| 摘要 |
1,091,203. Controlling reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Sept. 10, 1964 [Sept. 26, 1963], No. 38048/63. Heading G6C. In a fast breeder reactor, a loss of coolant results in a fall in reactivity. A central fission zone is surrounded by a fertile region, separation between the two being effected by an annular gap, filled with coolant. The coolant in the gap and the fertile region function as a reflector under normal operation. A loss of coolant empties the gap, reflection is reduced, neutron leakage rises and reactivity falls due to neutron decoupling. Either liquid sodium or a supercritically pressurized aqueous medium may be used as a coolant. In the latter case, in order to enhance the leakage control, the coolant in the gap is maintained at subcritical temperture, as the density of supercritical steam decreases with rising temperature. In one embodiment, a second fission zone is mounted above the fertile region and the reactor criticality is dependent on fission in this zone. A loss of coolant causes melting of the central fission zone and hence compacting downwards away from the second fission zone. A negative reactivity charge is thus caused by the decoupling consequent upon the loss of coolant reflectivity and the separation of the fission zones. The second fission zone may contain moderator to effect thermal fission. In a modification separation between the fission and fertile regions is effected by an axial gap and an epithermal neutron absorber, e.g. hafnium, may be used.
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