To maintain the reactor coolant compositions within predetermined tolerance levels, bypass gas processing plant comprising filters, a recombination unit, a dry­ing plant and associated control systems, pipework

and valves is required. The bypass system is connected

to:

• The carbon dioxide storage and distribution system for reactor filling and make-up.

• The methane store or production plant for coolant chemistry control.

• The reactor blowdown system.

Just under one per cent of the total reactor gas flow is diverted through the gas bypass plant. A schematic arrangement of a typical bypass plant is shown in Fig 2.87. Flow to the bypass plant is taken from the gas circulator outlet. The gas first passes through a filter to remove any particulate matter which could contaminate the plant downstream, then to the re­combination unit and drier unit, and finally through another filter to remove any fine desiccant from the drier towers before returning to the reactor via an­other penetration in the pressure vessel wall. The pene-

trations in the vessel wall for the inlet to and outlet from the bypass plant are fitted with either venturis or orifices to restrict the maximum discharge area in the event of the rupture of the bypass plant pressure boundary. Isolating valves are provided in the circuit. To support the plant, carbon dioxide storage, meth­ane storage or production, and oxygen production plant are necessary.