Analysing and Imaging of Fuel Debris Fallout Particles from Fukushima Daiichi Power Plant Accident

Research Area: Nuclear Hazards and Risks
PI: Dr Peter Martin
Partners: Diamond Light Source, Japan Atomic Energy Agency

The Challenge

Although the three nuclear reactors at the Fukushima Daiichi Nuclear Power Plant (FDNPP) were not damaged by the magnitude 9.0 earthquake in 2011, the entire site was inundated by the ensuing 15m high tsunami. Despite the best efforts of the plant’s operators, TEPCO, the progressive failure of emergency infrastructure led to the meltdown of multiple reactor cores and a large release of radioactivity into the environment. Eight years after the accident, significant areas surrounding the FDNPP remain evacuated with some people likely never able to return to their homes.

Relatively little is known about the physical and chemical nature of the large radioactive particles deposited close to the plant and their long-term environmental effects. Therefore, University of Bristol and Japan Atomic Energy Agency (JAEA) researchers have collaborated to jointly undertake fieldwork in the contaminated Fukushima Prefecture before using cutting-edge analytical techniques to establish the source of the material and the potential environmental risks.

The Solution

A small radioactive particle (450μm x 280μm x 250μm) was brought to the UK from within the Fukushima restricted zone, in an area to the north of the nuclear plant.

This was the first experiment of its kind to be performed at Diamond and produced a comprehensive and independent analysis of the sub-mm particulate’s internal structure and 3D elemental distribution. The research used Diamond’s unique combined capabilities of X-ray imaging and fluorescence measurements of the I13 and I18 beamlines, to look at the material from an environmental stability point of view alongside the associated risks.

An X-Ray Tomography scan of the particle

Having identified uranium inclusions, the team then analysed the specific physical and chemical nature of the uranium using the Microfocus Spectroscopy (I18) beamline. By targeting the highly focused x-ray beam onto the regions of interest within the sample and analysing the specific emission signal generated, it was possible to determine that the uranium was of nuclear origin and had not been sourced from the environment.

Final confirmation of the FDNPP origin of the uranium was performed on the particulate using mass-spectrometry methods at the University of Bristol, where the specific uranium signature of the inclusions was matched to reactor Unit 1.

The Impact

The results were able to attribute the material to a specific source on the FDNPP and provide crucial information to explain the events that occurred. The likely scenario is that it was formed when the thermal insulation material in Reactor Unit 1 melted during the loss of cooling. Radiocaesium and other fission products were incorporated into the molten material, and fragments of the structural steel and concrete stuck to the surface after the hydrogen explosion.

                     The elemental make-up of the particle

The particle seems to have been stable for nearly 4 years – the time between being ejected from the plant and being collected for analysis – suggesting a lower potential for radionuclides to leach out into the environment.

This study forms part of an ongoing EPSRC-sponsored project investigating the environmental impact of such Fukushima-derived spent-fuel containing particulate distributed within the environment. The work also has significant relevance beyond nuclear accidents. The analytical approach and techniques developed could be used to image particles in air pollution to attempt to reduce health conditions that result from poor air quality.

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