Cutting of a real pipe system by explosive technique has been tested and proven feasible inside the HDR reactor containment. Circumferential cuts were performed on a pipe loop with 400 mm diameter, 20 mm wall thickness. The cutting tool consists of an array of modular explosive charges which are wrapped around the pipe in a collar like mode. Mounting of the charge array is performed manually in a quick and easy way. In order to retain the fragments originating from the charge a fragment retaining structure was used in the experiments. This ring shape structure (fragment catcher) also substantially reduces the explosive blast load on the immediate vicinity. However, handling a fragment catcher of 700 kg weight requires a pulley or crane and, consequently, rather restricts the application of this technique. In addition to the control of the fragments and the blast wave in the area of cutting operation the transient load on the pipe system and on the reactor containment structure has to be kept below critical values. In principle, the load produced in pipe cutting by explosive methods must be subdivided into the local and the global loads acting on the HDR. The various contributions of the dynamic loading have been measured and analyzed carefully. Fourier analyses conducted on the basis of displacement measurements indicate the frequencies. The ground mode, of the long pipe branch are between 2.5 Hz and 3.5 Hz, and for the second ground mode, between 7.5 Hz and 8.5 Hz. Predictions of the axial momentum on the basis of short pipe segment cutting are a factor of 3 too high in the calculated deflection of the separated pipe ends, while the calculated pipe excitation frequencies (2.5 to 10 Hz) are in rather good agreement with the measurement. Plastification outside the cutting seam of the pipe can be excluded because of the rather small deflection. This conclusion is backed by the stresses calculated on the basis of the strains measured at critical points of the pipe system. The vibrations generated in the plant as a result of the impulsive loads besides the pipe system vibrations have very high frequencies, which will cause no damage to the HDR containment. The handling and economic feasibility of the method depend critically on two major aspects: • - Fast and safe installation of the explosive charge collar around pipes of different nominal widths, and subsequent fast and safe installation of the fragment retaining device (fragment catcher). • - Fragment retention of the confinement material must be ensured, if necessary, and must be economically meaningful.