Japan, South Korea agree on visit to Fukushima nuclear plant ahead of planned water release

[Kid Berwyn]

21. And to the four winds.

Fukushima may have scattered plutonium widely



The upper side of the unit 3 reactor building at Fukushima Daiichi was damaged by a hydrogen explosion. This area housed the spent fuel pool and the fuel handling machines. (Courtesy: TEPCO)

Physics World, 20 Jul 2020

Tiny fragments of plutonium may have been carried more than 200 km by caesium particles released following the meltdown at the Fukushima Daiichi nuclear power plant in Japan in 2011. So says an international group of scientists that has made detailed studies of soil samples at sites close to the damaged reactors. The researchers say the findings shed new light on conditions inside the sealed-off reactors and should aid the plant’s decommissioning.

The disaster at Fukushima occurred after a magnitude-9 earthquake struck off the north-east coast of Japan and sent a 14 m-high tsunami crashing over the plant’s seawalls. With low-lying back-up generators knocked out, the site’s three operating reactors overheated and melted down. At the same time, hot steam reacted with the zirconium cladding of the nuclear fuel, generating hydrogen gas that exploded when it escaped from containment.

Caesium is a volatile fission product created in nuclear fuel. During the Fukushima meltdown, it combined with silica gas created when melting fuel and other reactor materials interacted with the concrete below the damaged reactor vessel. The resulting glass particles, known as caesium-rich microparticles (CsMPs), measure a few microns or tens of microns across.

Snip…

Utsunomiya and co-workers also used mass spectrometry to measure the relative abundance of different plutonium and uranium isotopes within the microparticles. They found that three ratios – uranium-235 to uranium-238, as well as plutonium-239 compared to both plutonium-240 and -242 – all agreed with calculations of the proportions that would have been present in the fuel at the time of the disaster. This agreement, coupled with the fact that the measured amount of uranium-238 was nearly two orders of magnitude greater than would be the case if it had simply evaporated from the melted fuel, led them to conclude that the uranium and plutonium existed as discrete fuel particles within the CsMPs.

Implications for decommissioning

The researchers note that previous studies have shown that plutonium and caesium are distributed differently in the extended area around Fukushima, which suggests that not all CsMPs contain plutonium. However, they say that the fact plutonium is found in some of these particles implies that it could have been transported as far afield as the caesium – up to 230 km from the Fukushima plant.

Continues…

https://physicsworld.com/a/fukushima-may-have-scattered-plutonium-widely/

So. That’s only three years old. Bet a lot of people have never seen it before.