nuclear fission reactor fuel rods replacement rate

In addition, it can identify the degree of fuel failure if the fuel cladding is defective ( Li et al., 2017). It is based on the ratios of specific activities of two isotopic FPs, which can be used to determine whether the fuel cladding is defective ( Menéndez, 2009). Among these strategies, the isotopic ratio method is the one that is most frequently used to detect fuel failures during reactor operation. Generally, these strategies are developed in consideration of the FP release model or reactor operation experience. By analyzing the specific activities of FPs derived by sampling or online monitoring, fuel rod failures are discovered by various methodologies, such as the release-to-birth ratio method ( Zanker, 1989), fitted escape rate coefficient method ( Yamamoto and Morishita, 2015), and isotopic ratio method ( Kalinichev et al., 2018 Li et al., 2017) ( Qin et al., 2016). In order to determine whether the fuel cladding is defective, either a chemical sampling approach from the let-down flow or the real-time online monitoring system is used to collect specific activities in the primary coolant.

Otherwise, it may increase the risks of occupational exposure and harm the safety of reactor operation ( Iqbal et al., 2007 Qin et al., 2020). If the specific activities or defect sizes exceed the critical values, the reactor must shut down according to the regulation ( Likhanskii et al., 2006 Qin et al., 2019). When the fuel cladding is defective, FPs can migrate from the fuel cladding gap to the primary coolant, considerably increasing the specific activity of the coolant. While the performance of the fuel rods keeps improving, the fuel cladding is inevitably defective during operation for a variety of reasons ( Qin et al., 2020), including the following: 1) power ramp defects caused by stress corrosion cracking (SCC) or pellet-cladding interaction (PCI) 2) circumferential cracking caused by hydrogen embrittlement 3) fabrication defects and 4) fretting defects caused by interaction with the grid spacer or debris in the primary coolant ( Lewis et al., 2017). Under normal operating conditions, the fission products are contained within the fuel cladding which prevents them from escaping into the primary coolant and maintains the coolant’s specific activity within the management limit. The reactor generates a substantial amount of fission products (FPs) during operation. Finally, the most important nuclides are determined through the sensitivity analysis, and the neural network is simplified according to the importance of nuclides and the limitation of the radioactive detector in practical application. It is shown that the improved method is more accurate and responsive than the previous neural network when recognizing the onset of fuel failure.

The performance of the improved neural network is demonstrated. The training set is constructed using the Booth-type diffusion model and the first-order kinetic model. The degree of fuel failure is determined by the neural network’s output, which is labeled using one-hot encoding. The input of the neural network is the specific activity of FPs measured in the coolant. In this study, we propose a cascade-forward neural network with a decision tree for fuel failure detection that performs well at classifying the degree of fuel failure and, in particular, at differentiating between an intact fuel rod and a defective fuel rod with a small size defect. The feedforward neural network (FFNN) has been used to identify fuel failures in order to overcome the shortcomings of the isotopic ratio method, although there is still inadequacy in the ability to distinguish between an intact fuel rod and a defective fuel rod with a small defect. The isotopic ratio of two radioactive fission products (FPs) is a typical technique for evaluating the degree of fuel failure, although this is not applicable in the case of little fuel failure but large tramp uranium mass. The operators can decide whether to continue operating the reactor or shut it down based on the severity of the fuel failure. When a fuel rod is damaged, determining the degree of fuel failure makes sense.

2China Nuclear Power Engineering Company, Beijing, China.1School of Nuclear Science and Engineering, Shanghai Jiao Tong University, Shanghai, China.Bing Dong 1 Kang Yang 2 Wei Zhang 2 Junlian Yin 1 Dezhong Wang 1*

Nuclear fission reactor fuel rods replacement rate