MA核素的嬗变对快堆k_eff和中子通量的影响

Effects on k_eff and Neutron Flux of MA Transmutation in Fast Reactor

摘要:

乏燃料中大量的次锕系元素(MA核素)要经过上万年的衰变才能消除其放射性危害。分离和嬗变技术(P&T)将乏燃料中的MA核素分离出来，再将MA核素放入反应堆中嬗变为短寿命核素或稳定核素，从而达到消除其放射性危害的目的。快堆是效率较高且技术较成熟的MA嬗变装置。为研究和比较²³⁷Np，²⁴¹Am，²⁴³Am，²⁴⁴Cm，²⁴⁵Cm和混合MA核素的添加和上述核素装载量的不同对堆芯有效增殖因子(k_eff)的影响，采用MCNP程序搭建快堆模型进行模拟计算。计算结果显示，将²³⁷Np，²⁴¹Am，²⁴³Am或混合MA核素以嬗变棒的形式替换燃料棒加入堆芯时，堆芯k_eff均下降，而将²⁴⁴Cm和²⁴⁵Cm嬗变棒加入堆芯时，k_eff反而上升，且装载量越大，k_eff变化越多，这将威胁到反应堆的安全性，因此我们认为方案一为最佳装载量。中子通量密度的计算结果显示，MA核素的添加几乎对堆芯的中子通量没有影响，这是使用快堆嬗变MA核素的一个优点。 The radiation hazard of minor actinides (MA nuclides) in spent fuel cannot eliminate until tens of thousands of years’ decay. Partitioning and Transmutation technology (P&T) is a method to elim-inate MA nuclides’ radioactive hazard. By loading into the operating nuclear reactor, MA nuclides separated from the spent fuel are transmuted to short-lived nuclides or stable nuclides. Fast reactor is efficient and mature neutron source for transmuting MA nuclides. We build a simulation model of fast reactor by MCNP code to study the effects on effective multiplication factor (k_eff) caused by the addition of MA nuclides and to compare different loading amounts and different nuclides include ²³⁷Np, ²⁴¹Am, ²⁴³Am, ²⁴⁴Cm, ²⁴⁵Cm and the mixture of MA nuclides above (MA mixture). Results show that the addition of ²³⁷Np, ²⁴¹Am, ²⁴³Am and MA mixture can cause a decrease of k_eff, while the addition of ²⁴⁴Cm and ²⁴⁵Cm boost the keff instead, and the effects on effective multiplication factor (k_eff) of the reactor core enhance with the raising of MA loading amount, which threatens the safety of the reactor, thus, we consider the minimum amount as the best loading amount. Simulation results of neutron flux show that the minimum loading amount of MA barely affects the neutron flux, which is a advantage to transmute MA nuclides in fast reactor.