Mustafa S S, Amin E A
Faculty of Science, Zagazig University, Zagazig, Egypt.
Nuclear & Radiological Regulatory Authority, Cairo, Egypt.
Sci Rep. 2019 Nov 8;9(1):16308. doi: 10.1038/s41598-019-52560-4.
Thorium-plutonium mixed oxide, (Th,Pu)OX, is currently used as an alternative fuel in the light water reactors in the world. The main objective of this paper is not only to show the benefits of using the thorium, but mainly to study how the way thorium is introduced in the fuel affects the neutron parameters. Among these benefits is the possibility of extending the operating cycle length and the reduction of the increasing stockpiles of plutonium. The first investigated method is introducing thorium as (Th,Pu)OX. The second one is a homogeneous model of thorium plutonium oxide. It is carried out by adding an amount of plutonium separated from the uranium oxide cycle at 50 GWd/ton of heavy metal to the same amount of thorium. Thus, we studied three assemblies; the reference assembly is uranium oxide of 4.2% enrichment containing borated water as a moderator of concentration 500 ppm (part per million) of B-10. The second is a (Th,Pu)OX and the third one is an assembly with homogenized thorium plutonium. All three assemblies are modeled using MCNPX. A comparison is held between the results of the three lattices. The factors compared are the effective multiplication factor, the inventory of plutonium and uranium isotopes, and the depletion of B-10, the pin by pin power distribution at 0 and 60 GWd/ton and the relative pin radial power for the three lattices. The comparison is aimed to show the effect on the cycle length, the reduction in the Pu content and the power flattening across the assembly. It is found that the evolution of the multiplication factors shows a similar behaviour using (Th-Pu)OX fuel in the assembly as UOX cycle inspite of lowering the K-eff of fresh (Th-Pu)OX fuel (1.19847). The power flattening which is favorable in reactor operation is clearer in (Th,Pu)OX fuel. It is noticed that the mass of Pu-239 decreases by 1.07% from its initial value at the end of life. For homogeneous (Th,Pu)OX, the mass decreases by 0.0832%. The high power peaking factor for (Th,Pu)OX is not expected to cause significant effects during reactor operation but it can be reduced by adding burnable poisons.
钍钚混合氧化物（Th,Pu）OX目前在世界上的轻水反应堆中用作替代燃料。本文的主要目的不仅是展示使用钍的益处，更主要的是研究钍在燃料中的引入方式如何影响中子参数。这些益处包括延长运行周期的可能性以及减少钚库存的增加。第一种研究方法是将钍作为（Th,Pu）OX引入。第二种是钍钚氧化物的均匀模型。它是通过将从铀氧化物循环中分离出的一定量钚，在每公吨重金属50吉瓦日的情况下，添加到等量的钍中实现的。因此，我们研究了三个组件；参考组件是富集度为4.2%的铀氧化物，含有浓度为500 ppm（百万分之一）的硼化水作为慢化剂。第二个是（Th,Pu）OX，第三个是钍钚均匀化的组件。所有三个组件都使用MCNPX进行建模。对这三个晶格的结果进行了比较。比较的因素包括有效增殖因子、钚和铀同位素的存量、B - 10的消耗、在0和60吉瓦日时逐棒功率分布以及三个晶格的相对棒径向功率。该比较旨在展示对循环长度、钚含量的减少以及组件内功率展平的影响。结果发现，尽管新鲜（Th - Pu）OX燃料的有效增殖系数（K - eff）较低（1.19847），但在组件中使用（Th - Pu）OX燃料时，增殖因子的演变与UOX循环表现出相似的行为。在反应堆运行中有利的功率展平在（Th,Pu）OX燃料中更明显。注意到在寿期末，Pu - 239的质量从其初始值下降了1.07%。对于均匀的（Th,Pu）OX，质量下降了0.0832%。（Th,Pu）OX的高功率峰值因子预计在反应堆运行期间不会产生显著影响，但可以通过添加可燃毒物来降低。
