硝酸浓度对临界安全的影响研究

Study on Influence of Nitric Acid Concentration on Criticality Safety

在核燃料溶解过程中,通常使用硝酸对核燃料进行溶解。针对核燃料溶解过程中的临界安全问题,在中试厂核临界安全实验装置上开展了硝酸浓度影响效应临界实验,在保持核燃料溶液浓度不变的情况下改变硝酸浓度,完成临界实验。获取了核燃料溶解过程酸度影响效应临界实验数据,通过3种临界方法得到的实验数据相对误差平均值为0.068%。同时使用蒙特卡罗程序进行了模拟计算,临界实验测量结果与理论计算值的相对偏差平均值为0.39%。研究结果表明,随着硝酸浓度的减小,系统的反应性逐渐增大,因此燃料溶解过程中需考虑由于硝酸浓度变化引起的反应性变化情况,其对乏燃料溶解过程的临界安全具有较大影响,需引起高度重视。

The nuclear criticality safety issue in spent fuel reprocessing facilities is closely related to the main process and is almost equally important.It is closely related to the design and operation of reprocessing facilities.The requirement of nuclear criticality safety greatly restricts the operational capacity of the spent fuel reprocessing process,thereby affecting the economic efficiency of reprocessing.In the post-processing process,both multiphase uranium-plutonium mixed systems and multi body interaction systems are involved.The system characteristics are complex,and experimental simulation is difficult,which greatly restricts the further improvement of the production and operation capabilities of the pilot plant.However,due to the criticality safety challenges caused by reactivity changes such as the non-uniformity,dynamic complexity,and instability of the solution in the reactor under boiling nitric acid during the dissolution process,it has become a key research topic in various countries.According to the criticality safety problem of nuclear fuel dissolution process,the criticality effect of nitric acid concentration was studied.The criticality experiment data of nuclear fuel dissolution process were obtained by keeping the concentration of nitric acid in the same fuel concentration.Four experiments were conducted with different concentrations of nitric acid.During the experiment,the subcritical extrapolation method,reactivity interpolation method,and stable power method were used to complete the criticality experiment.The experimental results show that with the increase of nitric acid concentration,the relative deviation of the criticality experiment data is 0.068%,and the relative deviation between the criticality experiment results and the theoretical calculated values is 0.39%.The research results show that the reactivity of the system gradually increases as the concentration of nitric acid decreases.Therefore,it is necessary to consider the reactivity changes caused by changes in the criticality safety of the spent fuel dissolution process,and high attention is needed.According to the agreement between the experiment and the theoretical calculation,it is appropriate to use the Monte Carlo code MONK to calculate and analyze the acidity effect of the solid-liquid two-phase solution system,which can be used as a nuclear criticality safety control engineering design process for the solid-liquid two-phase nuclear fuel dissolution system.This series of experiment data can be used for calculation,verification,and safety evaluation of critical analysis under solid-liquid coexistence conditions of nuclear fuel.This paper results provide data support for improving the criticality safety control level of critical post-processing equipment.