A.11. Activity measurements are especially useful for detecting breaches that could otherwise go undetected by the measurement of other parameters. Activity should be measured to detect breaches in, and releases from, any of the multiple protective barriers. Hence, measurement locations should include:

— The reactor cooling circuit, to detect fuel failures;

— The containment atmosphere and drains, to detect failures in the primary circuit and connected circuits inside the containment;

— The secondary side circuit, to detect primary to secondary side leaks.

A.12. To detect leaks from the containment structure, the activity in the stack or in connected ventilated buildings should also be measured. Measurements of activity in the stack can be used to detect releases into the containment atmosphere before isolation and to detect leaks from the valves following isolation.

A.13. For double wall containments, it should be considered whether to make measurements of activity in the annulus ventilation system to detect leaks of radioactive material from the primary containment.

A.14. Provisions should be considered for obtaining samples of the containment atmosphere from outside the containment building, to be used for radiochemical analysis.

A.15. In addition, activity measurements in the following areas should be considered:

— In or around systems into which high energy contaminated fluids could enter owing to a lower functional pressure;

— In or around parts of systems connected to the primary circuit or the containment atmosphere but extending outside the containment.