There are many possible alternative types of containment building. Some of the suggested varieties (14b) include:

(a) Underground containment, in which excavation alone may cost millions of dollars.

(b) Hemispherical containment with a wall and footing below grade.

(c) A prestressed concrete containment designed with compressive stresses of over 2000 psig at pouring, which can give a leakage rate below

1%

(d) Conventional wall and roof panels for which leakage rates of less than 1% can be achieved with differential pressures of up to 0.5 psig for metal panels and 5 psig for a concrete building.

(e) Designs which include internal or external expansion volumes, such as in the case of the CP-5 at ANL which had a hold-up volume with a floating neoprene diaphragm to allow a hold-up of any fission gas release for up to 20-30 days.

As the LMFBR system contains plutonium, any gross fuel aerosol release to the containment system may necessitate leakage dilution factor of 10~3 or 10-4. Such values cannot be achieved with a single barrier because such values cannot be tested. However it can be done with two enclosure buildings

with a combined leakage of the right value, say 2 and 0.5 vol%/day or 10 and 0.1 vol%/day. Thus, for plutonium containment, two barriers are usually required although one containment volume may be merely a rather leaky aerosol settling volume.

There are many other containment design requirements. The building must house the plant with convenience and layout is of importance. The design must account for lateral stability, withstand windload, snow and roof loads, and lightning loads, and it must allow these loads to be trans­mitted to the foundations. It must accommodate internal mechanical and heating loads, cope with penetrations, and be designed to withstand seismic loads.

The windload, for example, is calculated according to the equation

F = PAS = Cdou2AJ2g (5.9)

where q is the air density; и is the wind velocity; g is the acceleration due to gravity; As is the exposed surface area; P is the wind pressure; F is the wind force; and Q is a shape factor.

The internal loads must also include those which arise from reactor transients, and particular attention must be paid to the design of air locks and various penetrations to achieve the leakage rates required.

Figure 5.6 shows the EBR-II containment building and its two barriers; the inner containment barrier comprising the reactor vessel and vaults that withstand an internal pressure of 75 psig, and the outer containment shell of steel in the form of a cylinder that would withstand at least 24 psig with an overall leakage rate of 0.25 wt%/day. Similar designs modified to include a refueling cell have been suggested for the large 1000 MWe LMFBR plants.