05000336/LER-2003-002, From Millstone, Unit 2 Regarding Reactor Trip While Performing RPS Matrix Testing

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From Millstone, Unit 2 Regarding Reactor Trip While Performing RPS Matrix Testing
ML031260630
Person / Time
Site: Millstone Dominion icon.png
Issue date: 04/28/2003
From: Sarver S
Dominion Nuclear Connecticut
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
B18890 LER 03-002-00
Download: ML031260630 (4)
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LER-2003-002, From Millstone, Unit 2 Regarding Reactor Trip While Performing RPS Matrix Testing
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
10 CFR 50.73(a)(2)(ix)(A)
10 CFR 50.73(a)(2)
10 CFR 50.73(a)(2)(x)
10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat
10 CFR 50.73(a)(2)(v), Loss of Safety Function
10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown
10 CFR 50.73(a)(2)(i)
3362003002R00 - NRC Website
v • d • e

text

domDoinions Dominion Nuclear Connecticut, Inc.

Millstone Powver Station Rope Ferry Road Waterford, CT 06385 APR 28 2003 Docket No. 50-336 B18890 RE: 10 CFR 50.73(a)(2)(iv)(A)

U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Millstone Power Station, Unit No. 2 Licensee Event Report 2003-002-00 Reactor Trip While Performing RPS Matrix Testing This letter forwards Licensee Event Report (LER) 2003-002-00, documenting a condition that was discovered at Millstone Unit No. 2, on March 7, 2003. This LER is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A).

There are no regulatory commitments contained within this letter.

Should you have any questions regarding this submittal, Mr. David W. Dodson at (860) 447-1791, extension 2346.

please contact Very truly yours, DOMINION NUCLEAR CONNECTICUT, INC.

and Maintenance Attachment (1):

LER 2003-002-00 cc:

H. J. Miller, Region I Administrator R. B. Ennis, NRC Senior Project Manager, Millstone Unit No. 2 Millstone Senior Resident Inspector

---Ie' 9,;) -

I 0

Docket No. 50-336 B18890 Millstone Power Station, Unit No. 2 LER 2003-002-00

NRC FORM 366 U.S. NUCLEAR REGULATORY APPROVED BY OMB NO. 3150-0104 EXPIRES 7-31-2004

, the NRC may not conduct or sponsor, (See reverse for required number of diaits/characters for each block) and a person is not required to respond to, the information collection FACILITY NAME (1)

DOCKET NUMBER (2)

PAGE (3)

Millstone Power Station - Unit 2 05000336 1 OF 2

TITLE (4)

Reactor Trip While Performing RPS Matrix Testing EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

MO DAY YEAR YEAR SEU ENTIAL REV MO DAY YEAR FACILITY NAME l

DOCKET NUMBER NUMBER NO.

l 05000 03 07 2003 2003 -

002 -

00 04 28 2003 FACILITY NAME l1DOCKET NUMBER I-I-1 05000 nPFRATImJO I

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

MODE (9) 20.2201(b) 20.2203(a)(3)(ii) 50.73(a)(2)(ii)(B) 50.73(a)(2)(ix)(A)

POWER 1nn 20 2201 (d) 20.2203(a)(4) 50.73(a)(2)(ill) 50.73(a)(2)(x)

LEVEL (10) 20 2203(a)(1) 50.36(c)(1)(i)(A)

X 50.73(a)(2)(iv)(A) 73 71 (a)(4)

'tF>

20 2203(a)(2)(i) 50.36(c)(1)(ii)(A) 50 73(a)(2)(v)(A)

_ 73 71(a)(5) 20.2203(a)(2)(ii) 50.36(c)(2) 50.73(a)(2)(v)(B)

_ OTHER 20 2203(a)(2)(iii) 50.46(a)(3)(i) 50.73(a)(2)(v)(C)

Specify In Abstract below or 20.2203(a)(2)(Iv)

_ 50.73(a)(2)(i)(A)

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

_ In NRC Form 366A 20 2203(a)(2)(v)

_507((2(B)50.73(a)(2)(vli 20.2203(a)(2)(v) 50.73(a)(2)(i)(C) 50.73(a)(2)(vIii)(A) 3 ;___Ad __a _________

\\

20 2203(a)(3)(i) 50.73(a)(2)(i)(A) 50.73(a)(2)(vlii)(B)

S0.7_)_

50_3_

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (Include Area Code)

David W. Dodson, Supervisor-Licensing 1860-447-1791 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

I ISTRACT (Limit to 1400 spaces, I e., approximately 15 single-spaced typewritten lines) (16)

On March 7, 2003, at 1439, with the unit in Mode 1 at 100% power, an automatic reactor trip occurred during normal monthly Reactor Protection System (RPS) matrix testing due to a fault in the test circuitry. Specifically, Control Rod Drive trip circuit breaker (TCB) pair TCB-1 and TCB-5 tripped open in addition to the expected opening of TCB pair TCB-3 and TCB-7 when AC Matrix Relay Trip Select switch was rotated to position "3." The opening of both pairs of trip breakers resulted in a reactor trip from full power followed by an automatic turbine trip.

All control rods inserted into the core and all electrical busses transferred properly following the trip. Auxiliary Feedwater (AFW) initiated as expected, on low steam generator level. The post-trip plant response was complicated by several additional equipment failures, the most notable being a malfunction of the charging system leading to a loss of all charging. This latter condition is addressed in a separate report.

The root cause of the event was historical in nature and determined to be poor workmanship of the original RPS matrix test module dating back to plant startup. Specifically, the keying pin hole was drilled too large in the adapter plate for the AC matrix relay trip select switch (Micro switch model X6210-25AS4-7448) allowing excessive movement of the switch. This movement, in addition to poor quality of soldering and lack of wiring strain relief in the test module, caused strain failure of the wiring at the switch terminal joint.

Corrective actions to prevent recurrence included re-drilling the switch keying pin hole to remove excessive switch play, and to inspect for and repair damaged wiring and provide adequate strain relief for wiring as necessary, in the RPS matrix test module. These actions were completed prior to startup.

NHtC 1FuHmub 361-;x01)

I (If more space Is required, use additional copies of NRC Form 366A) (1 7)0

1.

Event Description

On March 7, 2003, at 1439, with the unit in Mode 1 at 100% power, an automatic reactor trip occurred during normal monthly Reactor Protection System (RPS) [JC] matrix testing due to a fault in the test circuitry.

Specifically, Control Rod Drive trip circuit breaker (TCB) pair TCB-1 and TCB-5 tripped open in addition to the expected opening of TCB pair TCB-3 and TCB-7 when AC Matrix Relay Trip Select switch was rotated to position 3." The opening of both pairs of trip breakers resulted in a reactor trip from full power followed by an automatic turbine trip. All control rods inserted into the core and all electrical busses transferred properly following the trip.

Auxiliary Feedwater (AFW) [BA] initiated as expected, on low steam generator level. The post-trip plant response was complicated by several additional equipment failures, the most notable being a malfunction of the charging system leading to a loss of all charging. This latter condition is addressed in a separate report.

This event is being reported pursuant to 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in automatic actuation of RPS and AFW.

2.

Cause

The root cause of the event was historical in nature and determined to be poor workmanship of the original RPS matrix test module dating back to plant startup. Specifically, the keying pin hole was drilled too large in the adapter plate for the AC matrix relay trip select switch (Micro switch model X6210-25AS4-7448) allowing excessive movement of the switch. This movement, in addition to poor quality of soldering and lack of wiring strain relief in the test module, caused strain failure of the wiring at the switch terminal joint.

3.

Assessment of Safety Consequences

The RPS test circuit consists of selector switches that dial in the select TCBs to open, however, until the RPS test pushbutton is depressed, the contacts and mounting of the switch are out of the circuit. There was no adverse impact on the ability of the RPS to performing its safety function as required by the Technical Specifications. The safety consequences of the strain failure of the switch wiring alone did not pose any more of a safety consequence than that of a normal reactor trip. The risk associated with a reactor trip is generally considered the same as for any general plant transient. For these reasons, the safety significance of this event is considered low and no loss of safety function occurred. Loss of safety function associated with the charging system is addressed in a separate report.

4.

Corrective Action

Corrective actions to prevent recurrence included re-drilling the switch keying pin hole to remove excessive switch play, and to inspect for and repair damaged wiring, and provide adequate strain relief for wiring as necessary, in the RPS matrix test module. These actions were completed prior to startup. An extent of condition review determined that the strain failure of the wiring was limited to matrix relay trip select switches in the RPS test modules requiring adapter plates, and additional suspect switches were replaced during troubleshooting. An investigation was conducted and additional corrective actions will be entered into the Millstone Corrective Action program.

5.

Previous Occurrences

No previous similar events/conditions were identified.

Energy Industry Identification System (EIIS) codes are identified in the text as [XX].

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