GB954101A - Improvements in or relating to nuclear reactors - Google Patents

Abstract

954,101. Controlling nuclear reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Nov. 26,1962 [Nov. 28, 1961], No. 42580/61. Heading G6C. In a nuclear reactor in which control is effected by supplying and withdrawing a liquid, moderator to and from a tubular member extending into the reactor core, the bore of the tubular member is enlarged as it progresses towards the centre of the core. One embodiment (Fig. 1) relates to a steam generating and super-heating reactor 1 having tubular members 2,3 and 4 extending vertically into a core vessel 5 containing heavy water moderator 6, the moderator entering the tubular members 2, 3 and 4 through bleed holes 7, 8 and 9 andleaving through pressure-controlled liquid traps in the form of weirs 10,11 and 12, the bores 13, 14 and 15 of the tubular members 2, 3 and 4 being enlarged at 13a, 14a and 15a as they progress towards the centre of the core vessel 5. The reactor is fuelled by cluster-type fuel elements 16 disposed in pressure tubes 17 located in calandria tubes 18, water entering the tubes 17 at 19 and leaving as steam at 20 to be led in counterflow through pressure tubes similar to the tubes 17 where it is superheated. The moderator 6 is circulated through an external heat exchanger 21 by a pump 22. Under emergency conditions, the moderator 6 can be dumped through a series of pipes 25 and weirs 27 into a storage tank 26, whereas under normal conditions, a level of heavy water is maintained in the core vessel 5 by pressurising the tank 26 with helium so that, acrossthe weirs 27, the pressure of helium balances the head of heavy water. The helium is fed to the tank 26 by a compressor 28 drawing from a gas holder 29. Heavy water spills from the weirs 10, 12 into a drain chamber 32 sub-divided into compartments 32a, 32b by a partition 43 and from the weir 11 to a chamber 44, the compartments 32a, 32b being pressurised with helium from the compressor 28 through a central valve 40 and the chamber 44 through a control valve 48. Control valve 48 can be adjusted independently of the central valve 40 so that the level of moderator in the tubular members 2 and 4 can be altered without affecting that in the tubular member 3. Heavy water entering the tank 26 from the compartments 32a, 32b and the chamber 44 through non-return valves 35, 36 and 46 is returned to the core vessel 5 by way of a pump 30 and line 31. The tubular members 2,4 provide a "coarse" control effect as their enlarged bores 13a, 15a extend over a substantial depth of the core vessel 5 whereas the tubular member 3 provides a "fine" control effect as its enlarged bore 14a is of relatively short length and lies in that region of the core where the neutron flux is greatest. In a second embodiment (Fig. 2), a nuclear reactor 71 cooled by pressurised heavy water has a tubular member 72 extending horizontally through a core vessel 73 containing heavy water 74, this entering the underside of the tubular member 72 through a bleed hole 75 and leaving through a weir 76, the bore 77 of the member 72 being enlarged at 77a at the centre of the core vessel 73. Under emergency conditions, the heavy water 74 is dumped through a weir 89 and drain line 90 into a storage tank 91 while, under normal conditions, a level of heavy water 74 is maintained in the core vessel 73 by pressurising the tank 91 with helium discharged through a line 93 from a compressor 92 drawing from a gas holder 101. Helium is fed under pressure to an end-compartment 106 by way of a branch 97 of the line 93 and variation of the pressure in this compartment by means of a control valve 98 controls spillage of heavy water over the weir 76 and hence the level of the water in the tubular member 72. As the water level in the tubular member 72 falls, helium enters from an end-compartment 107 which is open to the free space 103 in the core vessel 73. Heavy water spilling over the weir 76 into the endcompartment 106 is returned to the core vessel 73 by way of a pump 108 and branch line 110. Although only a single tubular member 72 is shown, a number of such members are provided and in one convenient form are disposed in a number of spaced groups, each in a horizontal plane, the members of each group being provided with a common weir 76 of trough-like form extending across the end face of the core vessel 73.