COVER STORY | SWEDEN
While the specific concept developed may be uniquely applicable to the specifics of control rod segmentation at Ågesta, the overall approach which combines standard equipment
and technology to deliver a unique bespoke solution may offer a
useful model for projects elsewhere
Above: Linda Ekstrand, Vattenfall’s project leader for the control rod segmentation at Ågesta
V was mounted on the guide rod head. In several cases the locking mechanism offered stubborn resistance before releasing. In March 2020 the remaining 26 control rods were
lifted, cut and replaced in their original position without additional problems. Nuclide specific activity measurement was done with a CZT-probe on each concrete package. Once all the control rods’ absorber parts were segmented, the remaining parts of the control rods could be segmented using a metal band saw. Here, too, standard equipment could be combined with custom- made equipment to solve the task of sawing, lifting and sorting to different waste fractions. The activity levels of the different neutron-induced material fractions were assessed separately and later combined in the same containers before transport.
The amount of loose activity released from the absorber
during cutting was less than had been prepared for, but the enclosure around the scissors fulfilled its function well and kept the any freed contamination enclosed. All parts of the rods have been transported in the shielded containers to SVAFO’s interim intermediate level waste storage facility in Studsvik. SVAFO has reloaded all
barrels into larger containers which can hold five 80 litre barrels. The control rod dummy unit will be donated to the Technical Museum in Stockholm, along with some other artefacts from Ågesta.
Overall assessment By using a tailor-made arrangement of proven equipment and technology it was possible to develop an innovative technical solution to enable the in-situ segmentation of control rods. This enabled the work to proceed safely in a challenging work space with limited access and constraints on equipment volume and logistical areas. To proceed from the initial design concept to delivery of an optimised functional technical solution, entailed considerable up-front work and adaptations to mitigate risks. This development was driven by Vattenfall in close cooperation with designers and manufacturers. “While the specific concept developed may be uniquely
applicable to the specifics of control rod segmentation at Ågesta, the overall approach which combines standard equipment and technology to deliver a unique bespoke solution may offer a useful model for projects elsewhere,” says Ekstrand. ■
Future D&D and waste management plans The decommissioning programme at Ågesta started in 2020 and is due to be finalised in 2025. Clearance measurements have already been completed for the cooling tower, turbine building, control room and switchgear building, and the cooling tower has been demolished.
Inside the controlled zone, other D&D activities are under way: removal of reactor internals and RPV; removal of other systems; and equipment decontamination which has been ongoing during the whole decommissioning period. The control rod cutting was the third major project to be completed. The next large project will be reactor pressure vessel and internals in situ segmentation.
Preparatory work is under way on site, and first segmentation is planned in early 2022. The total amount of waste generated during decommissioning activities will be about 2000t, of which 1000t is estimated to be radioactive. To date around 650t has been dismantled. Active waste is being sent to AB SVAFO’s interim storage facility at Studsvik, pending disposal.
The aim of the Ågesta D&D project is to leave the decontaminated underground facility structure in place and seal the underground cavern and tunnel. When the work is completed and the facility is cleared and sealed, Vattenfall will return the sealed cavern and the area surrounding it to the City of Stockholm, which owns it. The released site can be used for any purposes. ■
36 | February 2022 |
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