5.6.1 Condition monitoring of coolant

It is important to monitor the level of radioactivity in the COi cooiant to provide warning of the fol­lowing potential hazards:

• Release of long-lived fission products that could contaminate and limit access to reactor internals.

• Release of gaseous and volatile fission products from the vessel through leakage in normal opera­tion and in a depressurisation accident.

A recent development is the use of an online gamma spectrometer using a gas chamber near a Ge/Li-drifted semi-conductor gamma detector cooled with liquid nitrogen. This enables gaseous radio isotopes to be identified and their quantitative concentrations dis­played for each isotope. This technique enables very small leaks in the fuel cans to be detected and sup­plements the main failed fuel detection system.