Evolution of spent nuclear fuel in dry storage conditions for millennia and beyond

TLDR

Significant amounts of spent uranium dioxide nuclear fuel are accumulating worldwide from decades of commercial nuclear power production, and out‑of‑reactor radiation damage from alpha decay can threaten its structural stability. The study experimentally examined radiation damage in plutonium dioxide, uranium dioxide doped with short‑lived alpha‑emitters, and urano‑thorianite minerals using XRD, TEM, TDS, and hardness tests to evaluate long‑term stability under high alpha‑decay doses. Defect accumulation leads to atomic swelling and reduced fracture toughness, while helium bubbles cause larger gaseous swelling and increased stresses. These effects predict significant radiation‑ageing of spent fuel over more than 10,000 years.

Abstract

Significant amounts of spent uranium dioxide nuclear fuel are accumulating worldwide from decades of commercial nuclear power production. While such spent fuel is intended to be reprocessed or disposed in geologic repositories, out-of-reactor radiation damage from alpha decay can be detrimental to its structural stability. Here we report on an experimental study in which radiation damage in plutonium dioxide, uranium dioxide samples doped with short-lived alpha-emitters and urano-thorianite minerals have been characterized by XRD, transmission electron microscopy, thermal desorption spectrometry and hardness measurements to assess the long-term stability of spent nuclear fuel to substantial alpha-decay doses. Defect accumulation is predicted to result in swelling of the atomic structure and decrease in fracture toughness; whereas, the accumulation of helium will produce bubbles that result in much larger gaseous-induced swelling that substantially increases the stresses in the constrained spent fuel. Based on these results, the radiation-ageing of highly-aged spent nuclear fuel over more than 10,000 years is predicted.