Clarification of Equivalent Control Capacity FOP Standby Liquid Control Systems (Generic Letter No. 85-03)

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                           WASHINGTON, D.C. 20555

                              January 28, 1985

TO ALL BOILING WATER REACTOR LICENSEES AND APPLICANTS  

Gentlemen: 

SUBJECT:  CLARIFICATION OF EQUIVALENT CONTROL CAPACITY FOP STANDBY LIQUID 
          CONTROL SYSTEMS (Generic Letter 85-03) 

Paragraph (c) (4) of 10 CFR 50.62 states, in part: 

     Each boiling water reactor must have a standby liquid control system 
     (SLCS) with a minimum flow capacity and boron content equivalent in 
     control capacity to 86 gallons per minute of 13 weight percent sodium 
     pentaborate solution. 

The "equivalent in control capacity" wording was chosen to allow flexibility
in the implementation of the requirement. For example, the equivalence can 
be obtained by increasing flow rate, boron concentration or boron 
enrichment. 

The 86 gallons per minute and 13 weight percent sodium pentaborate were 
values used in NEDE-24222, "Assessment of BWR Mitigation of ATWS, Volumes I 
and II," December 1979, for BWR/4, BWR/5 and BWR/6 plants with a 251 inch 
vessel inside diameter. That different values would be equivalent for 
smaller plants was recognized in NEDE-24222: 

     The flow rates given here are normalized from a 251-inch-diameter 
     vessel plant to a 218-inch-diameter vessel plant, i.e., the 66 GPM 
     control liquid injection rate in a 218 is equivalent to 86 GPM in a 
     251. This is done to bound the analysis...(pp. 3-12) 

The important parameters to consider in establishing equivalence are vessel 
boron concentration required to achieve shutdown and the time required to 
achieve that vessel boron concentration. The minimally acceptable system 
should show an equivalence in these parameters to the 251 inch diameter 
vessels studied in NEDE-24222. 

There are no reporting requirements associated with this generic letter. 

                              Sincerely, 


                              Darrell G. Eisenhut, Director 
                              Division of Licensing 
                              Office of Nuclear Reactor Regulation  





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