在传统线性子链方法（TTA）采用的Bateman表达式基础上,利用极限运算推导出允许重复特征值出现的广义解析表达式,克服了重复核素对线性子链方法计算稳定性的限制,并通过回溯算法的应用实现了对核反应链的自动搜索。通过以上对线性子链方法的改进,显著提高了计算效率,最终形成了用于中子活化计算的程序ITACT。基于ITACT程序和EAF-2007数据库,计算了压水堆燃料包壳材料和聚变堆第一壁材料活化等例题,并将计算结果与欧洲活化程序FISPACT进行对比。结果表明: 对于长寿命核素,两者的计算结果较为接近,对于短寿命核素,ITACT程序的计算精度更高,初步验证了ITACT程序的可用性和准确性。

Nuclear reactors will produce a large number of neutrons when the plant is in operation. The neutrons could have strong effect on in-core materials and generate active products which could cause destructive effects on staff. Therefore, the high precision and high efficiency calculation of material neutron activation has a significant value for reactor radiation protection. Based on Bateman equation which is used in traditional Transmutation Trajectory Analysis (TTA), in this paper, limit operation is used to derive the expression of generalized TTA in which repeated eigenvalues are allowed. In this way, the restriction of similar decay constants are removed. Meanwhile, the backtracking algorithm is included for automatically searching nuclide linear chains and the computational efficiency is improved visibly by using the improved TTA. On this foundation, an activation calculation code named ITACT(Improved TTA ACTIVATION) is developed. Finally, this paper combines ITACT with EAF-2007 database to study the activation of cladding material in PWR reactor and first wall material in fusion reactor. Compared with the European general activation code FISPACT, for long life nuclei, the results are in good agreement with each other. But for short life nuclei, ITACT gets higher calculation accuracy, which verifies its feasibility and accuracy.