Nuclear forensics in response to the Fukushima Daiichi Nuclear Power Plant accident

The Challenge

The accident at Japan’s Fukushima Daiichi Nuclear Power Plant (FDNPP) in March 2011 released vast quantities of highly-radioactive material into the local as well as global environment, having been rated by the International Atomic Energy Agency (IAEA) at the same “globally-significant” severity as the Chernobyl accident in 1986.

However, despite a large international effort having been made in the years since the accident, little is still known about much of this ejecta particulates form, composition in addition to its resulting long and short-term environmental behaviour.

The Solution

Resulting from the unique collaboration that exists between the University of Bristol and the Japan Atomic Energy Agency (JAEA) Collaborative Laboratories for Advanced Decommissioning Science (CLADS), a unique set of sub-mm particulate samples were donated to the University.

To investigate the cause of the accident and its environmental legacy, cutting-edge analytical techniques utilised more extensively within conventional materials analysis were employed to detail the fundamental form and compositions of this ejecta particulate.

After successfully developing a unique sample environment to safely contain the radioactive material; x-ray tomography (XRT), x-ray fluorescence (XRF) and secondary ion mass spectrometry (SIMS) alongside synchrotron radiation x-ray absorption spectroscopy (SR-XAS) and routine electron microscopy were together used to interrogate the sample material.

The Impact:

Analysis of material isolated from localities surrounding the FDNPP has identified a wide range of fission and activation products in addition to fragments of spent nuclear fuel and reactor construction materials contained as inclusions within the larger (sub-mm) sized particulate.

Synchrotron radiation analysis of the oxidation state of each of the uranium fragments has confirmed that each exists in the reduced (IV) state, with SIMS analysis confirming its origin from the FDNPP reactors.

With the repopulation of numerous formerly evacuated towns and villages already underway or set to commence in the coming months, this knowledge of not only the state but also the distribution of such radioactive particulate will be crucial in redefining the “risk-map” associated with the incident.

Fig 1: Synchrotron radiation XRT cross-sections through a typical ejecta particle. Highlighted is a steel composition inclusion that exists within the highly-porous (24%void volume) bulk particle.