ML20087L336

Ao:On 740529,minor Leak Discovered in Main Steam Safety Valve & Secondary Side Steam Pressure Substantially Reduced to Reseat Safety Valve & Terminate Minor Leak. Caused by Incorrect Concentration of Borated Water

ML20087L336
Person / Time
Site:	Point Beach
Issue date:	06/08/1974
From:	Burstein S WISCONSIN ELECTRIC POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8403270149
Download: ML20087L336 (4)

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• -p/ June 8, 1974 cp Mr. John F. O' Leary, Director Directorate of Licensing U. S. Atomic Energy Commission Washington, D. C. 20545

Dear Mr. O' Leary:

DOCKET NO. 50-266 VIOLATION OF TECHNICAL SPECIFICATION LIMITING CONDITION FOR OPERATION 15.3.10.A.4 POINT BEACH NUCLEAR PLANT This letter is to report the details of an abnormal oc-currence at Point Beach Nuclear Plant, Facility Operating License No. DPR-24, as defined by Section 15.1.a.B of the Technical Spe-cifications. This written report, filed in accordance with Sec-tion 15.6.6.A.2 of the Technical Specifications, follows a tele-phone report made on the incident to Mr. K. R. Baker of Region III, Directorate of Regulatory Operations, on May 30, 1974, as required by sone. inn 15,6.6.A.1 of r.he Technical Speci ficati one:.

Following the Unit 1 refueling shutdown of April 6 to May 26, 1974, and prior to power operation of the unit, a minor leak of a main steam safety valve was discovered May 29, 1974, and the decision wasmade to substantially reduce secondary side steam pressure to see if a lower secondary steam pressure would permit reseating of the safety valve and termination of the minor leak. While not the subject of this report, this action was in fact successful.

Partial cooldown of the reactor coolant system for the above mentioned purpose was accomplished between 0140 hours0.00162 days <br />0.0389 hours <br />2.314815e-4 weeks <br />5.327e-5 months <br /> and 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> on May 30, 1974, and heatup was initiated at approxi-mately 0730 hours0.00845 days <br />0.203 hours <br />0.00121 weeks <br />2.77765e-4 months <br /> the same date.

In conjunction with the heatup, the Reactor Engineer utilized the opportunity to perform additional core physics tests to substantiate and verify previously collected data. The reactor was taken critical during the course of these physics tests at 1010 hours0.0117 days <br />0.281 hours <br />0.00167 weeks <br />3.84305e-4 months <br /> on May 30, 1974. The data collected at this time was such as to raise a question on the part of the Reactor Engineer and he requested that an analysis of the boron concentration of

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t Mr. John F. O' Leary June 8, 1974 the reactor coolant system be conducted. The analysis indicated a boron concentration of 1435 ppm, this being 43 ppm below the expected valve of 1478 ppm. Boration was immediately initiated to return the reactor coolant system to the desired concentration.

An investigation of the reasons leading to the 43 ppm reduction in boron concentration disclosed that during the cool-down of the reactor coolant system the blender controls had been correctly set to maintain the correct concentration of 1478 ppm but the blender, in fact, had delivered borated water to the reactor at approximately 20% less concentrated than the desired value. The lower boron concentration from the blender was caused by the actual concentrated boric acid flow rate to the blender being lower than the flow rate instrumentation indicated to the operator.

Calculations by Reactor Engineering then determined that based on the gradual reduction to 1435 ppm boron ccncentration dur-ing the cooldown, the Technical Specification provision 15.3.10.A.4 was violated at approximately 0200 hour0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br /> on May 30, 1974, and con-tinued until the commencement of the physics test program at 0950 hour0.011 days <br />0.264 hours <br />0.00157 weeks <br />3.61475e-4 months <br /> the same date.

For convenience in analyzing this report, Section 15.3.10 A.4 of the Point Beach Nuclear Plant Technical Specifica-tions is quoted in full, as follows:

"When the reactor is subcritical, except for ,

physics tests, the critical rod position, i.e.,

the rod position at which criticality would be ,

achieved if the control rods were withdrawn in normal sequence with no other reactivity changes, shall not be lower than the insertion limit for zero power." j It should be stressed that at all times the reactor was sufficiently subcritical to protect the core from all potential '

reactivity accidents.

Following the loading of two regions of new fuel in the Point Beach Nuclear Plant Unit 1, core physics tests indicated that the temperature coefficient for the core was less negative than de-sign calculations had indicated, this becoming more pronounced, of course, as boron concentration increased. Conservative calculations indicated a negative temperature coefficient commenced at 530*F and 1505 ppm boron; 1500 ppm boron was therefore chosen as the maxi-mum permissible boron concentration at the BOL zenon free condi-tion. Critical rod position under these conditions was calculated

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. d U Mr. John F. 0" Leary June 8, 1974 to be betwcon 160 and 170 steps on Control Bank B. With the zero power insertion limit at 153 steps on B, it was decided to insert the part length rods to their maximum integral worth to gain some additional maneuverability for operation. This raised the criti-cal rod position to 190-200 steps on Control Bank B, thus giving the operator a " window" from 153 to 200 steps on Bank B in which to take the reactor critical while still maintaining a conserva-tively negative temperature coefficient and being above the in-sertion limit.

The reactor was taken subcritical prior to the reduction in secondary system pressure because the primary system has to be cooled down and this would cause the temperature coefficient to become positive. This cooldown resulted in the reduction of the boron concentration which caused the critical rod position to move down, eventually closing the window described above and creating a violation of Technical Specification Section 15.3.10.A.4.

Calculations indicated that throughout this occurrence a shutdown margin in excess of 4% Ak/k remained at all times.

These calculations accounted for such possibilities as (a) a stuck rod of maximum worth .66 ok/k; (b) an ejected rod of .91 ok/k worth; (c) depressurization of the reactor coolant system. It should be noted that by snutting cown tne reactor privt Lu Lim cooldown, ' the stuck rod worth was reduced from 1.13 to 0.66 Ak/k because the higher worth stuck rods were inserted in the core.

No attempt was made to take the reactor critical until the commencement of the core physics test. Achieving criticality below the minimum rod insertion limit during a physics test is covered by Section 15.3.10.A.4 of the Point Beach Nuclear Plant Technical Specifications.

An analysis of the reactor configuration at the time of the occurrence and a review of the event by the Manager's Super-visory Staff has determined that the occurrence did not pose a hazard to the health and safety of the public.

A tag has been placed on the controls of the boric acid blender to indicate to the operator the present percentage error between actual and indicated flow rate of boric acid to the blen-der. A maintenance request has been issued to the Instrument and Control Department to place a correction factor into the instru-mentation such that the indicated and actual flow rates for boric acid injection to the blender coincide.

Very truly yours, Sol Burstein ExecftiveVicePresident

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Mr. John F. O' Leary - 4- June'8, 1974 5

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I cc: Mr. James G. Keppler,-Regional Director Directorate of Regulatory Operations, Region III

U. S. Atomic Energy Commission 1

799 Roosevelt Road Glen Ellyn, Illinois 60137, 4 I i

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