压水堆中涂层式轴向非均匀MA/^(6)LiD嬗变棒的嬗变性能研究

Transmutation properties of coated axially non-uniform MA/^(6)LiD transmutation rods in PWR

为提高次锕系核素(Minor Actinides,MA)在压水堆中的嬗变效率,同时利用MA核素展平堆芯轴向功率分布,以华龙一号(HPR1000)177压水堆堆芯结构作为参考,研究利用热-快中子转换材料^(6)LiD设计的涂层式轴向非均匀MA/^(6)LiD嬗变棒性能。嬗变棒内部为UO2,外部为MA核素与^(6)LiD混合组成的嬗变涂层材料,该涂层材料在嬗变棒上的布局为轴向三、五、七段式结构,涂层厚度由中间向两端依次减小。计算研究嬗变棒在堆芯内照射540 d的嬗变性能发现,当嬗变涂层材料中^(6)LiD与MA的质量之比为2∶8时,嬗变率达到23.25%的最好效果;涂层式轴向三、五、七段式非均匀嬗变棒中七段式嬗变棒的嬗变率最高,为25.43%,三段式非均匀嬗变棒的裂变效果最好,MA核素裂变率为4.48%;同时该轴向非均匀结构的嬗变棒可将堆芯轴向功率峰因子由1.778降低至1.375。研究结果表明:相较于轴向均匀的嬗变棒,轴向非均匀嬗变棒不仅具有较高的嬗变效率,而且具有良好的轴向功率展平效果。

[Background]The nuclear transmutation is the only way to reduce the radioactive hazard of the high level long-lived radioactive minor actinides (MA).The majority of commercial reactors in operation in the world are pressurized water reactor (PWRs),hence the transmutation efficiency of minor actinide nuclide (MA) in PWR are crucial problem in the area of the nuclear waste disposal.[Purpose]This study aims to improve the transmutation efficiency of MA and flatten the core power distribution by using MA nuclide for PWR.[Methods]First of all,the HPR1000 (Hualong#1) model 177 core structure was taken as reference PWR,thermal-fast neutron convertible material ^(6)LiD was introduced to design coated axially non-uniform MA/^(6)LiD transmutation rods which structurally applicable to the PWR.The internal component of the transmutation rods was UO2,and the external component was the transmutation coating material composed of MA and ^(6)LiD nuclides.The layout of the coating material on the transmutation rods was axially three,five and seven segments structure,and the coating thickness gradually decreased from the middle to both ends.Then,the Monte Carlo program RMC2.0 developed by the Reactor Engineering Calculation and Analysis Laboratory of Tsinghua University was employed to establish the core and calculate the effect of transmutation coating material composition on core keff.[Results]The results show the best transmutation effect up to 23.25%is realized when the mass ratio of ^(6)LiD to MA in the transmutation coating material is 2∶8.Among the coated axially nonuniform transmutation rods,the seven-segment transmutation rod has the best transmutation effect,and the transmutation rate is 25.43%.The best fission effect of three-segment transmutation rod has the fission rate of 4.48%for MA nuclide.At the same time,the transmutation rod with axial non-uniform structure can reduce the axial power peak factor of the core from 1.778 to 1.375.[Conclusions]Compared with axially uniform rods,these axially non-uniform MA/^(6)LiD transmutation rods have good transmutation efficiency,especially the fission rate,and good performance on flatten axial power distribution is achieved,simutanously.