The Advanced Gas-Cooled Reactor

This too had its drawbacks the oxide was a good deal less dense than the metal and so took up more space, but a bigger issue was that the oxide was not nearly as good a conductor of heat as the metal. This meant that the fuel rods had to be very much thinner in order for the heat to able to escape. 

Beryllium had been proposed as the canning material for the fuel rods, since it had the great advantage that it was an extremely good moderator. Unfortunately, it also reacted with fast neutrons producing helium gas, which would form pockets within the metal. There were also problems with its mechanical properties as well as its toxicity. However, the main reason for abandoning it was rather more mundane  

The development programme was stopped before beryllium elements were made which could be safely irradiated in large numbers. It should be clear that this was not because there was an insuperable technical problem, but at the low U235 prices now ruling the economics of a beryllium canned A.G.R. did not seem so much more attractive than one based on stainless steel as to justify further expenditure on development.  

Other sources differ Beryllium Hits Snag in British Reactor was the headline of an article in American Metal Market. The article went on to say The new and unexpected problem is corrosion of beryllium in the carbon dioxide coolant of the reactor at its high designed operating temperature...  

Any canning metal had to be compatible not only with the uranium oxide fuel but with carbon dioxide. A form of stainless steel (containing 20% chromium and 25% nickel together with niobium) was found to be satisfactory at temperatures up to about 850°C. It had a melting point of almost 1,500°C. The maximum can surface temperature selected was 650°C (this meant the system could produce steam at the same temperature as conventional power stations), which allowed for local hot spots. One drawback to stainless steel was that it had a relatively high cross-section area for thermal neutrons, which meant using enriched fuel, of the order of 2.5% enrichment. 

As mentioned earlier, the advanced gas-cooled reactor (AGR) represents the second generation of reactors in the United Kingdom nuclear power program, which is planned to provide a total generating capacity of 8600 MWe in seven twin-reactor stations. Typical features of the planned reactors of the AGR type include the following  

On-load refueling with a machine of simpler design than that used in the magnox stations maximum fuel burn-up of 18,000 MW d/tonne. 

To illustrate the AGR design, the 625-MWe unit of the twin-reactor station at Hartlepool, in the northeast of England, has been chosen. One of the most interesting features of the design adopted by the contractors, the U.K. National Nuclear Corporation, is the pod-boiler concept, where the boilers are located in cylindrical cavities within the walls of the concrete pressure vessel, in contrast to the more conventional layout where both the reactor core and the boilers are grouped together within the central void. 

The arrangement of the reactor core and boilers is shown in Fig. 8.3. The pressure vessel is in the form of a cylinder, of external dimensions 96 ft (29.3 m) in height by 85 ft (25.9 m) in diameter. The eight boilers are placed in circular cavities of 9-ft (2.75-m) diameter within the 21-ft-thick walls of the pressure vessel. The cavities run the full height of the vessel and are joined by gas ducts to the main core void. The gas circulators are mounted below the boilers. The advantages of the pod-boiler design include the following  

These advantages are offset to some extent by the increased thickness needed for the pressure vessel wall and an increase in the total area of the insulating liner which has to be fitted to protect the inner surface of the pressure vessel from the hot circulating gas. 

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Other newer designs include the advanced, gas-cooled reactor (AGR), Canadian deuterium reactor (CANDUR), sodium-cooled reactor (SCR), sodium-heated reactor (SHR), and fast breeder reactor (FBR). These reactors employ either natural or enriched uranium fuels that may be modified in some way (e.g., graphite-moderated fuels). 

The advanced gas-cooled reactors (AGR) are a further development of the Magnox-reactors. They were only built in Great Britain. They utilize lightly-enriched uranium in oxide form. The gas exit temperatures are significantly... 

The Advanced Gas-cooled Reactors (AGR) are built into PCPV with internal boilers and gas circulators. The uranium-enriched oxide fuel is clad in stainless steel so that the risk of a charmel fire or fuel meltdown under fault conditions inherent in the Magnox design has been greatly reduced. 

The main responsibility of the Remote Inspection Project is the design, developaent and procurement of the remote visual Inspection equipment provided by the Generation Development and Construction Division of the CEGB for use on the Advanced Gas-Cooled Reactors (AGR). Papers presented to previous BNES symposia (Refs.l, 2) describe the equipment being developed by the group for carrying out routine remote visual Inspection on all the AGR s with the exception of Heysham 2 and Torness and also the evolution of techniques used for specialist non-routine inspections using TV cameras and fibrescopes. 

Surface roughening is used for the Advanced Gas-Cooled Reactors in the United Kingdom and is being considered for the gas-cooled fast-breeder reactors being studied in the United States. A doubling of the heat-transfer coefficient is obtained, for example, by tripling the friction factor (27), thus improving the merit index h f 18). 

The advanced gas-cooled reactor plants under development include the Gas-Cooled Heavy-Water Reactor, the Advanced Gas-Cooled Reactor, the High-Temperature Reactors, and the Gas-Cooled Fast-Breeder Reactor. The future trends in the development of gas-cooled reactors can be indicated by an examination of the potential performance characteristics for these reactors. 

The Advanced Gas-Cooled Reactor (AGR) was previously discussed in some detail. The AGR is reported to have a development potential beyond the Dungeness B design. If the unclad fuel element development for the reactor is successful, the conversion ratio of the AGR may be improved significantly with some probable decrease in fuel cycle cost. 

R. W. M. D Eye, Dispersed ceramic fuels and the Advanced Gas-cooled Reactor. United Kingdom At. Energy Authority TRG Rept. 1210(S), March 1966. 

Gas cooled nuclear generating plants In commercial operation In the U.K. at the present time are based either on the magnox reactor system or the advanced gas cooled reactor system. The magnox reactor systems utilise single cavity pressure vessels, the earlier ones being of steel construction, the later ones of prestressed concrete. The advanced gas cooled reactor systems utilise either single cavity or multicavity pressure vessels of prestressed concrete construction. 

This zero-energy reactor was designed to complement the Advance Gas-cooled Reactor at Windscale in providing physics information on the AGR... 

The advanced gas-cooled reactor systems are given in Table 1.4. The reactor pressure vessels are made either in prestressed concrete pressure vessels or in double PCCV. 

The origins of the SGHWR system can be traced back to the middle of 1957 when the Initial design study of the advanced gas cooled reactor (AGR) was reviewed within the UKAEA. It was decided that, while all promised well, It would only be prudent to have some alternative advanced thermal reactor system under study. Accordingly, the features of a power reactor were broken down Into five main headings - fuel, cladding, coolant, moderator and form of construction. The solutions selected for the AGR were considered and possible alternatives put down which could be evaluated for this, so far, unidentified new system. 

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