ML20211G046

Requests That NRC Events Assessment Panel Reconsider Classification of March 1997 Event Re Sqn,Unit 1 Loss of Pressurizer Level Instrument Due to Partial Voiding in Reference Leg

ML20211G046
Person / Time
Site:	Sequoyah
Issue date:	09/24/1997
From:	Zeringue O TENNESSEE VALLEY AUTHORITY
To:	Callan J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
References
NUDOCS 9710010430
Download: ML20211G046 (5)

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Tennessee Valley AutNnty,1101 Mamet Street. Chananecga. Terressee 37402-2601 I

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i September 24, 1997 Mr. Joseph Callan Executive Director for Operations U.S. Nuclear Regulatory Commission Mail Stop 05E6 Washington, D.C. 20555-0001

Dear Mr. Callan:

In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328

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SEQUOYAH NUCLEAR PLANT- (SQN) - CLASSIFICATION OF SIGNIFICANT EVENT FOR THE PERFORMANCE INDICATOR PROGRAM In March 1997, SQN Unit i experienced a loss of pressurizer level instrument due to partial voiding in the reference f leg. Subsequently, plant operators relying on that-instrument reduced the water level in the pressuriter more than had been-planned as part of the refueling outage underway at the time. On June l', 1997, the NRC Events Assessment Panel classified the SQN problem as a significant event for its performance indicator program due to the perceived potential for a loss of cooling capability. TVA became aware of the event classification through information posted to the NRC Internet home page (MR Number: H-97-0107) on September 4, 1997.

The daily report notice did not clearly identify the basis for the classification. Subsequent discussions with the NRC '

staff did not identify the basis for the classification of //

the event. The following information was provided in the /g/

notice:

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Shutdown cooling was not affected and Reactor Coolant System (RCS) temperature remained at approximately 140*F throughout the event. However, had the operator not recognized that an excessive inventory loss had occurred, level could have decreased to the point of affecting shutdown cooling.

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Mr.: Joseph callan Page 2 September 24, 1997 The apparent basis for the classification appears to be a perception by the NRC Events Assessment Panel that the '

inventory. loss could have continued to the point that shutdown cooling was lost without recognition by the plant operating staff. TVA disagrees with the Panel's conclusion that the event be classified as a significant event because the progression of events necessary to have led to the loss of shutdown cooling was not credible. We note that the Panel's decision was made before all the facts surrounding the event were presented by TVA. T"A presented the .

substantial information about the loss of inventory at a meeting in the NRC Region II office on June 27, 1997. The following.information was provided in that meeting.

The event had no safety consequences since the pressurizer was not emptied.

• The problem with the pressurizer level indicaticn was identified by the incoming crew.

• The RCS level decrease was terminated with over 1-1/2 feet of water level still in the pressurizer.

• An additional 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> of drain time would have been needed to reach mid-loop level and a loss of shutdown cooling.

Undetectsd progression to a loss of shutdown cooling was not credible..

• The voiding of reference leg for the instrument resulted in a situation where-the instrument had an offset which 1+sulted in the indicator reaching the

" bottom" of its range while reading approximately -

25 percent.

• The instrument offset resulted in a condition where the indicator would stop moving before the operator reached the end of the level reduction operation.

• The level indicator stopped moving when RCS level in the pressurizer reached the bottom tap for the level instrument.

• - The lack of movement in the indicated level was readily recognized by the operating crew, and the level change operation was stopped.

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} Mr. Joseph callan Page 3

. September 24, 1997

• Refueling outage activities scheduled to commence early in the next shift once the level reduction operation was completed would have resulted in regular progress checks.

• The lack of progress in scheduled activities would have triggered additional management reviews well before an undetected level reduction reached mid-loop.

• As noted above, an additional 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> of drain time would have been needed to reach mid-loop level and a loss of shutdown cooling.

TVA finds it incredible to consider that the full range of barriers that ensure shutdown cooling capability would be missed, ignored, or bypassed. TVA further finds it incredible to consider that such a condition could persist for over 13 hours1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br />. The lack of safety significance, coupled with the lack of a credible scenario for the evolution to progress to a loss of shutdown cooling, supports TVA's f position that the problem was not a significant event.

The NRC separately noted that the actual safety consequence of the event was low in a letter to Oliver D. Kingsley, Jr.,

dated July 10, 1997, which cited TVA with a violation for the event. In the same letter, the NRC provided mitigation credit for TVA's identification of the violation. The Panel's conclusion on significance appears to be at odds with the assessment of the NRC staff involved with the enforcement action and having access to all available information associated with this problem.

TVA fully supports the NRC's efforts to develop an objective performance indicator program for use in improving the regulation of commercial nuclear power plants. However, TVA is concerned that fnadequate or incomplete reviews of plant events that result in overstatement of the safety significance will negate the improvements sought by the '

performance indicator initiative. -

An a result, key stakeholders and interested parties will be unnecessarily alarmed.

The effectiveness of the performance indicator program must necessarily rely upon the objectivity of the review and classification of data fed into the performance indicator models. We recommend that the NRC evaluate the process used by the Events Assessment Panel to classify events. We strongly believe that the Panel should not render a decision w

i Mr.-Joseph Callan .

. Page 4 I September 24, 1997 until the' licensee has an opportunity to present all relevant j information associated with the event under review. It '

should be pointed out that in TVA's letter dated April 21, 1997, transmitting the incident investigation surrounding

.this event,'TVA requested a meeting to review this event with the NRC staff. .This request was subsequently turned down.

TVA respectfully requests that the NRC Events Assessment Pancl reconsider the classification of the SQN event. TVA requests that the information provided to the NRC in this l

letter and at the June 27, 1997, meeting be used in the reassessment. TVA also requests to meet with the NRC to

. review the preliminary conclusions following the Panel's

! reassessment.

Please contact Mark J. Burzynski at (423) 751-2508 to schedule a meeting. ~

, sincerely, l

0 . Zeringua cc: U.S. Nuclear Regulatory Commission s ATTN:- Document Control Desk Washington, D.C. 20555 Mr. Ronald W. Hernan, Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. Ashok C. Thadani Deputy-Executive Director U.S.' Nuclear Regulatory Commission Mail Stop 05E6 Washington, D.C. 20555 cc: Continued on page 5

Mr.' Joseph callan

., Page'5-September 24, 1997

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-cc: - Mr.-Hugh L. Thompson Deputy Executive Director U.S. Nuqlear Regulatory commission

- Mail Sto,p.05E6 Washington, D.C. 20555 NRC Resident Inspector

- Sequoyah Nuclear Plant L 2600 Igou Ferry Road j' Soddy Daisy, Tennessee 37379 L

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