Environmental gamma spectrometry for Polish Nuclear Power Plant – preliminary considerations

Poland faces a choice of an environmental radiation monitoring systems (ERMS) for newly designed Nuclear Power Plant (NPP). Contemporary radiation monitoring systems can be based on gamma detector cooperated with Multichannel Analyzer (MCA). This solution will give a tool for very fast assessment of radiological situation around NPP and allows authority to react in case of radiological circumstances. The level of radioactive isotopes of cesium and iodine must be the subject of permanent monitoring because of their large amount in the hypothetical radioactive elements fallout from NPP. Thus ERMS must be high sensitive for the mentioned radionuclides and simultaneously should provide information about other radionuclides present in contingency radioactive fallout. The above radionuclides are taken into consideration because of their dominant role in the radioactive fallout after nuclear disasters in ’Grand Slam’: Windscale, TMI, Chernobyl and Fukushima. Two types of gamma detector were examined for their further implementation for the ERMS. The pre-calibrated HPGe detector was applied to cooperate with Inspectot2000 MCA while the second spectrometric system was based on LaBr scintillation probe combined with Tucan 8k MCA. The mockup experiment was fulfilled with stainless sample obtained by neutron activation using Am-Be source with strength of 1.5 10 n/s. In results of activation radionuclides of Co, Co, Cr, Fe, Mn occurred in the sample. They were a source of gamma photons with energy ranging from 320 keV to 1332 keV and several other belonging to that limits. Basing upon the above source of gamma radiation the efficiency calibration of LaBr probe was done and two series of separate measurements were performed on both spectrometric systems. During each gamma spectrum analyzes peak net area, total area, background, resolution, efficiency, and activity were determined. These data allows to estimate Lowest Limit of Detection (LLD) and Relative Minimum Detectable Activity (MDAr). Both of those parameters are useful for assessment spectrometric system ability. The LaBr probe shows better LLD and MDAr than HPGe detector however its resolution is worse by one order of magnitude. Thus preliminary test shows that LaBr with MCA could be taken into consideration as the future environmental gamma monitor for newly designed Polish Nuclear Power Plant.