POLLUX Casks for Permanent Storage of Radioactive Materials

What are POLLUX casks used for?

The POLLUX cask is developed by the Gesellschaft für Nuklear-Behälter mbH (GNB) for transport and the direct permanent storage of spent fuel elements in deep geological formations, e.g. closed salt mines, etc. However, it is not yet certain whether POLLUX will one day be used in this manner.

The POLLUX consists of an inner and outer cask. The inner cask is made of forged steel and tightly closed by a welded lid to take up compressed nuclear waste and ensure that radio nuclides are locked in. The outer cask made of ductile cast iron serves to shield off the radioactive radiation. It is closed by a massive screw cap.

POLLUX in oblique drop position in the moment of lifting up to the drop height of nine metres

Depending on the respective type of nuclear fuel rods, POLLUX could take up 18 to 30 fuel elements from pressurized water reactors or boiling water reactors. The cask has a diameter of almost 2 metres, its length is approx. 5.50 metres, and the weight is 65 tons.

The POLLUX must comply with the traffic regulatory requirements for type B(U) packagings and the german atomic law. It could be used for transport, intermediate storage and permanent storage.

Tests with a prototype of the POLLUX cask

BAM performed in total six regulatory drop tests using an original-sized prototype of the POLLUX cask: The tests included a drop from a height of nine metres onto an unyielding target vertically down onto the lid side, as well as a drop in horizontal position. The shock absorbers in the transport configuration were deformed; the container itself showed no cracks or deformations.

The container also remained undamaged when another drop test was carried out with the bottom facing downwards, as well as a test in which the container was dropped from a height of five metres onto concrete slab without using shock absorbers. On the other hand, the concrete foundation was struck through by the trunnions, and several deep cracks ran into the slab.

POLLUX with deformed shock absorbers after the horizontal drop test of nine metres

The resistivity of the cask´s lid edge was tested in an oblique drop from a height of nine metres. In this test, both shock absorbers were severely damaged. However, the threaded area of the outer cask´s lid showed not even the most minimal deformation: The lid could be unscrewed without any problem.

POLLUX after the oblique drop test from a height of 9 metres with damaged shock absorbers

Strain and deceleration m easurements performed on the cask showed that the severest stresses only occur after the main impact, during the phase of free rebound. This phenomenon is a result of the interaction between loose single masses: The 34 tons outer cask contains the 21 tons inner cask, which contains again a massive steel cylinder with a weight of 10 tons simulating a real content. Due to elastic spring reactions between these single masses, so-called relative movements with internal impacts are caused. These impacts between the single masses take place offset by a few milliseconds and cause considerable material stresses.

After completion of the drop test series, the POLLUX was transported back to GNB and opened in the presence of BAM experts. None of the container components showed any damage that could have affected the function of the POLLUX, the shielding or the safe enclosure of radioactive material.