ML18043B128

Provides Addl Info Re Gaseous Releases Described in 781030 Ltr.Cause of Increase in off-gas Activity Is Believed to Be Fuel Leakers & Corrective Action for High Gaseous Activity Is to Maintain Minimum Leakage by Close Surveillance

ML18043B128
Person / Time
Site:	Quad Cities
Issue date:	12/13/1978
From:	Kalivianakis N COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
NUDOCS 7812270225
Download: ML18043B128 (2)

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Commonwe. Edison Quad Cities Nuclear Power Station 22710 206 Avenue North Cordova, Illinois 61242 Telephone 309/654-2241 NJK-78-715 December 13, 1978 H. R. Denton, Director Off ice of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555

REFERENCE:

Quad-Cities Nuclear Power Station Docket No. 50-254, DPR 29, Unit 1 Docket No. 50-265, DPR 30, Unit 2 Appendix A, Sections 3.8.B.3.c(l) and 3.8.B.3.b.

Dear Mr. Denton:

The purpose of this letter is to provide you with additional information concerning our gaseous releases as described in my letter of October 30, 1978. Additional investigation of possible causes for the increase in the main chimney release rates during Jul~, 1978, identified a significant increase in Unit l off-gas recombiner effluent activity in July. The cause of this increase in off-gas activity is fuel leakers. This theory is corroborated by a corresponding increase in reactor water iodine activity. An increase in the fission product inventory in reactor water would cause an increase in activity releases from normal primary system leakage. This would then cause an increase in the effluent activity.

Since the initial report, close surveillance of leakage throughout the plant has been maintained, including entry into the primary containment to identify and stop suspected leakage. As a result, it is felt that during the current calendar quarter, leakage has been maintained at a m1n1mum. Nevertheless, gaseous effluent release rates have remained above the design objective limit.

Consideration must also be given to inherent conservatism in our methods for measuring effluent radioactivity. In accordance with our Technical Specifications, these measurements are performed by gross beta counting.

For this analysis, it is conservatively assumed that all nuclides measured after an eight-day decay have a half-life of eight days. For long lived cesium and cobalt isotopes, the resulting decay correction can overestimate the effluent activity for these isotopes by a factor of as much as two.

The gross activity method of measurement also necessitates the use of an assumed constant counting efficiency for all nuclides. The measured counting efficiency for barium and lanthanum, a parent-daughter equilibrium comprising a major contribution to our particulate releases, is more than a factor of two higher than that assumed for gross activity calculations.

7812270~~

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e This also causes overestimation of effluent activities. Typically, one-half of the gross activity calculated release is identifiable by isotopic analyses. Thus, it can be seen that the gross activity method may significantly overestimate the actual gaseous effluent activity.

Our corrective action for the high gaseous activity is to maintain primary system leakage at a minimum by continued close surveillance of all plant areas. In addition, the fission product inventory available for release will be reduced when leaking fuel is replaced during the Unit l refueling outage scheduled to begin in January, 1979.

N. J. Kali vi anak is Station Superintendent NJK:RAF:aaa cc: M. S. Turbak L. Hueter, NRC Region I II