Patent GB-1031158-A (GB)
Title: Improvements in nuclear reactors and methods of operating the same
IPC: G21C1/08
Filed: 1962-12-07
Abstract: 1,031,158. Reactors. BABCOCK & WILCOX CO. Dec. 7, 1962 [Dec. 8, 1961], No. 46242/62. Heading G6C. A heterogeneous nuclear reactor has conduits which traverse a moderating space of the reactor core and through which flows a coolant fluid under pressure, means being provided for maintaining in the moderating space gaseous fluid under higher pressure than the coolant fluid providing neutron moderation by hydrogen atoms and including at least one gaseous fluid component comprising other than hydrogen atoms. The reactor shown in Fig. 1 comprises a plurality of tubes 24 mounted between grids 20, 22 and containing fuel elements over which coolant is passed, the coolant being impelled by a pump 30 through inlet and outlet lines 26, 28 and a heater exchanger 32. The coolant may, for example, be steam or pressurized light or heavy water. The moderator flows through the space surrounding the tubes 24, being impelled by a pump 38 through input and output lines 34, 39 and a heat exchanger 40, moderator being added when necessary through a supply line 42 and metering device 44 and removed through an exhaust line 46 and a metering device 48. The core is designed so that it cannot go critical by virtue of the presence of coolant fluid alone in the core, the presence of moderating gaseous fluid also being necessary. Suitable moderating gaseous fluids include steam and hydrocarbon vapours and mixtures of these with gases or vapours having relatively little or no moderating effect such as helium, nitrogen and carbon dioxide. In the reactor described, both the coolant and the moderator are steam. The moderation may be varied but the total pressure in the moderating circuit maintained constant by varying the partial pressure of the steam in a gaseous fluid moderator comprising a mixture of steam and another gas or vapour. The reactor may be shut-down by discharging moderating steam through a relief valve 49 from exhaust line 46. Upon the reception of a " scram " or emergency shutdown signal from the reactor control system in the case of a selectively operated valve, or an increase in the moderator steam pressure above a predetermined value in the case of a pressure relief valve, the valve opens to vent the moderator circuit to a lower pressure receiver (not shown). As a safety factor, it is arranged for the core moderator space pressure to be always higher than the core coolant space pressure so that should a leak occur between the moderator and the coolant circuits, there will be a flow of moderator into the coolant circuit and a consequent decrease of core reactivity. The reactor described has a negative coefficient of reactivity with temperature changes of the coolant and is safe and selfregulating in adjusting itself to the output demand of the system. Thus, as the output demand increases, the temperature of the coolant fluid entering the core will be reduced, therefore it will have a higher density and the core will have a higher moderation with a resulting increase in reactor power output. The converse occurs should the output demand decrease. In the modification shown in Fig. 2, which is substituted for that part of Fig. 1 to the right of line 54, a portion of the coolant steam leaving the reactor by outlet line 28 goes directly to a turbine 56 and is exhausted into a condenser 58 while the remainder by-passes the turbine and goes directly to a vaporizing chamber 62 via a line 60. The condensed steam is introduced by a pump 64 into the vaporizing chamber 62, where it is converted into steam by mixing with the steam from line 60 and the resulting steam is introduced into the reactor via the pump 30 and inlet line 26. The reactor may have a central fast-fission core region, a blanket thermal-fission region surrounding the core region, and a neutron reflector surrounding the blanket region, control being effected by varying the hydrogen concentration of a gaseous fluid moderator in the blanket region.