Nuclear fuels breeding

In the current structure of nuclear power, light water reactors (LWRs) are predominant over a small number of heavy water reactors (HWRs), and even smaller number of fast breeder reactors (FBRs). However, an increase of FBR share can be predicted for the future, taking into account their unique properties. First of all, there is the capability of nuclear fuel breeding by involving into the fuel cycle. Secondly, there is the fast reactor s flexibility permitting its use as plutonium incinerators and minor actinides transmutation. Thus, unless new sources of energy are found, the development of nuclear power will be necessarily based on fast breeder reactors. 

For the next few decades, saving of uranium resources by nuclear fuel breeding will not be of primary importance for countries with a significant nuclear power sector. This is caused by a number of factors, namely (a) accumulation of plutonium as a result of reprocessing of spent fuel of the operating NPPs (b) release of considerable amount of plutonium and enriched uranium owing to disarmament (c) decrease of uranium consumption in the military industry (d) slowing down of the rate of nuclear power development and (e) ready availability of fossil fuels (natural gas and oil). 

It should be noted that in other South and East Asia countries with few indigenous fossil fuel and little uranium ore reserves there is the same situation concerning effective nuclear fuel breeding by LMFR. Republic of Korea s LMFR program consists of development, design and construction of a prototype reactor of 150-350 MW(e) power. The first fully-proven reactor is planned to be in operation by 2025. In China, experimental fast reactor CEFR-25 is planned to become critical in 2005. 

Apparently, realization of this scenario of the nuclear power development in Russia after 2015 will require more extensive inculcation of fast reactors using their fundamental feature nuclear fuel breeding. 

The main objective of the development of the RBEC lead-bismuth cooled fast reactor was to provide a reliable solution for nuclear fuel breeding, while using an approach alternative to sodium cooled fast reactors. It was assumed that design development of a nuclear power plant (NPP) with such reactor could be completed in a rather short period, with modest expenditures for additional testing and qualification of separate equipment units. 

The only large-scale use of deuterium in industry is as a moderator, in the form of D2O, for nuclear reactors. Because of its favorable slowing-down properties and its small capture cross section for neutrons, deuterium moderation permits the use of uranium containing the natural abundance of uranium-235, thus avoiding an isotope enrichment step in the preparation of reactor fuel. Heavy water-moderated thermal neutron reactors fueled with uranium-233 and surrounded with a natural thorium blanket offer the prospect of successful fuel breeding, ie, production of greater amounts of (by neutron capture in thorium) than are consumed by nuclear fission in the operation of the reactor. The advantages of heavy water-moderated reactors are difficult to assess. 

Along with these power plants, the U.S. could build up a fuel reprocessing capability to allow spent nuclear fuel to be reused which would lower fuel cost and eliminate the storage of high-level nuclear waste. Fuel for the reactors has been estimated to be available for 1,000 years using standard reactors with high breeding ratios and breeder reactors where more fuel is produced than consumed. 

Thorium, as well as uranium, can be used as a nuclear fuel. Although not fissile itself, thorium-232 (232Th) can be used as a nuclear fuel through breeding to 233U, which is fissile. Hence, like 238U, it is fertile. 

As the reactor runs and is split, some of the excess neutrons are absorbed by 2 U to produce Pu. The Pu is then separated out and used to fuel another reactor. Such a reactor thus breeds nuclear fuel as it operates. 

Uranium (ca. 20% is used as the fuel, but mainly with 239pu in the form of a UO2/PUO2 mixture. The breeding blanket consists of depleted uranium from isotope separation plants or from reprocessing plants for spent nuclear fuels. Axially movable boron carbide absorbers are distributed in the fuel zone for shutting down purposes. The uranium utilized can be ca. 100 times better utilized than e.g. in light-water reactors. 

The Integral Fast Reactor would also be capable of breeding plutonium which could be used as nuclear fuel. This type of reactor was seen as the key to a nuclear future. Liquid sodium is a volatile substance that can burst into flames if it comes into contact with either air or water. An early liquid sodium-cooled breeder reactor, the Fermi I, had a melting accident when 2% of the core melted after a few days of operation. Four years later when the reactor was about to be put into operation again a small liquid sodium explosion occurred in the piping. 

In a typical breeder reactor, nuclear fuel containing uranium-235 or plutonium-239 is mixed with uranium-238 so that breeding takes place within the core. For every uranium-235 (or plutonium-239) nucleus undergoing fission, more than one neutron is captured by uranium-238 to generate plutonium-239. Thus, the stockpile of fissionable material can be steadily increased as the starting nuclear fuels are consumed. It takes... 

The sole reason for using thorium in nuclear reactors is the fact that thorium ( Th) is not fissile, but can be converted to uranium-233 (fissile) via neutron capture. Uranium-233 is an isotope of uranium that does not occur in nature. When a thermal neutron is absorbed by this isotope, the number of neutrons produced is sufficiently larger than two, which permits breeding in a thermal nuclear reactor. No other fuel can be used for thermal breeding applications. It has the superior nuclear properties of the thorium fuel cycle when applied in thermal reactors that motivated the development of thorium-based fuels. The development of the uranium fuel cycle preceded that of thorium because of the natural occurrence of a fissile isotope in natural uranium, uranium-235, which was capable of sustaining a nuclear chain reaction. Once the utilization of uranium dioxide nuclear fuels had been established, development of the compound thorium dioxide logically followed. 

The nuclear properties of a material must be the first consideration in the selection of a suitable nuclear fuel. Principle properties are those bearing on neutron economy absorption and fission cross sections, the reactions and products that result, neutron production, and the energy released. These are properties of a specific nuclide, such as Th, and its product during breeding,... 

Estimates of world energy resources are summarized. It is pointed out that the great effort to exploit nuclear energy can be justified only if it is directed toward a full utilization of uranium and thorium. Without breeding, nuclear fuels will only supply energy for a few decades in the future energy-hungry world. 

If the consumption of uranium continues at the current level and is used only for LWRs, the uranium resources for energy sources will be available for less than 100 years. However, if the nuclear fuel cycles are established and fuel breeding is achieved in FRs, then the duration of the use of uranium resources will be extended to several thousand years. In addition, if uranium in seawater becomes usable, the duration of use will exceed more than a million years. To that end, it is important to build nuclear reactors that can breed fuel and to develop nuclear fuel cycles, which can efficiently extract reusable nuclear fuel materials after burning. 

RUMYANTSEV, A., et al.. Comparison of the wide-scale nuclear power development concepts with expanded fuel breeding and without it from the viewpoint of minimizing the proliferation risk (Paper presented at Int. Workshop on Methodologies of Quantitative Assessment of Nuclear Fuel Cycle Proliferation Resistance, June 2003, Obninsk, Russia). 

Being a fast reactor with a breeding ratio of-1.0016, the RAPED could also contribute to the effective use of uranium resources, once a closed nuclear fuel cycle is established. 

The capability of fissile self-sustainable regime (core breeding ratio 1) in a closed nuclear fuel cycle with mixed uranium-plutonium fuel (oxide or nitride) ... 

All aspects of closed uranium-plutonium (U-Pu) and thorium-uranium (Th-U) fuel cycles with optimal utilization/ breeding of the nuclear fuel ... 

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