Dounreay Site Restoration Ltd -Uranium criticality cells

Uranium criticality cells - D1249

Construction of the experimental criticality laboratory started in February 1956. Initially, it consisted of a single test cell housing one assembly, controlled from a room at the edge of a 90-metre radius exclusion zone.
A rig – known as the Zero Energy Thermal Reactor – was installed in September 1956 and went critical for the first time on August 13, 1957. This was the first nuclear reaction to take place on Scottish soil.
The cell was rudimentary by today’s standards. There was no ventilation installed and the north face and roof did not have shielding.
The rapid success of the first experiments resulted in two more cells being built within the D1249 complex in 1958.
The cells were unsuitable for plutonium tests and a fourth cell, in the building known as D8550, was constructed inside a fully shielded cell.
The experiments in D1249 ceased in the early 1960s, when the facility was decontaminated and converted to a sodium facility. Later known as Supernoah, it was used to test reactions involving water and the liquid metal being used as coolant in the UK’s fast reactor research and development programme.
The rig was modified in 1977 to allow studies on intermediate leaks on the evaporators, superheaters and reheaters of the prototype fast reactor. It was refurbished again in 1991 for tests in support of the PFR intermediate heat exchanger safety case.
The final series of experiments were carried out in support of the steam generators for the European Fast Reactor programme. These finished in March 1995, heralding the end of the UK’s contribution to the European programme.
The dismantling and demolition work started in September 2000 with isolation and rerouting of electricity and water lines.
A local company, Nicolson Engineering, carried out the main strip-out. Holt Drainage and C & D Industrial Services did civil work.
The work was carried out in phases, starting with removal of the ventilation stack, followed by the vessels and pipework. Finally, in 2005, all the buildings were demolished.
Today, all that remains are concrete floorslabs.
In 2006, on the run-up to the 50th anniversary of the first criticality, Dounreay invited the site stakeholder group to consider how this occasion could be marked.
Local schoolchildren took part in a competition to design a commemorative plaque, which now features in the Caithness Horizons exhibition in nearby Thurso.