The Fukushima Daiichi nuclear disaster on Japan’s east coast in April 2011 was the largest since Russia’s Chernobyl catastrophe in 1986, with potentially even more devastating long-term consequences.
The Fukushima incident followed a strong earthquake with a magnitude of 7.1 Mw, which in turn created a tsunami that sent water flooding into the power plant’s emergency generators.
When these failed, they cut power to the pumps that so critically circulated coolant water to the reactors.
As a consequence the reactors overheated, leading to a significant nuclear incident, with consequential events and damage of sufficient severity for it to be designated a level 7 disaster on the International Nuclear Event Scale, the highest possible.
While there was potentially a brief window of opportunity when flooding the reactors with sea water could have controlled the situation, the moment was missed for fear of damaging the expensive reactors. This left the response team at the site with one major difficulty – they were effectively blind to what was going on deep within.
With conditions worsening by the moment, standard monitoring systems were knocked out one by one, until the response teams were left with a total lack of factual information on which to base rational decisions about how to remedy the situation.
Now, engineers at America’s Penn State University have developed a solution that should prove invaluable when dealing with a similar scenario in future.
Rather than trying to maintain power to sensors, the Penn State University team has developed a monitoring system that doesn’t rely on outside power sources, but is instead driven by the heat of a nuclear reactor itself.
If these ‘thermoacoustic’ sensors had been in place at Fukushima, operators would have been able to monitor the reactor’s fuel rods and the spent fuel in the storage ponds, even though the station’s own systems had gone down.
The sensors have no moving parts that could malfunction under severe conditions, and have need for an external power source, as they are driven by a ‘thermoacoustic engine’ that requires a heat source. In this instance the fuel rod, a stack of ceramic sheets helps channel the heat, and a gas-filled resonator converts heat to sound waves, based on temperature differences along the ceramic stack.
The sound waves, which are of different amplitudes, then pass through the water in storage ponds or surrounding the reactor.
So even when a plant’s electronic networks have long since failed, the new sensors will continue to reveal the vitally important data that the containment teams need.
Further research is now being done to see whether thermoacoustic sound can be used to monitor microstructural changes in nuclear fuel rods and so be employed as a fail-safe device in case of emergency.
With the scientists at the UK’s National Physical Laboratory also working on acoustic sensors for thermometers capable of operating within the extreme conditions of a nuclear reactor, disasters like that at Fukushima will hopefully become a thing of the past.