Thursday, January 29, 2009

The Aqueous Homogeneous Reactor Lives!

I'm a big fan of the aqueous homogeneous reactor. These are nuclear reactors that have their fissile fuel in an aqueous solution, rather than as solid fuel rods. Back in the late 1950s there was a major program at ORNL to try and develop an AHR on the Th-U233 cycle for commercial power production, but extreme corrosion issues resulted in the cancellation of the program. ORNL researchers decided (rightly, in my opinion) that molten-salt reactors were a better idea.

Soviet researchers never attempted to develop AHRs for power production, but they did develop these reactors for a practical application: radioisotope production for medical use, in addition to certain research applications. To this end they developed a series of AHRs culminating in the ARGUS: a miniature AHR producing a mere 20-50 kw thermal.

The ARGUS reactor: it's a wee little beastie

The AHR has two big advantageous for medical isotope production: firstly, its fluid fuel form makes extraction of isotopes from the fuel much simpler than from solid-fuel reactors. Secondly, AHRs have excellent safety characteristics. They have strongly negative temperature and void coefficients, making them essentially self-controlling. However, the corrosion issues associated with uranyl sulphate fuel have resulted in the abandonment of AHR research in most of the world. This is not the case, however, in Russia. In September of last year the Physico-Energetic Institute in Obninsk (normally known as the Institute for Physics and Power Engineering) announced plans to build a new nuclear medicine facility on the basis of a modernized AHR:
На промышленной площадке ГНЦ РФ «Физико-энергетический институт» в г. Обнинске Московской области предлагается создать комплекс по производству радиоизотопов на основе новой технологии с применением растворного реактора малой мощности. Как отметили в ФЭИ, проект растворного реактора для наработки и выделения радиоизотопов непосредственно из топливного раствора является одной из самых существенных разработок, осуществленных с участием радиохимиков. По словам директора отделения изотопов и радиофармпрепаратов ФЭИ Николая Нерозина, проект позволяет использовать реактор малой мощности 50(82) кВт для получения следующих изотопов медицинского назначения: Mo-99, Sr-89, Xe-133, а также смеси изотопов йода.

In the industrial sector of the GNTs RF "Physico-Energetic Institute" in the city of Obninsk, Moscow Oblast, the construction of a complex for the production of radioisotopes on the basis of new technology utilizing a solution reactor of low power is planned. As described by FEI, the project for a solution reactor for the production and extraction of radioisotopes extracted directly from the fuel solution is one of the most significant developments, being carried out with the assistance of radiochemists. In the words of the director of production of isotopes and radiopharmaceuticals Nikolai Nerozin, the project will utilize a reactor of low power 50(82) kWt for the production of the following isotopes with medical uses: Mo-99, Sr-89, Xe-133, and also a variety of isotopes of iodine.
From the published articles I gather that this reactor will be an evolved version of the ARGUS, designed to operate on 20% U-235 rather than the HEU utilized in the original ARGUS. Given the recent economic downturn, these plans for a new AHR in Obninsk may be scrapped, but clearly the researchers at the Kurchatov Institute and IPPE believe that the AHR is the solution to the worldwide problem of producing radioistopes for nuclear medicine without resorting to reactors using HEU. Personally, I wish them all the success in the world.


DV8 2XL said...

Good for them if they pull it off. Frankly I'll wait till I see something actually working before I'll believe it.

I have spent a lot of time studying this type of reactor, and the problems of running one economically are enormous. If they have come up with some new ideas, or new materials, or are using novel bath chemistry in the core, this is news indeed.

But like I said; I won't hold my breath.

Sovietologist said...

They seem confident that they have solved the problems of the original ARGUS reactors, but none of the articles I've seen explains quite how. I'm not sure if the Russians are just leagues ahead of everybody if if they're overly anxious to deploy exotic nuclear technologies--for instance, the big push to build the BN-800 LMFBR, which has been heavily criticized even within the Russian nuclear establishment. Time will tell. It would be very nice if they make this work, though, since medical isotope production could really benefit from some modern capacity.

Charles Barton said...

My father worked briefly on the ORNL Aqueous Homogeneous Reactor project, I have written about the Aqueous Homogeneous Reactor at ORNL. Eugene Wigner was the big sponsor. Alvin Weinberg was a supporter until the AEC decided to shut the project down. An AEC evaluation had determined that the Molten Salt Reactor was a far more promising project than the Aqueous Homogeneous Reactor. My father worked briefly on the Aqueous Homogeneous Reactor just before its shutdown, but was associated with Molten Salt Reactor research from 1950 to 1969.

Wigner liked the Aqueous Homogeneous Reactor because of its ability to do continuous online fuel processing, which also makes it attractive for radio isotope production. Of course continuous radioisotope processing is also possible with MSRs, but the technology is more challenging, even if the rewards are potentially far greater.

DV8 2XL said...

I see they are not planning to produce isotopes in the core solution proper, but are they just using the reactor a neutron source. If this is so there are other ways of generating a neutron flux which might be easier, and less expensive.

Sovietologist said...

Are you thinking of spallation?

DV8 2XL said...

Spallation and Farnsworth-Hirsch fusors, plasma focus,(which Nikolay Filippov has been working on at Kurchatov), and light ion accelerators, all of which seem to me to be better in that the neutron production can be turned on and off with a switch.

What the comparative flux of these sources are I cannot say, but I would think that it would be comparable with a 20% enriched U aqueous core reactor.

Sovietologist said...

It turns out that I goofed up in my hurried translation and rendered непосредственно as though it were непосредство. The plan, as it turns out, it to produce radioisotopes directly from the fuel. I apologize; I was sloppy.

I found a 2006 journal article that explained the rationale for the new AHR as follows:

The advantage of a solution minireactor with a power of only 20 kW is obvious. The expected productivity of the
Argus reactor (1.5–1.8)·103 GBq 89Sr per year is not much less than that of the BOR-60 reactor at power 60 MW
(≈4·103 GBq/yr). It should be kept in mind that 89Sr in a solution reactor is a secondary product. The target radionuclide is
separated spontaneously, most of the fission products remain in the fuel, and the amount of radioactive wastes escaping from
the reactor, using the new technology, is negligible. The separated impurities 133Xe and 135Xe also find application in
medicine and 137Cs is used in industrial technology.

The aggregate state of the fuel of a solution reactor opens up prospects for using nuclear facilities of this type to produce
medical radionuclides. Separation of radionuclides directly from the fuel solution makes it possible to use a ~50 kW reactor to obtain 90Mo in quantities of at least 18.5·103 GBq/day, 133Xe in quantities of about 700 GBq/day, and certain other radionuclides [18, 19].

The most significant advantages of the new technology over the conventional technology are as follows:
• use of a low-power reactor;
• substantial decrease of the production of radioactive wastes;
• use of almost 100% 235U, as opposed to 0.5%, when irradiating targets for producing medical radionuclides;
• possibility of using low-enrichment fuel (up to 20% 235U); and
• substantial decrease of technological costs by eliminating labor-intensive, radiation-hazardous, and expensive

DV8 2XL said...

Well that is interesting and quite astonishing, if it is true. I doubt we will know all the details of how they doing this, but I will be waiting to see if they do pull it off.

I can tell you right now the core chemistry to produce what they are claiming is - unclear - to me at the moment, and I will have to do some calculations to see if the neutronics work out as stated. Time to dust off my notes.

Sovietologist said...

Here's the link to the journal article: 89Sr production in a reactor with solution fuel published in the May 2006 issue of Atomnaia Energiia. Let me know what you think.

DV8 2XL said...

Thank-you for linking to the paper. Yes indeed this method of producing SR 89 would work, however I cannot see it being a huge improvement over the current method of converting strontium salts via thermal neutrons in as it is done currently. At any rate there isn't a shortage of this isotope at present.

I was more interested in the claim from the press release that they were able to produce Mo 99 and the iodine series with this system, and the paper was silent on those.

Current work being done in the States using a LINAC that can service multiple targets seems more promising.

I'm going to say that I suspect that the story in press was a bit over enthusiastic and poorly researched (as these things are wont to be these days) and I think that what we are seeing is an excuse to keep working on AHRs, which in itself is a good thing, but this is no easy solution to radioisotope production.

DV8 2XL said...

I have found an older paper from about ten years ago which reports on the production of Mo-99 with the ARGUS at the Kurchatov Institute.


Details are very sparse but it would seem that they had some success. There is much detail on the purity of the recovered material, although precious little on just how much of the isotope was produced.

I'm sorry if I sound suspicious and jaded, but this reactor type has been the subject of several attempts to make it practical and enthusiasm tends to run higher than the evidence warrants. This I'm afraid doesn't look like it's panning out any different than usual.