United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 94-64, Supplement 1: Reactivity Insertion Transient and Accident Limits for High Burnup Fuel

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

                                 April 6, 1995

                                             AND ACCIDENT LIMITS FOR HIGH      
                                             BURNUP FUEL


All holders of operating licenses or construction permits for nuclear power
reactors and all fuel fabrication licensees.


The U.S. Nuclear Regulatory Commission (NRC) is issuing this supplemental
information notice to provide addressees with additional information on high
burnup fuel performance data acquired since the original notice and to discuss
NRC and industry actions.  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 are not NRC requirements; therefore, no specific
action or written response is required.  


In the original information notice, dated August 31, 1994, the NRC staff noted
recent experimental data suggesting that high burnup fuel could be more prone
to failure during design-basis transients and reactivity insertion accidents
than previously thought.  These data, on the relationship between fuel failure
enthalpy and burnup for pressurized water reactor fuel rods tested in foreign
experimental facilities, indicated that failure initiation enthalpy thresholds
(measured in differential joules per gram) may be lower than those considered
in the evaluation of currently approved fuel burnup limits.  On October 26,
1994, the NRC staff presented additional technical information at the NRC 22nd
Water Reactor Safety Information Meeting (WRSM).


The data prompting the original information notice raised concerns about the
adequacy of current fuel damage criteria for reactivity transients.  The
current fuel enthalpy limit criteria are (1) 1172 joules per gram (J/g)    
[280 calories per gram (cal/g)] (peak radially averaged), to ensure fuel
coolability, and (2) for boiling water reactors, 711 J/g [170 cal/g], as the
measure of fuel rod cladding failure (by boiling transition).  The recent
data, presented at the WRSM, indicate that fuel rod cladding failure might
occur at enthalpy conditions of 126 J/g [30 cal/g] for high burnup fuel  
(i.e., fuel with more than 60 gigawatt-days per metric ton [GWd/t] uranium).

9503310049.                                                            IN 94-64, Supp. 1
                                                            April 6, 1995
                                                            Page 2 of 3

These data did not provide information on the enthalpy limits for fuel
coolability.  The NRC staff is closely following work to confirm the validity
of the preliminary results by verifying the conditions of the experimental
tests.  The NRC is also reviewing data reduction, data interpretation, and the
implications of the observed failure results at low enthalpy rise levels for
the safety evaluation of light water reactor design-basis transients and

On October 27, 1994, the NRC staff held a public meeting with nuclear industry
representatives, including fuel vendors and owners groups, to discuss the
regulatory and safety issues regarding the new experimental data on RIAs with
high burnup fuel.  The purpose of the public meeting was to discuss the impact
of the new information and planned NRC actions.  Robert C. Jones, Chief,
Reactor Systems Branch, issued a letter to the fuel vendors on November 14,
1994, that transmitted the WRSM papers and requested industry action
(Accession No. 9411220131).*

The NRC staff has contracted with three national laboratories to perform
various safety analyses for high burnup fuel.  It will then define best-
estimate failure criteria, based on reactivity insertion data, and will
consider changes to existing fuel failure criteria.  Although, in view of the
recent data, additional fuel failures could occur during design-basis events,
fuel coolability is expected to be maintained.  The staff has performed a
preliminary assessment and concludes that no immediate concerns for public
health and safety are raised.  

The industry has performed an initial generic safety assessment of the
preliminary data and concludes that there is no significant impact on the
public health and safety.  Their assessment and related information was
provided to the staff in a letter of December 28, 1994, from the Nuclear
Energy Institute (Accession No. 9503280347).*  The staff plans continuing
interaction with the industry until final resolution of this issue.

*Copies of these documents are available for inspection and copying at the NRC 
Public Document Room, 2120 L St., NW, Washington, DC  20037..                                                            IN 94-64, Supp. 1
                                                            April 6, 1995
                                                            Page 3 of 3

This supplemental 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   
Office of Nuclear Reactor Regulation (NRR) project manager.

                                    /s/'d by BKGrimes

                                    Brian K. Grimes, Director
                                    Division of Project Support
                                    Office of Nuclear Reactor Regulation

Technical contacts:  L. E. Phillips, NRR        
                     (301) 415-3232             

                     S. Wu, NRR
                     (301) 415-3284
1.  List of Recently Issued NRC Information Notices
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