Enhance particle size

DOE-STD-3028-2000

specification for the material prepared for the light-water breeder reactor (LWBR)

program [Parrott, Sr. et al, 1979]. Given that the material has already seen

elevated temperatures for extended time, it is unlikely that further heating will

show extensive enhancement.

4. The Standard requires verification that materials have been adequately stabilized.

Stabilizing above 750C (1382F) and appropriate handling prior to packaging

ensure that the only significant mechanism for container pressurization is radiolysis

of readsorbed water into pressurizing gases. Thus, verification of adequate

stabilization requires measurement (e.g., LOI) to ensure that residual volatiles in the

packaged material is below the threshold specified in Criterion 6.1.2.1. The LOI test

is accomplished by heating the oxide sample to at least 800C (1472F) for at least

one hour and determining the resulting weight loss. The temperature selected must

be higher than the stabilization temperature. However, the temperature should not

be so high as to decompose U3O8, which forms gaseous UO3 from 900-1500C

(1652-2732F) depending on surface area [Kirk-Othmer 1997]. Therefore, 800C

(1472F) was chosen as the LOI temperature. The LOI test has great attractiveness

because of its simplicity and low cost. However, LOI does not directly measure the

parameter of greatest interest hydrogenous material content. Indeed, because of

the chemistry of uranium oxides, LOI may give false results when applied to the

forms UO3 and UO2. At temperatures greater than 450C (842F) in air, UO3 will

begin to convert to U3O8. Thus, a portion of the LOI result will be from oxygen loss

and the LOI measurement will be greater than the volatiles loss. UO2 will also

convert to U3O8 at temperatures greater than 450C (842F) in air. In the case of

UO2 the LOI measurement will be less than the volatiles loss and may even show a

"gain on ignition." Even U3O8 heated above 500-700C (932-1292F) may give off

oxygen to form substoichiometric U3O8-x [Gmelin 1978]. This Standard therefore

encourages use of LOI with mass spectroscopy analysis of the off gas. Note that if

the material is stabilized as part of the repackaging process, it should be U3O8 (see

Section A.6.1.2.3).