The brief Asahi Shimbun news item on October 25, 2011, did not clarify where the radioactive ash at the Nagareyama incineration plant was coming from. It was clear there was a lot of it, though; 493 tons in 1,260 bags, crammed into six storage tents in Chiba Prefecture, Japan.
It was also clear the material was a problem. “Disposal sites refuse to accept the waste,” said the report, adding that the bags had been building up since high levels of radioactive caesium were discovered in July. “No decision has been made on where to send the ash.”
But among the handful of insightful reader comments about how to deal with the problem (including “Shoot it into the sun”) was an idea that is getting a lot of attention from nuclear experts at the moment, and not just for handling Nagareyama’s particular challenge.
Facebook user Oleg Tikhon posted a lengthy message extolling the virtues of radioactive waste disposal using a plasma arc torch.
The text bears an uncanny resemblance to that on the website of High Temperature Technologies Corp of Montreal, Canada, one of the few companies worldwide currently espousing plasma-based radioactive waste disposal.
In essence, the concept is a simple one: take low or intermediate-level waste (ILW) and blast it within a sealed furnace, using a plasma arc, to burn off any extraneous materials so nothing but the radioactive residue is left. This can then be packaged in an inert vitreous form.
The reason plasma-based disposal is attracting interest in the nuclear industry is that, as the Nagareyama incineration plant has found, radioactive waste has a habit of building up.
The traditional way of dealing with waste is to encase it in cement, which can easily double the overall volume of the material being handled.
Plasma-based disposal
In contrast, a UK study by the construction company Costain and the plasma-based disposal company Tetronics found that, for wet ILW sludge at least, “the final packaged waste volume produced … is approximately one-tenth that achieved with cement encapsulation.”
Because, according to the study, “the final volume of the packaged waste is likely to be the single biggest factor influencing through-life cost,” this potentially leads to a significant reduction in the costs of handling ILW.
In the UK, for example, Costain and Tetronics estimated that the plasma processing of the country’s wet ILW sludge right up to the repository gate would cost just £287 million, compared to £1.325bn for cementation.
Jeremy Gordon, an analyst at the World Nuclear Association, says: “I understand that all the radioactivity is retained, but you get rid of all the rest of the material, so you don’t have to pay for those non-radioactive substances to be stored and disposed of underground.”
Currently, plasma-based disposal is being employed in Russia and is being looked at in Japan.
But given its economic benefits, and the fact that it is a fairly established procedure for getting rid of other forms of waste, it seems unusual the process has not caught on more widely.
The reason seems to be that plasma-based disposal is not without some catches. Paul Campbell, Costain’s Nuclear Sector Director, says Sellafield in the UK rejected the procedure because of concerns over what to do with any secondary waste that might come from it.
“We have not pushed it for a while,” he says. “We did not really know enough about how much secondary waste we would create within such a plant, but for organic-type kinds of material it seemed to be a good solution.”
Worthy investment
Nevertheless, he hints that sources at Sellafield have stated it would have been worth paying closer attention to the plasma-based disposal option. “I always thought it was worth some investment in parallel with other technologies,” he says. “There are two benefits. “One is volume reduction and the second is the homogeneous, stable end product.”
And others stand by plasma-based disposal’s potential in the nuclear energy industry. The Israeli firm Environmental Energy Resources (EER), for example, is working in Russia on a refinement of the process, called plasma gasification melting (PGM), for low-grade waste.
Developed by the Kurchatov and Radon Institutes in Russia and the Technion Institute in Israel, PGM involves heating waste up to 7,000 degrees centigrade so it turns into an inert, rock-like substance.
EER claims the vitrified material is safe enough to be turned into building blocks and the process itself leaves no surface water, groundwater or soil pollution behind it.
Currently, says EER’s chief executive Ofer Sandelson: “We are focused on municipal waste, hazardous waste and medical waste. But we do plan to be in the nuclear business in the next year or two.
“And we do feel very strongly that we have the most promising technology and we’re confident that once we go to that segment we are going to be very successful.”
Source: NuclearEnergy Insider