Muon scattering at the Fukushima nuclear reactors

On 11 March 2011 a 9.0-magnitude earthquake and enormous tsunami created human and economic catastrophes in Japan on an almost unimaginable scale. (For more about the earthquake, see the news story on page 22 .) Among the infrastructure casualties was the Fukushima Daiichi nuclear power station; more than two years later, the buildings remain almost entirely inaccessible due to high radiation levels. A team from Los Alamos National Laboratory hopes to hasten the dismantlement and remediation efforts by remotely imaging the damaged reactor cores with atmospheric muons produced by cosmic rays. The particles’ penetrating power would produce an x-ray-like image that includes shadows from the denser regions (see the Quick Study by Giulio Saracino and Cristina Cârloganu, Physics Today, December 2012, page 60 ). But because muons are strongly scattered by uranium and other heavy elements, the researchers plan to use their recently developed method that tracks both incident and transmitted particles using two muon detectors, fore and aft of the building. The resulting scattering information can be used to reconstruct the spatial distribution of fuel materials. To demonstrate the feasibility of the approach, the group tested a detector at Fukushima, radiographed both a mockup reactor and a university research reactor, and performed simulations. The simulation results shown here depict an intact 4-m-diameter core (left) and one that is 70% melted with two 40-cm spheres of debris (right). If the proposal is approved and the equipment installed, a few months of data collection would yield the required information. (H. Miyadera et al., AIP Advances 3, 052133, 2013, doi:10.1063/1.4808210 .)