Preparatory work has begun at the construction site of the PALLAS reactor in the Netherlands. The PALLAS reactor is intended to replace the existing 45 MWt High Flux Reactor (HFR), operated by NRG on behalf of the European Union’s Joint Research Centre, which began operation in September 1960. While HFR has provided about 60% of European and 30% of the world’s use of medical radioactive sources, the 55MWt tank-in-pool type PALLAS reactor will be able to deploy the neutron flux more efficiently and effectively than the HFR.

In February 2023, the Nuclear & Radiation Protection Authority (ANVS – Autoriteit Nucleaire Veiligheid en Stralingsbescherming) granted a construction licence for the reactor and Rijkswaterstaat issued the Water Act permit for the intake and discharge of cooling water. First concrete for the foundation was poured the following May and the Ministry of Health, Welfare & Sport instructed PALLAS to continue with project preparations to avoid unnecessary delays.

Although funding has been allocated for the construction of the PALLAS reactor, the government has yet to make a final formal decision on its construction. This will depend on the Dutch parliament approving the creation of a new state-owned company and the European Commission approving public investment.

Work is being carried out in stages by Belgian construction firm BESIX, which was awarded a contract in November 2022. To date, 380 foundation piles have been put in place. The 33-metre-long posts are drilled from the pontoon, with the pile cleaning device positioned precisely on the bottom. Quality testing was undertaken before the start of this work to verify predetermined parameters for drilling the posts, such as speed, torque and flow rate of the grout.

Thirty trenches measuring one and a half meters wide were dug into which concrete was poured to create the diaphragm walls. The ring beam was placed around the top part of the walls to connect the walls together. Activities were then started in the construction pit itself, such as reinforcing the diaphragm walls with 162 drilled steel pipes with 15 anchor cords. The anchors are between 48 and 64 metres long and are tensioned to the ground by a grout mixture.

To reach the depth of 21 metres, the construction pit was excavated – first by dry excavation. In the second phase it was excavated underwater. Sand has been extracted, clay and peat have been removed to the sand depot. The construction pit is still filled with water to groundwater level to balance the groundwater pressure.

In the next step, the gravel layer is applied to the bottom of the excavated pit to enable a good quality concrete pour. In a final step, 48,000 cubic metres of water will be pumped from the construction pit. So far, the works have progressed smoothly and thanks to successful collaboration between the teams of PALLAS, ICHOS (main designer) and BESIX (contractor for the pit and foundation phase). The work is expected to be completed by the end of 2024 and the construction pit will be ready for the next phase, construction of the reactor.