Nuclear graphite research
Understanding the relationship between graphite microstructure and properties and applying this understanding to model behaviour through life is providing new input to support graphite performance in reactors and to assess decommissioning options.
Crack Propagation in Nuclear Graphite
Andrew Hodgkins, PDRA
In the UK both the 1st generation Magnox nuclear reactors and the 2nd generation advanced gas reactors are moderated using graphite. Previous studies have concluded that many grades of nuclear graphite exhibit rising resistance to crack propagation with increasing crack length. A range of techniques have evolved to measure this effect in different types of material; the most appropriate to any particular material is determined by the microstructural mechanisms that cause it. It has traditionally been assumed that graphite's brittleness lends it well to characterisation by linear elastic fracture mechanics (LEFM) methods. In recent years however it has become clear that these techniques may not accurately describe the true nature of the fracture processes in graphite. The purpose of this project, which was completed in Oct 2005, was to help provide a mechanistic understanding of the crack propagation behaviour of nuclear graphite in order to resolve this issue. Further details on Crack Propagation in Nuclear Graphite.
Irradiation Damage in Graphite Crystal Structures
Keyun Wen, PDRA
Graphite irradiation produces defects that increase the internal energy of the structure. The generally complex defect population evolves over many different length scales. Models for the defect structure and behaviour in graphite have been largely semi-empirical. The behaviour of irradiated graphite during immobilisation and its long-term stability is therefore difficult to predict with certainty. To date, there have been no observations that directly verify the existence of predicted defect structures. Further details on Irradiation Damage in Graphite Crystal Structures
Microstructure/Property Relationships in Nuclear Graphite
Graham Hall, PDRA
Graphite is used in UK gas-cooled reactors as a moderator, a reflector and a structural component, the integrity of which is of major importance for the safe operation and shut-down of the reactor. During reactor operation, fast neutron irradiation and a form of corrosion known as radiolytic oxidation cause significant graphite dimensional and material property changes. This work aims to develop a mechanistic model to relate the changes in microstructure to bulk material properties such as thermal conductivity, strength, Young's modulus and coefficient of thermal expansion.
Microstructure Strains in Graphite
Mark Joyce, PDRA
One of the fundamental property relationships for nuclear graphite is the relationship between elastic modulus (E) and fracture strength (σ). Recent theoretical work has suggested that fracture of nuclear graphite may be modelled may be explained by the statistical combination of multiple fractures of simple brittle elements covering ranges of size and strength and acting in parallel.
Processing and Characterisation of Fuel Particles
Eddie Lopez-Honorato, PhD Student
Developing high temperature reactors is one of future options for use of nuclear energy. Fuel particles will be needed in such reactor. The purpose of this project is to develop CVD technique for producing fuel particles and examine fuel particles using various characterisation techniques. Further details on Processing and Characterisation of Fuel Particles
Relationships between Bulk Mechanical Properties and Microstructures of Nuclear Grade Graphite
Christophe Berre, PDRA
It is well established that bulk properties of materials are related to their microstructures and phenomena like ageing or corrosion play an important role in materials behaviour. 3D images of nuclear graphite microstructures can now be obtained using non-destructive X-ray tomography at many stages of a material's ageing/loading history. This allows changes to be studied in detail. The present study aims to demonstrate the capability of using Finite Element models of microstructures created from 3D tomographic images to evaluate the bulk mechanical properties of nuclear graphite and to relate them to the microstructural changes. Further details on Relationships between Bulk Mechanical Properties and Microstructures of Nuclear Grade Graphite
Stress Analysis of Nuclear Graphite
Derek Tsang, PDRA
During their lifetime, nuclear graphite reactor components distort and develop internal stresses. This is a result of irradiation assisted creep and its complex interaction with thermal gradients, constraints imposed by adjoining components and the structural loads borne. This project aims to develop a constitutive law than includes all these interactions together with the non-linear property changes exhibited by graphite when irradiated. This new constitutive law will be used in more accurate and less conservative predictions of component life and to ensure reactors can run safely for longer. Further details on Stress Analysis of Nuclear Graphite.