5.5.1 Types of measurement

The measurements fall into two main categories:

• Condition monitoring to monitor the chemical con­stituents that are critical to corrosion of and de­position on metal and graphite components.

• Indication of gross effects such as the ingress of water into the reactor caused by boiler leaks.

5.5.2 Condition monitoring

Lists of magnox reactor gas analysis measurements indicating duty, typical ranges and type of measure­ment are shown in Table 2.I2.

Helium is added to the coolant gas and its mea­surement is used to indicate coolant leak rate. The measurement of nitrogen indicates air ingress that may occur during refuelling operations, whilst the measurement of hydrogen may indicate oil in-leakage (hrough the gas-circulator gas/oil seal. Hydrogen, carbon monoxide and methane are effective condition
monitoring measurements with respect to graphite and/or steel corrosion, these factors being more cri­tical for the AGRs because of the increased tempera­tures and coolant pressures.

Typically for condition monitoring purposes, a magnox station may use a katharometer and/or flame ionisation gas chromatograph with a local integrator/ controller arranged to sample each reactor in turn and provide a data printout every 30 minutes. Cali­bration gas mixtures are used to provide standards which have been checked against research laboratory standard mixtures.