Monitoring radioactive waste with muons

Thursday, 5 July 2018

Muons are high-energy subatomic particles that are created when cosmic rays enter Earth's upper atmosphere. These particles naturally and harmlessly strike the Earth's surface at a rate of some 10,000 muons per square metre per minute. Muon tracking devices detect and track these particles as they pass through objects. Subtle changes in the trajectory of the muons as they penetrate materials and change in direction correlate with material density. Nuclear materials such as uranium and plutonium are very dense and are therefore relatively easy to identify.

The project was led by scientists from National Nuclear Laboratory (NNL), the University of Glasgow and Lynkeos Technology Limited. Lynkeos was founded in August 2016 to develop and build muon tomography detector systems for commercial applications. It was spun off from the Sellafield Ltd Muon Project, which began in 2009 to assess the feasibility of using muons to passively interrogate the contents of legacy waste containers on the Sellafield site.

A full scale detector system has been built in Glasgow using scintillating fibre and photomultiplier technologies after a small-scale prototype system successfully demonstrated, on a variety of industrial test scenarios, high spatial resolution and a high degree of discrimination between different test materials.

NNL said it is currently deploying the technology at Sellafield and the detector has now been commercialised by Lynkeos, ready to be sold on the global market.

Craig Shearer, project leader at NNL, said: "When we first looked at [muon detection technology] in 2009, we thought we had a 50/50 chance of turning this idea into a product that could be commercialised for the nuclear industry. But the results surpassed expectations at every stage."

According to NNL, the technology "could have major implications for nuclear decommissioning, the storing of historic waste and the testing of new waste management techniques". Traditional x-ray technology cannot be used to examine the contents of radioactive waste containers as they are designed to prevent radiation penetration. The new system uses muons to create high-resolution 3D images of shielded objects without opening the containers.

Ralf Kaiser, CEO of Lynkeos, said: "The Muon Imaging System can be used for a variety of purposes, whether that's inspecting old/spent material used in nuclear production to see if it's safe to store, for imaging the products of thermal treatment processes or inspecting historic waste without needing to chip away at its concrete encasing."

He added, "This form of detection is providing the nuclear industry with an inexpensive method for testing waste materials, to which there is currently no other technological option. This should help to significantly lower costs within the nuclear industry."

Muon detection systems have been used to investigate the location of molten fuel within the damaged reactors at the Fukushima Daiichi plant in Japan.