Converter reactors

The metal is a source of nuclear power. There is probably more energy available for use from thorium in the minerals of the earth s crust than from both uranium and fossil fuels. Any sizable demand from thorium as a nuclear fuel is still several years in the future. Work has been done in developing thorium cycle converter-reactor systems. Several prototypes, including the HTGR (high-temperature gas-cooled reactor) and MSRE (molten salt converter reactor experiment), have operated. While the HTGR reactors are efficient, they are not expected to become important commercially for many years because of certain operating difficulties. 

When produced from natural gas the synthesis gas will be impure, containing up to 5 per cent inerts, mainly methane and argon. The reaction equilibrium and rate are favoured by high pressure. The conversion is low, about 15 per cent and so, after removal of the ammonia produced, the gas is recycled to the converter inlet. A typical process would consist of a converter (reactor) operating at 350 bar a refrigerated system to condense out the ammonia product from the recycle loop and compressors to compress the feed and recycle gas. A purge is taken from the recycle loop to keep the inert concentration in the recycle gas at an acceptable level. 

A liquid phase reaction, 2A = 2B, is conducted in a CSTR with 20% recycle through a heater as shown. Fresh input is at 300 K and consists of 500 kg/hr of water and 20 kgmol/hr of substance A. The recycle is at 350 K. Heat capacity of the solute is 40 kcal/gmol-K, the reaction is endothermic with AHr = +2000 cal/gmol of A converted, reactor volume is 25,000 liters and the specific rate is... 

The process begins with the vaporization of ammonia at 550 kPa and 7°C, followed by superheating to 76°C using heat from the compressed bleached air. Filtered air is compressed in an axial compressor to 350 kPa and is mixed with the superheated ammonia vapour (1 O-l 1% ammonia by volume) prior to entering the converter/reactor. 

Natural uranium contains only 0.7 per cent of the fissionable isotope U-235. In burners (burner reactors) only this 0.7 per cent of the total energy content of the uranium is utilized, and even this fraction cannot be utilized completely. Converter reactors are somewhat more efficient in their present-day embodiments, they produce enough plutonium to permit, in principle, the doubling of the energy content of the U-235. 

The French CEA has concentrated on the development of the gas-cooled heavy-water reactor as an advanced converter reactor powerplant 61,62). The design and expected performance characteristics of a 500-MWe plant of this type were reported at the 1964 Geneva Conference (61). The plant would have a gas oulet temperature of 510°C, a steam temperature of 490°C, a steam pressure of 87 atm (1280 psia), and a net plant efficiency of 35 %. Assuming the successful development of a beryllium cladding for the fuel elements, the fuel bumup with natural uranium is expected to be 8700 MW-d/tonne and, with 0.93 % enriched uranium,... 

S. Jaye, C. L. Rickard, and H. B. Stewart, High temperature gas-cooled advanced converter reactors and the Colorado project. Paper presented at British Nucl. Energy Soc. Conf., London, May 23-24, 1966. 

Furukawa, K. 1992. The Combined System of Accelerator Molten-Salt Breeder (AMSB) and Molten-Salt Converter Reactor (MSCR). Japan-US Seminar on Th Fuel Reactors, Nara, Japan. Furukawa, K. et al. 1990. Summary Report Thorium Molten-Salt Nuclear Energy Synergetics./. Nucl. Sci. Technol. 27,1155-1178. 

XXX-4] FURUKAWA, K., KATO, Y, OHMICHI, T., OHNO, H., The combined system of accelerator molten-salt breeder (AMSB) and molten-salt converter reactor (MSCR), Japan-US Seminar on Thorium Fuel Reactors (October 1982, Nara, Japan), Thorium Fuel Reactors, Atomic Energy Society of Japan (1985) p. 271-281. [Russian Translation Atomnaja Technika za Rubezhom , 1983 [6], p. 23-29] (1983). 

Purpose of converters. In converter reactors, is burned to produce or Pu by absorption of excess neutrons in fertile material. Thus the purpose of converter reactors is the production of power, fissionable material, or both. Since homogeneous reactors have to operate at temperatures above 225°C and pressures above 1000 psi because of problems of corrosion and gas production, homogeneous converters are thought of as dual-purpose reactors for the production of power and fissionable material or power-only reactors. Such reactors are also considered mainly in connection with the fuel cycle, whereas the homo-... 

A single-region converter fueled with natural or slightly enriched uranium oxide as a suspension avoids the problems of plutonium precipitation, phase separation, and corrosion mentioned above. The advantage of such a converter reactor for power production is the elimination of radiation damage and fuel bumup problems encountered with solid-fuel elements however, the problem of radiation damage to the reactor pressure vessel must be considered. 

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. 

In the succeeding sections some cciuilibrium results are given for the nuclear characteristics of one-region breeder and converter reactors. 

---