A and B condensers.

The steam plant and reactor protection system responded as expected to the initial event. After the reactor trip, operators responded in accordance with procedures, recovered vacuum, and continued with the Unit 2 shutdown.

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

Mark A. Schimmel Site Vice President, Prairie Island 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 50-30612010-001-00 4 Pages Follow

I 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 industrv. Send comments reaardina burden estimate to the Records and LICENSEE EVENT REPORT (LER)

FOIAIPrivacy service Branch (T-5 f52). b 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 Affa~rs, NEOB-10202, (3150-(See reverse for required number of 0066), Office of Management and Budget, Washington, DC 20503 If a means used dig~tslcharacters for each block) to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person 1s not required to respond to, the information collection

3. PAGE Prairie Island Nuclear Generating Plant Unit 2 05000306 1 of4 I
4. TITLE Un~t 2 Turbine Tr~p during Reactor Shutdown Resulting in a Reactor Scram

--.- 5. EVENT DATE

6. LER NUMBER
7. REPORT DATE
8. OTHER FACILITIES INVOLVED FACILITY NAME DOCKET NUMBER SEQUENTIAL REV MONTH DAY

\\EAR YEAR NUMBER NO MONTH DAY YEAR FACILITY NAME DOCKET NUMBER 04 16 2010 2010 - 0 0 1 -

00 06 15 2010

9. OPERATING MODE
11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR 9: (Check all that apply)

I Mode 1 20.2203(a)(2)(i) 50.36(c)(l)(i)(A) 50,73(a)(2)(iii)

Cj 50.73(a)(2)(1x)(A)

10. POWER LEVEL H

20.2203(a)(2)(ii) 50,36(c)(l)(ii)(A) 50,73(a)(2)(iv)(A)

(7 50.73(a)(2)(x)

I 20.2203(a)(2)(iii) 50.36(~)(2)

(7 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)

OTHER 20 ~203(a)(2)(vi)

(7 50 73(a)(2)(i)(B)

(7 50 73(a)(2)(v)(D)

NRC Fp~p) 3i;fiA Spec~fy In Abstract below or In

12. LICENSEE CONTACT FOR THIS LER TELEPHONE NUMBER (Include Area Code) 651.388.1 121 x7350 I
- MANU-REPORTABLE MANU-REPORTABLE
- CAUSE SYSTEM COMPONENT FACTURER TO EPlX

CAUSE

SYSTEM COMPONENT FA CTURER TO EPlX I

I I

I I I I

I

14. SUPPLEMENTAL REPORT EXPECTED
15. EXPECTED MONTH DAY YEAR O NO SUBMISSION C YES (If yes, complete 15. EXPECTED SUBMISSION DATE).

DATE ABSTRACT (Limit to 1400 spaces, I e, approximately 15 single-spaced typewritten lines)

On April 16, 201 0, the Prairie Island Nuclear Generating Plant's (PINGP) Unit 2 reactor down power began in preparation for 2R26 refueling outage. At approximately 13% power the turbine automatically tripped due to a greater than 2.5 inch Hg pressure differential between the A and B condensers The steam plant and reactor protection system responded as expected to the initial event. After the reactor trip, operators responded in accordance with procedures, recovered vacuum, and continued with the Unit 2 shutdown.

I Y RC FORM 366 19-20071

EVENT DESCRIPTION LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION g 'OO-'

CONTINUATION SHEET At 19:04 on 411 61'201 0, the Prairie Island Nuclear Generating Plant's (PINGP) Unit 2 reactor down power began in preparation for 2R26. At 22:37 with reactor power at approximately 13% power the turbine' automatically tripped due to a greater than 2.5 inch Hg pressure differential between the A and B condensers2 This caused an automatic trip of the turbine, and a subsequent automatic trip of the reactor. The steam plant and reactor protection system3 responded as expected to the initial event. After the reactor trip, operators responded in accordance with procedures, recovered vacuum, and continued with the Unit 2 shutdown.

3. PAGE 2 o f 4 1 FACILITY NAME P1alrle Island Nuclear Generating Plant Unit 2

EVENT ANALYSIS

The causal evaluation determined that at 19:04 on 4/16/2010, Unit 2 began a normal shutdown in preparation for 2R26. At approximately 13% power, the turbine automatically tripped due to a greater than 2.5 inch Hg pressure differential between the A and B condensers.

2. DOCKET NUMBER 05000306 7 his was due to a partial openin of the Moisture Separator ~ e h e a t e r ~

(MSR) safety valves caused s'

by a lack of gland sealing steam to the MSR safety valves. Stagnant steam in the relatively cool prping on the 715 ft level of the Unit 2 turbine building condensed and collected at low points in the gland seal steam line to the MSR safety valves on the south side of the turbine. This condensation eventually blocked the flow of sealing steam.

6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2010 -

001

- 00 As the MSR shell pressure became sub-atmospheric the lack of sealing steam to the MSR safety valves allowed the MSR safety valves to partially open and air to flow into Condenser A, rapidly decreasing its vacuum. Since the vacuum in Condenser B did not immediately drop, a differential pressure of greater than 2.5 in. Hg between the condensers developed. This caused an automatic tr~p of the turbine, and a subsequent automatic trip of the Unit 2 reactor.

r h ~ s event IS reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) because of the automatic reactor scram while critical. The turbine condensers have no active safety function. Therefore, this event does not represent a safety system functional failure for Unit 2.

Ells System Code I-A Ells System Code SG Ells System Code JC Ells System Code SB Ells System Soue TC

SAFETY SIGNIFICANCE

- LICENSEE EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION 9 007 CONTINUATION SHEET The operating crew responded to the reactor trip utilizing emergency operating procedures for reactor trip and reactor trip recovery and transitioned into normal shutdown procedures. Therefore, this event dld not affect the health and safety of the public.

CAUSE

3. PAGE 3 o f 4 i FACILITY NAME Pra~r~e Island Nuclear Generating Plant Unit 2 Root Cause The causal evaluat~on determined that the root cause of the event was a build up of condensation that blocked the flow of sealing steam to the MSR safety valves. This allowed the MSR safety valves to partially open and caused condenser vacuum to decrease rapidly. This led to the chain of events that resulted in the Unit 2 reactor trip.
2. DOCKET NUMBER 05000306

Contributing Causes

1. Inadequate procedural guidance associated with gland sealing steam and alarm responses were identified.
2. Degraded gland seal segments on Low Pressure Turbine (LP) 2 allowed more air into the condenser, creating more potential for a loss of vacuum, and could degrade air ejector performance.
3. Several of the actions identified for similar events in 2001 and 2003 were not completed or were not effective, allowing the same circumstances to be present to cause a repeat event.
6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2 0 1 0 -

001

- 00

CORRECTIVE ACTION

7-he slope of the Unit 2 gland seal steam line to the MSR safety valves on the south side of Unit 2 was adjusted to prevent water build up in that line. The slope of the other gland seal steam lines (including both sides of Unit I),

will be inspected for the appropriate slope.

Additional Correctwe Actions:

1. Procedure Change Requests (PCRs) for Power, Shutdown and Alarm Response procedures have been initiated to address the procedural deficiencies.
2. The degraded LP1 and LP2 steam gland seal segments were replaced as part of the originally scheduled Unit 2 outage work. The Unit 1 turbine(s) gland seal segments were replaced in the prior Unit 1 outage.
3. Improvements to the Corrective Action Process were identified by a separate causal evaluation.

PREVIOUS SIMILAR EVENTS LICENSE-EVENT REPORT (LER)

U.S. NUCLEAR REGULATORY COMMISSION 3,307)

CONTINUATION SHEET A LER historical search was conducted and no similar LER events at PlNGP with the same root cause were identified in the last three years.

1 FACILITY NAME Pra~r~e Island Nuclear Generating Plant Unit 2

2. DOCKET NUMBER 05000306
6. LER NUMBER YEAR SEQUENTIAL REV NUMBER NO 2 0 1 0 -

001

- 00
3. PAGE 4 o f 4

Retrieved from "https://kanterella.com/w/index.php?title=05000306/LER-2010-001,_Regarding_Unit_2_Turbine_Trip_During_Reactor_Shutdown_Resulting_in_a_Reactor_Scram&oldid=5297505"