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Babcock’s nuclear division has designed, manufactured and commissioned a build facility capable of processing highly caustic, radioactive liquids from Dounreay’s PFR reactor in just 18 months.

The contract with UKAEA Dounreay was worth GBP3.4m.

Babcock International Group recently completed its acquisition of UKAEA, the commercial arm of the UK Atomic Energy Authority.

‘The new PFR ETP [effluent treatment plant] completed active commissioning trails prior to operations being taken over by the facility personnel from the project team,’ said Mick Moore, UKAEA project manager.

The test results of the recent effluent through the facility processing train were positive.

Dounreay’s PFR reactor is undergoing decommissioning.

While in operation, it was cooled by sodium.

As part of the decommissioning activities, sodium-wetted components are cleaned, producing a caustic, radioactive effluent.

The purpose of the PFR ETP is to process this effluent, removing the radioactivity and returning the pH to neutral.

Tim Brafield, consultant engineer at Babcock Nuclear, said: ‘We were appointed principal contractor in a ring-fenced site and were given ultimate responsibility for a diverse range of specialists working to a tight deadline.

‘As the scheme designs for the building, the process plant and the ventilation system had been developed separately, the Babcock team took six months to produce the manufacturing design using advanced modelling techniques to remove clashes and conflicts,’ he added.

Babcock based six site engineers at Dounreay full time for the duration of the project.

Safety was paramount throughout, with the detailed designs featuring bespoke lead shielding and interlocks.

AutoCAD’s Inventor software was used by the team on a large scale for the first time.

The 3D model prevented many potential design and installation problems, allowing them to be solved virtually.

The model will aid future operations, maintenance and decommissioning.

The batch-process automated pH correction system consists of a pumped recirculation loop providing continuous pH monitoring and the correction of effluent in the 10m3-capacity neutralisation vessel.

The allied nitric-acid facility features a 30m3-capacity tank, pumps with interlocks and a ventilation scrubber chimney that ensures only clean air leaves the nitric-acid storage tank.

Babcock used proportional, integral and derivative (PID) controls for the control system it fitted to the pH neutralisation part of the process.

This ensures that the minute quantities of acid that have to be added to the liquid as it approaches neutral pH are constantly monitored, so there is little danger of adding too much nitric acid.

Tests have shown that the end result is consistent, regardless of the starting point.

The entire system is linked to PFR’s Scada system for added safety.

Once the liquid is pH neutral, it is passed through an ion exchange and filtration system.

The specialist ion exchange columns and resins for the removal of cobalt and caesium were supplied by UKAEA.

Particulates bigger than one micron are removed by filtration at this stage.

Processed effluent is then passed to the effluent sentencing vessel.

Extra safety features include shielding to the effluent sentencing vessel and a further filter to ensure that none of the resins from the ion exchange process are contained within the liquid.

Samples are drawn off in an automated cabinet once the process is complete and analysed by the station’s chemists.

If the liquid is found to be acceptable, it is then pumped to the low-level liquid ETP (LLLETP) for final discharge.

The plant ventilation system was the complete responsibility of Babcock.

Fans extracting air from the plant pass it through HEPA filters before discharge through the PFR stack.

Creating interlocks and interfaces with the existing system, as well as coping with space constraints, led to the need for a highly specialised engineering design.

The UKAEA project team worked closely with the Babcock team, which provided the interface service connections to the new facility.

This involved managing the radiological hazards and providing ventilation, low active drain, fibre optics, telephones, fire alarms, water services, drains, electrical supplies and low active drain connections.

Two of the biggest challenges were providing ventilation and low active drains connections.

A ventilation ducting was designed and installed using local contractors.

Connection was made at the fan outlet and a new route provided over the top of the PFR containment building joining into an existing active duct within the PFR vent annex.

Then 1.5m square fire dampers and non-return valves were installed to an active duct at the connection point.

The connection into the LLLETP active drain line was made by construction of a 3m-deep by 3m-diameter chamber over the low active drain connection point, outside the new facility.

This construction was used to provide containment boundaries for the classified radiological area.

The new coaxial stainless pipe from the facility was welded into the existing low active drain system.

On completion of the service connections, the facility commenced active commissioning in the week forecast at start of the construction phase.

Space constraints within the plant meant that, logistically, the installation was complex, with the order of operations being crucial.

The 3D model proved to be vital when the team needed to determine the order of operation.

For example, the local control-room cubicle, which is sited on a mezzanine floor in the plant, had to be fitted before the end wall of the control room was constructed.

Nigel Parkin, chief engineer at Babcock, said: ‘Integration of the entire process plant to PFR’s Scada allows full remote control from the PFR control room.

‘This involved a great deal of complex electrical design, power distribution, motor controls and instrumentation measuring levels and pressures,’ he added.

Babcock Nuclear Division

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