10 CFR Part 50 Appendix K

["Tord P. Walderhaug" <tordw@mail.hrp.no>]

Dear Radsafers,

In Appendix K to Part 50 of 10 CFR, ECCS Evaluation Models, it is 
stated that:

The heat generation rates from radioactive decay of fission products
shall be assumed to be equal to 1.2 times the values for infinite
operating time in the ANS Standard (Proposed American Nuclear Society
Standards -- "Decay Energy Release Rates Following Shutdown of
Uranium-Fueled Thermal Reactors." Approved by Subcommittee ANS - 5,
ANS Standards Committee, October 1971). This standard has been
approved for incorporation by reference by the Director of the Federal
Register. 

The factor 1.2 comes from the uncertainties in the values 
of the ANS-5 of 20 %.

However, the ANS proposed standard from 1971 did not become an 
ANSI standard (American National Standards Institute). Instead 
another document from ANS, the ANSI/ANS-5.1 from 1979, revised in 
1994, became a standard. This document seems to give slightly lower 
values for the effect of fission product activity shortly after 
shutdown than the ANS-5, and the uncertainties are also lower.

My question is whether NRC has taken the ANSI/ANS-5.1 into account 
when evaluating the effect of an ECCS system, or if there are new 
regulations taken this into account.

Best regards,

Tord Walderhaug

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Tord P. Walderhaug
Institutt for energiteknikk
OECD Halden Reactor Project
P.O. Box 173
N-1751 Halden
Norway

Telephone direct: +47 6921 2119
Telephone switchboard: +47 6921 2200
Telefax: +47 6921 2470
Email: tordw@hrp.no
http://www.ife.no/
http://www.nea.fr/html/jointproj/halden.html
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