Light optical and electron microscopy have been used to study both laboratory-scale and full scale hot isostatically pressed (HIPed) copper as employed for encapsulation of spent nuclear fuel elements. Particular attention has been paid to the degree of densification achieved, as well as to the status of the joins between the sleeve, lid and the HIPed powder. The work includes the development of computing models for predicting the optimal conditions for HIPing copper and other possible encapsulation materials such as lead and alumina. Mechanical testing of HIPed samples has also been carried out.

The current method of using hydrogen to reduce oxides at powder surfaces prior to HIPing is questioned on the basis that metallography reveals definite signs of hydrogen embrittlement. An alternative method of reduction is to use CO/CO2 mixtures instead of hydrogen, and it is suggested that this approach could be strongly advantageous in future.