The dissipation of decay heat is accomplished in present generation water reactors via redundant and diverse emergency core cooling systems (ECCS). One approach in evolutionary reactor development, both ALWRs and AHWRs, is to utilise the best features of these present systems in an optimal way (Yadigaroglu et al., 1998), without significant recourse to new passive systems. Reactors based on this approach employ:

— improved system design with more redundancy, separation and diversity;

— increased pressure vessel water inventory;

— increased volume of pressuriser;

— direct in-vessel injection of cooling water;

— design features to reduce the risk of a LOCA, e. g. elimination of primary circuit piping;

— improved containment water storage tank facilities;

— introduction of cavity water flooding facilities

— automatic depressurisation of primary system followed by low pressure safety injection; and

— utilisation of a fire water system for containment sprays.

Plants in this class include EPR, ABWR, BWR 90, System 80 + and KNGR. There are in addition some CANDU and VVER designs. Table 11.1 summarises a few of the design highlights of these reactor types, which have been developed from optimisation of the best features of present generation plant.

Table 11.1. Classical evolutionary water reactor systems

Reactor Description

EPR Improved decay heat removal via active

systems, e. g. ECCS

System 80+

KNGR Greater redundancy, diversity, independence,

and separation of safety systems

ABWR

BWR90

VVER-1000

CANDU 6, 9 Improved containment cooling systems

Yadigaroglu et al. (1998).