[ RadSafe ] NRC Computer Program COGAP

Hal C hacrad at comcast.net
Thu Oct 27 12:08:13 CDT 2005

This is a request for help on determining the correct reactor decay profile for iodine.

In 1982, the NRC via Los Alamos Lab produced a computer code, COGAP, and a report, NUREG/CR-2847, "COGAP: A Nuclear Power Plant Containment Hydrogen Control System Evaluation Code".  One of the equations (From Standard Review Plan 6.2.5, revision 2, NUREG-0800, page 6.2.5-13.) for iodine reactor decay is (FORTRAN) (my coding)

HI = 1.0E+22 * ( 0.8197*exp(-6.1E-5*t) + 0.3279*exp(-1.1E+5*t) + 0.0574*exp(-1.0E-6*t))

If we use the above equation in an Excel workbook and attempt to reproduce the two sample cases in the COGAP code (not having the code ourselves), we find the results to be off by a factor of 0.8 roughly.  If the sign of the exponent on the second exponential term is changed from plus to minus ( 0.3279*exp(-1.1E-5*t) ), the results agree with the COGAP to within a factor of 0.97.  

If you own a copy of the COGAP code, would you please look at the coding and confirm the sign on the exponent term to be plus or minus?  

The NRC says the sign should be plus.

Hal Careway

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