Ion Exchange Example Assessment cont'd

DOE-HDBK-3010-94

7.0 Application Examples; Liquid Storage and Ion Exchange Examples

require a TNT equivalent of 203 g, or almost 0.5 lb of TNT. In the more likely event of an

exotherm in only one column, the required TNT equivalent would be 406 g, or almost

1 lb of TNT. Experimental studies performed at Rocky Flats (Tuck, G., et al, 1975)

indicated a TNT charge of 227 g would destroy most internal equipment, blow out all

windows, and badly bow structural walls of a typical glovebox. Standard overpressure plots

indicate 227 g of TNT will produce at least partial demolition effects to a distance of

7 to 8 m. This level of damage is simply not observed in the historical record of nuclear

processing, which uses small ion exchange columns. That level of damage is rarely

approached even for very large industrial size ion exchange units.

The thermal explosion estimate, which has itself used very conservative assumptions, bounds

the phenomena more than adequately. A realistic estimate would, in all likelihood, be

significantly less than the 65-g bounding estimate. The thermal explosion model can be

accused of being nonphysical, but the same criticism would ultimately be true of any claim to

accurately specify TNT yield in a hypothetical detonation. The only physical basis for

judgement is the historical record of occurrences for which significant experimental work has

already been performed. At this point in the process, arguing over the appropriate

theoretical model to apply to an observed phenomena for the source term is an unproductive

activity. It inappropriately elevates the significance of source term at the expense of

objectively evaluating the process for compliance with known empirical rules for preventing

the phenomena. One does not need to know the exact source term to know that the ion

exchange column explosion discussed is a highly undesirable event that deserves special

attention. By the SAR preparation process outlined in DOE-STD-3009-94, the only question

the source term may specifically be answering is whether or not certain preventive and/or

mitigative controls will be labelled as safety-class structures, systems, and components by

comparison to dose criteria, or safety-significant structures, systems, and components for

defense in depth.

The danger of inappropriately focusing on source term arguments is real. At one extreme,

mathematical arguments could be used to reduce the source term below a given value

attributed special significance. If the non-definitive nature of almost any model is not

appreciated, that fact alone could be used to preclude further examination of the system. At

the other extreme, the source term could be just as inappropriately inflated. For example,

historical experience and the conservatism of the burning resin assumption could be ignored.

The heat of combustion of all the resin could be used in an adiabatic temperature calculation

turning the process room into a furnace with resulting severe estimates of facility damage and

releases from all processes. Such exaggerations can seriously distort evaluation by provoking

very time-consuming arguments as, again, the non-definitive nature of the source term is not

appreciated. How much actual safety information of real significance can be missed by

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