March 1960: Berkeley nuclear power station

With civil works nearing completion. The Engineer reported on efforts to install the reactors at Berkeley nuclear power station in Gloucestershire

Sat on the eastern bank of the River Severn in Gloucestershire, Berkeley nuclear power station came into service in 1962 and produced electricity for 27 years.

Built for the CEGB by AEl-John Thompson Nuclear Energy Company, Berkeley was one of the UK’s 11 Magnox reactor nuclear power stations that were built from 1956 to 1971 and would provide a fleet average of 37 years of operational life. Work began on Berkeley in 1956 and in March 1960 The Engineer provided an update of progress at the site, which at that stage was concentrating on installing the reactor.

“ln No. 1 pressure vessel the graphite core, which contains the fuel elements and control rods and serves as moderator and reflector, is being laid,” our reporter noted. “This core is a structure consisting of about 97,000 pieces of graphite, in the form of blocks and tiles, built up into a regular polygonal prism, 30ft high and 48ft diameter overall.”

Our unnamed reporter continued: “The core proper, that part of the structure in which the fuel elements are located, is 24ft high and 42ft in diameter and is surrounded by the reflector, which has a radial thickness of 2ft and an axial thickness of 3ft at the top and bottom. The core is built up of twelve layers of 8in by 8in by 30in graphite bricks, successive layers being interleaved with two thicknesses of graphite tiles, keyed together.”


The vertical channels for the fuel elements and coolant consisted of a 4” diameter hole in each brick and tile, with two diametrically opposed keyways 13/16” wide by ¾” deep, cut in each hole to accommodate the fuel element support struts.

The Engineer added that vertical channels, 3” diameter - for control rods, flux measurement and a neutron source - were formed by machining quadrant grooves from the corners of certain bricks that were to be grouped in fours so that the four quadrant grooves form a cylindrical channel. The coolant channels were on a square pitch of 8”. All the bricks were machined from extruded graphite blocks of nominal size 8.55” square by 32” long, the finished size tolerance being ± 0.002”.

“Between the ends of the bricks in successive layers two rectangular tiles are fitted,” said The Engineer. “Each tile is made so that the longer side (in plan) is in the direction of extrusion and is equal to the lattice pitch of 8in.”

The two consecutive tiles in each stack were assembled with their shorter sides at right angles to each other, to allow for Wigner growth, which is the displacement of atoms in a solid caused by neutron radiation.

“Under all conditions of growth, channel alignment is maintained by the cruciform arrangement of keys and keyways in the tiles and blocks,” said The Engineer. “There is sufficient clearance between each keyway and its mating key to ensure that the columns are supported on the faces of the bricks in all stages of differential growth, to keep the coolant leakage to a minimum. To prevent neutrons from streaming through the gaps that allow for Wigner growth, the bricks in the moderator are rotated through 2 degrees about the vertical axis.”

The core structure was held together radially by tubular tie-bars with peripheral restraining bands. The tie-bars were made up of mild steel and stainless steel members to give them the same effective thermal expansion as that of graphite.

The Engineer added: “The core rests on a steel support plate 4in thick which contains 3,275 circular holes to locate the fuel element/gas coolant channels, and the whole assembly is carried on cross-braced ring girders. Positive location is effected at the plan centre of the pressure vessel by having the four central columns of the core spigoted to the support plates. To allow for differential expansion between graphite and steel, all the remaining columns of the core rest on ball bearings on the support plates.”

Building of the core was carried out under clean conditions with access to the pressure vessel obtained via changing rooms and all workers and visitors wore special clothing, including caps, rubber-soled shoes and buttonless overalls.

“The setting up of the first layer of the core governs the accuracy of the subsequent stages of assembly,” said The Engineer. “First, the area of the support plate is divided into quadrants. In the first quadrant straight- edges are accurately positioned to include a 90 degree angle in which four graphite bricks are positioned on a fixed base to act as a locational centre.”

Flat movable ball races were mounted on the adjacent cavities to carry the other bricks in the quadrant. When the first quadrant had been filled, the straight edges were removed and realigned on the second quadrant and the laying proceeded.

The report went on to add that the circulating water requirements of the station would be 21,000,000 gallons of water per hour, pumped from the River Severn through intake screen chambers situated about 650ft off-shore.

Although decommissioned in 1989, the Berkeley site looks set to remain at the forefront of nuclear energy with plans to establish facilities that will attract companies developing SMRs.