Fully Moderated/Reflected Solids

DOE-HDBK-3010-94

6.0 Inadvertent Nuclear Criticality; Summary

Fully Moderated/Reflected Solids

This configuration covers reflected bulk metal and metal pieces or solid fines, such as

powders, that are moderated or reflected. The equation assumes some softening and local

deformation of metals to allow fission product release, but no severe molten eructations,

reactions, or vaporizations are considered credible for the configuration due to the limited

time of the excursion and the significant heat transfer occurring to the moderator. The

moderator and/or reflector typically assumed is water. A coherent solid cannot be moderated

and solids < 100 m in diameter must be intimately mixed with the moderator to be fully

moderated.

Airborne Source Term = MARc2 x DRc2 x ARFc2

(6-2)

where: MARc2 = inventory of fissionable material and radionuclides from

criticality in reflected/ moderated solids calculated by

computer codes such as ORIGEN2 based on 1E+18 total

fissions; or, [1E+18 fissions/1E+19 fissions] X table (see

footnote 1).

DRc2 = Damage Ratio for radionuclides generated by criticality:

metal pieces, 0.1

fines, (e.g., powders), 1.0.

ARFc2 = Airborne Release Fraction: fissionable material and non-

volatile fission products can be neglected, 5E-1 for noble

gases, 5E-2 for iodine3

Bare, Dry Solids

This configuration covers solids that may be reflected but have no moderation (i.e., not

immersed in liquid). The equation assumes some softening and local deformation of metals

to allow fission product release, but no general oxidation or molten dispersion. To achieve

criticality, kg quantities of material must be involved as a minimum. Generally, single

parameter limits will be significantly exceeded as sphere configurations are not common.

Table 6-10 indicates quantities of radionuclide groups released from molten ceramic oxide fuel. For non-

volatiles, these values would be multiplied by 5E-4 for release from the moderating solution, which will render

them an insignificant contributor to dose. The values for gases and semi-volatiles are taken directly from Table

6-10 without any additional credit taken for capture in solution as these values are already less than the NRC

solution values. As a potential gas, the value from Table 6-5 for ruthenium could be used without capture as well,

but the quantities of ruthenium generated would typically make it a minor contributor.

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