ources in a slab shield due to neutrons from a small cylindrical reactor core. The shield may be either on top of or beside the cylindrical core.
The kernel is integrated numerically using the Gauss quadrature technique. The amount of computing time required is dependent on the quadrature order which also determines the accuracy of the calculation. Tests have been carried out to discover the most suitable choice of quadrature order for the type of problem for which SCRIM was originally designed, that is for a core similar to that of the LIDO reactor. The results of these tests are used by a routine that will automatically select the quadrature order.
Although the module will operate for field points inside the core, the method of integration is unsuitabl for accurate calculations at such points, even if high order quadrature is used. The calculation of removal fluxes within the core should therefore be avoided in general.
Removal fluxes and sources are calculated for each of a series of energy groups so that they can be fed into a multigroup diffusion calculation. Fluxes and sources in the removal group scheme must first be converted into the so-called output group scheme which is used in the diffusion calculation.
For each material used, group-averaged macroscopic cross sections are either input or calculated from a library of microscopic removal cross sections stored on magnetic tape or disc. The present tape contains data for 32 elements averaged over a standard 18 removal group scheme.
SREM (WRS system module No. 3348) Calculates the uncollided flux and first-collision source from a disc source in a slab geometry system, a line source at the centre of a cylindrical system or a point source at the centre of a spherical system. An energy group treatment is used. In each case the source particles are emitted isotropically. The source energy spectrum is defined group-wise, and a fission spectrum in 18 groups is built in for use if required.
For different applications of the module the cross sections used may be either total cross sections or some form of empirical removal cross sections. The module can make use of a library of removal cross sections on magnetic tape or disc containing microscopic cross sections for a selection of elements in a number of removal groups. For example, there is a standard tape containing neutron data for 32 elements in 18 removal groups.
The calculation is performed in two stages: the removal flux through the shield is calculated in a number of removal groups, and the removal flux and source are then obtained in an output group scheme which may be different. The removal source can be calculated by multiplying the removal flux in each group by the corresponding removal cross section and assigning each result to an output group. Alternatively, a full matrix of transfer cross sections may be used. The module produces a functional representation of the flux and source in each group and each region using Chebyshev series. This ensures that the execution time does not depend on the number of printout points requested, and that the module output is in a form from which values at any point may be calculated.
PARAMETERS (WRS system module No. 35836) Calculates multigroup neutron diffusion parameters for use in the age- diffusion method. Parameters are derived for materials of specified compositions from a library of microscopic data. This data is normally held on a magnetic tape and is written by an auxiliary program which processes files from the UKAEA Nuclear Data Library. For each material and each energy group the module calculates values of the diffusion coefficient D, the inverse slowing down length K and the absorption coefficient Alpha.
REGROUP (WRS system module No. 13774) Converts multigroup flux spectra from one energy group scheme to another. Several spectra can be processed during one execution of the module, and there is a facility for applying scaling factors to the converted spectra. There are two alternative modes of operation. In one mode a 1/E spectrum shape is assumed within each 