A container hangs several metres up on the crane of the drop tower on the Test Site for Technical Safety in Horstwalde.

Storage containers are tested for safety in drop tests from great heights.

Source: BAM

BAM examines and checks the safety-related suitability of containers for the final storage of radioactive waste on behalf of the Bundesamt für Strahlenschutz (BfS) [Federal Office for Radiation Protection]. Drop tests and numerical simulations are used to examine what would happen in the event of an accident involving such a container in a repository.

A container specifically for every purpose

Container types are differentiated according the nature of their usage and statutory requirements: for highly radioactive waste there are particularly stringent safety-related requirements in place. Storage containers are subject to different regulations than transport containers. Around 90 percent of waste consists of low to intermediate level radioactive materials, which generate only a negligible amount of decay heat, such as waste from the decommissioning of nuclear power plants or operational waste, for example contaminated tools or protective clothing. This sort of waste should be packed in sheet steel containers and stored permanently.

Christian Protz, from BAM's Safety of Storage Containers Division is examining selected test samples of this sort of container. To do this he lets them fall from heights of up to 5 metres from the drop tower at BAM's Test Site for Technical Safety (TTS) in Horstwalde, Brandenburg. He first fits the test objects with various sensors. High-speed cameras and other measuring devices on the ground record the fall and moment of impact of the items being drop-tested. "I would like to know precisely which stresses are caused and what sort of damage these might do to the container," he says. He pays particular attention to screws, welded joints and side sections.

Simulation of an edge drop using the finite element method: red areas represent high and blue areas represent low deformity.

Simulation of an edge drop: colours indicate the scale of deformation.

Source: BAM

Like a crash test for cars

Then Protz compares the results from the experiments with stress analyses that he has conducted using the finite element method on computer. This creates mathematical container models and simulates various crash scenarios. It is comparable to the process of conducting crash tests for cars, where most accident scenarios are first played out on a computer and are then verified using experiments. The advantage is that BAM can make more precise predictions about how containers will behave and therefore better judge the safety reserves of the final storage container.

BAM is not only examining mechanical influences on the containers, however. It is also analysing possible effects of fires and explosions plus corrosion with regards to the safety of containers. In this way it is assisting the technical implementation of the concept of radioactive waste management in Germany, the primary objective of which is to preserve the safety of people and nature.