The increase of the world’s electricity need is approaching a quick surge due to the spread of mobility electrification, the increase in the global population, and the growing use of air conditioning and electronic systems.
One of the strategic objectives of the National Recovery and Resilience Plan (PNRR) is represented by the energy transition: here, a substantial part of the available resources will go to projects and interventions to achieve it. The Plan — in line with the Green Deal launched by the European Union at the end of 2019 aiming to achieve climate neutrality in Europe by 2050 — will finance initiatives for energy efficiency to improve and increase production from renewable sources.
The different reactors across the world
And yet, is it possible to keep pace the climate neutrality schedule? According to the EIA’s forecasts, worldwide growth in the production from renewable energy will not be able to even compensate for the increase in consumption in the 2018-2050 period. Therefore, the use of oil, natural gas (+ 40% in the reference period), and even coal are also expected to grow.
Given the situation, in the perspective of a rapid decarbonisation of energy sources, nuclear fission will continue to play its global role of providing base load and mitigating risks due to climate change. In particular, in Asia, dozens of new nuclear power plants are currently under construction and will remain operational for a few decades.
France has long been the main nuclear power in continental Europe. President Macron, in his presentation of the France 2030 strategy, has envisioned the construction of small, new-generation, nuclear reactors to boost French energy production vis-à-vis the green transition. This plan also allows Paris to compete on a global scale, switching the object of competition away from large-size reactors (dominated by China and the US) towards the smaller scale domain, where the sheer size and capacity mobilization of a country are less important. China currently has around 50GW of nuclear capacity, with further 17GW under construction, while the US, with 94 operating reactors, can generate around 96GW of nuclear energy. France, despite the much smaller size of its economy, currently has a larger nuclear energy production than China, with 64,4GW produced by 57 reactors.
Nuclear fission: is the future in small reactors?
One of the basic principles of nuclear engineering is the construction of large plants as the only way to use the scale economy effect in order to justify the initial investment. Following this concept, the sizes had gradually grown up to 1000 - 1500 MWe and large plants characterized by active (EPR French model) or passive (AP1000 US model) safety and controls systems were designed.
Recently, however, the experience of the French EPR of 1650 MWe (over 10 years of delay in the construction and huge rise in costs) has questioned this principle: at present, main efforts are addressing the design and realization, in the next ten years, of small-sized reactors (so-called SMR or AMR, i.e.: Small or Advanced Modular Reactor) to try and reduce the impact of the scale effect on kWh production costs and to meet the criteria of the fourth generation of nuclear reactors. This includes:
- enhanced safety by means of passive safety and control systems, plus a mitigation of risks due to the reduced power;
- waste minimization aiming to a closed fuel-cycle producing nuclear waste that remains radioactive for a few centuries instead of millennia;
- resistance to proliferation, because the characteristic of such systems impedes the diversion or undeclared production of nuclear material in order to acquire nuclear weapons.
This kind of nuclear power plants could replace the current fleet and better integrate future hybrid energy systems: smaller, more flexible, economically competitive, able to produce more than electricity alone. The lack of economy of scale is compensated by standardized series production, while financial risks are reduced by smaller and more diluted capital investments. Passive safety is favoured by smaller power, allowing for reduced emergency planning and risks for the environment.
The most promising type of small reactor is the one using lead as a coolant (Lead-cooled Fast Reactor, LFR): due to the high temperature involved, on top of pure energy production it allows both Thermal Energy Storage and H2 production, an energy vector that has shown great promise worldwide as a solution for meeting climate challenges.
A further evolution, studied by some international consortia composed mainly of private subjects, aims to realize the so-called ADS reactors (Accelerator Driven System, literally systems forked by an accelerator) by 2030. Here, in order to function, the reactor needs neutrons produced from the outside thanks to a proton accelerator. The safety level is much higher because in the event of an electrical blackout (the riskiest event ever for a nuclear power plant), the accelerator stops working and the reactor, not receiving the necessary neutrons, shuts down.
The challenge of the nuclear fusion
Looking beyond the near future, developed countries including Europe, are focusing research efforts on a new energy source, nuclear fusion, to make the energy mix fully sustainable over time.
In this perspective, economically advanced countries are investing in the development of fusion energy and collaborating on the construction of the first experimental fusion reactor. Taking into account the development achieved by technologies in this field and assuming that the current level of investments is maintained over time, fusion electricity production is expected in the second half of the century.
The interest in fusion energy is justified by many advantages, including:
- it’s virtually unlimited - in sea water there is enough fuel (deuterium and lithium) to keep the Earth going with current consumption for some tens of millions of years;
- the availability of fuel, being uniformly distributed and usable by all peoples of the world, would not generate geopolitical conflicts;
- the reaction on which it is based does not produce CO2;
- it’s intrinsically safe due to the low amount of radioactive materials used;
- it’s clean - the fusion reaction produces only a small quantity of radioactive waste that remains radioactive for a few decades.
However, to obtain fusion reactions, it is necessary to heat two isotopes of hydrogen, deuterium (D). and tritium (T) to temperatures of about 100 million degrees (higher than those at the centre of the sun). At such temperatures, D and T assume the form of ionized gas (plasma) and must be confined by intense magnetic fields, because no mechanical containment is possible. Like plasma in stars, laboratory plasmas are complex systems. They exhibit a variety of turbulent phenomena and instabilities which tend to deteriorate their confinement. The laboratory plasmas have been "tamed" little by little thanks to an impressive scientific effort of an experimental and theoretical nature.
In the experiments that currently ongoing, plasma density and temperature values similar to those required in a fusion reactor have already been achieved. However, the power injected into the reaction chamber to reach these conditions has always been higher than that released by the fusion reactions.
Nuclear fusion’s international projects
The first experiment in which the fusion power should greatly exceed that injected into the chamber will be ITER, which is currently under construction in Cadarache in France. hTis reactor will produce 500 MW of thermal fusion power compared to 50 MW of power injected into the reaction chamber (a power amplification factor of 10) for pulses lasting from a few hundred seconds to about an hour, demonstrating without any doubt the feasibility of using fusion as energy source, while the design and realization of DEMO (the demonstrator plant) will make a big step forward.
Meanwhile, the scientific community must proceed with its best efforts to:
- develop and qualify new materials able to work under the effect of damages induced by the neutrons produced in fusion reactions;
- improve the technologies for the new generation of tritium that has to be produced inside the reactor, starting from lithium;
- consolidate the knowledge of the basic mechanisms of plasma physics in reactor conditions.
To achieve these results, the European Research Roadmap to the Realization of Fusion Energy foresees the realization, in parallel or just after ITER, of some facilities addressing the issues that are still open.
One of these facilities is under construction in Italy and addresses the problem of plasma exhaust removal: the removal is made through a particular component, the Divertor, for which the geometric configuration and the materials suitable for DEMO — or for a commercial reactor — have not yet been identified. Over the next thirty years, the Divertor Tokamak Test facility will allow to study different configurations of the divertor to identify the most suitable one.
There’s still a long way to go, but all the studies on the penetration of fusion energy show that it can valuably contribute to the production of electricity by the end of the century by providing the base load in an energy mix with a strong presence of intermittent sources, even with substantial availability of energy storage. On the one hand, the success of this penetration will depend on the cheapness of the energy produced or on the technological solutions adopted. On the other hand, it will largely depend on society’s determination to pursue the goal of decarbonisation.
Contenuti correlati:
