Dimensions of RPVs are dependent on reactor size. The largest integral reactor pressure vessels that are currently considered (SPWR, SIR, VPBER-600) have the following dimensions:

Diameter 6.5 — 7.2 m,

Height 20 — 25 m,

Wall thickness 265 — 280 mm

(cylindrical part).

These dimensions are comparable with the largest pressurized water reactor (PWR) pressure vessels (diameters, wall thicknesses) and boiling water reactor (BWR) pressure vessels (heights, diameters). Some designers have made enquiries with potential manufacturers and they received positive answers on the possibilities of manufacturing these large pressure vessels. Existing manufacturing technologies in the following areas can be used in the manufacture of integral RPVs

• materials

• forging of semi-products

• welding and cladding

• machining

• inspection and testing

Guard vessels/containment can be manufactured at existing manufacturing facilities. No specific problems have been identified concerning the manufacturing of these large components also The feasibility of RPV transport may be an important issue to be taken into account in site selection Access by water can solve most transport problems

4 3 Primary circulation

Natural circulation of primary coolant is an inherent feature of the integral reactor arrangement due to its simple configuration and low hydraulic resistance of the primary circuit Reactor coolant natural circulation has reliability, simplicity and safety advantages These advantages override economic considerations at lower unit powers As the power level increases, economic considerations become more important and hence forced circulation may be preferred However, under special conditions, for example in marine reactors, forced coolant circulation is utilised even in units with a low rated power

For heat only reactors of any power level, natural circulation seems to be the most preferred solution due to a lower core power density and high reliability requirements typical of this kind of reactor

Cost considerations and technological limitations in RPV manufacture appear to limit the use of natural convection cooling At present integral reactors with reactor coolant natural circulation are limited in their power level to 1000 MWt