Environmental radioactive particles

Research purpose and contents

The main objective of this research theme is to protect persons from the environmental release of materials originating from the Fukushima Daiichi Nuclear Power Station (FDNPS) accident.

Extremely unique radioactive particles (termed Cs-bearing particles, Cs microparticles, and so on…) were widely emitted into the environment in the early of Fukushima Daiichi Nuclear Power Station (FDNPS) accident. These unique particles, composed predominantly of silicate, also contain significant amounts of radioactive caesium that has not been observed during similarly nuclear power station and facility accidents. Several questions exist associated with this particulate material, including; where was it generated, how much remains in the reactor buildings, and the mechanisms associated with their release. Protecting people and the environment from an unexpected environmental release, particle characterisation, and estimating the total number of particles remaining in the reactor building are therefore important.

All particles were obtained from land close to FDNPS owing to the CLADS main building (Tomioka, Futaba-gun, Fukushima prefecture) not possessing the required handling permissions for samples collected on the FDNPS site. Particle isolation from environmental samples (such as soil and dust) was performed ahead of characterisation using a scanning electron microscopy (SEM) with associated elemental analysis using an Energy Dispersive X-ray Spectroscopy (EDS) - all performed at CLADS. Following this analysis, the particles were then transported for non-destructive synchrotron analysis (e.g. SPring-8 (Hyogo), Diamond Light Source (Didcot, UK)), and also other collaborating institute and universities. Destructive analysis to determination Pu and Sr was performing by Prof Atsushi Shinohara and his team in Osaka University. This research in the UK uses the strong international collaboration with Prof Thomas B. Scott (University of Bristol, Bristol, UK) and his team, to analyse the internal structure of the particulate and reveal its likely production history.

Autoradiography system

Scanning electron microscope (SEM) with Energy Dispersive X-ray Spectruscopy(EDS)

Dynamic Secondary ion mass spectrometer(SIMS)

Type B particle from Unit 1 of FDNPS

Current achievement

Research results show that particles discharged from Unit 1 on the 12th March 2011 (termed ‘Type B’) have a structure and composition suggestive that it formed from materials associated with the reactor Unit 1 building explosion, with fuel debris fragments such as uranium and iron embedded into the particles surface. In addition, the particles contain a significant void volume. Such a high void ratio, comparable to geological pumice, suggests such material formed during a rapid depressurisation in hydrogen explosion of 12th March 2011.

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