Smaller size reactors are going to be an important component of the worldwide nuclear renaissance. An inappropriate application of the economy of scale would label the small-medium size reactors as not economically competitive with larger plants because of capital costs ($/kWe) and O&M costs ($/kWh) that would appear to be significantly higher. However, the economy of scale applies only if the considered designs are similar, which is not the case here, since the small size allows original design solutions not accessible to large size reactors. In the paper the historical trend of capital costs vs. plant size is estimated from literature, and a reference exponent factor for the economy of scale for the light water reactor is derived. Then the paper identifies and briefly discusses the various factors which, beside size, contribute in differentiating the capital cost of smaller reactors with respect to large reactors. In this reference frame the evaluation for of the following factors is provided: · design characteristics · modular build · multiple units · accelerated learning in construction · operation, and shorter construction time. The IRIS reactor is used as the example of small modular reactor (SMR), but the analysis and conclusions are applicable to the whole spectrum of small nuclear plants. The results show that when all these factors are accounted for in a set of realistic and comparable configurations, and with the same power installed in the site, the capital costs of small and large plants installations are practically equivalent. Considering the O&M cost the paper shows how the plant size is not the only and fundamental cost driver. In fact there is a range of other factors (e.g. location, regulatory issues, capacity factor, plant obsolescence and number of reactors on a site) able to influence the annual O&M cost for a specific plant. The paper provides a preliminary evaluation of these factors by historical analysis of reactors built in the United States, concluding, also in this case, that when all the factors are considered the difference between the average cost ($/KWh) of Large Size vs. SMR is about 20% less than would be expected.
IRIS is an advanced integral pressurized water reactor, developed by an international consortium led by Westinghouse. The licensing process requires the execution of integral and separate effect tests on a properly scaled reactor simulator for reactor concept, safety system verification, and code assessment. Within the framework of an Italian R&D program on Nuclear Fission, managed by ENEA and supported by the Ministry of Economic Development, the SPES3 facility is under design and will be built and operated at SIET laboratories. SPES3 simulates the primary, secondary, and containment systems of IRIS with 1 : 100 volume scale, full elevation, and prototypical thermal-hydraulic conditions. The simulation of the facility with the RELAP5 code and the execution of the tests will provide a reliable tool for data extrapolation and safety analyses of the final IRIS design. This paper summarises the main design steps of the SPES3 integral test facility, underlying choices and phases that lead to the final design.
The safety-by-design™ approach adopted for the design of the International Reactor Innovative and Secure (IRIS) resulted in the elimination by design of some of the main accident scenarios classically applicable to Pressurized Water Reactors (PWR) and to the reduction of either consequences or frequency of the remaining classical at-power accident initiators. As a result of such strategy the Core Damage Frequency (CDF) from at-power internal initiating events was reduced to the 10−8/ry order of magnitude, thus elevating CDF from external events (seismic above all) to an even more significant contributor than what currently experienced in the existing PWR fleet. The same safety-by-design™ approach was then exported from the design of the IRIS reactor and of its safety systems to the design of the IRIS Nuclear Steam Supply System (NSSS) building, with the goal of reducing the impact of seismically induced scenarios. The small footprint of the IRIS NSSS building, which includes all Engineered Safety Features (ESF), all the emergency heat sink and all the required support systems makes the idea of seismic isolation of the entire nuclear island a relatively easy and economically competitive solution. The seismically isolated IRIS NSSS building dramatically reduces the seismic excitation perceived by the reactor vessel, the containment structure and all the main IRIS ESF components, thus virtually eliminating the seismic-induced CDF. This solution is also contributing to the standardization of the IRIS plant, with a single design compatible with a variety of sites covering a wide spectrum of seismic conditions. The conceptual IRIS seismic isolation system is herein presented, along with a selection of the preliminary seismic analyses confirming the drastic reduction of the seismic excitation to the IRIS NSSS building. Along with the adoption of the seismic isolation system, a more refined approach to the computation of the fragility analysis of the components is also being developed, in order to reduce the undue conservatism historically affecting seismic analysis. The new fragility analysis methodology will be particularly focused on the analysis of the isolators themselves, which will now be the limiting components in the evaluation of the overall seismic induced CDF.
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