Resolution of Enhanced Fission Gas Release Concern (Generic Letter 80-19)

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

                                March 10, 1980
Docket No. 50-263 

Mr. L. O. Mayer, Manager
Nuclear Support Services
Northern States Power Company
414 Nicollet Mall - 8th Floor
Minneapolis, Minnesota  55401

Dear Mr. Mayer: 

During the last several years, data have begun to indicate that the fission 
gas release rate from LWR fuel pellets is increased (enhanced) with burnup. 
Many of the current fuel performance analyses do not consider the impact of 
burnup release on safety.  By letters dated November 23, 1976, the NRC staff
requested all LWR licensees to assess the higher fission gas release for 
fuel burnups above 20,000 Megawatt-day per metric ton (MWD/T). 

Also, by NRC staff letter dated January 18, 1978, all U.S. LWR fuel 
suppliers were requested to revise their fuel performance analyses to 
include the enhancement of fission gas release at higher burnups. 

All responses to the November 23, 1976 letters have been reviewed.  We have 
concluded that no immediate licensing action is required for operating 
reactors.  This conclusion is valid for typical reported LWR fuel bundle and
batch burnups.  Any extension of these burnups or other factors which 
significantly affect fission gas release, LOCA PCT or fuel rod internal 
pressure is outside the scope of the conclusion. 

The effect of enhanced release on BWR ECCS performance has been discussed 
with General Electric (GE).  GE has pointed out that because of operational 
restrictions and physical limitations, the LOCA analysis is not limiting in 
high burnup fuel (25,000 MWD/T).  High burnup fuel generally cannot achieve 
linear power densities near the LOCA limit early in cycle.  The limiting 
fuel bundle is usually in its second cycle of reactor operations where 
burnup levels are below 20,000 MWD/T.  Late in a BWR fuel cycle, there is 
less axial power peaking reducing the feasibility for the fuel bundle power 
is generally limited by MCPR considerations.  Thus, it is unlikely that a 
high burnup bundle can exceed the ECCS performance criteria in case of a 
LOCA.  The argument is appropriate for Exxon fuel bundle design also based 
on the review of Exxon analyses for operating BWRs.  Therefore, no immediate 
licensing action is necessary on operating BWRs. 

Inasmuch as you and/or the staff will be evaluating all future reloads 
against fuel vendors' revised fuel performance codes which provide for 
increase in fission gas release at higher burnups, we consider this a 
satisfactory resolution of this concern. 
                                      Harold R. Denton, Director 
                                      Office of Nuclear Reactor Regulation 

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