Fuel corrosion processes under waste disposal conditions

In many parts of the world, groundwater resources are under increasing threat from growing demands, wasteful use, and contamination. To face the challenge, good planning and management practices are needed. A key to the management of groundwater is the ability to model the movement of fluids and contaminants. The purpose of this book is to construct conceptual and mathematical models that can provide the information required for making decisions associated with the management of groundwater resources, and the remediation of contaminated aquifers. The basic approach of this book is to accurately describe the underlying physics of groundwater flow and solute transport in heterogeneous porous media, starting at the microscopic level, and to rigorously derive their mathematical representations at the macroscopic levels.

Modeling groundwater flow and contaminant transport

To design reliable and safe geological repositories it is critical to understand how the characteristics of spent nuclear fuel evolve with time, and how this affects the storage environment.

Long-term storage of spent nuclear fuel

Thorium fuel cycle : potential benefits and challenges

The primary waste form resulting from nuclear energy production is spent nuclear fuel (SNF). There are a number of different types of fuel, but they are predominantly uranium based, mainly UO 2 or, in some cases, metallic U. The UO 2 in SNF is a redox-sensitive semiconductor consisting of a fine-grained (5-10 μm), polycrystalline aggregate containing fission-product and transuranium elements in concentrations of 4 to 6 atomic percent. The challenge is to predict the long-term behavior of UO 2 under a range of redox conditions. Experimental results and observations from natural systems, such as the Oklo natural reactors, have been used to assess the long-term performance of SNF.

Spent Nuclear Fuel

Many current concepts for the engineered barriers of high-level waste repositories include a bentonite buffer or backfill which will be exposed to significantly raised temperatures for a period of decades to centuries. To assess its stability, available experimental and natural analogue data on thermally-exposed bentonite is reviewed. The two main alteration processes identified are cementation by precipitation of SiO 2 and transformation of smectite to non-expandable illite layers. These may lead to reduced swelling and loss of plasticity as well as increased hydraulic conductivity and diffusivity. Relevant data for repository conditions from both laboratory and field studies is scarce, but nevertheless yields a fairly consistent picture. Thus, no significant changes of hydraulic and mechanical properties have been reported for bentonite materials exposed to temperatures of at least 120 °C under wet conditions. The data suggest significant cementation and perhaps also illitisation effects occur at 150 °C and beyond. Interestingly, natural analogue bentonite samples that showed substantial cementation and illitisation effects still displayed rather favourable hydraulic properties. Under dry conditions, bentonite is stable to higher temperatures – maybe as high as 350 °C. In order to verify the findings from this work and to get more reliable information at temperatures beyond 130 °C, a series of long-term experiments examining hydraulic, mechanical and mineralogical changes under realistic conditions would be useful.

Performance of the bentonite barrier at temperatures beyond 100 °C: A critical review

Spent fuel radionuclide source-term model for assessing spent fuel performance in geological disposal. Part I: Assessment of the instant release fraction

Performance of the bentonite barrier beyond 100 C: a critical review

An integrated experimental approach to mechanistic studies of the leaching and dissolution of irradiated UO2fuel is described. The program includes an investigation of the solubility of the UO2 mat...

L. H. Johnson

Papers

Performance of the bentonite barrier at temperatures beyond 100 °C: A critical review

Spent fuel radionuclide source-term model for assessing spent fuel performance in geological disposal. Part I: Assessment of the instant release fraction

Performance of the bentonite barrier beyond 100 C: a critical review

Mechanisms of Leaching and Dissolution of UO2 Fuel

The effects of the alpha-radiolysis of water on the corrosion of uo2