Gamma-Ray Spectrum of Cerium-145

The safety of activity-containing asphalt products kept in enclosed storage was evaluated from considerations of radiolysis and hydrogen evolution. The samples examined were mainly homogeneous asphalt products containing 43% of sludge produced in routine operation of the asphalt plant at the Japan Atomic Energy Research Institute (JAERI), the samples were irradiated with external ⁶⁰Co x-ray source to a dose of 10⁹R.

The bulk of the gases evolving from the asphalt product is hydrogen, which constitutes 75~95% of the total gas evolution. The total amount of gases generated during infinite time is proportional to the total exposure dose; hydrogen evolves at a rate of 5.5 × 10³ cm³/g-MR. The amount of total gas evolution is governed solely by the quantity of asphalt, and is independent of the sludge contained therein. Nor do differences in the rate of dose appear to have any significant effect. In so far as concerns smallness of radiolysis, slightly better performance can be expected from straight than from blown asphalt.

There is no danger of explosion of the asphalt products currently generated at JAERI (10~⁶Ci/kg), which can be expected to accumulate in infinite time no more than about 3 cm³ from a 200 l product. Only asphalt products containing activity in concentrations exceeding 10¹ Ci/kg risk explosion when kept in enclosed storage, through accumulation of hydrogen in quantity exceeding the explosion limit in a relatively short time.