ML20076F334

Ro:On 830530,reactor Shut Down When Shutdown Margin During Criticality Violated Tech Specs.Caused by Difference in Partial Fuel Element Added on 830525.Reactor Shut Down 830606.Control Rods Recalibr.Procedures Changed

ML20076F334
Person / Time
Site:	University of Virginia
Issue date:	06/09/1983
From:	Brenizer J VIRGINIA, UNIV. OF, CHARLOTTESVILLE, VA
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
NUDOCS 8306140005
Download: ML20076F334 (2)

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UNIVFRSITY OF VIRGINIA SCHOOL OF ENGINEERING AND APPLIED SCIENCE w C H AR LOTTESVILLE. 22901 CEPARTMENT OF NUCLEAR ENQiN EERIN G AND ENGINEERING ' PHYSICS TELEPHONE: 504-924-7136 EEACTOR FACILITY June 9, 1983 CS Mr. James P. O'Reilly U. S. Nuclear Regulatory Commission c=

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Dear Mr. O'Reilly:

This is to inform you as required by Section 6.4.2 of the Technical Specifications for the UVAR reactor, Facility License R-66, Docket No. 50-62 of a reportable occurrence.

Technical Specification 3.1 requires a shutdown margin of greater than 0.4% Ak/k with the highest worth rod fully withdrawn and a cold, xenon free condition with secured experiments in place. In violation of this requirement, the UVAR was operated approximately 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> and 25 minutes with a shutdown margin of approximately 0.2% Ak/k. This operation did not pose a threat to the public health and safety as the total shutdown margin with all rods inserted was approximately 2.6% Ak/k without xenon. .

On Monday, May 23, 1983 the UVAR reactor was started and the shutdown margin measured to be 1.00% Ak/k. On Wednesday, May 25, 1983 the reactor was shutdown to test a new experiment. The experiment had been previously measured to be worth -0.31% Ak/k, In attempting to restart the reactor, the negative xenon reactivity could not be overcome and the reactor was shutdown. A check of two previous loadings indicated that a partial fuel element added to the periphery of the core was worth +0.6% Ak/k. It was decided to add a partial fuel element and prior to startup, the shutdown margin was calculated as follows:

1.00% (on 5-23-83)

+0.07% (Burn-up from 5-23-83 to 5-25-83)

+0.31% (worth of experiment)

-0.6% (positive worth of partial fuel element) 0.78% (new shutdown margin) l The reactor was then started and operated for approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. The shutdown margin with the highest worth rod fully withdrawn plus the xenon in the reactor had a reactivity worth of approximately 2.9% Ak/k. The reactor was shutdown after approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> operation and the experiment removed. The shutdown margin was then estimated to be (0.78 - 0.31) Ak/k or 0.47% Ak/k. Since

- OFFICIALC 8306140005 830609 DR ADOCK 05  %-

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1 Letter to James P. O'Reilly l June 4, 1983 ,

Page 2 1 this is within the Technical Specification limits, it was agreed to recommence operation. The reactor was started at 7:00 p.m. on May 25, 1983 and operated at two megawatts until 11:25 a.m. on Thursday, May 26 or about 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> and 25 minutes. The reactor remained shutdown from 11:25 a.m. on May 26, 1983 until Monday afternoon, May 30, 1983 at 5:30 p.m. In preparation for an experinental run, the staff removed a graphite element worth +0.16% Ak/k from the front row of the grid plate. The reactor was started to do a reactivity check prior to loading the experiment. When the reactor achieved criticality the shutdown margin was measured to be 0.35% which would have been in violation of Section 3.1 of the Technical Specifications if the reactor had been operated at powers above 1 kw. The reactor was shutdown immediately and the Reactor Supervisor was notified by telephone (the Director of the Reactor Facility was out of town).

After a series of measurements of the reactivity worth of several experiments and graphite elements, an experiment was removed from the reactor core region and the shutdown margin was measured to be 0.71%. The reactor war then taken to a 2 megawatt power level at 9:48 p.m. on bhy 30, 1983.

An investigation by the Reactor Starf on Monday, May 30, and Tuesday, May 31, 1983 revealed that the partial fuel element added to the reactor on May 25, 1983 was worth 0.83% Ak/k instead of 0.6% as originally estimated. Thus, during the 16 hour1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> and 25 minute run from 7:00 p.m. Wednesday, May 25, 1983 until 11:25 a.m., Thursday, May 26, 1983, the reactor was operated with a clean, cold, shutdown margin of 0.19% Ak/k. Mr. J. P. Farrar, Reactor Supervisor placed a call to your office at approximately 2:40 p.m. on Tuesday, May 31, 1983 and Mr.

Caudic Julian was informed of the incident. Mr. Austin Hardin of your office called our facility twice on Wednesday, June 1,1983 for more information and informed us that two inspectors from the North Anna plant would be at our facility on Thursday, June 2, 1983 to investigate the incident. Messrs. M. Shymlock and J. Leahman of your office vere at our facility on Thursday and Friday, June 2nd and 3rd to investigate the incident.

The UVAR reactor was shutdown on June 6,1983. The control rods are currently being recalibrated and the experiment reactivity worths remeasured. The reactor will not be operated at power again until procedure changes are made concerning shutdown margin and experiment handling and reviewed and approved by our Reactor Safety Committee. Your office will be notified before the reactor is operated at power.

The incident will be reviewed by our Reactor Safety Committee on Thursday, June 9, 1983.

Sincerely,

! J. S. Brenizer, Jr., Director l UVA Reactor Facility JSB:ph l cc: T. G. Williamson l

J. P. Farrar 1 Reactor Safety Committee 1

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