Fully Moderated and Reflected Solids

DOE-HDBK-3010-94

6.0 Inadvertent Nuclear Criticality; Material Release in Criticality Excursions

(a)

Total Ci, except for Pu and Am, are based on cumulative yield for fission energy spectrum. The assumption of cumulative yield is very

conservative, i.e., it does not consider appropriate decay schemes. Calculations regarding individual nuclide yields and decay schemes may

be considered on an individual basis. Data in this table do not include the iodine reduction factor.

(b)

y = year, h = hour, d = day, m = minute.

(c)

Total radioactivity assumes the isotopic mix to be the equilibrium mix for recycled plutonium and 1 mg of PuO2 released.

finally terminated when adequate liquid has been boiled off to result in non-critical

conditions. The NRC Regulatory Guides assume that the boiloff of 100 liters of liquid is

required to terminate the reaction and that 0.05% of the salt content of the 100 liters is made

airborne as particulate material. The value is only a factor of 4 lower than the ARF assessed

for airborne release during the vigorous, continuous boiling of solutions containing

radionuclides.

The ARF of 5E-4 with an RF of 1.0 is adequate for base quantities of fissionable material in

solution. The value is applied to the amount of material in 100 liters, or all of the material if

less than 100 liters are involved. The 5E-4 factor can be applied to the fraction of other

fission products generated by the criticality in 100 liters of solution. However, the total

quantities of other fission products generated are small enough that they will not typically

result in a significant dose increase. If HEPA or sand filters attenuate the particulate material

carried in the gaseous effluents, particulates will not significantly contribute to doses outside

the facility.

For fuel reprocessing solutions, the NRC assumes a fraction of 1E-3 of the radioruthenium in

solution is released as well. For solutions that do not contain ruthenium prior to the

criticality, the small quantities generated in the criticality will not typically increase potential

dose consequences outside the facility.

6.3.2 Fully Moderated and Reflected Solids

The fission and activation products formed by an excursion in a solid are enclosed within the

matrix of the solid fissionable material. The fissionable solids that are generally found in

DOE non-reactor nuclear facilities are metal and ceramic oxides of the metals that may be

clad in metal (e.g., aluminum, zircalloy, stainless steel). Because of the wide range of

fissionable mixtures that may be used for fuel in the production, experimental, and test

reactors at DOE sites, each generating its own spectra of irradiation products, fuel

(unirradiated or spent) is not covered in this discussion.

It is postulated that the radionuclides generated by the criticality and present as fissionable

material are in the solid matrix but covered by water, which acts as a moderator and

reflector. Heat generated by the excursion is assumed to be dissipated in the water

surrounding the fissionable material resulting in boiling of the water. The criticality is

Page 6-21