reading / British practice / Vol D - 1990 (ocr) ELECTRICAL SYSTEM & EQUIPMENT

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rossil-fuel power stations. Telecommunication systems must be adequate to cater for postulated non - nuclear and nuclear emergencies which may arise during the +‘orking life of the power station.

Provision of telecommunications facilities and services in the nuclear areas is often difficult because of their physical isolation from the conventional plant areas of the power station. Radio communication, v, hich is required in all areas of the station, presents particular problems because of the civil construction 0 1 the nuclear areas including steel-reinforced concrete, steel containment of equipment and the tunnels.

Nuclear power stations have emergency centres which are brought into operation during nuclear emergencies on the site and require access to telecommunication systems. These are detailed in Section 13.4 of this chapter.

13.2 Public address systems

It is current CEGB policy to provide a public address system in new nuclear power stations but not in new non-nuclear power stations. A duplicated public address system is provided for nuclear power stations because it is essential to acquaint all on-site personnel

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immediately of action to be taken should a nuclear emergency occur. A duplicated public address system, having parallel operation of both separate systems, ensures maximum availability of equipment and should provide good overall intelligibility of verbal instruction and alarm tones in all areas of the power station. The loudspeakers of each separate system are interspaced, each system providing total cover of all locations, thereby ensuring total station cover if either system fails. There are two auxiliary telecommunication rooms ( ATRs) for a two-reactor nuclear power station. The equipment cubicles for each public address system are located in separate ATRs to minimise the possibility of loss of both systems in the event of a local fire.

In locations where the ambient noise level can vary from high to low, such as the turbine hall where noise level depends on whether or not the turbine-generators are running, noise volume sensors monitor the ambient noise level and remotely adjust the volume of the public address amplifiers serving the location to the appropriate level.

Facilities are provided to check the individual operation of the large number of loudspeakers. This is done by selecting the loudspeaker omnibus circuits to be tested and transmitting a 'click' sound on the circuit. The audible operation of each loudspeaker on the circuit may then he checked.

When the station siren system is operated, the public address system will enhance the siren sound by a simulated siren sound generated in the public address system control equipment, which is triggered and synchronised by signals from the associated station siren system. Figure 8.68 shows the block diagram of a nuclear power station duplicated public address system.

13.2.1 Power station zones

For the purpose of public address broadcasting (and

also for operation of the sirens via the siren system

described elsewhere), the power station is divided into eight internal zones and one external zone. This faci-

lity may be used to minimise interference by public address messages in zones of the power station not affected.

13.2.2 Controllers

The public address system at a typical AGR power station is controlled from:

•The CCR supervisor's desk.

•The Emergency Control Centre (ECC).

•The Emergency Indications Centre (EIC).

•The power station telephone operator/receptionist.

The ECC is staffed during a nuclear emergency to take over executive control of the emergency, leaving the CCR to carry on controlling the operation of the power station and/or shutdown of the reactor(s). The EIC is staffed to supervise the shutdown of the reactor(s) in the event of the transfer of control, during an emergency, from the CCR.

The EIC has indications of the reactor status but no direct reactor controls.

Each controller has a hands-free microphone and may broadcast to any or all zones by the operation of appropriate zone switch, or to all locations by operation of the 'All Zones' switch (Fig 8.69). A monitor loudspeaker on each controller, relays messages originating from any of the other controllers and the indication lamps also light to show the zone of the power station to which the broadcast is being transmitted. Each zone switch has three positions, i.e., off/speak normal/speak emergency, the last named position generates an 'emergency' signal to precede the message.

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Each controller operates on 110 V AC uninterrupted rower supplies,

13.2.3 Common equipment

The equipment of each public address system is located in a different ATR from its associated duplicated , ■ stem to minimise the risk of loss of both systems. Each system is connected to a different 240 V AC dieselbacked supply.

Each common equipment comprises a control cubicle containing equipment to interface with the controllers, le el and tone controls, pre-amplifiers, etc. Other cubicles contain the 100 W amplifier modules (or other unit power size) to power the 50 V or 75 V lines of the loudspeaker distribution network. A cubicle is also used io terminate all the loudspeaker distribution cabling.

Each amplifier module has a volume control, tone control and output indicating device or meter for Individual adjustment. Figure 8.70 shows a typical layout of the control cubicle and amplifier cubicles.

13,2.4 Loudspeakers

Loudspeakers are re-entrant, unidirectional or bidirectional, cabinet or ceiling type to suit the local conditions.

13.3 Siren systems

As with the station public address system, it is CEGB

policy to provide a duplicated siren system for nuclear power stations because it is essential to acquaint all on-site personnel immediately of action to be taken should a nuclear emergency occur at the station. A duplicated siren system, having paralleled operation of both separate systems ensures maximum availability of equipment to provide good overall coverage of all areas of the power station. The sirens of each separate system are interspaced, each system providing total coverage of all locations thereby ensuring total cover of the power station in the event of the failure of either system. The equipment cubicles of each siren system are located in separate ATRs in a similar way to the public address system to minimise the loss of both siren systems in the event of a local fire. Figure 8.71 shows the block diagram of the system.

13.3.1Siren signals

In areas of very high ambient noise, the siren sound is supplemented by discrete beacons to indicate the particular siren signal.

Three siren signals are generated by the system:

•Continuous signal mode (with operation of associated red beacons)

'Station or Zone Evacuate'

This signal is used for fire, flood or bomb alert when the suspected bomb is located indoors. Personnel

muster at outdoor muster stations.

•Waiting signal mode (with operation of associated yellow beacons)

'Station Incident'

This signal is used for radiation gas release, chlorine gas release or bomb alert when the bomb is located outdoors, e.g., in a car parking area. Personnel muster at indoor muster stations.

• Intermittent short period on signal mode 'All Clear or Stand-down'

This signal is an option available for use as determined by the Station Manager.

13.3.2 Controllers

The siren system at the most recent nuclear power station is controlled from:

•The supervisor's desk in the CCR.

•The EIC communication desks.

The CCR supervisor's desk controller has facilities for sounding the continuous signal (for 'Zone Evacuate' at nuclear stations) in any or all of the eight zones of the power station, with audible monitoring of the siren operation.

The CCR supervisor's desk controller also has facilities for operating all power station sirens by operating the 'All zones' switch to 'Station Evacuate' (continuous signal) and 'Station Incident' (warbling signal). The controller panel layout is shown on Fig 8.72.

The controller in the EIC can divert the control of the power station sirens to the EIC by operating a switch on the EIC controller. An indication that the control has been transferred is given on the supervisor's desk controller. Only the 'All zones' Station Evacuate' and 'Station Incident' signals can he initiated from the EIC controller.

13.3.3 Common equipment

The common equipment of each system, in addition to being located in a different AIR, is also connected to a different 48 V battery supply from that of its associated duplicated system to minimise the simultaneous loss of both systems due to a common mode failure.

13.3.4 Cabling and power supplies

The cabling of each siren system is segregated and

the power supplies to the siren contactors and sirens in the same area are from different sources to minimise the risk of simultaneous loss of both systems.

13.4 Emergency telecommunications

13.4.1 Nuclear incident

A nuclear incident at a nuclear power station would be reported to the CC R. The supervisor's desk in the CCR becomes the focal point in dealing with the initial stages of the emergency. Action would be taken from the supervisor's desk to initiate the emergency procedures and to inform all on-site personnel of the incident. The external emergency services are also informed.

The CCR follows the nuclear incident procedures until the on-site ECC is staffed and operational to take over control of the situation, thereby releasing the CCR to concentrate on the operational aspects of the plant unaffected by the incident.

Telecommunication services are diverted from the power station to each emergency centre as it is activated.

13.4.2 Emergency control centre (ECC)

All CEGB nuclear stations have an ECC which is usually located in the administration building. The ECC is equipped with telecommunication equipment which

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