4. METHOD OF SOLUTION
The basic equations in THT are similar to those of some widely used industrial design methods: they are derived from diffusion theory and use 3-group neutron constants, but only the fast fluxes are explicitly calculated. The THT theory includes, however, two features which both result in a refinement of the system coefficients evaluations with respect to the other methods:
(1) A new spectral model to evaluate the thermal and epithermal average flux inside the assemblies, based on local solutions of the thermal and epithermal flux equations.
(2) Discontinuity factors, as defined by Henry, are used in the equations to connect the fast, epithermal, and thermal fluxes across the node boundaries.
THT was mainly written to study the new coarse mesh method developed at AGIP Nucleare. The program is therefore particularly suited for comparison with reference data and allows the user to choose different values for some model parameters and different convergence strategies. For the same reason, however, there exists no interface with other programs.