Shielding, light water reactor

Most commercial nuclear power plants in the United States are light water reactors, moderated and cooled by ordinary water. Figure 26-12 is a schematic diagram of a light water reactor plant. The reactor core at the left replaces the furnace in which coal, oil, or natural gas is burned in a fossil fuel plant. Such a fission reactor consists of five main components (1) fuel, (2) moderator, (3) control rods, (4) cooling system, and (5) shielding. 

Since the severe core damage behaviour of PHWRs is somewhat different from that of light water reactors (LWRs), it is worth summarizing the phenomenology here. Analysis of events in category (3) initially started from heat balance calculations (to determine the times to boil off the water in the moderator, and then in the shield tank), followed by calculations of the characteristics of the debris once it collects on the bottom of the calandria vessel. 

In the first method, similar to that used in light water reactor power plants, the reactor core is contained within a relatively small reactor vessel. The main primary coolant (sodium) is pumped through the vessel into external heat transfer loops located in individual shielded vaults outside the reactor, as shown in Fig. 6 for a typical design. These vaults... 

Fig. 4 is a schematic view of the reactor enclosed in a water and concrete shield showing the light water cooling circuit, the helium circuit, and the heavy and light water leakage circuits ... 

Fig. 5 is an enlarged side elevational view of the reactor surrounded by the light water and concrete shield (in section) and showing the relationship bett een the reactor and the dumping coffin ... 

The concrete tank has 7 ft thick walls and is 28 ft long, x 8 ft wide and 24 ft deep internally and contains light water. Three large aluminium windows are fitted in the tank and these allow heavy shielding experiments to be set up outside. Three beam holes are also fitted. The reactor core is made up of uranium/aluminium plates clad in aluminium it can be moved through the water into position on the inner side of any window. The water is circulated for cooling and cleaning. 

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