Figures 2.126 to 2.128 show the general arrangement of building layouts and the plant within them.

The auxiliary building houses the bulk of the equip­ment for reactor auxiliary and safety systems includ­ing the chemical and volume control system (CVCS), the residual heat removal system (RHRS), the high pressure coolant injection system (HPCIS) and the containment spray system. The auxiliary building inter­faces directly with the reactor building to allow the direct passage of pipes and cables between the two buildings.

Main steam and feed pipework from and to the steam generators leaves the reactor building through the separate steam and feed cell, w’hich also houses auxiliary steam-driven safety equipment. The fuel build­ing contains the spent fuel storage pond and also interfaces directly with the reactor building to allow fuel to be passed between the reactor and the fuel storage pond. It is the reception point for new fuel and also contains the spent fuel flasking facility and loading bay for transport of spent fuel from site.

The control building houses the main control room, data processing room, the primary protection system, the component cooling water system (CCWS) plant and heating and ventilation plant.

The mechanical annexe interfaces with the steam and fuel cell to allow the optimum passage of the main steam and feed pipework between the reactor building and the mechanical annexe/turbine house.

As well as housing the main steam and feed pipe­work and major turbine system ancillaries, the me­chanical annexe contains the main change and power block security facilities.

The following major principles have been adopted for the layout of plant and service within buildings:

• Redundant safety classified equipment is located within different segregated principal fire areas, in accordance with the principles agreed with the Nu­clear Installations Inspectorate, particularly those concerning penetrations through principal fire bar­riers, and are allocated to electrical separation groups in an appropriate manner to maintain redundancy and hazard protection.

• As far as practicable, cables are routed away from corridors or plant rooms.

• Smoke vent stacks with pressure-actuated dampers are installed to facilitate heat and smoke removal from the control and auxiliary buildings. [22]

10.1.3 Heating, ventilating and air conditioning (HVAC)

Each building contains a HVAC system to provide a suitable environment for personnel and equipment and to control the spread of airborne contamination under normal and faulted conditions. The design of each HVAC system is dictated by the functional re­quirements of the buildings and equipment which it senices.

Typically the role of the HVAC systems has up to four elements:

• Cooling of important plant items.

• Control of radioactive release post-fault.

• Personnel comfort and safety (including smoke con­trol following fires).

• Control of contamination spread.

The cooling of safety classified plant is generally accomplished by independent room coolers served by the component cooling water system, or by closed loop air conditioning systems. Radiological releases are controlled by the use of filters and charcoal beds. Personnel comfort is maintained by fans, air condi­tioning and steam/electric heating systems, as appro­priate. Fire dampers are used to isolate designated fire areas; fans are provided to pressurise stairways following a fire and are also available for smoke re­moval following fires. Contamination control is dis­cussed in the next section.