ML20084F804

AO 250-75-1:on 750302,reactor Operated Outside Indicated Axial Flux Difference Target Band.Cause Attributed to Operators Not Understanding Tech Specs.New Procedures Will Be Discussed in Detail W/Operating Personnel

ML20084F804
Person / Time
Site:	Turkey Point
Issue date:	03/12/1975
From:	Schmidt A FLORIDA POWER & LIGHT CO.
To:	Rusche B Office of Nuclear Reactor Regulation
References
AO-250-75-1, NUDOCS 8304210282
Download: ML20084F804 (3)

Text

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Dear Mr. Case:

ABNORMAL OCCURRENCE NO. 250-75-1 MARCH 11, 1975 .

MARCH 2, 1975 OCCURRENCE DATE:

TURKEY POINT UNIT NO. 3 REACTOR OPERATION WITH AXIAL FLUX DIFFERENCE OUTSIDE TARGET BAND A. Conditions Prior to Occurrence No. 3 Unit was in steady-state power operation at 100% R.P.

with equilibrium Xenon established in the core until the unit was tripped by a non-nuclear system related occur-rence on March 1, 1975, at 7:20 p.m. The unit was returned

,, , to service at 1:01 a.m., March 2, 1975.

Load on the unit was increased at a controlled rate to

, 620 MWe (87% R.P.) over a period of seven hours.

B. Description of Occurrence About 9:45 a.m., March 2, 1975, it was concluded that the reactor had been operated outside the indicated axial flux difference target band for more than one hour (cumulative) in the preceding 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period specified in the Technical Specifications.

Immediate operator action was to reduce load on the unit from 620 MWe (87% R.P.) to 275 MWe (44% R.P.) and change the power range high neutron flux trip setpoint to a value of 55% R.P.

Load on the unit was maintained below 50% R.P. until the accumulated operating time outside the indicated axial flux difference was reduced to less than one hour in the pre-ceding 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period.

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' March 12, 1975 C. Designation of Apparent Cause of Occurrence The cause of this occurrence was attributed to the operators not fully understanding the requirements of the Technical Specifications for reactor operation outside the target band on axial flux difference.  ;

l D. Analysis of Occurrence Revl.ew and analyses of operating records concluded that about 65% of the accumulated time the reactor was operated out-side the indicated axial flux difference target band occurred when the reactor power level was less than 50% R.P. Strict contrcl of the indicated axial flux difference is not neces-sary av reactor power levels below 50% R.P. because of reduced average core power. Nonsymetrical power distribution and larger peaking factors are acceptable, at low reactor power levels, as far as local power density limits are concerned.

Operating records indicate that the reactor was operated with the indicated axial flux difference outside the target band for 31 -minutes at reactor power ,b9 tween 75% and 85% R.P.

During this time, the target band. limits were exceeded by less than 1%. When the load on the unit was greater than 50% R.P., the indicated flux difference was well within the outer envelope boundary conditions specified in the Technical Specifications. The instantaneous consequences u

of being outside the target band are not worse than a 10%

increment in peaking factor for axial flux difference in ,

the range +11 to -11 percent at 100% R.P.

l The long range consequences of reactor operation outside the l target band for more than one hour in any 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period ~are l associated with the effects of Xenon redistribution on the core. Since the total time the reactor was operated above 50% R.P. was less than four hours, it was concluded that this was insufficient time- for Xenon to adversely af fect axial power distribution in the reactor core.

During this occurrence, the reactor was protected-from adverse axial power distribution in the reactor. core by the overpower-AT protection system and the overtemperature AT protection system. Axial offset is a direct input to these reactor pro-tection systems and would reduce load automatically if'the measured axial offset approached the limits established for reactor protection. These reactor protection systems would automatically trip.the reactor if the established limits were exceeded.

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Mr. Edson G. d Page 2 a, Acting Director (}

March 12, 1975 An evaluation of the operating conditions at the time of this occurrence concluded that neither reactor safety nor the health and safety of the public was jeopardized by this occurrence.

E. Corrective Action When Operating Procedures are issued which implement changes '

to the Technical Specifications, these procedures will be discussed in detail with operating personnel to ensure that the change is clearly understood.

Special training material will be prepared, when appropriate, to supplement instructions given in operating procedures.

F. Failure Data This is the first abnormal occurrence involving reactor operation outside the indicated axial flux difference target band.

Very truly yours, c n!E Vice President Power Resources t

VTC:pg cc: Mr. Norman C. Moseley Jack R. Newman, Esquire i

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