The specific, per kWe of installed capacity, overnight capital cost is known to be reduced as the plant size is increased. This is due to economies of raw materials and optimisation that could be realised while building larger reactors.

Reference [6.4] suggests the following scaling function that can be used to illustrate the effect of changing from a unit size P0 to Pi (see Figure 6.3) for the same design but different capacity:

/Р n

Cost(P1) = Cost(P0) ^) (6.3)

where

Cost (P1) = Cost of power plant for unit size P1,

Cost (P0) = Cost of power plant for unit size P0, and

n = Scaling factor, obtained for reactors with unit power from 300 to 1 300 MWe, is in the range of 0.4 to 0.7 for the entire plant

Specific cost (in USD per kWe)

Cost (Po) ^ Cost (P,) Cost (Po) /P,

Po P, = Po VPo/

Example

Consider a single-reactor NPP of P0=1 000 MWe having a cost equal to Cost (1 000 MWe). Then a larger single-reactor power plant of similar design, say, of 1 500 MWe, would cost (for n = 0.5):

Cost (1 500 MWe)= Cost (1 000 MWe)x(1.5)05 =1.2x Cost (1 000 MWe).

Thus, the total cost of a larger plant is higher than the cost of a smaller plant. At the same time the specific cost (per kWe) of the larger NPP would be19% less than that of a smaller 1 000 MWe plant. [45] [46]

i. e., for two smaller capacity plants it is smaller than for two larger capacity plants. The total scaling factor from Table 6.6 is 0.51.

• A third study performed for the AP1000 and AP600 plants gives n = 0.6 for scaling of the direct costs, see reference [6.7].

Based on the above mentioned data, for the purposes of the present report it was assumed that the most probable values for the factor n are in the interval 0.45-0.6[47], with an average of n=0.51.

Table 6.7 illustrates the range of possible impacts of the scaling law (6.3) on the specific (per kWe) capital costs of SMRs compared to a nuclear power plant with large reactors. The data in Table 6.7 indicate the scaling law to be an important factor negatively affecting the specific capital cost and, consequently, the LUEC of SMRs. For example, if it were applied directly, replacing a large 1 200 MWe reactor with four small reactors of 300 MWe, it would require an investment 75-155% higher.

At the same time, there are other economic factors that could be favourable to smaller reactors and compensate, to a certain extent, the negative impact of the economy of scale. These factors and their impact are analysed in the following sub-sections.