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[en] Deliberately small nuclear reactors are making their way on the market. They are proposed by manufacturers worldwide (SMART, 4S, SSTAR, mPower, Nuscale, etc...). The idea of an economic attractiveness of Small and Medium sized Reactors (SMR) is counterintuitive, due to the loss of Economy of Scale on a capital intensive investment. Nevertheless a broader understanding of capital costs drivers has shaped a new concept of Economy of Multiples, that applies on multiple NPP deployment. It relies on learning accumulation to mitigate construction costs of later NPP units; design modularization to exploit the benefits of serial production; co-siting economies to decrease the incidence of fixed and site-related costs. We assume that smaller NPP size fosters design modularization and simplifications, with related cost savings. While the effect of modularization on construction costs has been modeled, the estimation of design-based savings may be the upmost arbitrary and controversial, but the underlying assumption is that the lower the plant size, the higher may be the Design cost-saving factor. This work aims to analyze at what extent and conditions the Economy of Multiples holds against the Economy of Scale, when NPP of different sizes are deployed in multiple units, considering that the Economy of Multiples smoothes its benefits with the increase in number of units installed and that the maximum size of the sites is a limit to its application on large reactors (LR). The limit case-study of Very Small Reactors (VSR) is investigated, representing a massive NPP deployment and a huge loss of Economy of Scale. Our analysis is performed by mean of INCAS (Integrated model for the Competitiveness Analysis of Small-medium modular reactors) Polimi's proprietary simulation code. Our results show that the Economy of Multiples holds as a competitive edge for Medium and Small Reactors even when nuclear site may host multiple LR: 8-9% design cost saving is able to grant the same economic performance of a fleet of LR, even with higher construction cost estimates. On the contrary, VSR need to achieve more stretching degree of design simplification and related cost savings (up to 15%) in order to be competitive with LR
[en] Small Modular LWR concepts are being developed and proposed to investors worldwide. They capitalize on operating track record of GEN II LWR, while introducing innovative design enhancements allowed by smaller size and additional benefits from the higher degree of modularization and from deployment of multiple units on the same site. (i.e. 'Economy of Multiple' paradigm) Nevertheless Small Modular Reactors pay for a dis-economy of scale that represents a relevant penalty on a capital intensive investment. Investors in the nuclear power generation industry face a very high financial risk, due to high capital commitment and exceptionally long pay-back time. Investment risk arise from uncertainty that affects scenario conditions over such a long time horizon. Risk aversion is increased by current adverse conditions of financial markets and general economic downturn, as is the case nowadays. This work investigates both the investment profitability and risk of alternative investments in a single Large Reactor or in multiple SMR of different sizes drawing information from project's Internal Rate of Return stochastic distribution. multiple SMR deployment on a single site with total power installed, equivalent to a single LR. Uncertain scenario conditions and stochastic input assumptions are included in the analysis, representing investment uncertainty and risk. Results show that, despite the combination of much larger number of stochastic variables in SMR fleets, uncertainty of project profitability is not increased, as compared to LR: SMR have features able to smooth IRR variance and control investment risk. Despite dis-economy of scale, SMR represent a limited capital commitment and a scalable investment option that meet investors' interest, even in developed and mature markets, that are traditional marketplace for LR. (authors)
[en] This work is based on an object-oriented approach for the modeling and simulation of the reactor dynamics. The model is applied and validated on a TRIGA Mark II reactor. The aim of this work is to investigate the neutronic reactivity model, accounting for the temperature feedback of the fuel and of the moderator, as well as the poisons accumulation effects. The reactivity model is validated on experimental data from extended transients of the system temperature, at nominal power. In particular, the positive value of moderator temperature coefficient and the negative value of fuel temperature coefficient are estimated at nominal power. There is good agreement of the extended experimental transients with the whole reactivity and thermodynamics model of the plant. The model simulation shows a good reliability against experimental data and a good trade-off to computational time. In the extended transients, the model tracks the effects of the reactor pool thermal inertia on the system dynamics.