熔岩玻璃体核素衰变热功率的计算

温度是影响熔岩玻璃体溶解速度的关键因素,为此,本文计算了核试验后10~300 000d内熔岩玻璃体中核素衰变热功率,评估了核素衰变热功率对熔岩玻璃体的温度和溶解速度的影响程度。采用了国际原子能机构给出的100kt TNT当量地下核试验产生的、半衰期大于1a的放射性核素含量,利用其中裂变产物核素137 Cs的含量推算累积裂变产额大于0.1%、半衰期为1d~1a的短寿命裂变产物核素的含量。分析了各核素的放射性衰变特点,采用ENDF/BⅦ库中核素衰变辐射的平均α能量、平均电子能量和平均电磁辐射能量计算各核素在熔岩玻璃体内因衰变而沉积的能量。计算结果表明:核素衰变热功率呈分段幂函数衰减;在10~2 000d、2 000~60 000d和60 000d之后的时段内,衰变热功率分别主要源于短寿命裂变产物核素、长寿命裂变产物核素和锕系元素。核素衰变热功率对熔岩玻璃体的温度和溶解速度的影响不大,1 000d后影响非常小。

Calculation of Radionuclide Decay Heat Power for Melt Glass

As the temperature is a key factor affecting melt glass dissolution rate, the decay heat power generated by radionuclides within melt glass from 10 d to 300 000 d after an underground nuclear test was calculated to assess its influence on temperature and dissolution rate. Radioactive inventories with half-life longer than 1 a, produced by 100 kt TNT nuclear explosion published by IAEA report were used. The inventories of short-lived fission products with half-life of 1 d-1 a and accumulate yield greater than 0.1% were estimated from the inventory of ¹³⁷Cs. The decay characteristics of each nuclide were analyzed. The decay energy deposited in melt glass was calculated by the mean alpha, beta and gamma energy released by radioactive decay from ENDF/B Ⅶ database. From the calculation, it can be concluded that the decay heat power decays by power function, short-lived fission products, long-lived fission products and actinides are the main contributions to the power at 10-2 000 d, 2 000-60 000 d and after 60 000 d, respectively. The influence on melt glass temperature and dissolution rate is indistinctive, especially after 1 000 d.