Development of methodology to optimize management of failed fuels in light water reactors

Abstract

Fuel cladding is one of the key components in a fission reactor that confines radioactive materials inside a fuel tube. During reactor operation, however, cladding is sometimes breached, and radioactive materials leak from the fuel pellet into the coolant water through the breach. The primary coolant water is therefore monitored so that any leak is quickly detected; coolant water is periodically sampled, and the concentration of radioactive iodine 131 (I-131), for example, is measured. Depending on the measured leakage concentration, the faulty fuel assembly with leaking rod is removed from the reactor and replaced immediately or at the next refueling. In the present study, an effort has been made to develop a methodology to optimize the management for replacement of faulty fuel assemblies due to cladding failures using measured leakage concentration. A model numerical equation is proposed to describe the time evolution of an increase in I-131 concentration due to cladding failures and is then solved using the Monte Carlo method as a function of sampling rate. Our results indicate that, to achieve rationalized management of failed fuels, higher resolution to detect a small amount of I-131 is not necessarily required, but more frequent sampling is favorable.

Statistical arguments towards the development of an advanced embrittlement correlation method for reactor pressure vessel materials

“…Some plants have high values, and others have small values. With this parameter, the embrittlement correlation can be improved within the framework of the probabilistic risk assessment [31,32]. This is an advantage of the Bayesian correction method, and the details will be published elsewhere.…”

An Improved Method for PWR Fuel Failure Detection Using Cascade-forward Neural Network With Decision Tree

“…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. 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). Generally, these strategies are developed in consideration of the FP release model or reactor operation experience.…”