The equipment used to place the viewing device at the various inspection positions inside the reactor may be divided into hoist units and units that move the viewing device out sideways once access has been ob­tained from the inspection penetration.

Hoist units form part of the inspection equipment of all AGRs and are used where gravity, together with a combination of fixed and temporary guides, can be utilised to insert the viewing device to the required position. In these cases the viewing device is lowered on a metal flexible hose which carries the cooling gas and the weight of the viewing device and any attach­ments; it also houses the electrical cabling required for services, control and telemetry of the viewing device. A typical hoist unit is shown in Fig 2.103, working in conjunction with an articulated TRIUMPH camera.

In order to inspect the relatively large area above the gas baffle dome and below the vessel roof, there is a requirement to traverse the camera horizontally once it has been lowered through the 7 m long small diameter (105 to 260 mm) access penetration. The first manipulator designed and developed for inspecting this area was for Hinkley Point B. It is capable of lower­ing the camera (housed within a 10 ш mast) through a 260 mm diameter peripheral fuel channel into the reactor, extending a telescopic boom horizontally up to 5 m and subsequently lowering the camera on its service hose to a further depth of 13 m, Additionally the whole machine is capable of slewing through 360°, can elevate or lower the telescopic boom and is fitted with a knuckle joint at the end of the boom to pivot the camera up through the horizontal. Figure 2.104 shows the general arrangement of the manipulator.

Fig, 2.101 Arrangement of boiler closure viewing equipment

Aboe-dome manipulator at Hlnkley Point В

At Dungeness B, the only available access penetra­tion for viewing the above-dome region has a diameter of 170 mm. This restraint has led to the concept of the ‘links manipulator* where a ‘break-back* chain is used to feed the camera into the reactor and the chain itself forms the boom of the manipulator. This principle has been extended to cover inspection re­quirements for Hartlepool, Heysham 7, Heysham 2 and Torness. Fig 2.105 shows the Heysham 2 inter­stitial manipulator which is an example of the ‘links’ principle. For Hartlepool and Heysham 7, a manipu­lator has been built which has a boom extension of up to 7 m; it has five movements of freedom — slew, elevation, extension plus ‘wrist and knuckle’ at the boom tip.

The various motions of these manipulators are pushbutton-controlled from a central console and there is also a microprocessor-based ‘teach and repeat* control system to allow semi-automatic control. All manipulators are filled with hand drive facilities for emergency retrieval in case of power failure.

A variant of the links idea is used to deploy ca­meras from penetrations in the bottom of the pressure vessel. For these routes, the links are stored on a drum and they are driven up the standpipes to get across either to the boiler annulus (Heysham 2) or into the undercore region (Hartlepool/Heysham 7). For the former, the viewing angle of the camera is extended by using the combined ‘wrist and knuckle* action of a drive head fitted to the end link.

In addition to the above, boom manipulators have been developed to view the under-boiler region (Hink — ley Point B), outlet duct viewing (Hartlepool/Heysham 7) and the sub-diagrid region (Heysham 2) using the access available when a gas circulator is removed. For the first two, the boom consists of a series of tubes that are screwed together and extended from the ac­cess position. For the latter, a telescopic rectangular section boom can be extended from the access position and the camera viewing angle extended by using the combined ‘wrist and knuckle* action of a drive head fitted to the end of the boom.