A Diamond Detector for Monitoring Of Neutron Irradiation and Criticality

Lead Research Organisation: University of Bristol
Department Name: Physics

Abstract

Novel detector instrumentation systems are required to support the operation and decommissioning of our nuclear power stations, either based on fission or fusion technologies. In this project, synthetic diamond will be used as a radiation detector for the measurement of gamma and neutron radiation.

This project will commercialise a well-proven detector which has been used to make measurements inside some of the most hazardous buildings in the world, where fissile and radioactive materials are present.

Based on diamond technology first used in the Large Hadron Collider, this commercialisation project will take the technology from operational proof-of-principle demonstrators developed by the University of Bristol and Sellafield (and used inside reprocessing tanks) to a series of products which will be operated as a service by Cavendish Nuclear Limited.

To achieve commercialisation, this project has solicited support from a wide range of industrial and academic partners in the UK, Japan and Italy. Each member of this international team brings specific expertise and facilities, from Kyoto University's nuclear research reactor, where we will demonstrate the detector's capability to measure the reactor's power output (through neutron flux measurement), to Sellafield's Highly Active Storage Tanks, in which we will demonstrate real-time high gamma dose rate measurement.

Our industrial partners have requested a focus on neutron detection, an important capability they are currently struggling to achieve using existing technology. Neutron detection will be important to prevent accidental criticality and recover from any such event. Our Japanese partners have specifically requested this capability to allow them to safely remove the fuel from within the stricken nuclear reactors at Fukushima Daiichi, and it will be useful in UK facilities safely containing fissile material. A Criticality Incident Detection System (CIDS) is needed in any industrial facility holding fissile material, to mitigate risks to personnel in the event of an accidental criticality. This must detect a criticality and continue to measure afterwards in case of knock-on events. Further testing and development are still needed, but the potential for superseding existing CIDS technologies with a cheaper, more compact and robust alternative is exciting. Neutron detection alongside gamma detection would be highly desirable: on-going pulsed/continuous criticality is not measured by any current devices after an initial event; and there are a multitude of applications in gloveboxes and large facilities for a portable system.

There is equally a need for rapid neutron detection in reactor core environments (fission and fusion), where the neutron flux is far more sustained and intense. Diamond is potentially very well-suited to such applications, with a proven sensitivity to thermal and fast neutrons better than that of gamma radiation. Accordingly, the aim of the current proposal is to develop a diamond detector system capable of detecting moderate-to-high neutron fluxes in real time, with the operator and detection electronics at a safe remote working distance. This will build on the software and hardware already developed for high-dose gamma measurement, increasing the value of the detection system. Such technology will be invaluable for Gen IV fission reactor concepts, including small modular reactors, as well as future fusion reactors, including JET, ITER and DEMO projects, and the UKAEA's recently announced Small Tokomak for commercial Energy Production (STEP) programme.

Longer term, the measurement of neutron energies through spectroscopy will help enable fusion technologies to become realistic. Not only can we use the diamond neutron detectors being developed in this project to measure the reactor power (as above), but we will also be able to demonstrate that the operational fusion reactor is self-sufficient in tritium by breeding its own fuel!

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