Tritium concentration at Fukushima Water Treatment Facility

[alexzive]

Hello there,

maybe I am wrong but I found something inconsistent between the espected tritium concentration in Newly RO Treated Water (6.7 10^4 bq/l --> graph at pag. 16 here) and last measurement published by Tepco on 22th of August at the Water Treatment Facility (1*10^3 bq/cm3)

Converting the second one 1*10^3 bq/cm3 into bq/l one gets 1*10^6 bq/l = 1.000.000 bq/l much higher than espected concentration of 67000 bq/l !

Where am I wrong ?
Somebody knows if the two data sources are comparable?

Since the last news were about japan governament declaration to consider radioactive water release into the ocean, I think it could be nice to clearify this point.

thanks for any help and regards
Alex
.

 

[DEvens]

It's very hard for me because I don't read (nor speak) Japanese. And one of your citations seems to be labeled in Japanese.

Anyway, it's about a factor of 15. This could easily be one of many things.

• Some mistake in the units
• Different step in some process such as concentrating or diluting
• An operational limit rather than a measurement
• An alarm level rather than a measurement
• A regulatory limit rather than a measurement

The background of Tritium is round about a few Bq/l. This value bounces around some because natural processes can affect isotopic content. For example, evaporation and precipitation can change it.

https://www.sciencedirect.com/topics/materials-science/tritium
The process for releasing Tritium is to dilute it down to a very low value, then release it. So one would dilute that 10^6 Bq/l by a factor of 500,000, then release the result. That's 500 cubic meters of sea water to release 1 liter of contaminated water from the station, if the 10^6 is correct. That's a slug of water 10 meters by 10 meters by 5 meters. Not impossible. Maybe not practical for the amount they have.

The alternative is to extract it from the contaminated water, then store it until it decays. The half life is `12.3 years. Depending on the quantity on hand it may be more reasonable to do this. There are a few places around the world with Tritium removal facilities.

https://betacanteach.candu.org/Content Library/NJC-1-4-12.pdf
One such is at Darlington nuclear station. This facility is used by all the CANDU reactors in Ontario. They have some kilograms of Tritium stored. After it is removed it is stored as metal hydrides. It decays into Helium-3, which in principle can be harvested and sold.

 

[etudiant]

The referenced paper dates from 2016, but does explicitly say in the chart on page 5 that the tritium burden is about 10**6 Bq/liter before and after treatment.
As DEvens notes, there is no graceful way to extract tritium from water, it is hugely expensive, which is why TEPCO would much prefer to dump it. That has not happened, partly because of local opposition, but also because the accumulated water still carries other contaminants as well.
It may be that TEPCO (as a ward of the Japanese government) will need to punt the problem into the future.
Storing the water for some decades in a small number of chartered tankers would be one option for buying time, another would be to use a large in ground tank.
I think some such deferral of the release will happen.

 

[DEvens]

Reporting on nuclear in general, and this incident in particular, is really outstandingly poor. Here is a quote from the Guardian. It seems TEPCO does not have a Tritium extraction plant. There is one in Canada, and one in South Korea. And one planned for Romania. Transporting all that water to a removal facility might be impractical. If that million tonnes is correct then it would require about 8 or 10 of the largest oil tankers.

But the tech exists.

Tepco has attempted to remove most radionuclides from the excess water, but the technology does not exist to rid the water of tritium, a radioactive isotope of hydrogen.

https://www.theguardian.com/environ...-radioactive-water-into-pacific-minister-says

 

[gleem]

The current US standard for allowable concentrations of Tritium in drinking water is 740 Bq/L. This is based on the dose limit for normal water consumption of 4 mrem/yr. International standards vary significantly e.g., Canada's limit is 7000 Bq/L.

 

[Rive]

Maybe you should try contact @turi : he had many contribution in the Fukushima topic about non-english sources.

 

[alexzive]

thanks to all for the replies.

I wonder why the storage of 2 MIL liters of new radioactive water on site would be so expensive for Tepco. It would be a short time temporary storage of about 15 max 20 years to get down to < 100 Bq/l. No special tanks required I suppose since it is "just" tritium water after Cs-137 etc extraction.
Certainly direct dump into the ocean would be the cheapest option. But a well done dilution into the ocean would have some costs too, as it should be on a very large area to maximize dilution and minimize environmental impact.
Also they could have governament money to fund the on-site storage option..

 

[trurle]

It's very hard for me because I don't read (nor speak) Japanese. And one of your citations seems to be labeled in Japanese.

Anyway, it's about a factor of 15. This could easily be one of many things.

• Some mistake in the units
• Different step in some process such as concentrating or diluting
• An operational limit rather than a measurement
• An alarm level rather than a measurement
• A regulatory limit rather than a measurement

The background of Tritium is round about a few Bq/l. This value bounces around some because natural processes can affect isotopic content. For example, evaporation and precipitation can change it.

https://www.sciencedirect.com/topics/materials-science/tritium
The process for releasing Tritium is to dilute it down to a very low value, then release it. So one would dilute that 10^6 Bq/l by a factor of 500,000, then release the result. That's 500 cubic meters of sea water to release 1 liter of contaminated water from the station, if the 10^6 is correct. That's a slug of water 10 meters by 10 meters by 5 meters. Not impossible. Maybe not practical for the amount they have.

The alternative is to extract it from the contaminated water, then store it until it decays. The half life is `12.3 years. Depending on the quantity on hand it may be more reasonable to do this. There are a few places around the world with Tritium removal facilities.

https://betacanteach.candu.org/Content Library/NJC-1-4-12.pdf
One such is at Darlington nuclear station. This facility is used by all the CANDU reactors in Ontario. They have some kilograms of Tritium stored. After it is removed it is stored as metal hydrides. It decays into Helium-3, which in principle can be harvested and sold.

The single-exponent extrapolation is incorrect for the mix of neutron producers (still generating tritium) found in shutdown reactor. Generally for complex isotope mix, radioactivity falls slower than exponentially, therefore 6.9e4 Bq/l extrapolation is meaningless. I would not be much surprised if tritium concentration will be at 2e5 Bq/l in 2019 even in perfectly intact cooling loop. On the other hand, reported much higher 1e6 Bq/l is likely indicating the cracking/disintegration/rusting of irradiated materials somewhere in cooling loop, exposing additional sources of radioactivity to water. Fortunately, data are ruling out new criticality - no short-lived isotopes are detected.

 

[Rive]

Neutron activity there is expected to be low: new tritium production is not significant.

The main problem is that the inflow of ground water also contains tritium, and the concentration might even vary depending on weather/season/work schedule. So the simple decay based approach is not really applicable so long after the accident. This effects the considerations regarding the planned release too: the rate of release is likely to be calculated to keep the final concentration below drinking water limits.

The information about the dangers related to the weak β (electrons, actually) of tritium are controversial: some sources hinting that the lack of actual experimental results are due the need of absurdly high concentrations for the first observed negative effects. With all that, the 'safe' levels might be based only on very conservative assumptions, rather than evidences.

 

[etudiant]

Reporting on nuclear in general, and this incident in particular, is really outstandingly poor. Here is a quote from the Guardian. It seems TEPCO does not have a Tritium extraction plant. There is one in Canada, and one in South Korea. And one planned for Romania. Transporting all that water to a removal facility might be impractical. If that million tonnes is correct then it would require about 8 or 10 of the largest oil tankers.

But the tech exists.https://www.theguardian.com/environ...-radioactive-water-into-pacific-minister-says

Afaik, the tritium extraction is essentially an enrichment process, so hugely expensive if applied to a million ton of source material. Buying a dozen large tankers (cost of around $1 billion) for use as long term (>50 years) storage and leaving them parked until the tritium has decayed sufficiently seems a cheaper alternative.
What remains murky is the degree to which this pool still has other contaminants which would make it unacceptable to dump even then. Otherwise, the tritium levels involved are acceptable, at least compared to existing radiation hot spots such as the Irish Sea or the Baltic.

 

[Gary7]

Its been a while since I waded into rabbit hole of data coming from Tepco, but from what I can gather, the difference is the location of the two sources of the water containing tritium. In the presentation from 2014 (the page 16 to which was previously linked), the water with 67000bq/liter is presumed to be water coming from storage. Note that is an expected value, and not an actual measurement. In Tepco's measurements of August 2019, the water is being taken from the outlet of the desalination system (淡水化装置). I don't know how or why this might account for the difference.

 

[Rive]

Buying a dozen large tankers (cost of around $1 billion) for use as long term (>50 years) storage and leaving them parked until the tritium has decayed sufficiently seems a cheaper alternative.

It is also a solution to pump it down the ground to some layer formation which restrains it for a hundred years or so. But to keep it piling up - that's just not good.