ML20027E789

Revised LER 82-052/03X-1:on 820928,reactor Quadrant Power Tilt in Wx Quadrant Exceeded Tech Specs.Caused by Xenon Oscillation Producing Large Negative Imbalance.Control Rod Group 7 Borated Out to Reduce Negative Imbalance

ML20027E789
Person / Time
Site:	Davis Besse
Issue date:	11/04/1982
From:	Dibert D TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20027E784	List: ML20027E783 ML20027E789
References
LER-82-052-03X, LER-82-52-3X, NUDOCS 8211160175
Download: ML20027E789 (3)

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l EVENT DESCRIPTION AND PROSABLE CONSEQUENCES h j o I (NP-33-82-61) At 0745 hours0.00862 days <br />0.207 hours <br />0.00123 weeks <br />2.834725e-4 months <br /> on 9/28/82, the Shift Supervisor found the reactor quad- I r.u sia l rant power tilt (QPT) in the WI quadrant to be exceeding its Technical Specification I g l steady state limit by approximately 0.2%. This places the unit in the action state- I o s I ment of Technical Specification 3.2.4 which requires within two hours either reduce I oe i the QPT to within limits or reduce the thermal power, high flux trip setpoints, and 1 -

l the flux- d flux-flow setpaint per Technical Specification Action Statement i o8 l 3.2.4(a)(1)(b) . QPT was brought within the steady state limit by 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br />.

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TOLEDO EDISON COMPANY

, DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-82-61 DATE OF EVENT: September 28, 1982 FACILITY: Davis-Bessee Unit 1 IDENTIFICATION OF OCCURRENCE: Reactor Quadrant Power Tilt slightly exceeding the steady state Technical Specification limit Condtitions Prior to Occurrence: A5 0745 hours0.00862 days <br />0.207 hours <br />0.00123 weeks <br />2.834725e-4 months <br /> on September 28, 1982, while continuously monitoring the computer display of reactor parameters, the Shift-Supervisor found the reactor quadrant power tilt (QPT) in the WX quadrant to be exceeding its Technical Specification steady state limit (3.03%) by approximately 0.2%, as measured by the symmetrical incore detector system. This placed the unit in the action' statement of Technical Specification 3.2.4. This requires within two hours either reduce the QPT to within limits or reduce the thertnal power, high flux trip setpoints and the flux-delta flux-flow setpoint per Technical Specification Action Statement 3.2.4(a)(1)(b). QPT was brought within the steady state limit at 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br />.

Designation of Apparent Cause of Occurrence: Due to the natural flow character-istics of the Davis-Besse Reactor Coolant System and the " cross-core" shuffle of the fuel for Cycle 3 which was done during the 1982 Refueling, a QPT of approxi-mately 2.60% has existed since startup of this cycle in the WX quadrant. This tilt was reduced to approximately 2.40% by rerating feedvater inducing a 4Tc across the core of about 2*F. On September 27, 1982 a plant transient occurred which caused the 2*F 4 Tc to be removed and an axial xenon oscillation. The combination of these two things caused t% QPT in the WK quadrant to exceed the steady state limit as the zenon oscillation produced a large negative imbalance on September 28, 1982.

Analysis of Occurrence: There was no danger to the health and safety of the public or station personnel. For there to be any adverse effects on the fuel when the QPT is beyond its steady state limit, three conditions must be met:

(1) control rods beyond their insertion limits, (2) the imbalance outside its Technical Specification limits, and (3) a loss of coolant accident must occur.

Since these three conditions did not exist and tilt was only slightly above its steady state liait, there was no adverse effect on the fuel.

LER f82-052

TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-82-61 PAGE 2 Corrective Action: The Control Rod Group 7 was borated out to reduce the nega-tive imbalance and a feedwater induced 4 Tc of approximately 2'F was produced across the core. These two actions reduced the QPT to less than the steady state limit within the two hour requirement of the Technical Specification action state-ment. A memo was written to the reactor operators explaining why we have a l higher than normal tilt within the core this cycle, what to expect this tilt to do over core life, and what steps to take should the Technical Specification limit on QPT be approached. Over core life the natural tilt of the core should reduce to .6 to .8 in the WK quadrant due to burnup of the fuel.- The 4 Tc induced will be removed when the QPF is reduced by fuel burnup to the point where removing the d Tc won't cause QPT to approach the T:S. limit.

Failure Data: There have been no previous similar occurrences.

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