Stored energy of gamma-irradiated WIPP salt

Samples of WIPP salt exposed at 3630K to gamma radiation from a 60Co source were annealed at constant rates of heating in a differential scanning calorimeter in order to release the energy stored. Radiation doses were 2.2, 5.4, 8.2, 11 and 13 x 109 rad, and temperature scans were conducted from room temperature to 8000K. The specific stored energy-dose relationship deduced from 80 K/min scans could be only approximately established due to the extreme variability of the specific energy in samples of a given dose. This variability probably results from unequal amounts of impurities in the 10 to 25 mg samples required for the calorimeter. The energy-dose relationship is best described empirically by lnQ0(cal/g) = (-40.6 +- 2.6) + (1.84 +- 0.12) lnD(rad). Temperature scans of 10, 20, 40, and 80 K/min were performed to determine the activation energy E of the annealing process. For the four more highly dosed samples, E = 31.1 +- 5.6 kcal/mole. Based upon criteria established elsewhere, there appears to be no danger of the stored energy being released quickly in a nuclear waste repository of bedded salt, nor could serious consequences result from such a release by some unforeseen mechanism