ACFA, Isotope Activation of Coolant and Structure Materials

1 - Description of program or function: The ACFA code calculates the neutron-induced activation, afterheat, biological hazard potential, transmutation and gamma-ray spectra in a nuclear system. The quantities of interest may be calculated by interval and/or by zone of the system considered. To calculate the transmutation coefficients for the neutron - induced reactions the code uses multigroup activation cross sections and space - dependent multi- group neutron fluxes in one- or two-dimensional geometry. The neutron reaction types incorporated in the code are (n,n'), (n,2n), (n,gamma), (n,p), (n,alpha), (n,n'p), (n,n'alpha), (n,t), (n,3n), (n,He-3), (n,d), and (n,n'd) considering both reactions to the ground state and to isomeric states. 2 - Method of solution: The code uses the matrix exponential method and the Bateman solution to solve a large system of coupled linear first-order ordinary differential equations with constant coefficients. 3 - Restrictions on the complexity of the problem: The code is flexibly dimensioned which means that the storage requirements are determined for the particular problem at execution time. The length of the decay chains constructed by the code only depends on the decay and cross section data given in the nuclear data libraries