NEUTRON LIFE CYCLEDOE-HDBK-1019/2-93Reactor Theory (Nuclear Parameters)Example:Calculate the thermal utilization factor for a homogeneous reactor. The macroscopicabsorption cross section of the fuel is 0.3020 cm-1, the macroscopic absorption crosssection of the moderator is 0.0104 cm-1, and the macroscopic absorption cross section ofthe poison is 0.0118 cm-1. Solution:f SUaSUaSmaSpa0.3020 cm10.3020 cm10. 0104cm10. 0118cm10.932ReproductionFactor,(h)Most of the neutrons absorbed in the fuel cause fission, but some do not. The reproduction factor(h) is defined as the ratio of the number of fast neurtons produces by thermal fission to the numberof themal neutrons absorbed in the fuel. The reproduction factor is shown below. h number of fast neutrons produced by thermal fissionnumber of thermal neutrons absorbed in the fuelThe reproduction factor can also be stated as a ratio of rates as shown below.h rate of production of fast neutrons by thermal fissionrate of absorption of thermal neutrons by the fuelThe rate of production of fast neutrons by thermal fission can be determined by the product of thefission reaction rate (Sfufu) and the average number of neutrons produced per fission (n). Theaverage number of neutrons released in thermal fission of uranium-235 is 2.42. The rate ofabsorption of thermal neutrons by the fuel is Saufu. Substituting these terms into the equationabove results in the following equation.h SUffUnSUafUTable 1 lists values of n and h for fission of several different materials by thermal neutrons andfast neutrons.NP-03Rev. 0Page 6
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business