Shielded Blast Effects From Detonations and Large Volume, Confined Deflagrations cont'd

DOE-HDBK-3010-94

4.0 Solids; Powders

parameters not readily determined for accident conditions. Estimates of entrainment rates

still require estimates of the duration of the pressure wave/accelerated flow over the deposit

to arrive at estimates for ARFs. Singer, Cook and Grumer (1972) reported entrainment rates

of ~ 10 g/m3 at 5 m/s to ~ 90 g/m 3 at 40 m/s (89 mph) for velocities at the mid-height of the

deposit. Freeman (1972) reported concentrations of 700 to 1100 g/m3 in 1 second at an

explosion equivalent to 1E+8 g TNT but did not indicate if this was entrainment or due to

blast effects.

In the absence of any directly applicable predictive models or release data, other related

experimental values are applied. From the information quoted above, it appears the

entrainment process results from the creation of surface flaws by the detachment of particles

or clumps. Once created, the surface flaws allow more general lifting of the surface until the

entire surface is disrupted. The process requires some period to initiate as shown by the 0.1

to 0.5 seconds necessary to entrain 2 grams from a cohesive surface (Singer, Cook and

Grumer 1972).

Mishima and Schwendiman (August 1973) reported the entrainment of UO2 powder and air-

dried UNH from various surfaces at two air velocities (~ 1.1 and 8.9 m/s 1-ft above the

surface) at ambient temperatures. The experimental apparatus is shown in Figure A.3 and

the experimental results reproduced in Table A.3 in Appendix A. An ARF and RF of

7.6E-2 and 0.14 were measured for the higher of two values for the suspension of UO2

powder from a stainless steel surface for a wind velocity of 8.9 m/s 1-ft above the surface

(comparable to a 22 m/s under normal wind speed measurements) in a 24-hour period. The

velocity of the bulk fluid at distances above the surface may not be a meaningful

measurement and the velocity profile near the surface may be more relevant. In the case of

explosion-generated air velocities, the duration of the peak velocity is in terms of

milliseconds. Approximately 60% of the resuspended powder (4.56E-2) was made airborne

during the first hour of the wind as shown in Figure 4-16 taken from the referenced

document. If resuspension is assumed to be linear over the initial hour the ARF would be

7.6E-4 per minute. It is noted that recent studies indicate resuspension of sparse particle

contamination is not linear, especially at the beginning and end of the suspension period and

that the suspension from the bed of a cohesive material appears to be initiated at surface

imperfections. However, for the flow to be parallel over the surface, the center of the

explosion must be some distance from the deposited material. The entrainment due to the

pressure wave over the surface will be limited as the wave will only be over the deposit for a

short period of time (fractions of a second).

Fry (July 1991) specifically evaluated the effects of a flammable gas detonation outside a

typical glovebox on clump powder sitting on the floor of the glovebox. The simulation used

the HULL hydrocode to model detailed interactions of blast waves loading onto structures

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