January 7, 2012

Thorium Reactors - Indian and Australian Prospects

This post is about the highly complex scientific and economic topic of thorium reactors. Much is claimed but little appears to have been achieved in any country over the last four decades of thorium breeder reactor research and development. India has put in a considerable amount of its nuclear effort into developing such reactors. My views are:
- thorium reactor research is as difficult a set of tasks (see "Disadvantages" below) as the intense multinational effort that produced the world's first nuclear weapons.
- Compared to building a miniturised submarine reactor (which, in the end, required Russian assistance) India faces a tougher technical hurdle in independently making thorium a mature process.
- there are currently perceptions in most other countries of uranium abundance including all the major nuclear countries, except India.

- Most countries that have embarked on thorium in reactor research programs have closed down programs due to technical difficulties and high relative cost of using thorium. See List of Thorium Fueled Reactors for reference to Indian and foreign reactors partly using thorium.
- if ample uranium were available to India in future its nuclear research effort might also move away from thorium (a complex issue which needs to be considered)

- At least two reactors (CIRUS and DHRUVA) that partly use thorium also have produced significant amounts of weapons grade plutonium. This association of inputs and outputs suggest that part of India's interest in thorium might be weapons driven. This runs conter to the standard belief that reactors using thorium produce less plutonium and thus are more "peaceful". The peacefulness or otherwise of thorium is thus an open question.
- with the post 1998 test sanctions being lifted by most countries (Australia has maintained sanctions) it may well be that India already has sufficient uranium to make continued thorium research (other than for plutonium production) a lower priority.
- without considerable US, European, Japanese and Russian involvement, thorium fuel cycles will not be complete, cost-effective or efficient in other respects for decades. -
Australia's position (or lack of...)
- while Australia has good scientists and some useful theoretical knowledge it has nowhere near the government, academic or commercial resources to assist India with practical thorium applications or standand uranium nuclear reactors.

- India like most major countries is way ahead of Australia in applied nuclear matters.
- in Australia all nuclear research has been intentionally run down by the government for Labor Party unity, environmental green and nuclear free regional utopian reasons.

- the very abundance of Australian uranium and coal likely means that Australia would not seriously consider undeveloped thorium technology for domestic use for decades - and that is after we build our own standard uranium reactors
- any Australian standard power reactors (none are planned) might not go on line before 2035 - probably much later, then add 20 years for thorium/fast breeders.
Comments arising from my post Indian-Australian Differences but Hope November 19, 2009 covered India's nuclear, specifically thorium technology prospects:

jbmoore said... ...If Australia played its cards better, it could come out ahead on any deal. Help the Indians develop thorium reactors (you guys have a lot of thorium deposits). Setup joint research programs between India and Australia...Friday, November 20, 2009 11:07:00 AM"

Parminder Grewal said...
"I have been going through your blog for the last few days. It has a lot of interesting stuff. ...3. Regarding Australia and the uranium politics: India and Australia are both rich in another ore called as thorium. Thorium is a much more cleaner source of nuclear energy than uranium(less dangerous by products), it cannot be used to make nuclear weapons, it is much more abundant (conservative estimates say that Indian reserves can satisfy Indian needs for 350 years, optimistic estimates talk in terms of millenia).
The technology to use thorium exists with the United States since the 1970's but has not been used (my speculation is that this was ensured by the oil companies and uranium industry). India has been planning to do the same and is at stage 2 of her 3 stage plan to develop thorium based reactors (there is speculation that the civilian nuclear deal was partly aimed at blocking this thorium based energy cycle). Thorium could be the ultimate solution to the climate/energy problem for centuries to come but the vested interests of a few companies is stopping that from happening. Its very sad I'd say. Saturday, November 21, 2009 6:43:00 AM"
Wiki contains this fairly clear description of the Thorium fuel cycle:
The thorium fuel cycle is a nuclear fuel cycle that uses the naturally abundant isotope of thorium, 232Th, as fertile material, and the artificial uranium isotope, 233U, as fissile fuel for a nuclear reactor.
However, unlike natural uranium, natural thorium contains only trace amounts of fissile material (such as 231Th) that are insufficient to initiate a nuclear chain reaction. Thus, some fissile material must be mixed with natural thorium in order to initiate the fuel cycle. In a thorium-fueled reactor, 232Th will absorb slow neutrons to produce 233U, which is similar to the process in uranium-fueled reactors whereby fertile 238U absorbs neutrons to form fissile 239Pu.
Depending on the design of the reactor and fuel cycle, the 233U generated is either utilized in situ or chemically separated from the used nuclear fuel and used in new nuclear fuel.

A thorium fuel cycle offers several potential advantages over a uranium fuel cycle, including greater resource abundance, superior physical and nuclear properties of fuel, enhanced proliferation resistance, and reduced plutonium and actinide production.

Concerns about the limits of worldwide uranium resources motivated initial interest in the thorium fuel cycle. It was envisioned that as uranium reserves were depleted, thorium would supplement uranium as a fertile material. However, for most countries uranium was relatively abundant, and research in thorium fuel cycles waned. A notable exception is the Republic of India which is developing a three stage thorium fuel cycle. Recently there has been renewed interest in thorium-based fuels for improving proliferation resistance and waste characteristics of used nuclear fuel.

Thorium fuels have been used in several power and research reactors. One of the earliest efforts to use a thorium fuel cycle took place at Oak Ridge National Laboratory in the 1960s. An experimental Molten Salt Reactor (MSR) technology to study the feasibility of such an approach, using thorium(IV) fluoride salt kept hot enough to be liquid, thus eliminating the need for fabricating fuel elements. This effort culminated in the Molten-Salt Reactor Experiment that used 232Th as the fertile material and 233U as the fissile fuel. Due to a lack of funding, the MSR program was discontinued in 1976.
- Advantages of thorium as a nuclear fuel
There are several potential advantages to thorium-based fuels.
Thorium is estimated to be about three to four times more abundant than uranium in the earth's crust
, although present knowledge of reserves is limited. Current demand for thorium has been satisfied as a by-product of rare-earth extraction from monazite sands. Also, unlike uranium, naturally occurring thorium consists of only a single isotope (232Th) in significant quantities. Consequently, all mined thorium is useful in thermal reactors.
Thorium-based fuels also display favorable physical and chemical properties which improve reactor and repository performance. Because the 233U produced in thorium fuels is inevitably contaminated with 232U, thorium-based used nuclear fuel possesses inherent proliferation resistance. Uranium-232 can not be chemically separated from 233U and has several decay products which emit high energy gamma radiation. These high energy photons are a radiological hazard that necessitate the use of remote handling of separated uranium and aid in the passive detection of such materials. [can also be seen as a toxic disadvantage].
[however plutonium may be worse in toxicity] The long term (on the order of roughly 103 to 106 years) radiological hazard of conventional uranium-based used nuclear fuel is dominated by plutonium and other
minor actinides, after which long-lived fission products become significant contributors again.
Disadvantages of thorium as nuclear fuel
Unlike uranium, natural thorium contains no fissile isotopes; fissile material, generally 233U, 235U, or plutonium, must be supplemented to achieve
criticality. This, along with the high sintering temperature necessary to make thorium-dioxide fuel, complicates the fuel fabrication process. Oak Ridge National Laboratory experimented with thorium-tetrafluoride as fuel in a molten salt reactor from 1964-1969, which was far easier to both process and separate from fuel poisons (contaminants that slow or stop the chain reaction.)

If thorium is used in an
open fuel cycle (i.e. utilizing 233U in-situ), higher burnup is necessary to achieve a favorable neutron economy. Although thorium dioxide has performed well at burnups of 170,000 MWd/t and 150,000 MWd/t at Fort St. Vrain Generating Station and the German AVR reactor [closed 1980], there are challenges associated with achieving this burnup in light water reactors (LWR), which compose the vast majority of existing power reactors.

Another challenge associated with a once-through thorium fuel cycle is the comparatively long time scale over which 232Th breeds to 233U. The
half-life of 233Pa is about 27 days, which is an order of magnitude longer than the half-life of 239Np [Neptunium]. As a result, substantial 233Pa builds into thorium-based fuels. Protactinium-233 is a significant neutron absorber, and although it eventually breeds into fissile 235U, this requires two more neutron absorptions, which degrades neutron economy and increases the likelihood of transuranic production.
Alternately, if thorium is used in a closed fuel cycle in which 233U is recycled, remote handling is necessary for fuel fabrication because of the high radiation dose resulting from the decay products of 232U. This is also true of recycled thorium because of the presence of 228Th, which is part of the 232U decay sequence.
Further, although there is substantial worldwide experience recycling uranium fuels (e.g. PUREX), similar technology for thorium (e.g. THOREX) is still under development.

Although the presence of 232U makes it a challenge, 233U can be used in
fission weapons, but this has been done only occasionally. The United States first tested 233U as part of a bomb core in Operation Teapot in 1955. However, unlike plutonium, 233U can be easily denatured [rendered not suitable for weapons ] by mixing it with natural or depleted uranium.

Despite the fact that thorium-based fuels produce far less long-lived
transuranics than uranium-based fuels, there are some long-lived actinides produced that constitute a long term radiological impact, especially 231Pa.