Metal Dissolution Example Assessment

DOE-HDBK-3010-94

7.0 Application Examples; Dissolving Operations Examples

ARF and RF for burning of plutonium metal, at 5E-4 and 0.5 (subsection 4.2.1.1.3),

yield a considerably higher ARF x RF (2.5E-4 vice 1E-5).

The plutonium metal reaction phenomena will not be the same as the hydride reaction,

but Table 4-8 of subsection 4.2.1.1.4 indicates that highly energetic combustion of

plutonium-sodium mixtures at 300 oC exceeded the 2.5E-4 ARF x RF value in only 2

of 12 successful ignition experiments. The two larger ARF x RF values obtained

were 4E-4 and 2E-3, with the other 10 combined values being comparable to heating

of reactive powders or less. Subsection 4.2.1.1.4 states that the ARF and RF of 1E-2

and 1.0 for disturbed molten metal can be applied to very energetic compound

reactions. This value is accepted as very conservative and used. Such an

approximation, however, is not intended to cover all situations where small amounts

of hydride may be present intermingled with other materials. The initial respirable

release is:

100 * 1.0 * 1E-2 * 1.0 = 1.0 g

7.3.4.3

Metal Dissolution Example Assessment

The source term determined for the hydrogen explosion might exceed a dose of 100 mrem at

the site boundary if the release were completely unmitigated. Using the unrealistic estimates

of stoichiometric detonation of a limited quantity of hydrogen could possible result in

exceeding a dose of 1 rem. These are not major doses for an unlikely accident.

Examination of the explosion, however, would be a primary focus of any design or

evaluation process because it is not necessary to even know what is being processed to know

that an explosion, and especially a detonation, must be precluded if possible.

As was previously noted, the second means to prevent developing an explosive concentration

of hydrogen in the example is a continuous air purge of the spray chamber supplied by the

process air system. In systematically evaluating the functioning of the dissolver system, the

original hazard analysis training allowed discovery of a design flaw based on actual precedent

within the DOE complex. The air-operated valve on the air purge line is discovered to be an

air-to-open valve. Therefore, a loss of instrument air will cause the valve to shut and the air

purge to be lost with metal dissolution still occurring. Given that the instrument and process

air systems are unrelated, and the supply line is equipped with a check valve to prevent

reverse flow, the only functional need in this regard is for the valve to be an air-to-close

valve. This is an example of a safety improvement or correction that can easily be

determined without the need for a source term calculation. As presented in the example, it is

not an uncovered flaw for which blame must be fixed. It is an opportunity to make a

tangible improvement in safety, which is the purpose of the evaluation.

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