Reactor tester branches out

Portable remote-controlled material analysis system gives rapid answers

A remote technique developed by the nuclear industry looks certain to find widespread application wherever material analysis is needed in a hazardous environment.

Magnox Electric developed the instrument, which uses laser-induced breakdown spectroscopy, to distinguish between different batches of highly radioactive nuclear reactor rods. The spectroscopy technique itself is not new, but the breakthrough has been to devise an instrument to carry out the technique remotely and analyse the results on site.

The machine consists of a probe which is `posted’ into the reactor area through a hole during general maintenance. The probe is moved about within the reactor area by a master/slave manipulator and is connected by an umbilical to a computer-controlled sampling spectrometer. The umbilical contains two optical fibres and a controller for the probe’s integral camera, used for positioning. Magnox Electric team leader Dr Anna Duckworth says the umbilical could be up to 100m long.

Analysis is carried out by sending a high-power infrared laser pulse down one of the optical fibres. This blasts off a microscopic amount of material – less than a millionth of a gram – which forms a light-emitting plasma. The light is collected by the second optical fibre and sent to the computer for spectrum analysis. Swansea University physics department has independently verified the operation of the instrument.

The laser pulse also removes any oxide on the surface of the specimen before the test proper. Reflectivity measurements indicate when the parent metal has been reached.

After setting up, which takes a day or less, results from a pulse can be analysed on site in 10 minutes. The analysis equipment fits into two laboratory racks and is transported to site by van.

For its original task at Sizewell the different batches of control rods were identified from the different manganese and copper content of the casing material. Traces of copper down to 0.01% and of manganese of 0.05% can be detected. Dangerous cutting up of samples for analysis has been eliminated.

Duckworth reckons the technique could be used in any hostile environment or where access is difficult. Examples could be to detect the spread of oxide under paint on bridgesor to detect heavy metal pollutants in rivers or the sea.

BNFL and Swansea University are already working on development of the technique for other areas. Duckworth says the probe’s versatility for the nuclear industry could be enhanced by developing it to use as a tool to fit the more sophisticated multilink in-reactor manipulators.

Because no sample preparation is required, the system can easily be incorporated into the programme of regular maintenance of the nuclear control rods.