Abstract:

FUEL PROPERTIES AND NUCLEAR PERFORMANCE OF FAST REACTORS FUELED WITH MOLTEN CHLORIDES

P.A. NELSON, D.K. BUTLER, M.G. CHASANOV, and D. MENEGHETTI

Argonne National Laboratory, Argonne, Illinois 60439

Received December 9, 1966 Revised April 13, 1967

The characteristics of fast reactors having molten fuels consisting of uranium and plutonium trichlorides dissolved in alkali chlorides and alkaline-earth chlorides were studied. The study included considerations of the physical and chemical properties of the fuel, the heat-removal problems, and neutronic characteristics for three types of chloride reactors: a homogeneous reactor and two internally cooled reactors. Optimization of the core size for 1000-MWe reactors resulted in a core volume of 10,000 liters for each type. These reactors have the favorable characteristics (even for natural chlorine) of high breeding ratio, large negative temperature coefficients of reactivity, and low fuel-cycle costs. However, the unattractive characteristics of large plutonium inventory, large volume, complex design, and container material problems indicate that a sizeable program to develop chloride-fueled reactors would be required.

INTRODUCTION

Some recent studies of large solid-fueled fast reactors have indicated the need for reactor con- figurations such as flat cylindrical (small length/ diameter ratios) cores1, annular cores2, or multiple cores3,4 to avoid a positive sodium-void coefficient of reactivity. These reactor configurations have the disadvantage of requiring a larger fissile mass than was once thought necessary for plutonium-fueled fast reactors. The present study of mobile fuels for fast plutonium breeder reactors was undertaken because, relative to solid fuels, such fuels have the potential advantage of a high coefficient of thermal expansion which provides a large negative temp-erature coefficient of reactivity.

The particular type of fuel chosen for more detailed study was a solution of trichlorides of uranium and plutonium dissolved in alkali chlorides and alkaline-earth chlorides. The attractive physical and chemical properties of this type of fuel prompted a study of heat-removal problems and the nuclear performance of chloride- fueled reactors. Chloride-fueled fast reactors were studied by Goodman et al.5 as early as 1952. A group of students at the Oak Ridge School of Reactor Technology in 1956 concluded that a solution of trichlorides of plutonium and uranium dissolved in a solvent of magnesium chloride and sodium chloride was the most promising salt fuel for a fast reactor6. Taube in Poland also decided that plutonium trichloride and uranium trichloride fuels were promising7-9. More recently, Alexander concluded that chloride-fueled reactors that were either gas-cooled or cooled by circulating the fuel to external heat exchangers would have attractive nuclear performance and low fuel-cycle costs10.

The present study consisted of: 1) estimation of fuel properties from examination of data on chlorides and other salts; 2) calculations of reactor design to establish approximate fast-reactor core and blanket configurations and compositions; and 3) reactor physics calculations of critical mass and the breeding ratio for the various reactor designs. After preliminary reactor physics calculations were completed, it was necessary to adjust the reactor core and blanket design and: repeat the reactor physics calculations.

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