NRC Generic Letter 85-16, High Boron Concentrations

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WASHINGTON, D. C. 20555

August 23, 1985

TO ALL LICENSEES OF OPERATING REACTORS AND APPLICANTS FOR AN OPERATING LICENSE (Generic Letter 85-16)

Gentlemen:

SUBJECT: HIGH BORON CONCENTRATIONS

Boron Injection Tanks were originally incorporated into Westinghouse plant designs as a means of mitigating steam line break events. To overcome the reactivity addition resulting from a rapid cooldown, a high concentration of boron in the form of boric acid was used in the injection tanks. High concentrations of boron result in maintenance and operational burdens to licensees because of the need to prevent boron precipitation.

In the recent past, there have been incidents at operating reactor plants in which boric acid has crystallized in the internals of vital safety related pumps and piping, thereby rendering those systems inoperable. One example is an incident at Indian Point 2 on December 28, 1984 in which the safety injection system was inoperable because all three pumps in the system were frozen with crystallized boric acid.

Over the past several years, the analysis methods for calculating the consequences of a steam line break have improved. These revised calculations demonstrate that the negative reactivity that needs to be added is lower than originally thought and consequently the need for highly concentrated

'boron injection is reduced or eliminated. Many licensees with Westinghouse plants (e.g. Surry 1&2), have requested that they be allowed to either physically remove the boron injection tank from the safety injection piping, or at least reduce boron concentrations in the tank to the leVels safely used in other sections of the safety injection piping and refueling water storage tank (e.g., to 2000 ppm). To support their requests, licensees have submitted new analyses of the steam line break event that demonstrated the regulatory criteria (i.e., 10 CFR 100 guidelines dose values) were met. The staff has reviewed these analyses and granted these requests.

In light of the safety risks inherent in the present system and these new calculations which show a reduced need for boron injection, the staff encourages you to reevaluate the need for maintaining high concentrations of boron in your boron injection tanks. In the event you perform a reanalysis of the steam line break event or any other event which requires or assumes credit for boron injection, the staff is willing to consider a relaxation of excess conservatism in your analyses, provided the relaxation can be justified. As a result, it may be possible to remove the boron injection tanks or reduce the boron concentration.

8508210258If you require any further information regarding this subject, please contact your project manager.

Hugh L. Thompson, Director Division of Licensing Office of Nuclear Reactor Regulation

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