The waste management and disposal of irradiated graphite from decommissioned Magnox and AGR reactors is a major challenge for the UK nuclear industry. It is estimated that irradiated graphite (~90,000 tonnes) from the UK's decommissioned reactors represents about one third of the current Intermediate Level Waste (ILW) inventory, a significant financial liability. This classification arises from the predicted carbon 14 concentration of irradiated graphite which equates to approximately 40% of the national carbon 14 inventory. The UK nuclear industry is not alone with this irradiated graphite waste management challenge5. It is currently estimated that the global inventory is of the order 250,000 tonnes; with significant quantities in France, Russia, USA and smaller amounts in Japan, Italy, Germany and Spain.
This proposal seeks to address this waste problem and provide a cost effective solution for its disposal; re-cycling the material as a feedstock for a novel type of thermionic energy converter, termed a Beta-enhanced Thermionic Diamond Converter (BTDC).
This proposal will investigate how beta radiation can be used to improve the operating performance of diamond electrode materials and seek to demonstrate a disruptive technology for producing renewable energy at a lower unit cost and with improved efficiency. Concentrated thermal energy can be harvested from numerous sources including Solar, Geothermal and Nuclear. This energy may be converted into electricity by a device called a thermionic energy converter. Such devices were under intensive development in the 1950s and 1960s as a means to power space craft and extract power from nuclear reactors. The performance of these devices was primarily constrained by the lack of a material electrode surface that could exhibit a stable low work function of less than 1 eV. This limited applications of the technology to those that could supply heat at temperatures exceeding 1200 centigrade. Lithiated nanodiamond offers a key part of a potential solution to this technological barrier. It possesses a very large negative electron affinity due to a unique functionalisation of the diamond surface. This surface has a number of beneficial properties including, chemical, temperature stability, high photoelectric yield and low work function. The novel properties of this lithiated diamond surface also make it attractive for applications in radiation detectors, high brightness electron sources, current amplifiers and ion sources. This proposal seeks to maximise the benefits of this diamond material in a thermionic converter: combining it with plasmonic nanostructures to absorb thermal energy, incorporating a beta radiation source to enhance the conversion of heat to thermionic energy.
Concentrated Solar Thermal Power is a means to generate electrical energy from heat. This project seeks to demonstrate that semiconducting synthetic diamond may be used as a low temperature thermionic emitter material and that its emission performance can be significantly enhanced by harnessing two physical processes, namely, beta irradiation and plasmonic heating.