Nuclear Data for Reactor Design—II

Effects of Fission Spectra on the Calculated Nuclear Parameters In the PCX Reactor, S. Salah (W Astro) 

The FCX is a cylindrical twb-zoned reactor.. The central zone is essentially a graphite enriched uranium mixture and the outer zone is a graphite reflector. The core region Of this reactor has an intermediate energy spectrum typical of NERVA reactors with a median fission energy of 300 eV. 

Radial material reactivity worths of C are 5 to 8% higher in the present computations compared with the previous calculations and were found to be in better agreement with the experimental measurements Present results of radial reactivity coefficients of enriched uranium are also higher by 2 to 4% over previous calculations but are in less agreement with the measurements. The hydrogen reactivity coefficients showed small change in reactivity ( 1%) due to use of Grundl and Fabry s fission spectra. 

Effective multiplication of the assembly decreased by about 1% because of Grundl and Fabry fission spectra resulting in a subezitical prediction. [ ace- and energy-dependent spectra changed appreci ly only above 1 MeV. 

This change was about 20 to 30% higher in magnitude using Grundl and Fabry fission spectra compared to the results obtained % using Cranberg data. 

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