Some Notes

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\”La generación estable de electricidad (energía) es la columna vertebral del desarrollo económico sostenido.\”

\”Stable electricity production is a backbone for sustained economic development.\”  

The currently available carbon-free energy sources include “traditional” technologies hydro and nuclear, and “non-traditional” alternative sources such as wind, solar, geothermal and other technologies.

Source: N., Gulik, V. & Tkaczyk, A. H. Cost optimization of ADS design: Comparative study of externally driven heterogeneous and homogeneous two-zone subcritical reactor systems. Nucl Eng Des 270, 133–142 (2014).

The evolution of Nuclear Power Plants (NPPs) is usually divided into four generations (GIF, 2014):

  • I generation (1950–1970): early prototypes to test different technologies;
  • II generation (1970–1995): medium-large commercial NPPs, mostly Light Water Reactors (LWRs), conceived to be reliable and economically competitive;
  • III/III + generation (1995–2030): mostly an evolution of the II generation LWR;
  • IV generation (2030+): designs called “revolutionaries” because of their discontinuity with the III/III + generation NPPs. The Generation IV International Forum (GIF) lists six GEN IV tech­nologies (GIF, 2014):
    • VHTR (Very-High-Temperature Reactor) is a thermal reactor tech­nology cooled by helium in the gaseous phase and moderated by graphite in the solid phase;
    • SFR (Sodium-cooled Fast Reactor) is a fast reactor technology cooled by sodium in the liquid phase. It is the most investigated fast reactor;
    • SCWR (Supercritical-Water-cooled Reactor) is a thermal/fast reactor technology cooled by supercritical water. It is considered as an evolution of the actual boiling water reactor because of its compa­rable plant layout and size, same coolant and identical main appli­cation, i.e. electricity production;
    • GFR (Gas-cooled Fast Reactor) is a fast reactor technology cooled by helium in the gaseous phase. This technology aims to put together a high-temperature reactor with a fast spectrum core;
    • LFR (Lead-cooled Fast Reactor) is a fast reactor technology cooled by lead or lead-bismuth eutectic. It is a liquid metal reactor (similar to SFR) for electricity production and actinides management;
    • MSR (Molten Salt Reactor) is a fast or thermal reactor technology cooled by molten salts in the liquid phase and moderated, in most cases, by the graphite. In this technology, the fuel can be in either liquid or solid form (Zheng et al., 2018).

Source: N., Mignacca, B. & Locatelli, G. Economics and finance of Molten Salt Reactors. Prog Nucl Energy 129, 103503 (2020).

Smaller size reactors are going to be an important component of the worldwide nuclear renaissance.
However, a misguided interpretation of the economy of scale would label these reactors as not economically competitive with larger plants because of their allegedly higher capital cost ($/kWe).
 
\”Los reactores de menor tamaño serán un componente importante del renacimiento nuclear mundial. Sin embargo, una interpretación equivocada de la economía de escala, etiqueta a estos reactores como no competitivos económicamente con las plantas más grandes debido a su costo de capital supuestamente más alto ($/kWe).\”
 
Smaller size reactors (IAEA defines as “small” those reactors with power <300 MWe and “medium” with <700 MWe) are the logical choice for smaller countries or those with a limited electrical grid.
The capital cost ($/kWe) of a nuclear reactor decreases with size, because as the size and power increase, the numerator ($) increases less than the denominator (kWe). Thus, in large, developed countries the reactor size has steadily increased from a few hundred MWe 40 years ago to 1500 MWe and more today.
Given that nuclear reactors have mostly been deployed in developed countries, an immediate question is how will SMR fare economically compared to larger reactors (1000 MWe or more)? One assumes that both small and large reactors are candidates for power plants in any market.
 
The reality is that for many countries large reactors are not an option at all. Conditions that prevent large plants from being candidates are:
  • Power grids with limited capacity. It is a general rule that a network should not be subject to power variations greater than 10% of the total capacity of the network. Therefore, 1000 MWe plants cannot be deployed on networks of 10 GWe or less.
  • Remote areas that require small, localized power centers to avoid long and expensive transmission lines.
  • A geography and demography with urban areas of medium size and that need energy quite dispersed, instead of concentrated in a few “mega centers”.
  • Financial capabilities that preclude raising the several billion dollars of capital investment required by larger plants, and are instead limited to the hundreds of millions of dollars typical of smaller plants.
  • Need for cogeneration (desalination, district heating, industrial steam). Although, in principle, cogeneration is independent of the size of the nuclear plant, in practice economic considerations have led the larger plants to be purely electricity producers.
La realidad es que para muchos países los reactores grandes no son una opción en absoluto. Las condiciones que impiden que las plantas grandes sean candidatas son:
  • Redes eléctricas con capacidad limitada. Es una regla general que una red no debe estar sujeta a variaciones de potencia superiores al 10% de la capacidad total de la red. Por lo tanto, las plantas de 1000 MWe no se pueden implementar en redes de 10 GWe o menos.
  • Áreas remotas que requieren centros de energía pequeños y localizados, para evitar líneas de transmisión largas y costosas.
  • Una geografía y demografía con áreas urbanas de tamaño mediano y que necesitan energía bastante dispersas, en lugar de concentradas en unos pocos “mega centros”.
  • Capacidades financieras que impiden recaudar los varios miles de millones de dólares de inversión de capital que requieren las plantas más grandes y, en cambio, se limitan a cientos de millones de dólares característicos de las plantas más pequeñas.
  • Necesidad de cogeneración (desalación, calefacción urbana, vapor industrial). Si bien, en principio, la cogeneración es independiente del tamaño de la planta nuclear, en la práctica las consideraciones económicas han llevado a las plantas más grandes a ser puramente productoras de electricidad.
 
Source: Economic Comparison of Different Size Nuclear Reactors, Carelli, M. D., Petrovic, B. & Mycoff, C. W., Simposio LAS/ANS 2007 / 2007 LAS/ANS Symposium (2007)