05000249/LER-2009-001, Re Group I Isolation and Automatic Reactor Scram

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Re Group I Isolation and Automatic Reactor Scram
ML093440062
Person / Time
Site: Dresden Constellation icon.png
Issue date: 12/01/2009
From: Hanley T
Exelon Generation Co, Exelon Nuclear
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
SVPLTR# 09-0059 LER 09-001-00
Download: ML093440062 (5)


LER-2009-001, Re Group I Isolation and Automatic Reactor Scram
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation

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)(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
2492009001R00 - NRC Website

text

Exelkn.

Exelon Generation Company, LLC www.exeloncorp.com Nuclear Dresden Nuclear Power Station 6500 North Dresden Road Morris, IL 60450-9765 December 1, 2009 10 CER 50.73 SVPLTR # 09-0059 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Dresden Nuclear Power Station, Unit 3 Renewed Facility Operating License No. DPR-25 NRC Docket No. 50-249

Subject:

Licensee Event Report 249/2009-001-00, "Unit 3 Group I Isolation and Automatic Reactor Scram" Enclosed is Licensee Event Report 249/2009-001-00, "Unit 3 Group I Isolation and Automatic Reactor Scram" for Dresden Nuclear Power Station, Unit 3. This event is being reported in accordance with 10 CFR 50.73(a)(2)(iv)(A), "Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section."

There are no regulatory commitments contained in this submittal.

Should you have any questions concerning this letter, please contact Ms. Marri Marchionda at (815) 416-2800.

Respectfully, Site Vice President Dresden Nuclear Power Station Enclosure cc:

Regional Administrator - NRC Region III NRC Senior Resident Inspector - Dresden Nuclear Power Station

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2010 (9-2007)

, the NRC may digits/characters for each block) not conduct or sponsor, and a person is not required to respond to, the informntion rmllp.rtion.

13. PAGE Dresden Nuclear Power Station, Unit 3 05000249 1 OF 4
4. TITLE Unit 3 Group I Isolation and Automatic Reactor Scram
5. EVENT DATE
6. LER NUMBER
7. REPORT DATE J
8. OTHER FACILITIES INVOLVED SEQUENTIAL I REV IFACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR NUMBER NO.

MONTH DAY YEAR N/A N/A t

IFACILITY NAME DOCKET NUMBER 10 03 2009 2009 001 -

00 12 01 2009 N/A N/A

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

El 20.2201(b)

El 20.2203(a)(3)(i)

El 50.73(a)(2)(i)(C)

El 50.73(a)(2)(vii)

El 20.2201(d)

[I 20.2203(a)(3)(ii)

El 50.73(a)(2)(ii)(A)

El 50.73(a)(2)(viii)(A)

El 20.2203(a)(1)

[I 20.2203(a)(4)

El 50.73(a)(2)(ii)(B)

El 50.73(a)(2)(viii)(B)

[I 20.2203(a)(2)(i)

El 50.36(c)(1)(i)(A)

El 50.73(a)(2)(iii)

[I 50.73(a)(2)(ix)(A)

10. POWER LEVEL

-] 20.2203(a)(2)(ii) 0l 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)

El 50.73(a)(2)(x)

El 20.2203(a)(2)(iii)

El 50.36(c)(2)

El 50.73(a)(2)(v)(A)

[1 73.71(a)(4) 100 El 20.2203(a)(2)(iv)

El 50.46(a)(3)(ii)

[I 50.73(a)(2)(v)(B)

[1 73.71(a)(5) 1E 20.2203(a)(2)(v)

El 50.73(a)(2)(i)(A)

[I 50.73(a)(2)(v)(C)

El OTHER El 20.2203(a)(2)(vi)

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

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

Specify in Abstract below or in The Unit 2/3 EDG automatic start is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A), "Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B) of this section."

Unit 3 was returned to the grid on 10/7/2009 after completion of the forced outage plan.

C.

Cause of Event

The Probable Cause for the pressure pulse initiating Reactor Water Level Low-Low Group I Isolation Signal and Unit 3 Reactor SCRAM is attributed to a latent procedural deficiency. DOP 1200-03 provided inadequate guidance for the 3-1201-7 valve position during system restoration with the RPV at pressure. In GEK-323399, "Dresden 3 Reactor Water Clean-Up Operation and Maintenance Instructions," Section 3-11, the reactor vendor, General Electric, recommended that the Return to Reactor line MOV be in the open position for RWCU system start-up when the reactor is at power.

This recommendation was not incorporated into DOP 1200-03. The procedure deficiency is historical.

The Cause of the Unit 2/3 EDG automatic start when auxiliary power transferred to the reserve power source is due to breaker contact response timing. During the fast transfer between the main and reserve feed breakers to the 4 kilovolt (kV) Bus 33, the "b" contacts on both the breakers (which are connected in series) were closed simultaneously for approximately 74 milliseconds. This provided sufficient time for the auto start relay of the Unit 2/3 EDG to be activated. Even though the EDG autostart was not expected, it is possible as there is no delay mechanism built into the electrical circuitry to absolutely prevent the autostart during a fast power transfer. The potential for EDG actuation in a particular situation depends on the relative speed and timing of the "b" contacts for the main and the reserve feed breakers to go from "closed" to "open" and from "open" to "closed,"

respectively.

D.

Safety Analysis

The risk significance of the event was analyzed. The core damage probability (CDP) and Large Early Release probability (LERP) calculations, in conjunction with the plant response and appropriate Operator actions taken, showed the event to be of low risk significance.

The safety significance of this event is minimal. The RPS and the Unit 2/3 EDG responded in a manner consistent with the protection of public health and safety and personnel safety. Operator actions were appropriate and consistent with normal and emergency operating procedures.

E.

Corrective Actions

Procedure DOP 1200-03 has been revised, requiring the 3-1201-7 valve to be open prior to initiating RWCU system fill and vent activities.

Planned corrective actions for the Group 1 isolation and automatic reactor scram event include:

Review of Operations procedures for RWCU and Feed Water [SJ] systems line-ups and valve sequencing that could create precursors for a hydraulic transient and subsequent pressure pulse that could reach the RPV Engineering evaluation of existing RWCU fill and vent procedure for adequacy and potential enhancements Revision to Operations' Pre-Job Briefings to include the potential for hydraulic transient induced pressure pulse Planned corrective actions for the EDG autostart event include:

Inspection of the main feed breaker and auxiliary feed breaker actuation mechanisms by the end of the refueling outage in 2010 to evaluate if the actuations are occurring at the optimal points in relation to each other.

F.

Previous Occurrences

A review of DNPS Licensee Event Reports (LERs) for the last three years did not identify any LERs associated with a similar hydraulic transient event, or an EDG actuation caused by a similar electrical system lineup.

G.

Component Failure Data

N/APRINTED ON RECYCLED PAPERPRINTED ON RECYCLED PAPER