先进反应堆精确活化计算方法及关键技术研究

发布时间：2019-02-22 13:13

【摘要】：在反应堆运行过程中,堆芯内部产生的大量中子对回路中的腐蚀产物和堆内的结构部件有很强的活化作用,所形成的活化产物是反应堆运行与检修人员职业照射的主要来源。因此精确的活化计算对反应堆检修、换料、退役过程中工作方案的制定和人员的辐照安全有着重要意义。随着先进反应堆技术的发展,堆芯的结构材料与中子能谱愈发复杂,导致在活化计算中将会涉及到大量的短寿命核素、激发态核素等,且反应路径繁多,为精确和高效的活化计算带来挑战。围绕上述问题,本文基于超级蒙卡核模拟软件系统SuperMC,开展了先进反应堆的精确活化计算方法研究。本课题研究了一种基于指数变换的切比雪夫有理逼近方法(CRAM)的点活化计算方法,提高了 CRAM在计算核素长衰变问题时的求解精度。在采用精细反应链模型的基础上,考虑了 2231种核素的活化物理过程,共计66256种核反应。并进一步考虑了轻核素产额、短寿命核素和激发态核素对活化计算结果正确性的影响,支持活度、余热、潜在生物危害、剂量率和清洁因子等活化特征量的计算。本文的创新之处包括:(1)发展了基于深度优先搜索的嬗变链动态构建方法。反应堆中核素种类众多且转换关系复杂,嬗变链的精细程度直接影响活化计算的精度。本文提出的嬗变链动态构建方法从核素的反应截面信息和衰变信息出发,结合初始计算核素搜索添加活化产物并构建嬗变链,并考虑了轻核素产额,搜索精度高、扩展性强。(2)发展了基于大规模矩阵自适应降阶的加速方法。在利用CRAM对活化方程进行数值求解时,大量的短寿命核素会导致系数矩阵规模大,刚性强,影响数值求解的效率。该加速方法能够结合实际的辐照条件,采用矩阵重构的方式,有效地降低系数矩阵的规模和刚性,从而提高活化计算的求解效率。以国际活化基准例题为例,在保证计算结果正确的前提下,使用该加速方法后的求解效率提高了 2倍以上。为了验证本文所发展的活化计算方法的正确性和有效性,首先选取了活化计算中常见的β-、β+等衰变反应进行测试,计算结果与参考程序的计算值吻合良好。然后选取了天然核素例题进行测试,计算了从H到Th共计90种天然核素在辐照方案下的核素密度及活化特征量的变化情况,计算结果与参考程序的结果符合良好。此外,从裂变和聚变两个方面选取了压水堆燃料包壳例题和IAEA-ACB国际活化基准例题进行了验证。测试结果分别与参考程序的计算值和基准值的相对偏差均在0.5%左右,证明了本方法的正确性和有效性,可用于先进反应堆的精确活化计算中。
[Abstract]:During the operation of the reactor, a large number of neutrons produced in the reactor core can activate the corrosion products in the loop and the structural components in the reactor, and the activated products are the main sources of occupational irradiation for the reactor operators and overseers. Therefore, the accurate activation calculation is of great significance to the design of the work plan and the radiation safety of the personnel during the reactor maintenance, reloading and decommissioning. With the development of advanced reactor technology, the structural materials and neutron spectra of the reactor core become more and more complex, which leads to a large number of short-lived nuclides, excited state nuclides and so on, which will be involved in the activation calculation, and the reaction paths are various. It poses a challenge for accurate and efficient activation calculation. In order to solve the above problems, the accurate activation calculation method of advanced reactor is studied based on the super Monka nuclear simulation software system SuperMC,. In this paper, a Chebyshev rational approximation method (CRAM) based on exponential transformation is studied, which improves the accuracy of CRAM in solving the long decay problem of nuclides. On the basis of fine reaction chain model, the activation physical processes of 2231 nuclides were considered, a total of 66256 nuclear reactions were considered. Furthermore, the effects of light nuclide yield, short-lived nuclides and excited nuclides on the correctness of activation calculation results were further considered, supporting the calculation of activation characteristics such as activity, residual heat, potential biological hazard, dose rate and cleaning factor. The innovations of this paper are as follows: (1) the dynamic construction method of transmutation chain based on depth first search is developed. There are many kinds of nuclides in the reactor and the conversion relationship is complex. The precision of transmutation chain directly affects the accuracy of activation calculation. The method proposed in this paper is based on the reaction cross section and decay information of nuclides, combined with the initial calculation of radionuclide search to add activation products and construct the transmutation chain, considering the yield of light nuclides, the search accuracy is high. (2) A method of adaptive order reduction based on large-scale matrix is developed. When the activation equation is solved numerically by CRAM, a large number of short-lived nuclides will result in large scale of coefficient matrix and strong rigidity, which will affect the efficiency of numerical solution. The acceleration method can effectively reduce the scale and rigidity of the coefficient matrix and improve the efficiency of the activation calculation by using the matrix reconstruction method combined with the actual irradiation conditions. Taking the example of international activation datum as an example, the solving efficiency of the accelerated method is improved by more than 2 times under the premise that the calculation results are correct. In order to verify the correctness and validity of the activation calculation method developed in this paper, the 尾 -, 尾 iso-decay reactions commonly used in the activation calculation are first tested, and the calculated results are in good agreement with the calculated values of the reference program. Then, the natural nuclides were selected for test, and the densities and activation characteristics of 90 natural nuclides from H to Th were calculated. The calculated results are in good agreement with the results of the reference program. In addition, the fuel cladding of PWR and the IAEA-ACB International Activation benchmark are selected for verification from fission and fusion. The relative deviation between the test results and the calculated values and the reference values of the reference program is about 0.5%, which proves the correctness and validity of this method and can be used in the accurate activation calculation of advanced reactors.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TL329

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