ISOTEX-1, Time-Dependent Heavy Isotope and Fission Products Concentration in U Reactor or Pu Reactor

1 - Nature of physical problem solved: The code ISOTEX-1 is a one-group neutron code which computes in double precision the time-dependent concentrations of 82 isotopes produced in an uranium and/or plutonium reactor. The U-235 depletion, the fuel depletion, and the burnup are also computed. The isotopes form five chains: - 17 isotopes ranging from U-234 to Am-242; - 7 isotopes with mass numbers between 81 and 86; - 1 isotope with mass number 106; - 19 isotopes with mass numbers 129-137; - 38 isotopes with mass numbers 140-155. Most of these isotopes have half-lives greater than one day. The value of the neutron flux, the cross sections (capture and fission) and the ratios of activation cross sections may be changed after each time step. The concentrations and ratios of concentrations may be printed during the irradiation. 28 different units may be used for the printing of the results. The ratios of concentrations may be chosen among a list of 41 ratios built into the code or may be defined by the user as ratios of sums or of products of concentrations. Several different problems may be treated. 2 - Method of solution: The analytical solution of the system of 82 differential equations describing the isotope transmutation schemes provides the values of the concentrations by assuming that the parameters entering the equations are kept constant during each time step and that there is no interaction between the isotopes. 3 - Restrictions on the complexity of the problem: There seems to be no upper limit in the range of applicability when high values of the fluxes and/or large time steps are used. A lower limit would probably correspond to the case of an irradiation time of the order of one hour in a flux of the order of 1010 n/cm2.sec