3.2 Nuclear stations

The CEGB has adopted the pressurised water reactor (PWR) as the basis for its new nuclear station which is being built at Sizewell construction works com­ menced in late 1987. It is hoped this 1200 MW ‘reference design’ will form the basis for a small programme of stations utilising similar technology which will be located at other suitable sites within the UK, subject to consents being given. Figures 2.11 and 2.12 show respectively a station plan and section through a typical PWR station.

3.3 Combined cycle gas turbines

These plants are an extension of gas turbine station developments where waste heat boilers are installed to recover heat from the gas turbine exhaust. This heat is utilised to produce steam which is employed to drive a steam turbine-generator, which can be either unitised with the individual gas turbines or ranged across a number of units.

The technology of such plants is well-established and their main benefit is the higher overall cycle efficiency which can be achieved. However, a premium fuel is normally required, and careful consideration of the relative merits of increased capital cost, long term fuel prices and reliability is required before such a plant can be installed. The CEGB has considered the station design options which could be adopted for this type of plant and Fig 2.13 illustrates a possible general plant configuration.

3.4 Wind power

Wind turbine-generators promise to play a prominent part in the field of alternative sources of energy, A 250 kW horizontal axis and a 100 kW vertical axis wind turbine generator have been installed as demonstration units on the CEGB’s Carmarthen Bay site, and a 1 MW machine is to be constructed at the Richborough site in the near future. There are also several other units with capacities up to 3 MW operational in the UK.

Figure 2.14 shows the wind turbines at the Carmar­ then Bay site.

The CEGB is supportive of the efforts of manufac­ turers to develop this source of energy and besides co­ operating with development proposals as they arise, is actively looking at the potential for wind turbine arrays for providing a contribution to its system capacity.

3.5 Tidal power

The potential for harnessing the tidal power of the River Severn and the River Mersey estuaries is being investigated. If found to be practicable and economic, such schemes could provide about 6% of the CEGB

Station design concepts

system needs, but probably not before the year 2000 at the earliest.

3.6 Geothermal energy

The CEGB will be providing substantial support for investigations into hot dry rock technology which will be carried out in the UK over the next few years. This involves tapping into hot dry rocks of 200°C and circulating water down to 6 km depths through fissures enlarged by hydraulic fracturing in order to capture heat. The best sites appear to exist in National Parks at exposed granite quarries in the south-west and north­ west of England. Reservoir behaviour, however, is proving currently more complex than anticipated.

3.7 Combined heat and power

Combined heat and power schemes have been used extensively by overseas utilities but not on a significant scale to date in the UK. The CEGB, however, remains interested in pursuing such schemes as and when suitable opportunities arise.

4Station design concepts

4.1Basic considerations

Major power stations on the CEGB system have for many years been planned from the onset to be com­ pleted with a given number of units of the same rating and to a similar layout. Where additional capacity is found to be necessary at a particular site in the future, then this has been accomplished by constructing a second 13 or third C station and so on until the total site capability has been developed.

The advantages of this process are that internally to an individual station’s development, the units are in all major aspects identical, and therefore the detailed station design is to a great measure reduced to design­ ing the first unit only. There are also operational advantages in having a standard arrangement for each unit in a station and a reduction in the quantity of spare parts which it is necessary to retain in stock. This concept of identical layout for each unit has become current practice for stations containing two or more units.

In terms of overall site layout, the construction of additional generating capacity by station rather than individual unit extensions has some practical advan­ tages. The design and construction of any new capacity can proceed independently of any existing generation facilities on the site and the designer is not required to make provision for some unknown future requirement. This allows the station design to be optimised with the proviso that it does not preclude future development of the remaining site area. . •

Station developments allow technological changes to be accommodated in discrete steps and with a reason­ able number of installed units, which allows an effec­ tive and efficient supporting infrastructure to be pro­ vided. It also permits an operationally-efficient staffing regime to be established avoiding the complexities of different technologies and operating procedures on the same station.

Ultimately, decommissioning and demolition of time-expired stations can be undertaken in a discrete package with the cleared area again being available for redevelopment as and when required, independently of any other generation facilities on the site. Figure 2.15 shows how this philosophy is currently being applied to the CEGB’s Hams Hall site.

4.2 Design objectives

/The objectives of any aspect of power station design, given a specific fuel type and choice of steam cycle, are to achieve the lowest capital cost and ease of construc­ tion, together with simplicity and efficiency in the

operation and maintenance of the station over its projected life. These objectives are not easily achieved. Realistic station designs are evolved over long periods of time and result from the input of experience and the continued re-evaluation of the variables which influence the design process. The experience and the rules and regulations which contribute to this process may vary from utility to utility and therefore a differing emphasis may be placed on the contributing elements which, ultimately, can influence the final result. How­ ever, whichever station design is finally adopted the process will require consideration of a range of factors which influence the primary objectives and which are outlined as follows; the order is not intended to denote priority as these will be utility specific:

Efficient operation

•Reliability of operation.

•Safety in operation.

•Simplicity of operation.