Year
2003
Abstract
Currently within the United Kingdom, the storage/disposal costs of Plutonium Contaminated Material (PCM) waste (a subtype of Intermediate Level Waste (ILW)) are significantly higher than those for the same volume of Low Level Waste (LLW). Much of the waste consigned as ILW comprises low activity items that may not have come into direct contact with plutonium, but because of the limitations of current measurement systems this waste has been conservatively treated and consigned as ILW. In the UK, the segregation of waste into either LLW or ILW requires a sentencing system that can measure down to below 4kBq/g (100nCi/g), previously only achievable using active neutron interrogation techniques. The recent development and use of sophisticated equipment employing multiplicity analysis techniques has, however, enabled the performance of passive neutron measurement systems to be improved sufficiently to achieve these measurement requirements at significantly lower costs than their active counterparts. Further improvements to the design, operation and maintainability of these neutron counters has been achieved through the incorporation of state of the art acquisition and processing electronics, based upon high speed time-stamping of detected neutron events, developed by BNFL Instruments. These improved techniques and enhanced electronics have been combined into the TRU-D®: Waste Drum Assay System (WDAS). This paper covers the design of the TRU-D®: WDAS with particular emphasis being placed on the description of the neutron detector acquisition system and processing electronics used to maximise the performance of the TRU-D®: WDAS and how this system can be effectively safeguarded.