20.08.2015   Design of Reactor Containment Systems for Nuclear Power Plants

Identification and quantification of loads

4.53. All loads (static and dynamic) that are expected to occur over the plant lifetime or that are associated with postulated design basis accidents should be identified and grouped according to their probability of occurrence, on the basis of operating experience and engineering judgement. Such loads should be specified for each component of the containment structure.

4.54. The metallic liner of the containment (where applicable) should be able to withstand the effects of imposed loads and to accommodate relative movements of the liner and the concrete of the containment without jeopard­izing its leaktightness. The liner should not be credited in the structural evaluation for the resistance of the containment.

4.55. The containment structure should be designed to protect the primary pressure boundary and associated components from all the external events that were taken into account in the design.

4.56. The metallic structures, penetrations and isolation valves of the containment should be protected against the jet forces and missiles that could be generated in the course of design basis accidents, preferably by means of protective structures.

4.57. The primary containment together with its support systems should be designed to withstand the following events:

(a) An inadvertent drop in internal pressure below atmospheric pressure during normal operations and in accident conditions (e. g. due to the inadvertent operation of a spray system); the provision of vacuum breakers would be a means to limit subpressure loads.

(b) The pressurization of the space between the primary and the secondary containments (where applicable) in the case of a high energy line break inside that space, unless such a break is precluded by the design.

Both concerns are of particular importance for steel containments.

4.58. In Table 2 a typical set of loads on the containment that should normally be considered at the design stage is presented (its applicability to any particular design should be verified).

Load category

Load

Remarks

Pre-service

Dead

Loads associated with the masses of structures or

loads

components

Live

Loads associated for example with component restraints

Prestressing

Only for prestressed concrete structures

Loads in

Temporary loads due to construction equipment or

construction

the storage of major components

Test pressure

See Section 5, paras 5.15-5.31

Test temperature

See Section 5, paras 5.15-5.31

Normal or

Actuation of safety

Boiling water reactors only

service loads

relief valve

Lifting of relief valve

Boiling water reactors only

Air cleaning of safety relief valve

Boiling water reactors only

Operating pressure

In normal operation, including transient conditions and shutdown

Operating

In normal operation, including transient

temperature

conditions and shutdown

Pipe reactions

In normal operation, including transient conditions and shutdown

Wind

Maximum wind speed assumed to occur over plant operating lifetime (see also Ref. [4])

Environmental and

For example, snow load, buoyant forces due to the

site related loads

water table and extremes in atmospheric temperature

External pressure

Loads resulting from pressure variations both inside and outside the primary containment

Extreme wind

Loads generated by extreme wind speeds, i. e.

speeds

maximum wind speed that may be associated with the site

Loads due to

Design basis

See also Ref. [12]

extreme

external

events

earthquake

Load category

Load

Remarks

Loads associated with extreme wind speeds

Associated missiles to be considered

Aircraft crash

See also Ref. [4]

External explosion

See also Ref. [4]

DBAa pressure

Calculated peak pressure in an accident

DBA temperature

Calculated peak temperature in an accident

DBA pipe reactions

See also Ref. [13]

Jet impingement and/or pipe whip

See also Ref. [13]

Local effects consequential to a DBA

See also Ref. [13]

Dynamic loads

Loads are design dependent (e. g. for a boiling

associated with a

water reactor design: discharge line clearing loads,

DBA

pool swell, condensation oscillation and discharge line ‘chugging’)

Loads due to

Actuation of the

Depressurization of the primary circuit (where

accidents

depressurization

system

applicable)

Internal flooding

See also Ref. [13]

a DBA, design basis accident.