At the present time, over a million tonnes of tritium-contaminated water are being held in about a thousand tanks at the site of the Fukushima Daichi nuclear power station in Japan. This is being added to at the rate of ~300 tonnes a day from the water being pumped to keep cool the melted nuclear fuels from the three destroyed reactors at Fukushima. Therefore new tanks are having to built each week to cope with the influx.
These problems constitute a sharp reminder to the world’s media that the nuclear disaster at Fukushima did not end in 2011 and is continuing with no end in sight.
Recently TEPCO / Japanese Government have been proposing to dilute, then dump, some or all of these tritium-contaminated waters from Fukushima into the sea off the coast of Japan. This has been opposed by Japanese fishermen and environment groups.
There has been quite a media debate, especially in Japan, about the merits and demerits of dumping tritium into the sea. It remains to be seen whether the newly-appointed (and reportedly anti-nuclear) Japanese Environment Minister, Shinjiro Koizumi, will agree to these proposals.
Many opinions have been voiced in the debate: most are either incorrect or uninformed or both. This post aims to rectify matters and put the discussion on a more sound technical basis – especially for Mr Koizumi’s information.
- TEPCO / Japanese Government have argued that, as tritium is naturally-occurring, it is OK to discharge more of it. This argument is partly correct but misleading. It is true that tritium is created in the stratosphere by cosmic ray bombardment but the argument that because it exists naturally it’s OK to dump more is false. For example, dioxins, furans and ozone are all highly toxic and occur naturally, but dumping more of them into the environment would be regarded as anti-social and to be avoided.
- TEPCO / Japanese Government have argued that it is safe to dump tritium because it already exists in the sea. Yes, tritium is there but at low concentrations of a few becquerels per litre (Bq/l). But the tritium concentrations in the holding tanks at Fukushima are typically about a megabecquerel per litre (MBq/l). In layman terms, that’s about a million times more concentrated.
- TEPCO / Japanese Government have argued coastal nuclear plants routinely dump water that contains tritium into the ocean. Yes, this does (regrettably) occur as their cooling waters become tritiated during their transits of reactor cooling circuits. But the annual amounts are small compared with what is being proposed at Fukushima. A one GW(e) BWR reactor typically releases about a terabecquerel (trillion Bq) of tritium to sea annually. But Fukushima’s tanks hold about one petabecquerel (PBq or a thousand trillion Bq) of tritium – ie a thousand times more. A much bigger problem.
- Readers may well ask where is all this tritium coming from? Most (or maybe all) the tritium will come from the concrete structures of the ruined Fukushima reactor buildings. After ~40 years’ operation they are extremely contaminated with tritium. (Recall that tritium is both an activation product and a tertiary fission product of nuclear fission.) And, yes, this is the case for all decommissioned (and by corollary, existing) reactors: their concrete structures are all highly contaminated with tritium. The older the station, the more contaminated it is. In my view, this problem constitutes an argument for not building more nuclear power stations: at the end of their lives, all reactor hulks will remain radioactive for over 100 years.
So what is to be done?
Some observers have argued that, ideally, the tritium should be separated out of the tank waters. Some isotopic tritium removal technologies have been proposed, eg by the IAEA, but it’s a complicated picture. The only operating facility I’m aware of, is located at Darlington near Toronto in Canada, though secret military separation facilities may exist in the US or France.
However the Darlington facility was extremely expensive to construct ( ~12 years to build and to get working properly), and its operation consumes large amounts of electricity obtained from the Darlington nuclear power station nearby. Its raison d’etre is to recover very expensive deuterium for Canadian heavy water reactors.
Other proposed remedies will probably be more expensive. One problem is basic physics. The tritium is in the form of tritiated water, which is water too so that chemical separation or filtration methods simply do not work. Another problem is inefficiency: with isotope separation, one would have to put the source hydrogen through thousands of times to get even small amounts of separated non-radioactive hydrogen. A third problem is that hydrogen, as the smallest element, is notoriously difficult to contain, so that gaseous tritium emissions would be very large each year.
None of these technologies is recommended as a solution for Japan as any such facility would release very large amounts of tritium gas and tritiated water vapour to air each year, as occurs at Darlington. Tritium gas is very quickly converted to tritiated water vapour in the environment. The inhalation of tritiated water vapour from any mooted Japanese facility would likely result in higher collective doses than the ingestion of tritiated sea food, were the tritium to be dumped in the sea.
I recommend neither of these proposed solutions.
There are no easy answers here. Barring a miraculous technical discovery which is unlikely, I think TEPCO/Japanese Govt will have to buy more land and keep on building more holding tanks to allow for tritium decay to take place. Ten half lives for tritium is 123 years: that’s how long these tanks will have to last – at least.
This will allow time not only for tritium to decay, but also for politicians to reflect on the wisdom of their support for nuclear power.
Dr Ian Fairlie
This post first appeared in Ian Fairlie’s blog