United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 90-08: KR-85 Hazards From Decayed Fuel

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                              February 1, 1990


Information Notice No. 90-08:  KR-85 HAZARDS FROM DECAYED FUEL


Addressees:

All holders of operating licenses or construction permits for nuclear power 
reactors and holders of licenses for permanently shutdown facilities with 
fuel on site.  

Purpose:

This information notice alerts addressees to potential problems resulting 
from the accidental release of Kr-85 from decayed fuel.  It is expected that 
recipients will review the information for applicability to their facilities 
and consider actions, as appropriate, to avoid similar problems.  However, 
suggestions contained in this information notice do not constitute NRC 
requirements; therefore, no specific action or written response is required.  

Description of Circumstances:

During the licensing reviews for the Oconee independent spent fuel storage 
installation, and in the decommissioning of the La Crosse and Dresden Unit 1 
power reactors, the NRC staff analyzed the radiological hazards associated 
with the gases in decayed spent fuel.  The age of the nuclear power industry 
and the lack of a permanent repository for spent fuel have resulted in the 
accumulation of decayed spent fuel.  Decayed spent fuel is manipulated after 
long shutdowns of operating reactors, during spent fuel pool re-racking, 
during movement to alternate reactor sites or independent spent fuel storage 
installations, and during decommissioning.  Analysis of hypothetical 
accidents involving decayed spent fuel has focused attention on potential 
difficulties that could be associated with the exposure of onsite personnel 
to an accidental release of Kr-85.  Kr-85 is a noble gas fission product 
that is present in the gaps between the fuel pellets and the cladding.  It 
has a 10.76-year half-life, and, as a result of the considerably shorter 
half-lives of virtually all other gaseous fission products (I-129 being the 
exception, but in low abundance), Kr-85 becomes increasingly the dominant 
nuclide in the accident source term for gap releases as decay times 
increase.  After 2 weeks of decay, Kr-85 is a significant nuclide in the 
source term, and after 190 days of decay, it is the predominant gaseous 
nuclide for a gap release.  The unusual decay characteristics of Kr-85 give 
cause for focusing attention on the onsite consequences of a gap release 
from decayed fuel.  





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                                                            IN 90-08
                                                            February 1, 1990
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Discussion: 

Kr-85 emits beta radiation with a maximum energy of 0.67 MeV for 
99.6 percent of the decays and 0.51 MeV gamma radiation for 0.4 percent of 
the decays.  Consequently, direct exposure to this gas would result in a 
dose to the skin approximately 100 times the whole-body dose.  Analysis of 
the relative consequences (in terms of radiological doses) of a cask-drop 
accident as a function of decay time of the fuel is illustrated in Figure 1.  
In the event of a serious accident involving decayed spent fuel, protective 
actions would be needed for personnel on site, while offsite doses (assuming 
an exclusion area radius of 1 mile from the plant site) would be well below 
the Environmental Protection Agency's Protective Action Guides.  
Accordingly, it is important to be able to properly survey and monitor for 
Kr-85, and to assess the skin dose to workers who could be exposed to Kr-85 
in the event of an accident with decayed spent fuel.  

Licensees may wish to reevaluate whether Emergency Action Levels specified 
in the emergency plan and procedures governing decayed fuel-handling 
activities appropriately focus on concern for onsite workers and Kr-85 
releases in areas where decayed spent fuel accidents could occur, for 
example, the spent fuel pool working floor.  Furthermore, licensees may wish 
to determine if emergency plans and corresponding implementing procedures 
address the means for limiting radiological exposures of onsite personnel 
who are in other areas of the plant.  Among other things, moving onsite 
personnel away from the plume and shutting off building air intakes downwind 
from the source may be appropriate.  

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate NRR project 
manager.




                              Charles E. Rossi, Director
                              Division of Operational Events Assessment
                              Office of Nuclear Reactor Regulation

Technical Contacts:  Charles S. Hinson, NRR
                     (301) 492-3142 

                     Robert A. Meck, RES 
                     (301) 492-3737

Attachments:  
1.  Figure 1, Dose Consequences of a 
    Spent Fuel Drop Accident
2.  List of Recently Issued NRC Information Notices

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