FORM-OTA, Multigroup Constant for Epithermal Neutron Slowing-Down in Homogeneous Media

1 - Description of problem or function: FORM-OTA performs a multi- group slowing down calculation for a fundamental mode of given buckling in a homogeneous medium to obtain space-independent energy spectra for the epithermal neutron flux and current. Using the calculated flux and current spectra the program produces group constants for desired few group schemes. 2 - Method of solution: FORM-OTA is a member of the MUFT family of programs. The one-dimensional transport equation for the flux in plane geometry is solved by removing the spatial dependence by a Fourier transformation and by treating the angular dependence in either B1- or P1-approximation. Elastic slowing-down by hydrogen can be solved in an exact manner using a differential equation formulation. Elastic slowing-down by all non-hydrogen elements is lumped together and treated in the Greuling-Goertzel approximation. For resonance absorption a rather simple formulation is used. A flux peaking in the fuel can be assessed, too. The energy group structure (54 groups in the range 10 MeV - .625 eV) is pre-programmed into the code. A facility is provided to modify library data and to introduce entirely new data at run-time. 3 - Restrictions on the complexity of the problem: Maximum 18 elements (isotopes) in a mixture. Of these 18 elements maximum 10 elements can have resonance data. Maximum 6 few group schemes. Maximum 25 group in any few group scheme. Maximum 25 groups in a heterogeneous two-region (fuel-moderator) calculation