BEPO was conceived by UK staff in Canada -- Montreal and Chalk River -- during the war and was designed and built by the Industrial Group at Risley under (Sir) Christopher Hinton. Construction started in the former RAF Hangar 10 in June 1946 and criticality achieved on 3 July 1948. To accommodate the emergency shutdown rods the roof of the former RAF hangar was raised 20 feet.
The reactor comprised a 26ft cube of granite encased in a barytes concrete shield 6 ft thick, penetrated by many vertical and horizontal experimental holes. The 20 ft diameter core contained 40 tons of uranium bars each one foot long and 0.9 in (inches?) diameter, canned in aluminium and disposed in 888 channels. The 25,000 graphite blocks were machined at Harwell to such accuracy that the 25 ft stack was within 0.03 inches of the design figure! The air was cooled by exhaust fans discharging 5 tons of hot air per minute up a 600 ft high chimney.
The many experimental holes enabled BEPO to be used to explore gas-graphite chemistry and irradiation damage in materials critical to the power reactor programme. A pneumatic system "shot" samples into the core and recovered them in the radiochemistry building (B220). Isotopes were made on a continuous basis and enabled Bob West, of Isotope Division (later to become Amersham International) to establish an international delivery service of radioactive isotopes for medical and industrial uses.
BEPO also provided, under Monty Finniston's guidance, the first UK experience of the problems of reliable fuel element design. In parallel it led to the development of the very successful "burst cartridge" detection system used on all subsequent UK reactors.
Among other firsts on BEPO were the installation of a heat-exchanger to provide district-heating to nearby buildings and special filters in the air outlet duct. A bank of Volkes filters, using oil sprays to improve particle size efficiency, was used and the technology later incorporated in the Windscale Pile chimneys.
Naval engineers, Dick Moore and Bob Jackson, were appointed to head the maintenace and operations teams under Jimmy Grout. Early BEPO shift engineers included Ken Henry, who went on to manage the Dounreay Fast Reactor, and Cliff Blumfield who became director of Dounreay.
George "Jock" Campbell had already made a considerable contribution to the start-up of the GLEEP reactor and he took charge of all the industrial staff for both reactors. He was a fund of practical advice and assistance and achieved seemingly impossible targets. Another "character" was Betty Flew, in charge of radiation safety, who could reassure new staff about radiation concerns and gently but firmly keep the older hands in line.
BEPO was the overall responsibility of John Dunworth and Fred Fenning, later to become a deputy director of Harwell, was the physicist in charge. Among the neutron experimentalists were Peter Egglestaff and George Bacon while Tom Fry and John Simmonds researched radiation damage in materials. Lewis Roberts, later to become director of Harwell, researched gas-graphite chemistry. BEPO operated successfully until it was shut down in 1968.
The chimney or "stack" was constructed by Devizes firm WE Chivers and Sons, whilst transforming the former RAF bomber station into a redbrick nuclear research campus. Construction started in the bitter conditions of the 1947 winter and was completed with a "capping out" ceremony the following year.
Demolition, 52 years later, started with the removal of the Portland stone cap early in January 2000. Subsequent courses of bricks, up to five courses at the base, were dropped down the chimney and removed by a "bob-cat" operating inside one of the air-ducts. Steeplejack Paul Wakefield of Connell Brothers said: "The chimney is a tribute to the local craftsmen who built it. We used jack-hammers to loosen the bricks but being so well built our progress was slow." The special "engineering" bricks, weighing 5 kg each, were monitored and then used to backfill the cavernous air ducts leading underground to the BEPO reactor.
BEPO, a prototype for Britain's Magnox power station series, needed five tons of air every minute to cool the natural uranium pile to a temperature of 200 degree Centigrade. The original Ministry of Supply specification called for an octagonal chimney to exhaust the filtered air, but Chivers said they could build a circular one quicker and their advice prevailed.
Massive fans sucked air through 10x8ft (3x2 metres) underground ducts and these had to be tested before BEPO's start-up. Staff and people in Didcot were displayed to hear a booming note being emitted from the stack! It is said that a scientist went home for a set of tuning forks to calculate the frequency. BEPO engineer Bob Jackson, now aged 78, recalled advice was sought from the National Physical Laboratory and the cause being found by Metropolitan Vickers in the ducting of their fan systems. A simple modification silenced the problem without delaying the project.
In addition to being the world's largest organ pipe, people recall that hot air from the BEPO stack pierced the densest of winter fogs!
