Patent GB-792972-A (GB)
Title: Control of atomic power reactors
IPC: G21C11/06
Filed: 1956-07-30
Abstract: 792,972. Nuclear reactors. ATOMIC ENERGY OF CANADA, Ltd. July 30, 1956 [Aug. 6, 1955], No. 23454/56. Class 39(4). A nuclear reactor comprises a core vessel for containing a liquid moderator, coolant circulating tubes therein, a storage chamber disposed at a level below the floor of the vessel, fine moderator level control means for effecting net transfer of moderator between the vessel and the chamber in either direction at a slow rate, an uninterrupted passageway of large cross-sectional area extending between the lower part of the vessel and the upper part of the chamber, the passageway including a downwardly projecting loop, means for maintaining a gaseous pressure in the chamber in excess of a gaseous pressure in the vessel sufficient at least substantially to support a body of liquid in the vessel by action against a stable free surface of liquid in the passageway adjacent the loop, and means for rapidly eliminating the excess gaseous pressure. Figs. 2 and 3 show diagrams of the moderator circuit and the coolant circuit respectively. The reactor chamber 1 is provided with a number of tubes 2 (of which one is shown in Fig. 3) in which are mounted fuel rods, e.g. of uranium, which can be withdrawn upwardly into tubes 2a. Coolant, which may be heavy water, is passed through the tubes and around the fuel rods, passing from a lower header 4 through the tubes to an upper header 5, and through a heat exchanger 7 and pump 6 back to the lower header. The system includes a tank 11 which is filled by a pump 14 from the moderator storage tank 15 ; any excess in the tank 11 can drain through conduit 13 into the vessel 1. Stand pipes 16, Fig. 2, connect the chamber 1 to the tank 15, and a second connection is provided by an annular passageway 17. The heavy water moderator can thus drain from the reactor chamber 1 into the storage chamber 15 whence it is pumped back by pumps 26 through control valves 29. A cooling circuit for the moderator comprises a pump 21, a heat exchanger 22, and a control valve 23 arranged in parallel with the heat exchanger. A high pressure is maintained in the vessels 1 and 15 by means of helium which occupies the spaces above the level of heavy water in these chambers. A balance between these spaces is maintained by a pump 31 which draws helium along the conduit 32 and feeds it along conduit 33 ; a dump valve 34 is arranged in parallel with the pump. The reactor may include a light water reflector contained in a spiral of tubing, Fig. 1 (not shown), and a cooling jacket of light water surrounding parts of the tubes 2a. In normal operation the pressure of helium in chamber 15 is slightly greater than that needed to support the moderator in chamber 1 so that helium slowly bubbles through passage 17 and up through the moderator in chamber 1. At the same time there will be a steady slow drainage of moderator, through stand pipes 16 into the chamber 15, which will continually be compensated by moderator being pumped back by pumps 26. Primary fine control of the level of moderator in the chamber 1 can thus be maintained bv valves 29. (Additional fine control is provided by controlling the temperature of the moderator by valve 23. The reactor can be shut down in an emergency by opening the dump valve 31 to reduce the pressure of helium in chamber 15 and thus allow the moderator to drain out of the reactor chamber 1. In an alternative arrangement, Fig. 4, there are no stand pipes 16 and conduit 27 from the chamber 15 is connected to one side of a pump 35 and valve 38, the other sides of which are connected to conduit 28. With a large opening of valve 38 there is a net flow of moderator out of the reactor chamber 1 into chamber 15, and with a small opening the flow is reversed. In a further alternative, Fig. 5, the moderator cooling pump 44 is situated on the downstream side of heat exchanger 22 and is also connected through a valve 46 and conduit 45 to the chamber 15 ; control over the moderator level is exercised through the valve 46. In another arrangement, Fig. 6 (not shown), moderator liquid is continuously pumped at a slow rate from the chamber 15 to the reaction chamber, and control of the moderator level is exercised entirely by control of the pressures of helium in the two chambers.