Criticality - h3010v10267

DOE-HDBK-3010-94

7.0 Application Examples; Feed Preparation Example

E. Criticality. A powder criticality in a dry operation is unlikely, but not

impossible. A yield of 1E+17 fissions is assessed to be bounding for bare, dry

criticalities (subsection 6.2.3.3). A simple method for estimating fission product

release from the criticality is to ratio the results indicated by the NRC for a 1E+19

fissions plutonium criticality to 1E+17 fissions. The DR refers to the fraction of

isotopes exposed for release, and it would be 1.0 for gases and volatiles in powder.

The ARF is 0.5 for noble gases and 0.05 for radioiodines. Table 7-3 on the

following page shows a simplified release estimation based on important isotopes

identified by the NRC. The potential dose associated with this release is well under

1 mrem at the site boundary, although prompt worker fatalities can occur due to

radiation produced by the criticality. This criticality is a good example of the

situation where material release estimates and associated potential doses have little if

any relevance to the principal safety concerns for a given phenomena.

Plutonium airborne releases are possible as well. Significant pressurization is not

possible with loose (i.e., uncontained powder) or loosely contained powder (i.e., non-

pressure tight seal, damaged can). For loose material, however, significant heating

can occur. Experimental data covers heating of plutonium oxides to sustained

temperatures of 1000 oC. The ARF and RF assigned for this condition are 6E-3 and

0.01 (subsection 4.4.1.1). Assuming 10,000 g of material are brought together to

initiate the criticality, the maximum initial respirable source term is:

10,000 g * 1.0 * 6E-3 * 0.01 = 0.6 g

Again, the exact value obtained is of little relevance to criticality safety management.

F. Large Room Fire. There is nothing inherent in the feed preparation glovebox or

associated operating and maintenance rooms that indicates a large room fire is

possible. However, one can be postulated to occur by an undefined mechanism. The

potential MAR is the powder in the glovebox and, at most, one pail of waste in the

maintenance room that had been bagged from the glovebox prior to the fire. The

maximum amount of material allowed at one time in the glovebox is 20,000 g as

plutonium, with all of this material essentially plutonium oxide. Up to 100 g of

plutonium can be in a waste package, but 1 to 2 g is typical. If a genuinely large fire

existed, the DR for oxide in the glovebox is 1.0, as heating is the release phenomenon

of concern. The DR for the waste pail, which would burn, is 1.0 as well.

As previously discussed under the examination of criticality, the ARF and RF for

heating oxide powders are 6E-3 and 0.01 (subsection 4.4.1.1). The ARF and RF for

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