ML19262A228

Abnormal Occurrence 75-10:on 750409,reactor Criticality at 505 F Primary Coolant Temp.Caused by Lack of Detailed Calculational Guidance in Boron Concentration Control Operating Procedure.Reactor Made Subcritical

ML19262A228
Person / Time
Site:	Three Mile Island
Issue date:	04/10/1975
From:	Herbein J METROPOLITAN EDISON CO.
To:
Shared Package
ML19262A223	List: ML19262A222 ML19262A228
References
NUDOCS 7910260567
Download: ML19262A228 (2)

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.TROPOLITAN EDtSON COMPANY sussimaav or ocnta.n rueuc uriuries coneo.urw.y FFICE BOX 480 M COLETOWN. PENN3YLV ANIA 17C57 TELEPHCNE 717 944 4041 April 10,1975 '[u/Y d up 2V Mr. J.P. O'Reilly D -

D ,l.,

Directorate of Regulatory 1

/iD r co.g Regicn I 631 Parr. Avenue King of Prussia, Pa. 19406 hi ij&O Operating License CPR-50 Docket 50-289

Subject:

Abnormal Occurrence No.,A0 75-10

Dear Mr. O'Railly:

This telegrari is to confirm the telecon between Mr. Burt Davis (Region I-DE:3),

and J.G. Hercein (Station Superintendent) at 11G0 hours, April 9,1975.

The following report is submitted in accordance with paragraph 6.7.2.a.1 (page 6-11) of the technical specificaticns.

On April 9,1975 at 0730 hours0.00845 days <br />0.203 hours <br />0.00121 weeks <br />2.77765e-4 months <br />, while heating up and skultaneously deborating the reactor coolant system in preparation for critical operations, reactor criticality occurred at a primary ccolant tempemture of 5050F. This is cen-trary to the recuirement of technical specification 3.1.3.1. While ci itical, reactor pcwer level increased to 2 x 10-11 a@s on the intermediate range and 5000 cps on the source range at a start up rate of 0.14 CPM.

The reactor was cude su' o critical by jecater thap 1% oK/K by the insertion of Group 4 contn)! reds and tne addition of conceintrated borte acid to the reactor coolant systen.

Subsequent investigation into the cause of criticality at 50SoF, revealed that the boren concentration control operating precedure did not provide detailed calculational guidance for sir altaneous deboration and heat un. In the absence of detailed guidance the reduced boron concentration desired at 5320 was achieved at 6050 Since, due to negative temperature deficit, the reactcr shutdown r.argin Wds loner at SG50, the additional decrease in SCM by premature deborating caused criticality.

Irrnediate procedure changes have been Instituted which prohibit deboration wnile in the iteat up r.2de, i.e. , prine to $250F. -

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Page 2 api ~i l ,1Y The above procedure changes will remain in effect until detailed calculational guidance for si.vitaneous deboration and heat up is developed and incorporated into the appropriate procedure.

Very truly yours, a Il r inM

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-y 4'G. H rhein Station Superintendent JGi/d n '

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