Tritium (the third and radioactive isotope of hydrogen) and Carbon-14 are included in the NIREX priority list of notifiable radionuclides for waste destined for storage either at their site of origin or at the DRIGG storage area in Cumbria. Hence the demand for the analysis of these two isotopes in decommissioning wastes has steadily risen in recent years. In addition, tritium (as tritiated water) and Carbon-14 are discharged to the environment from nuclear operations, so there is also a demand for the analysis of environmental materials for these two nuclides.
The only applicable analytical technique is to combust the sample to completion, aided by a suitable catalyst, and selectively trap the chief combustion products, ie carbon dioxide and water. The concentration of the Carbon-14 and tritium (tritiated water) in the trapping agents would then be assessed by liquid scintillation counting and thereby the sample tritium and Carbon-14 concentrations can be calculated.
These findings prompted the design and building of the Carbolite/AEA Technology combustion furnace, with the following important benefits:
The sample combustion tube is of a conventional type and is not an integral part of the furnace, hence replacement is achieved quickly and easily without the need for expensive refurbishment and avoids excessive instrument 'down-time'.
The sample combustion tube, gas bubbler train and associated connectors are fabricated entirely from glass and easily decontaminated, thereby avoiding analytical 'memory' effects.
The sample combustion tube and associated glassware are relatively inexpensive and therefore replicate sets can easily be kept and used for different classes of sample. So a particular furnace can easily be used to analyse a diverse range of materials, ranging from those of an environmental origin to those generated by decommissioning operations.
The Carbolite/AEA Technology furnace incorporates a uniquely designed manifold which permits oxygen to be delivered to the catalyst to operate at its optimum at all stages of the sample combustion. In addition, since the gas delivery tube runs through the heated catalyst there is no possibility of thermal decomposition products 'condensing out' on the outside surface of the gas delivery tube. The oxygen is also ejected at right angles to the main gas flow therefore reducing opportunities for the 'back flow' of sample combustion gases/products into the gas delivery tube.
The temperature control of the sample zone can be programmed via a comm linked PC. This has the advantage that different sample combustion protocols can be created and conveniently stored on disc. These can then be retrieved and downloaded to the furnace as and when required. The COMMS outputs from a number of furnaces can be 'daisy-chained' together to a single PC hence permitting their individual operation, each can be running a different protocol, from a single PC or workstation. This would also allow a furnace and its associated equipment to be placed in a hazardous environment and operated remotely if so required.