Release Estimation cont'd

DOE-HDBK-3010-94

7.0 Application Examples; Liquid Storage and Ion Exchange Examples

A condensed phase detonation is probably further ruled out by

theoretical thermochemical considerations. The energy density of a

7M HNO3 slurry with polystyrene beads is not great enough to

support a steady-state detonation.

There is at least one case on record, at a fertilizer manufacturing plant, where

ammonium nitrate is reported to have been present in a cation unit that suffered an

explosion upon addition of 54% nitric acid. This condition, while theoretically

possible, has not been reported for other incidents such as those that have occurred at

nuclear material processing plants. A rapid and violent decomposition reaction

involving ammonium nitrate would be expected to produce damage on the order of the

condensed phase detonation discussed above. This is not observed. In any case, the

knowledge base to determine how much ammonium nitrate might be generated or

involved in a reaction is not available.

The gaseous phase explosion is not directly ruled out by technical considerations. A

gaseous detonation, although not as violent as a condensed phase detonation, would

produce more damage and visible fireballs of a type not characteristic of historical

incidents either. Further, meaningful prediction of the explosive yield of such an

event is probably not attainable beyond the empirical observation that major

detonation effects have not been present in the incidents in nuclear processing plants.

The small diameter of the typical nuclear material ion exchange column, due to

criticality concerns, lends intuitive support to that observation as well.

In most of the incidents where detailed information is available, the timeframe

between initiation of a degradation reaction and vessel failure appears to have been in

the range of minutes, and noticeable heat flux was often reported in the vicinity of the

equipment shortly prior to failure. The explicit conclusion of the investigation of the

Hanford incident of 1976 is that the dominant effect of the degradation reaction was

accelerating heat and gas generation resulting in thermally induced pressure failure of

the ion exchange vessel. Factory Mutual labels such an event a thermal explosion

defined as "the result of an exothermic reaction occurring under conditions of

confinement with inadequate cooling ... the reaction rate and heat generation

accelerate until the container fails due to overpressure" (Factory Mutual, 1981). In

such cases, the initial source of the resin exotherm is highly localized. This localized

area may actually dry out resin and heat it above the resin autocatalytic ignition

temperature, at which point the column condition can no longer be stabilized. For the

purposes of example, a representative model of effects associated with the ion

exchange exotherm will be assumed to be a thermal explosion as discussed above.

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