In the CEGB, as with any organisation, it is impor­tant to know the costs of the operations being carried out, whether it be the production costs of the product or the maintenance costs of the production plant, so that strategies may be reviewed and the economics of the system examined. Details are sought of the com­position of the costs so that an indication is acquired of the areas in which costs can be reduced. Generally in industry, it is the labour and material costs of maintenance which are most easily controlled. How­ever, in the CEGB, the major cost of maintenance is represented by the down time of the reactor unit.

MANIPULATOR DRIVE FUNCTIONS

Fig. 3 59 Manipulator with seven functions of movement

When out of service, lost generation by the unit has to be made up by running less-economical plant elsewhere. This cost varies from hour to hour, day to day and from season to season. Typically, the replacement generation costs of a 250 MW(E) nuclear unit are of the order of £60 000/day; costs for a larger unit would increase pro rata. To this must be added the more familiar costs of manpower and revenue expenditure to arrive at the overall cost of maintenance. The purpose of this section is to illus­trate the magnitude of the costs involved and to indicate the relationship between the replacement costs and the additional costs. Since the replacement costs ‘■ary from station to station and the maintenance programmes are peculiar to individual stations, it is not feasible to give an overall picture. However, an example is taken from an Oldbury shutdown pro­gramme of about 80 days’ duration to fulfil the afore­mentioned object і v es.

The programme, typical of the station, consisted of a short phase of a few days during which the reactor was shut down and cooled. This phase was

followed by the maintenance period which occupied most of the programme time. On completion of main­tenance, a further few days were used to dry-out and re-start the reactor. The maintenance period was made up of three areas of activity which proceeded in parallel, of which the in-core inspection and main­tenance was one. In practice, the critical path for the piogramme could pass through either of these areas. The basic approach to analysing the programme was to calculate the effective proportion of the day used on any given task in terms of days. Due regard was paid to parallel activities so that the total re­placement generation cost of £60k per day was pro­portioned to each task. For this programme, the total replacement generation costs were £5.256 million of which £1.8 million was attributed to the reactor’s inspection and maintenance programme. Added to this was a further cost of £340k for labour, capital and revenue expenditure to give a grand total of £2.1 million.

It is immediately apparent that the replacement of generation costs far outweigh the costs of conducting the inspection and repairs; so there is always an in­centive to reduce the reactor downtime by optimising the overall programme and eliminating unessential work.

The reactor’s replacement generation cost was ana­lysed in the manner previously described to cost the seven main activities of its inspection and mainte-

nance programme. The opportunity was taken to identity w hat is designated the direct, the standpipe and the operational charges associated with each activity. These charges make up part of the costs and are de­fined as follows: [39]

volume of work involved.

• Standpipe charge — this is the cost allocated to gain access to the reactor by the removal, storage and reinstatement of standpipe closure units.

• Operational charge — this is the cost of time spent shutting down and re-starting the reactor. Some of which must be allocated to each specific task.

The distribution of these costs is illustrated by Fig 3.63 which shows that 50ro of the cost was employed on routine and special maintenance procedures at a cost of about £9Q0K. Routine maintenance is those procedures which cannot be carried out whilst the reactor is on load, such as the maintenance of stand­pipe housings, BCD isolation ahes and certain con­trol rod actuators. The special maintenance activities relate to in-reactor repair work, such as the fixing of fish plate bolts referred to earlier. The inspection and oxide investigations each absorbed about 20% (£360k) of the costs. The direct charge can only be reduced by the elimination of work done and this may not be acceptable. The standpipe charge can be reduced by carrying out as many activities as possible at the standpipes which have been opened, and this is the normal practice adopted in preparing a pro­gramme. The operational charge is maintained at a minimum by constantly reviewing the reactor shut­down and start-up procedures so that the minimum of time is involved.

The additional charges of manpower, revenue and capital expenditure (£340k) were calculated from in­formation that was readily available for each of the seven areas of interest. The manpower costs were derived from the salaries and wages of the staff em­ployed on the work. The revenue costs are the value
of material used in maintenance and the capital costs represent the value of capital equipment purchased (including research and deselopment charges) spread over a ten year period. The distribution of these costs is illustrated in Fig 3.64. It will be noted that all the special procedures, inspections and sampling tech­niques require the injection of significant capital. This is because access to the reactor is via the standpipe, which is essentially a 9 m long pipe with an effective 229 mm diameter, into a hostile ensironment.

With total costing assessed, it was possible to es­timate the cost of individual procedures and Table 3.9 illustrates some of these costs. It is worth while to note that the cost of sampling material for further chemical and physical analysis is considerable, e. g.. two bolts were trepanned from the charge pan area at a cost of £15 000 each and approximately 10 g of metal swarf from drill sampling for chemical analysis, cost a total of £26 000.

The above example serves to illustrate that the in­spection of reactors is an expensive procedure and that downtime must be kept to a minimum. Where feasible, access points are utilised for as many procedures as possible and work is carried out simultaneously at sev­eral sites. Every effort is made by the CEGB to reduce the shutdown time to a minimum by careful program­ming and monitoring the progress of work in hand.

RCUT’NE УД NTtNANCE

TV INSPECTION

OXIDE MEASUREMENT

MATERIAL ANALYSIS

OTHER