Abstract: To separate tritium from gases and/or vapors escaping accidentally from a clear reactor, before the gases or vapor are discharged into the atmosphere, the gases or vapor are fed through a line 5 into a reservoir 3 of deionized light water which is maintained at its boiling point in a heat insulated vessel 1. The tritium is accumulated in the water in the reservoir 3 and any tritium which passes from the reservoir 3 in light water steam is condensed by surface condensors 8 in a steam dome 9. Any possible residue of tritium in the steam leaving through an outlet 10 at the top of the dome 9 is separated out in the form of droplets by a drier cyclone connected directly downstream of the outlet 10.

Abstract: A liquid receiver which acts as a pressure relief valve for radioactive vapor or gases from a nuclear reactor comprises a container 4 holding liquid 3 and nozzles 13 which discharge vaporous or gaseous coolant from an outlet 2 from the reactor into the liquid 3. So that the liquid 3 does not lose its barrier capability during a temporary rise of pressure or at low outflow rates of the coolant from the outlet but can be expelled independently of the nature and temperature of the coolant, the nozzles 13 are mounted on a nozzle ring 11 which has a vertical axis and all the nozzles are directed tangentially in the same direction to generate a cyclone effect in the container 4. This causes the liquid 3 to have its surface lowered from the static level 5 to the rotational surface 15. This reduces the length of the path of the escaping gas or vapor through the liquid 3.

Abstract: A nuclear reactor, particularly a light water reactor or a helium-cooled high-temperature reactor, is provided with a pressure relief system for relieving pressure resulting under fault conditions from coolant in the reactor pressure vessel and/or the protective vessel of the reactor, wherein the coolant is conducted from the vessel or vessels to a pressure relief station downstream thereof. At the pressure relief station the coolant is fed into a liquid reservoir 4 from which the coolant in gaseous or vapor form is fed sequentially through a washing cyclone 13 and a drying cyclone 25. Most of the radioactive fission products carried by the coolant will have been removed by the liquid reservoir 4 and the washing cyclone 13, and the coolant leaving the cyclone 25 may be safely discharged to atmosphere. Both the liquid reservoir 4 and the washing cyclone 13 are provided with cooling circuits 8 to 12 and 14 to 23 respectively for the liquids.

Abstract: In the method of shutting down a high temperature nuclear reactor having a negative temperature coefficient of reactivity, such as a gas cooled pebble-bed nuclear reactor, while the core is operating in the critical state with the core having a predetermined critical average core temperature and with the heat generated in the critical state being removed by a coolant, effecting the shut down by reducing or discontinuing the removal of heat from the reactor core and increasing the average core temperature by an amount above the critical average core temperature for rendering the core hot sub-critical due to the negative temperature coefficient of reactivity. The core can be maintained in the hot sub-critical state by a controlled removal of after shut-down heat from the core.

Abstract: Disclosed is a control system and process for operating same for nuclear reactors, particularly gas cooled nuclear reactors, comprising in the control system a means for measuring the output produced in the reactor core and the output removed by a primary circuit or a secondary circuit, a means for integrating the integral of the core produced output over the output level, during the same time, of the primary or secondary circuit of the reactor and a means for forming a control signal from the value of the integral.

Abstract: A gas-cooled, and preferably helium cooled, graphite-moderated high temperature nuclear reactor of the kind having a pressure vessel containing a reactor core with fuel elements, graphite components and a primary coolant gas circuit including a steam generator and coolant gas blowers, has the steam generator disposed outside the pressure vessel and the steam generator includes a heat exchanger at least a portion of which is located above the level of the reactor core. This situation of the heat exchanger ensures that when the reactor is shut down, either intentionally or owing to a fault, a natural convection flow takes place through the coolant gas circuit and this natural convection flow is in the same direction as it is when the blowers are functioning so that the flow conducts away the decay heat from the core to the steam generator in the same way as when the blowers are in operation.

Abstract: The invention relates to a graphite side reflector in block form for a gas-cooled high-temperature nuclear reactor. The blocks of the reflector extend radially continuously through the entire reflector wall thickness and recesses are provided in the inner end faces of at least the blocks disposed in the upper region of the reactor core.

Abstract: The coolant gas of a gas-cooled high temperature nuclear reactor, structu components or the fuel elements of which are made predominantly of graphite, is circulated through a coolant circuit of the reactor and through a gas purification plant, and to further remove impurities from the coolant gas, carbon dust of colloidal particle size is fed into the coolant gas preferably on its passage back from the purification plant into the coolant circuit. The carbon dust may be monoatomic carbon or activated carbon, coke, carbon black or a mixture thereof. Preferably the coolant gas of the reactor is charged with the carbon dust before the reactor is initially started up and hot-run and the coolant gas charged with the carbon dust is circulated for a sufficiently long period to coat all metal surfaces in the coolant circuit with carbon dust before the initial starting up and hot-running takes place.

Abstract: A method of removing the decay heat of radioactive fission products from a gas-cooled high temperature nuclear reactor in an emergency situation wherein a fault or a combination of faults results in the normal operational systems of the reactor not being able to remove the decay heat satisfactorily, comprises introducing water into the reactor core. Preferably the water is completely desalinated water which is introduced into the core from above. Absorber material may also be mixed with the water before it is introduced into the core to effect permanent shutdown of the reactor by absorbing free neutrons within the core.

Abstract: A method of testing the circulation of a bulk charge of fuel elements in the core of a pebble bed type of nuclear reactor comprises increasing the electrical conductivity of a number of fuel elements and then injecting the marked elements into a bulk charge of other unmarked elements having a lower electrical conductivity at predetermined positions in the core of a nuclear reactor and a measured times. The marked fuel elements are subsequently detected electromagnetically as they are carried in the bulk charge of unmarked elements through an electromagnetic field generated by a detection and measurement station. The elements are marked by including a material having a greater electrical conductivity than the remainder of the element and this material may be coated on the surface of the elements or incorporated in the body of the elements.

Abstract: In a gas cooled pebble bed reactor the poison part of a control rod which s upper and lower portions and an interior cooling fluid channel is movable into and away from a bed of spherical fuel elements; the improvement includes a control rod security device which facilitates removal of the fractured control rod when the control rod breaks between its end portions. The security device includes an oblong member which is located and extends within the cooling channel and is slack relative to the control rod, a device attached to one end of the oblong member for preventing a fall of the oblong member into the lower portion of the control rod, and a device attached to the other end of the oblong member for preventing portions of the control rod from falling into the bed of fuel elements upon a fracture of the control rod between its end portions.

Abstract: In a nuclear reactor of the kind which is charged with spherical reaction elements and in which control rods are arranged to be thrust directly into the charge, each control rod has at least one screw thread on its external surface so that as the rod is thrust into the charge it is caused to rotate and thus make penetration easier. The length of each control rod may have two distinct portions, a latter portion which carries a screw thread and a lead-in portion which is shorter than the latter portion and which may carry a thread of greater pitch than that on the latter portion or may have a number of axially extending ribs instead of a thread.

Abstract: A reaction vessel which holds a charge of spherical reaction elements, for example a pebble bed nuclear reactor having a charge of spherical fuel elements, has the charge formed of at least two groups of spherical elements with all of the elements in each group being of equal diameter, but each group of elements having a different diameter from the other. The elements of both groups are uniformly mixed together and the different diameters are chosen in such a way that when the elements are continuously circulated through the reaction vessel during operation, the circulation does not cause the two groups of elements to segregate during the intended number of circulation cycles.