1.48. The performance of containment systems should be assessed against a well defined and accepted set of design limits and acceptance criteria. ‘Well defined and accepted’ generally means either accepted by regulatory bodies in States having advanced nuclear power programmes or proposed by interna­tional organizations.

1.49. A set of primary design limits for the containment systems should be established to ensure achievement of the overall safety functions of the containment. These primary design limits are usually expressed in terms of:

— Overall containment leak rate at design pressure;

— Direct bypass leakage (for a double wall containment);

— Limits on radioactive releases, dose limits or dose constraints, specified for operational states, design basis accidents and severe accidents, in relation to the function of confinement of radioactive material;

— Dose limits or dose rate limits and dose constraints for personnel, specified for the biological shielding function.

1.50. Furthermore, design limits should be specified for each containment system as well as for each structure and component within each system. Limits should be applied to operating parameters (e. g. maximum coolant temperature and minimum flow rate for air coolers), performance indicators (e. g. maximum closing time for isolation valves and penetration air leakage) and availability

measures (e. g. maximum outage times and minimum numbers of certain items of equipment that must be available).