While twin-units of nuclear power plants exist and the cost reduction factors for them are known and defined by equations (6.9) and (6.10), no experience data is currently available for multi-module nuclear plants. The apparent reason is that multi-module nuclear power plants have never been built. However, with reference to the current safety rules that prohibit safety system sharing among different reactor modules [6.10], near term multi-module plants could be reasonably approximated by sequentially built twin-units. Then, the evaluations provided in Sections 6.2.1-6.2.4 would apply.

In addition to this, reference [6.1] mentions that “for a 5-6 unit plant capital costs may be 15-17% lower than for the basic two-unit plant”. If we apply this to a 300 MWe marine derivative or the integral design PWR discussed in Section 6.2.4 and use the same assumptions, a five-module NPP with such reactors may have the overnight capital costs that are about 7 — 38 % higher (at a 5% discount rate) compared to those of a NPP with a single large PWR of 1 500 MWe, see Table 6.10.