The principal metal components surrounding and supporting the reactor core consist of welded metal structures which transmit the weight of the reactor core and its components to the concrete foundations, and ensure the leak-tightness of the inner reactor cavity. These structures also contribute to biological shielding.
The graphite stack is surrounded by a water-filled biological shield tank, where the water is contained in an annular metal tank (5). It has an outside diameter of 19 m, an inside diameter of 16.6 m, the plate wall thickness is 30 mm. Internally this reservoir is divided into 16 water-filled sealed vertical sections. Water is supplied to these reservoirs from the bottom, and is removed from the top. This shield component also contains the startup and operating range ion chamber channels, and instrumentation piping for thermocouples assigned to monitor shield water temperature. If required, the water can be used to provide emergency fuel element cooling. The space between the wall of the concrete vault and the shield tank (4) is filled with sand.
The most complicated heavy components are the top (2) and bottom (8) metal structures. The top cover is a 17 m diameter cylinder, 3 m high, an isometric representation of which is shown in schematic. The top and bottom of this cylindrical structure is made from a 40 mm thick steel plate. Along the outside periphery these plates are hermetically welded and internally they are joined together by means of rigid vertical plates. Axial holes through this structure are positioned to match the openings in the graphite stack. Tubes are welded into these holes, to serve as guides for the fuel channels and other components of the control and instrumentation system. The inside cavities of this metal structure are filled with serpentinite (a mineral containing bound crystalline water). The quality of the welds, must be adequate to meet helium leak-tightness requirements. The entire metal structure rests on 16 rollers, which in turn rest on the top of the reinforced structure of the radial biological shield tank. This structural Component supports the weight of the loaded fuel and control channels, that of the floor segment extending to the central refueling hall, and the weight of the water pipes.
The bottom segment of the biological shield (8), which forms the foundation of the graphite stack, has a 14.5 m diameter, and is 2 m high. This structure supports the weight of the graphite stack and the feeder pipes supplying coolant water to the fuel channels. The number and distribution of the openings is the same as those of the top biological shield. The leak-tightness of the structure is tested with an air-helium mixture at a pressure of about 0.125 MPa. The remaining internal spaces of the structure are filled with serpentinite and are pressurized with nitrogen.
The bottom metal core support (9)supports the weight of the entire graphite stack. the bottom biological shield, and the coolant water feeder pipes. The design of this support structure is rather simple: it consists of two heavy plates, which intersect at right angles along the center-line of the reactor and are in turn reinforced by 5.3 m high fins. These plates are welded to the bottom of the biological shield plate (8). The cylindrical shell (7) of the reactor core is constructed from a 16 mm thick plate, it has an outside diameter of 14.52 m and a height of 9.75 m. To compensate for axial thermal expansion, the shell is provided with a bellows compensator. The shell, together with the top and bottom metal structures, forms the sealed reactor core compartment.
The topmost structure, located above the coolant channel banks which pass through the core vertically and exit horizontally, is the upper shield cover (1). The cover serves several purposes: it is a component of the biological shield, provides thermal insulation and controls the access to the fuel channels. The top surface of this cover is the floor of the refueling hall, its central part consists of individual plugs which can be removed for accessing the fuel channels and the special purpose channels.
Air is continuously drawn from the refueling hall down through the gaps of the cover plates, and out into the ventilation system. This provides cooling for the cover and impedes the transport of radioactive material from the steam-water pipes to the refueling hall.
The gaps between the top and bottom plates and the blocks are used for positioning the wiring for the control system servomotors, the flux distribution instrumentation, and the temperature -monitoring instrumentation (thermocouples). All of the reactor metal structures, which are in a gas and steam environment, are covered by an anti-corrosive material.