Košťál Michal, Rypar Vojtěch, Losa Evžen, Harut David, Schulc Martin, Klupák Vít, Matěj Zdeněk, Cvachovec František, Jánský Bohumil, Novák Evžen, Czakoj Tomáš, Juříček Vlastimil, Zaritsky Sergey
Research Centre Řež, 250 68 Husinec-Řež 130, Czech Republic.
Research Centre Řež, 250 68 Husinec-Řež 130, Czech Republic.
Appl Radiat Isot. 2018 Dec;142:12-21. doi: 10.1016/j.apradiso.2018.09.005. Epub 2018 Sep 7.
The neutron flux distribution behind a reactor pressure vessel (RPV) is an important parameter that is monitored to determine neutron fluence in the RPV. Together with mechanical testing of surveillance specimens, these are the most important parts of in-service inspection programs that are essential for a realistic and reliable assessment of the RPV residual lifetime. The fast neutron fluence values are determined by a calculation. These calculation results are accompanied by measurements of induced activities of the activation foils placed in the capsules behind the RPV at selected locations, namely in azimuthal profile. In case of discrepancies between the measured and calculated activities of the activation foils placed behind the pressure vessel, it is difficult to determine the source of the deviation. During such analysis, there arises a question on the influence of power peaking near core boundary on neutron profile behind the RPV. This paper compares the calculated and measured increase of the neutron flux density distribution behind the reactor pressure vessel in the azimuthal profile that has arisen from the replacement of 164 fuel pins located close to reactor internals by pins with the higher enrichment. This work can be understood as the first step in the characterization of the effect of incorrectly calculated pin power or burn-up in the fuel assembly at the core boundary relative to the neutron flux distribution behind reactor pressure vessel. Based on a good agreement between the calculated and experimental values, it can be concluded that the mathematical model used to evaluate the power increase is correct.
反应堆压力容器（RPV）后方的中子通量分布是一个重要参数，通过监测该参数来确定RPV中的中子注量。连同监督试样的力学测试一起，这些是在役检查程序的最重要部分，对于对RPV剩余寿命进行现实且可靠的评估至关重要。快中子注量值通过计算确定。这些计算结果伴随着对放置在RPV后方选定位置（即方位角分布）胶囊中的活化箔的感生活度的测量。如果压力容器后方活化箔的测量活度与计算活度之间存在差异，则很难确定偏差的来源。在这种分析过程中，会出现关于堆芯边界附近功率峰值对RPV后方中子分布的影响的问题。本文比较了由于用富集度更高的燃料棒替换靠近反应堆内部构件的164根燃料棒而导致的反应堆压力容器后方方位角分布中中子通量密度分布的计算增加量与测量增加量。这项工作可被视为表征堆芯边界处燃料组件中燃料棒功率计算错误或燃耗相对于反应堆压力容器后方中子通量分布的影响的第一步。基于计算值与实验值之间的良好一致性，可以得出结论，用于评估功率增加的数学模型是正确的。
