The Office for Nuclear Regulation (ONR) has overseen the targeted and specialist explosive demolition of the turbine hall bases at Sizewell A nuclear power station – significantly reducing the timetable for their removal.
The longstanding structure on the Suffolk decommissioning site was substantially weakened using explosive materials by Nuclear Restoration Services (NRS) workers.
Following a series of enabling regulatory decisions, ONR inspectors were content to allow this novel and innovative method as part of the demolition of this key building.
Up to 700kgs of explosives were used to debilitate the reinforced concrete turbine bases, that support the low and high pressure turbines, together with the generators and condensers.
It means the very large turbine bases can now be completely removed using machinery within just two weeks, instead of deploying older and slower methods of drilling the structure apart which would have taken several months.
The explosive demolition was undertaken by contractors Precision Demolition Company Ltd who deployed the largest single use of electronic detonators and cartridge explosive ever used on a licensed UK nuclear site.
A series of test blasts were undertaken and the detonator timing sequence was specifically designed to meet stringent nuclear site requirements for air overpressure and ground vibration.
Both ONR and NRS, formerly Magnox, have hailed the collaborative working and modern thinking which has delivered significant efficiency savings in time and money, and reduced a prolonged period of noise pollution.
An area the size of a football pitch will be available for future decommissioning use by NRS in approximately March next year.
Andrew Bull, ONR's Nominated Site Inspector at Sizewell A, said: "This was a great example of joint working between regulator and dutyholder and everybody being open to considering and actioning novel and forward-thinking technological solutions to bring about efficiencies.
"Our stance as a consistently enabling regulator means that we will always support proactive and innovative methods of working provided these are conducted safely and securely."
Because of its novel nature, ONR placed a regulatory hold point on the work which prevented NRS from conducting the work until they had demonstrated that any risks had been minimised.
In one of the largest programmes of work at Sizewell A in many years, more than 7,000 tonnes of metal were removed and recycled from the turbine hall in the lead-up to the detonation.
The success of this project means NRS could consider rolling out this demolition technique to some of its other 12 sites moving through their decommissioning journeys.
Alan Walker, Sizewell A site director:
“It’s fantastic to see Nuclear Restoration Services (NRS), our contract partners and regulator, The Office for Nuclear Regulation, pushing the boundaries of innovation in de-plant and conventional demolition together.
“The detailed planning and stakeholder engagement for this were exemplary. Everyone involved has done an outstanding job and this success demonstrates our commitment to achieving safe, efficient decommissioning processes.”
Planning consent was given to demolish the turbine hall and electrical annexe after which more than 35 miles of cabling was removed and 8,000 scaffolding boards, clips and pipes taken out.
The twin reactors at Sizewell A were shut down on at the end of 2006 after 40 years of electricity generation.
John Wolstenholme, ONR's specialist civil engineering inspector, who leads on demolition and explosives:
"The success of this challenging job demonstrated how enabling regulation permitted the release of a series of technically underpinned regulatory hold points to deliver this job safely, meeting our expectations for Relevant Good Practice.
"This brought about a reduced permissioning time, significantly shorter clearance times, with reduced emissions to meet broader climate change requirements and recycling.
"It's hoped that these techniques and principles can be used to safely to accelerate demolition on the rest of the UK’s decommissioning nuclear licensed sites."