Abstract:
The paper gives an overview of the different methods for on-line and off-line detection for small amounts of activity used at the Hoger Onderwijs Reactor (HOR). The different installed techniques with their pro’s and con’s are discussed in more detail. During the HEU to LEU fuel conversion we encountered five cases in which the fission product concentration in the reactor pool water increased significantly. Although this increase never caused any exceeding of intervention levels as stated in our permit and safety analysis, the ALARA principle urged us to analyse the situation in more detail. As a result three new instruments were developed. The gained experience with all three new instruments is given. One of the new instruments, the ‘RID-cascade’, is described in more detail.