OBSERVE – Dose rate and temperature measurement programme

Activity and thus heat generation both decrease during storage as a result of the radioactive decay of the inventory. Likewise, there are temperature-dependent and radiation-induced changes in the properties of the materials used (for example, thermal expansion, density changes and radiolysis of the moderator material), which in turn effect shielding and heat dissipation.

The planned dose rate and temperature measurement programme OBSERVE aims to measure the entire surface of selected casks intermittently over a long period of time. Measurements provide immediate and integral information on the ageing behaviour of the casks or the inventory. The measured dose rate and temperature curves must be compared with the predicted values for this purpose. These comparisons and the respective distribution can be used to draw conclusions about actual shielding and heat dissipation properties. If the measured values are within the expected range, this confirms that no unexpected changes have occurred and that the ageing behaviour has been correctly assessed. In this way the measurement programmes can make an active contribution to ageing management.

In the first stage of the project, sensitivity studies were carried out to check the extent to which dose rate/temperature measurements are suitable for drawing conclusions about the condition of cask components and the inventory. The sensitivity analyses have shown that, to a certain extent, both changes in the fuel arrangement and gaps in the neutron shielding can be detected by close-meshed dose rate measurements on the cladding surface. It can therefore already be said that the OBSERVE measurement programme is in principle suitable for supplementing existing ageing management measures and for assessing the condition of the casks by measurement. The results of the sensitivity analyses will be used to determine the requirements for carrying out the measurements (equipment, measurement grid, measuring period) and to develop a corresponding measurement programme.