ML051940201

Change a Surveillance Requirement for Reactor Trip Circuit Breakers - Supplemental Information

ML051940201
Person / Time
Site:	Calvert Cliffs
Issue date:	07/08/2005
From:	Montgomery B Constellation Energy Group
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NUREG-1432, Rev 3 NPSD-951-A, Rev 0
Download: ML051940201 (6)

Text

-7 Calvert Cliffs Nuclear Power Plant 1650 Calvert Cliffs Parkway Constellation Generation Group, LLC Lusby, Maryland 20657 C) Constellation Energy July 8, 2005 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: Document Control Desk

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit Nos. I & 2; Docket Nos. 50-317 & 50-318 Change a Surveillance Requirement for Reactor Trip Circuit Breakers -

Sunpiemental Information

REFERENCES:

(a) Letter from G. Vanderheyden (CCNPP) to Document Control Desk (NRC), dated August 3, 2004, License Amendment Request: Change a Surveillance Requirement for Reactor Trip Circuit Breakers (b) Teleconferences with NRC Staff on June 15, 2005 and June 29, 2005 (c) Letter from C. P. Patel (NRC) to C. M. Dugger (Entergy), dated June 29, 1999, Waterford Steam Electric Station Unit 3 - Issuance of Amendment re: Reactor Trip Breaker Surveillance Frequency (TAC No. M96366)

Reference (a) submitted a request to change the frequency of the surveillance test interval for the reactor trip circuit breakers (RTCB) from 31 days to 92 days. This requested change was based on topical report CE NPSD-95 1-A, Revision 01, "Reactor Trip Circuit Breakers Surveillance Frequency Extension".

Subsequent discussion with the Nuclear Regulatory Commission (NRC) staff (Reference b) has resulted in the need to provide supplemental information for our original request. There are two areas requiring additional information; surveillance test scheduling requirements, and the failure rate calculation.

Changes to the marked up Technical Specification pages are contained in Attachment (1). The information contained in this letter does not affect the No Significant Hazards Determination or the Environmental Consideration provided in Reference (a).

Surveillance Test Scheduling Requirements In Reference (a), we proposed extending the RTCB testing (Surveillance Requirement [SR] 3.3.3.1) from monthly to quarterly and alternating the testing with the RTCB logic testing (SR 3.3.3.2). The alternating testing was proposed so the RTCB reliability to trip on demand would be verified approximately every six weeks instead of every three months. This testing schedule supports the probabilistic risk analysis performed in support of this request and described in Reference (a).

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Document Control Desk July 8, 2005 Page 2 We originally proposed putting the requirements to alternate the testing in the Technical Specification Bases. However, after discussion with the NRC staff (Reference b), we have determined that adding a note to the Surveillance Requirement would be a more appropriate means of controlling the test schedule.

The proposed note is contained on the marked up Technical Specification page in Attachment (1). The Note requires that the RTCB CHANNEL FUNCTIONAL TEST and the RPS Logic CHANNEL FUNCTIONAL TEST be performed such that the RTCBs are tested approximately every six weeks. This will accommodate the vendor recommended interval for cycling of each RTCB and is the interval evaluated by our risk analysis. The wording of the proposed note is similar to a note approved for the Waterford Steam Electric Station (Reference c). Placement of the note is in accordance with the Improved Technical Specification Writers Guide and is similar to other notes contained in NUREG-1432, Revision 3. A discussion of this note will also be placed in the Technical Specification Bases. The Basis change will also follow the format for similar notes.

Failure Rate Calculation During discussions with the NRC staff, questions were brought up concerning the impact (e.g., correlation) of a 24-month refueling cycle on the failure rate calculation in the topical report CE NPSD-951-A, Revision 01 and requested a discussion of our evaluation method and results. That discussion is provided below.

The failure likelihood of the RTCBs used in our risk evaluation is a combination of plant specific data and generic data using a Bayesian approach. Our value for failure likelihood is 1.69E-3 per demand; this is based on a generic estimate of 1.77E-3 combined with 2 RTCB failures in 1241 demands. As the generic data and our plant specific data are closely correlated, we have a high degree of confidence in our RTCB failure rate. This failure rate is based on our current surveillance interval (i.e., 31 days).

As the interval between tests increases, it is expected that the failure likelihood of the RTCB on demand will increase. The demand failure likelihood of the RTCB is comprised on two components: a shock component and an idle failure component. During operation, RTCB parts wear. After a certain number of cycles, the components can fail. When a component is I cycle away from failure, then the next demand will fail the RTCB. These are "shock" failures. While the breaker is idle (i.e., not opening or closing), corrosion can take place, lubrication can dry, etc. These are "idle" failures.

To adjust the failure rate, we conservatively assumed that "idle" failures drive the failure rate of the RTCBs. If "shock" failure drove the failure rate, then extending the surveillance interval would have minimal impact. Although we attempt to alternate our surveillance tests (i.e., one demand per 46 days

[half of 92 days]), it is possible that the surveillance will not be perfectly offset. To address this, we considered that the RTCB will be tested at least once per 60 days (i.e., two weeks beyond perfect offset

[60=46+14]). "Idle" failures are typically proportional to time. As a result, we doubled the failure rate of the RTCBs (change from 31 days to an assumed test period of 60 days mentioned above). This evaluation supports the proposed SR Note that requires testing the RTCBs at approximately six week intervals, because it assumes testing at less frequent intervals than required by the proposed Technical Specifications.

Please note that the refueling interval does not affect this calculation. The calculation is driven purely by the SR Frequency.

Document Control Desk July 8, 2005 Page 3 Should you have questions regarding this matter, please contact Mr. L. S. Larragoite at (410) 495-4922.

Very truly yours, STATE OF MARYLAND

TO WIT:

COUNTY OF CALVERT I, Bruce S. Montgomery, being duly sworn, state that I am Manager - Calvert Cliffs Nuclear Power Plant (CCNPP) Engineering Services, and that I am duly authorized to execute and file this License Amendment Request on behalf of CCNPP. To the best of my knowledge and belief, the statements contained in this document are true and correct. To the extent that these statements are not based on my personal knowledge, they are based upon information provided by other CCNPP employees and/or consultants. Such information has been reviewed in accordance with company practice and I believe it to be reliable.

Subscribed and sworn before me, a Notary Public in an for the State of Maryl/nd and County of C.\9v.. , this 8 day of 2005.

WITNESS my Hand and Notarial Seal:

N . -------

N~i--e My Commission Expires:

Date a _,:-

BSM/PSF/bjd A.-

Attachment:

(1) Marked-up Technical Specificati ion Page cc: P. D. Milano, NRC Resident Inspector, NRC S. J. Collins, NRC R. 1.McLean, DNR

ATTACHMENT (1)

MARKED-UP TECHNICAL SPECIFICATION PAGE Calvert Cliffs Nuclear Power Plant, Inc.

July 8, 2005

RPS Logic and Trip Initiation 3.3.3 ACTIONS (continued) ._--_

CONDITION REQUIRED ACTION COMPLETION TIME D. Two channels of RTCBs D.1 Open the affected Immediately or Trip Path Logic RTCBs.

affecting the same trip leg inoperable.

E. Required Action and E.1 Be in MODE 3. 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> associated Completion Time of Condition A, AND B, or D not met.

E.2 Open all RTCBs. 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> OR One or more Functions with two or more Manual Trip, Matrix Logic, Trip Path Logic, or RTCB channels inoperable for reasons other than Condition A or D.

SURVEILLANCE REQUIREMENTS ,-------"

SURVEILLANCE FREQUENCY SR 3.3.3.1 Perform a CHANNEL FUNCTIONAL TEST on each RTCB channel.

SR 3.3.3.2 Perform a CHANNEL FUNCTIONAL TEST on each 92 days RPS Logic channel.

CALVERT CLIFFS - UNIT 1 3.3.3-2 Amendment No. 227 CALVERT CLIFFS - UNIT 2 Amendment No. 201

Insert 1

~~-- -NOTE-- ----

The quarterly RTCB CHANNEL FUNCTIONAL TEST and the quarterly RPS Logic CHANNEL FUNCTIONAL TEST shall be scheduled and performed such that the RTCBs are tested approximately every 6 weeks to accommodate the appropriate vendor recommended interval for cycling of each RTCB.