Debris protection features of Westinghouse PWR and BWR fuel

This paper looks at the features which Westinghouse has developed to protect fuel assemblies from debris fretting failures. The methodologies behind the different features as well as the performance of the features are reviewed. Debris fretting makes up one of the top mechanism for leaking fuel rods. Therefore, it is important to understand this failure mechanism and provide defenses which improve protection against pieces of debris damaging the fuel. Westinghouse has developed features for each product line to protect the fuel from debris fretting. There are several different approaches to reduce debris fretting. The first method is filtering debris before it can enter the fuel assembly. The second method is trapping debris in a region within the fuel assembly where the debris is safely trapped to prevent it from mitigating into areas where it could cause damage. The third method is making the fuel rod cladding more resistant to wear by hardening the surface of the cladding. The final method is making the structural components within the active region less likely to catch debris such that any debris that enters the fuel assembly will not become lodged in one place such that it causes fretting damage. These approaches can be used separately or in combination to create a system which protects against damage from debris. The use of fuel features developed to protect the fuel against debris reduces the probability of debris related failures. It is also important that plants maintain effective foreign material exclusion (FME) programs. The combination of FME practices together with debris mitigation features in fuel provides layers of defense against debris fretting