There are designs proposed that are radically different from current generation technology and these would require substantial development and investment before building and licensing. Examples are given in Table 11.4.

Integral type pressurised water reactors such as PIUS, VPBER-600, SPWR and ISIS (PIUS, 1997; VPBER-600, 1997; SPWR, 1997; ISIS, 1997) are completely immersed in a large pool. Many of these concepts have been described as inherently safe, i. e. they depend entirely on the forces of gravity and natural circulation for operation. Typical design objectives are that they should be ‘operator forgiving’ and should incorporate simple safety principles (which should therefore imply increased reliability). For flexibility of supply and operation they should be available in small — or moderate-size units, which could be coupled if necessary. Such designs and other revolutionary approaches are considered in this chapter.

The PIUS reactor (PIUS, 1997) is immersed in a large pool where the boron concentration is controlled by several ‘density lock’ arrangements (Figure 11.4). There are no control rods and the required reactivity is maintained by control of the boron concentration and moderator temperature. In the event of an accident, a natural circulation loop through the core is established, resulting in reactor shutdown and core cooling.

The VPBER-600 (VPBER-600, 1997) is an integral PWR, located in a guard vessel. The design basis was taken from the AST-500 heating reactor, which was designed in the early 1980s. VPBER-600 includes passive safety systems and diverse operation principles with significant redundancy and self-actuation.

The SPWR (SPWR, 1997) is based on an integral design with the complete primary circuit including the core, MCPs, pressuriser and the SG encompassed within the reactor pressure vessel. It employs passive systems for shutdown and decay heat removal under normal operation and also accident mitigation. Highly borated water is used for shutdown in place of control rods.

ISIS (ISIS, 1997) is also an integral PWR reactor, which is completely immersed in cold borated water. It is similar to the PIUS concept except that the reactor components are derived from proven technology.

Unlike the integral designs described above, the JPSR is a passive two-loop PWR design (JPSR, 1997), adopting a boron-free concept to increase reactivity sensitivity to changes in moderator density. As a result, reactor power can be controlled by adjusting the steam generator feedwater flow rate. This simplification in design results in a reduction in manpower for operation and maintenance.