3. NATURE OF PHYSICAL PROBLEM SOLVED
One-dimensional neutron and gamma-ray shield penetration calculations. For neutrons the removal- diffusion method is used. For gamma-rays there is the option of using either kernel integration with build-up factors or diffusion theory with a first flight correction. Linked calculations are possible in which the gamma-ray sources are calculated from the neutron fluxes. Neutron reaction-rates and gamma-ray dose and heating rates may be printed out.
A detailed description of the different modules follows:
MINNIE (WRS system module No. 17133) Reads in material compositions in various forms and converts them to standard format.
NADCON (WRS system module No. 23016) Calculates multigroup data for use in shielding calculations employing the method of Adjusted Diffusion Coefficients (with first flight correction). NADCON prepares macroscopic data for materials of specified compositions by mixing microscopic data from a library supplied with the module.
BADCON (WRS system module No. 17066) Derives Adjusted Diffusion Coefficient Data without the first flight correction, from the multigroup data produced by NADCON.
REMOVAL (WRS system module No. 42869) Calculates the uncollided flux and first-collision source in a slab geometry system containing a source distributed through some or all of the slabs. The removal fluxes and the removal sources in the output groups (which may differ from the removal groups) are expressed in terms of Chebyshev series.
The module can make use of a library of removal cross sections on magnetic tape or disc containing micro- scopic 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 module can use this to calculate macroscopic removal cross sections for each material in the problem, or alternatively it can read these cross sections from the inputdata.
SCRIM (WRS system module No. 22947) Calculates the uncollided flux and first collision sources 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 e