This invention relates to the monitoring of pressure within a vessel and is particularly concerned with vessels which are used for the long term storage of irradiated nuclear fuel materials, for example fuel sub-assemblies after withdrawal from liquid metal cooled fast breeder reactors. The interiors of such vessels are pressurised to restrict the release of for example fission gases from the sub-assemblies.
In detecting a gas leak from a pressurized container it is known to directly measure the loss of pressure in the container. This requires access to the interior of the container which may be difficult and expensive and may increase the risk of loss of pressure. It is also known to measure particles of gas or material which have leaked from the container which may be difficult to achieve because of difficulty in obtaining access to and control of the leaking gas or material, or because of the low rate of leakage.
The object of the present invention is to provide a pressurised vessel with means for reliably indicating a significant change in internal pressure over long periods of time.