# Changes in the Structure and Mechanical Properties of the SAV-1 Alloy and Structural Fe-Cr-Ni Steels After Long-Term Service as Core Materials in Nuclear Reactors

## TL;DR

This study examines how materials in nuclear reactors degrade over time, affecting their strength and safety for potential service life extension.

## Contribution

The study provides new insights into the degradation of SAV-1 alloy and Fe-Cr-Ni steels after long-term reactor operation.

## Key findings

- Irradiated SAV-1 alloy showed decreased yield and tensile strength by 24–48% and reduced elongation.
- Secondary silicon-rich phases formed within and along grain boundaries of aged SAV-1 alloy.
- Irradiated structural steels exhibited hardening and damping creep due to dispersion and Hall–Petch effects.

## Abstract

This article presents the results of studies of the degradation of the structure and mechanical properties of the core materials BN-350 fast neutron and research WWR-K reactors required to justify the service life extension of early-generation power and research reactors. Extending the service life of nuclear reactors is a modern problem, since most operating reactors are early-generation reactors that have exhausted their design lifespan. The possibility of extending the service life is largely determined by the condition of the structural materials of the nuclear facility, i.e., their residual resources must ensure safe operation of the reactor. For the SAV-1 alloy, the structural material of the WWR-K reactor, studies were conducted on witness samples which were in the active zone during its operation for 56 years. It was found that yield strength and tensile strength of the irradiated SAV-1 alloy decreased by 24–48%, and relative elongation decreased by ~2% compared to the unirradiated alloy. Inside the grains and along their boundaries, there were particles of secondary phases enriched with silicon, which is typical for aged aluminum alloys. For irradiated structural steels of power reactors, studied at 350–450 C, hardening and a damping nature of creep were revealed, caused by dispersion hardening and the Hall–Petch effect.