Graphite stack

Platonov P.A., Chugunov. O.K., Manevsky V.N. and Karpukhin, V.I., Radiation damage and lifetime evaluation of RBMK graphite stack. In Proceedings of the IAEA Specialists Meeting on Graphite Moderator Lifecycle Behavior, lAEA-TECHDOC-901, IAEA, Vienna, 1996. pp. 79 90. 

Figure 3.3.A is a cut-away view of the. thermal, column with the graphite removed. The graphite stacking is shown in Fig. 3.3.B. In Fijj. 3.3.A, the steel liner adjacent to.the concrete serves to absorb radiation from the thermal column in a-manner analogous to the thermal shield around the reactor proper. The cadmium- sheet next to the steel absorbs impinging slow neutrons so that the steel liner will exhibit a minimum of induced radioactivity after pile shutdown.

Graphite stack 20 Overhead crane of main circulation pump room... 

Gross fission heat, MW Active core diameter m Active core height, m Diameter over reflector m Height over reflector, m No. of graphite columns Duct diameter mm Mass of graphite stack, t Number of fuel channels Fuel channel pitch (square lattice), mm... 

As the graphite stacking progresses, or perhaps after it is flnished, earth is filled in outside the concrete wall to the sides of the hole and up to a little below the top of the wall. The time at which this is done is immaterial, except that its pressure on the wall is to be taken into account. 

As the graphite stacking progrestes, earth is fsl ed in outside the ccacreie wall to the sides there jf, and i p to a little bclcw the lop of the wall. The time at /hich this is done is immaterial. At that time the helium expansion tanks arc installed. 

Figure 3.2 Various graphite stacking arrangements in carbon nanofibers (a) platelets of graphite stacked perpendicular to the CNF axis, (b) angled stacking, and (c) stacking nearly parallel to the CNF axis. Reprinted with permission from [15].

The thermal shield is a cast iron box that encloses all six sides of the graphite stack. The iron is approximately ten inches thick on the front, rear and bottom and eight inches thick on the top and sides of the reactor. The shield is made up of many small blocks with stepped, overlapping edges. The small size makes handling easier and limits the effects of thermal expansion and the steps prevent radiation beams between the joints. 

FIG. 1. Schematic diagram of an RBMK reactor 1, graphite stack 2, structure S 3, structure OR 4, structure E 5, structure KZh 6, structure L 7, structure D 8, drum separator 9, MCP casing 10, MCP motor 11, pressure gate valve 12, suction header 13, pressure header 14, distribution group header 15, water lines 16, steam and water lines 17, downcomers 18, refuelling machine 19, central hall crane. 

The top and bottom plates (the metal structures E and OR) are pierced by tube lines to house the fuel and other channels. The top plate, mounted on roller supports, rests on the structural components of the reactor building. It takes the weight load from all the reactor channels together with their internal components, as well as part of the weight load from the steam-water pipelines and other service lines (pipes and cables). The bottom plate supports the graphite stack of the core. 

Breaks in the process tubes could cause fuel overheating. However, fuel melting resulting from such a break is highly unlikely. If fuel melting should occur fission products would largely be confined within the graphite stack. 

The calculated upper limit assumes the most severe conditions and can never be experienced. Any of the following variations from the most severe condition would lower the reactivity Increase (l) cooling of the graphite during the time required to Inject cold water, (2) flooding of only a part of the graphite stack with water, and (3) flooding with more or less than an optimum amount of water. 

Steam vents have been provided within the graphite stack to vent the... 

At the eventual temperature fhen the uranium Is redistributed throughout the graphite stacks a very large negative change in reactivity vill occur As discussed In Reference the effect has been e erlmentally verified for natural uraxiLum ... 

Due to the spherical design of the pressure vessel, the standpipes which pen rate it and their associated nozzles are closer to the graphite stack and up to three times long, at the core edge channel positions, relative to those at the core caitre. 

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