Keyword:WALL

WALL wall

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This keyword allows the input of the total neutron first wall loading wall in units of MW per square metre for a fusion device. This is converted to a flux value by using data read from the neutron spectrum file. The neutron spectrum file (fluxes) contains a value of the first wall loading, e.g. 4.15 MW m^-2 . The energy integrated flux, e.g. 1.80 × 10¹⁵ n cm^-2 s^-1, which is approximated by the sum of neutrons in all the groups, is calculated from the entries for each energy group in the fluxes file and equated to the wall loading during library processing.

Note that it is the user’s responsibility to ensure that this wall loading is correct when the spectrum file is constructed. If a wall loading of 2.0 MW m^-2 was input then a flux value of (2.0/4.15) × 1.80 × 10¹⁵ n cm^-2 s^-1 would be used in the calculations. It is also important to ensure that the fluxes file used with the WALL keyword contains actual n cm^-2 s^-1 for each energy group; while this is good practice in general it is not essential for standard calculations using FLUX because that keyword overrides values in the fluxes file and only the relative distribution of fluxes in the different energy groups matters (e.g. the fluxes file could be normalised to one in that case and the simulation would still be valid). When using WALL, however, it is critical to have accurate absolute flux values in each energy group, which is entirely the responsibility of the user.

WALL is a convenient alternative to using FLUX for the irradiation of first wall materials, but great care must be exercised if it used for irradiations with other than first wall spectra. (In these cases the flux specified for the region must be that which would be present if the first wall loading shown in the file was present on the first wall.) It is recommended that FLUX is always used in preference to WALL unless the user has a run that makes its use essential.

It should be noted that the wall loading describes the power that impinges on the first wall, not what is actually absorbed by it. In this sense the wall loading represents a convenient, but not fundamental, parameter. The power carried by the neutron flux impinging upon the first wall is related to the 14 MeV neutron current not flux. If one works out the heating power of 14 MeV neutrons it is found that a current C, of 4.44 × 10¹³ n cm^-2 s^-1 is equivalent to 1 MW*m^-2 . The relationship between 14 MeV neutron current and flux depends upon the source and first wall geometry and will vary from plant to plant.

Example usage:

< -- Control phase -- >
...
FISPACT
* Title of the simulation
< -- Initial phase -- > 
...
WALL 3.0
ATOMS
< -- Inventory phase -- > 
TIME 1.0 HOURS
WALL 0.0
TIME 1.0 DAYS
WALL 4.0 
TIME 1.0 HOURS
...