Molten Salt Reactor Core Design

Example 1

A nuclear reactor core is formed from a series of molybdenum tubes containing a mixture of uranium fluoride and sodium fluoride. The uranium is enriched in U235 isotope. The tubes are located in channels in graphite blocks and a coolant liquid passes upwards through the channel between the graphite and the tube.

FIG. 1 shows an array of passive reactivity devices 100 in a graphite moderated liquid molten salt fuelled reactor core.

The reservoir 101 of the passive reactivity device is located above the level of the fuel salt 110 in the tube as shown in FIG. 1. The stem 102 of the device projects down through the annulus between the graphite 120 and the tube and terminates at the bottom of the fuel tube. FIG. 2 shows the location of the neutron absorbing fluid 103 in the bulb 101 and stem 102 at different coolant output temperatures T1<T2<T3. The remainder of each passive reactivity device contains a gas 104 which does not react with the neutron absorbing fluid. On the left is with the device at a temperature below normal reactor operating temperature, central is the device at normal operating temperature and right is above normal operating temperature.