Combustion Furnace for Carbon-14 and Tritium Analysis0 pages

Carbolite/AEA Technology Combustion Furnace

for Carbon-14 and Tritium Analysis

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.