Thermal breeder

Solvent extraction can be carried out in pulsated extraction columns, in mixer-settlers or in centrifuge extractors. Organic compounds such as esters of phosphoric acid, ketones, ethers or long-chain amines are applied as extractants for U and Pu. Some extraction procedures are listed in Table 11.11. The Purex process has found wide application because it may be applied for various kinds of fuel, including that from fast breeder reactors. The Thorex process is a modification of the Purex process and has been developed for reprocessing of fuel from thermal breeders. 

J. R. Lamarsh, Introduction to Nuclear Engineering, Addison-Wesley, Reading, MA, 1975 A. M. Perry, A. M. Weinberg, Thermal Breeder Reactors, Annu. Rev. Nucl. Sci. 22, 317 (1972)... 

FIG. 19.9. Conversion ratios and fuel utilization efficiencies. (From Thermal Breeder Consultants Group, Saldiuig, 1977.)... 

Consequently much more effort has been put into the development of fast plutonium breeders than into thermal breeders. 

In the thermal breeder reactor, is produced from Th. The reactor may be designed either with a core containing a mixture of Th and or with a central zone core) of surrounded by an outer layer blanket) of Th. However, it is necessary to minimize parasitic neutron capture in structmal materials including monitoring systems, control rods, etc. Calculations have shown that a conversion ratio of 1.06 should be possible. 

In the case of 23 breeders, except for the value of /, all fundamental problems appear capable of solution. This does not mean that a breeder can be built tomorrow, but that the problems are not too difficult and that after reaching a certain point in our studies, the balance of the unknowns can be solved in a reasonable time. A large part of this is due to the chemists at X who have done an excellent job of preliminary investigation. Fundamentally, the 23 thermal breeder would probably look something like the diagrammatic sketch below. 

Fig. 1. Early design of a thermal breeder. See text for a more detailed description...

Figure 1 may illustrate the general character of our thinking. It shows one of the early designs for a thermal breeder. Admittedly, it is a somewhat weird design, much more weird than the majority of our ideas, but it appears to me characteristic of the strengths, and perhaps even more, of the weaknesses of the early thinking. 

You will note that the breeding ratio of the mixed fast-thermal breeder is lower than that of the fast breeder, which may reach the value 2. The purpose... 

The MSBR was a Th-U cycle thermal breeder applying continuous chemical processing of fuel in situ and periodic core graphite replacement to improve breeding performance [XXX-3]. 

The power output of such a breeder with a three-year doubling time is about 10,000 kw, and this was established as a new goal for the homogeneous reactor. The reactor, then, was conceived to be a prototype homogeneous reactor and thermal breeder in addition, it was conceived as an all-purpose experimental tool with a neutron flux higher than any other reactor. 

Mwd/ton. Although such a fuel consumption might be obtaine.i in high-neutron-economy converter reactors through recycling of the fuel, it seems likely that even the best such reactor may fall short of this goal and that both fast and thermal breeders will be needed. 

Fig. 6-1. Poison effect as a function of chemical group in core of two-region thermal breeder.

A. T. Gresky and E. D. Arnold, Poisoning of the Core of the Two-region Homogeneous Thermal Breeder Study No. 2, USAEC Report ORNL CF-54-2-208, Oak Ridge National Laboratory, 1954. 

E. D. Arnold et al.. Preliminary Cost Estimation Chemical Processing and Fuel Costs for a Thermal Breeder Reactor Station, US. EG Report ORNL-1761, Oak Ridge National Laboratory, Jan. 27, 1955. 

The liciuid-metal system that has received the greatest emphasis to date is of the heterogeneous, circulating fuel type. This reactor, known as the Liquid iMetal Fuel Reactor (LMFR), has as its fuel a dilute solution of enriched uranium in liquid bismuth, and graphite is u.scd as both moderator and reflector. With as the fuel and Th as the fertile material, the reactor can be designed as a thermal breeder. Consideration is restricted here to this reactor type but, wherever possible, information of a general nature is included. 

This leads to the obvious conclusion that changes in the nuclear part of power station design will have a great effect on the fuel cycle. A detailed analysis of future fuel cycle expenditures in relation to the different assumptions that can be made for the development and utilization of specific reactor types could therefore be of great importance for decisions on present day reactor development activities. In this article we have tried to analyze some of these assumptions, in particular, the effect on fuel cycle expenditures of the utilization of fast and thermal breeders in future nuclear strategies. 

For the thermal breeders, liquid fuel reactors, such as molten salt or aqueous suspension reactors are considered (Section V,A). 

With the lower inventories of the thermal breeders it is possible, however, to install much more capacity in this reactor type as compared with the fast breeders, using the same amount of fissile material. This leads to much higher penetration rates into the total system nuclear capacity for the thermal breeders, or, in other words, a much higher fraction of the total system nuclear capacity will consist of thermal breeders. Furthermore, the low inventories of the thermal breeder reactors make it possible to start these reactors with even though this results in a higher... 

It should be emphasized that in this study it was always assumed that no Pu or would be available from outside sources to make up for any shortage of these materials. This means that only Pu and produced within the system itself could be used. In some cases this restriction puts a limit on the maximum installation rate of certain reactor types (fast or thermal breeders), when not enough fissile material was available to supply all the required first reactor cores. In the computer program based on the model outlined here a special adjustment feature was included to allow that no shortage of Pu or occurred. 

In view of the estimated low fuel cycle costs of these reactors, there will be a very strong economic incentive to follow this policy, which, however, could be counter-balanced by the higher capital investments that seem likely for these very advanced reactor types. Breeder or high-conversion reactors, as explained in Section II/D, can be divided into fast and thermal breeders. According to the latest estimates it seems possible that fast breeders will be commercially available around 1980, although possible setbacks in the development program could delay this another 5 years. The thermal breeders are at the moment in a much less developed stage, so it seems likely that these reactors will not be completely developed and tested before 1990. If, however, considerably more effort were spent on this development project it would be possible to advance this date by 5 years. 

The reduction in fuel cycle costs and uranium requirements in con-verter/breeder reactors, resulting in a lower sensitivity to uranium price increases achieved by the introduction of the fast or thermal breeders, both initially fuelled with Pu, depends significantly on the following two ratios ... 

The second scale in Fig. 5 indicates that in most of the converter/ liquid fuel reactor cases ratio (a) will not provide any limitation for the initial liquid fuel reactor penetration because of the very low inventory of these thermal breeders. Although ratio (b) will become significant in the future because of the assumed value of 0 (no excess fissile material production) for the liquid fuel reactors, it does not limit LFR penetration in the cases that were considered. 

The fissile material inventory of the breeders will be very important for the maximum rate at which breeder reactors can be incorporated in a nuclear program and thus the savings in fuel cycle costs and uranium requirements that can be obtained. In this respect the thermal breeder (the liquid fuel reactor) has a significant advantage over the fast breeder. In most nuclear programs the penetration of the latter reactor type is seriously limited by the vast amounts of plutonium required for the first reactor cores. 

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