Molten plutonium fuel reactor

The second reactor discussed in this chapter is the LAMPRE. This is a molten plutonium fueled reactor which is under development at the Los Alamos Scientific Laboratory. Although only in its beginning stages of development, it is conceived as a high temperature (6oO°C) fast breeder reactor utilizing plutonium as the fuel. 

Short-term tests indicated that the practical upper limit for tantalum as a container for uranium is about 1450°C. However, attack below this temperature is significant. A tantalum crucible with a wall thickness of 0.06 in. was completely corroded after 50 h at 1275°C. Other investigations have shown that tantalum is not attacked by uranium-magnesium and plutonium-magnesium alloys at 1150°C. Extensive tests on components for molten metal fuel reactors have demonstrated that tantalum is a satisfactory material for several thousand hours of service in liquid-metal... 

Plutonium is being investigated as an alternate fuel for the molten-salt reactor. Although it is too early to describe a plutonium-fueled reactor in detail, it is highly probable that a suitable PuFa-fueled reactor can be constructed and operated. 

Distribution coefficients may be further modified and operating temperatures reduced by dissolving uranium fuel in a low-melting metal such as bismuth or zinc. Separation of uranium from fission products by liquid extraction between molten bismuth and fused chlorides was extensively studied at Brookhaven National Laboratory [D5] in connection with the liquid-metal fuel reactor (LMFR), which used a dilute solution of in bismuth as fuel. Extraction of fission products from molten plutonium by fused chlorides was studied at Los Alamos [L2] in connection with the LAMPRE reactor. 

Because the plutonium-burning reactor proposed in this report is assumed to use a metal or oxide fuel, (such as Pu-Al, Pu-Zr02, or Pu-ZrH).6) the potential for an energetic steam explosion is of some concern, provided an accident sequence can be identified that leads to large quantities of molten fuel and cladding. The purpose of this section is to discuss some of the steam explosion concerns involving aluminum-water and zirconium-water in relation to the proposed low power density, low flow plutonium-burning reactor. 

Molten Salt Reactor (MSR). The MSR [3] uses a liquid molten-fluoride salt as fuel and coolant. The uranium or plutonium fuel is dissolved in the molten salt. Two test reactors were built. In the 1950s, the Aircraft Reactor Experiment operated normally with molten salt exit temperatures of 815 C with peak operating temperatures up to 860 C and very low primary system pressures. Work continued on MSR technology for power applications until 1976. The reactor can be built in large sizes with passive safety systems. 

It may be feasible to burn plutonium in molten fluoride-salt reactors. The solubility of PuFa in mixtures of LiF and BeFa is considerably less than that of UF4, but is reported to be over 0.2 mole % [8], which may be sufficient for criticality even in the presence of fission fragments and non-fissionable isotopes of plutonium but probably limits severely the amount of ThF4 that can be added to the fuel salt. This limitation, coupled with the condition that Pu is an inferior fuel in intermediate reactors, will result in a poor neutron economy in comparison with that of U -fueled reactors. However, the advantages of handling plutonium in a fluid fuel system may make the plutonium-fueled molten-salt reactor more desirable than other possible plutonium-burning systems. 

Basic components. Before discussing the Los Alamos Molten Plutonium Reactor (LAMPRE) proposal in detail, the following resume will treat some of the possibilities for the three basic components of a power reactor the fuel, the container, and the coolant. 

Several components are required in the practical appHcation of nuclear reactors (1 5). The first and most vital component of a nuclear reactor is the fuel, which is usually uranium slightly enriched in uranium-235 [15117-96-1] to approximately 3%, in contrast to natural uranium which has 0.72% Less commonly, reactors are fueled with plutonium produced by neutron absorption in uranium-238 [24678-82-8]. Even more rare are reactors fueled with uranium-233 [13968-55-3] produced by neutron absorption in thorium-232 (see Nuclear reactors, nuclear fuel reserves). The chemical form of the reactor fuel typically is uranium dioxide, UO2, but uranium metal and other compounds have been used, including sulfates, siUcides, nitrates, carbides, and molten salts. 

Recent studies on the electrochemical behavior of plutonium in molten salts have mainly been performed in LiCl— KCl based melts. The electrorefining step in a pyroprocessing procedure for the recycling of nuclear fuel from the Integral Fast Reactor (IFR) Program has been... 

In this process, oxide fuel is dissolved in a molten chloride salt mixture through which Q2-HCI gas is flowing. Dissolved uranium and plutonium are then recovered as oxides by cathodic electrodeposition at 500 to 700°C. The process was demonstrated with kilogram quantities of irradiated fuel, with production of dense, crystalline UO2 or UO2-PUO2 reactor-grade material. Difficulties were experienced with process control, off-gas handling, electrolyte regeneration, and control of the plutonium/uranium ratio. Development has been discontinued. 

Another promising uranium compound that can be used in nuclear fuels is uranium carbide that has a high melting point and better thermal conductivity than the oxide and in addition does not form oxygen when radiolyzed. Uranium nitride can also be used, but formation of from N could be problematic. In addition, other uranium compounds that can be used as a fuel in a nuclear reactor, ranging from aqueous solutions to molten salts that are brought to a high temperature in order to keep them in a molten state. MOX of uranium and plutonium also serve as a nuclear fuel in some reactors. 

A few advanced solid fuel concepts were considered in this study to indicate some of the improvements that might obtained in reactor design or operation. There are no operating data for these fuel forms,. so only the perceived advantages of each fuel form considered are briefly presented. The feasibility of the fabrication of these advanced fuel forms was assumed mostly on the basis of the known feasibility of the fabrication of similar systems. Liquid fuel forms, such as molten salts, were also considered, but the containment of these highly corrosive materials was considered to be a major unsolved problem that would significantly delay their u.se in plutonium burning. 

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