United States Nuclear Regulatory Commission - Protecting People and the Environment

Odyn Code Calculation (Generic Letter 80-91)


                              UNITED STATES 
                          WASHINGTON, D.C. 20555 

                             November 4, 1980 


The use of the ODYN code to calculate pressurization transients has been 
reviewed extensively by the staff and discussed with the General Electric 
Company. We have found that ODYN provides acceptable best estimate 
calculation predictions of the core responses to pressurization transients. 
A safety evaluation describing the basis for this conclusion will be mailed 
to you in the very near future. This letter is for the purpose of advising 
you as early as possible of our requirements for implementation of ODYN for 
licensing basis calculations performed by the General Electric Company. 
These requirements are applicable to license applications and all proposed 
license amendments, including core reloads for which analyses are provided 
by General Electric. 

Transient analyses performed by General Electric supporting reload 
submittals received prior to February 1, 1981, will be reviewed taking into 
account the results of recent generic transient analyses with ODYN. 
Appropriate CPR penalties will be applied on a case by case basis. Transient 
analyses performed by General Electric supporting reload submittals received 
after February 1, 1981, must contain appropriate ODYN analyses in place of 
those previously performed with REDY for the limiting transients. Generally, 
these will include generator load rejection/turbine trip without bypass 
(whichever is limiting), feedwater controller failure - maximum demand, and 
main steamline isolation valve closure (to satisfy ASME code pressure 
requirements). After January 1982, all operating BWRs with General Electric 
analyses must have the limiting transients recalculated with the ODYN code, 
even if no reload submittal has been received. The transients analyzed with 
ODYN must be justified to be the limiting transients. 

General Electric has provided an ODYN analysis for the two most limiting 
events for BWR 3 and BWR 4 plant types and has committed to provide analyses
for a BWR 2 plant type by November 1, 1980. Any 

                                  - 2 -                  November 4, 1980 

penalties resulting from our review of the analyses for any plant type will 
be applied to all plants of that type until plant-specific calculations have
been performed with ODYN for the two most limiting transients. 


                                        Darrell G. Eisenhut, Director 
                                        Division of Licensing 

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