Integrating renewable and nuclear power plants into the electrical grid

Firstly our research suggests the possibility of establishing an “optimum size capacity” for storage plants. Secondly, without subsidies, none of the existing energy storage technologies are economically sustainable. Thirdly, the possibility of operating energy storage plants for multiple purposes was identified as a mean of decreasing subsidies for the energy storage technologies.

The nuclear option
Other than renewables, the only other technology currently available to produce electricity with a negligible amount of carbon dioxide emissions is nuclear power. Small Modular Reactors (SMRs) are part of a new generation of nuclear power plant designs receiving increasing attention from industry and government.

Modern SMRs are a relatively “new product” in the nuclear industry, but there is a growing interest in the technology, both in the United Kingdom and overseas. The attractiveness of SMRs, as an investment, is mostly based on the principle of modular deployment. Their small size makes them a good option for locations that cannot accommodate large-scale plants and they also require limited upfront capital investment.

Given their fixed costs, nuclear reactors are considered a base load power technology — a technology that must produce energy continuously 24/7 to be economical. However, the combination of adding more nuclear power and intermittent sources of renewable energy — such as solar and wind — will require even greater flexibility and adaptability within the grid to compensate for the difference between energy supply and demand at various times.

Currently, nuclear reactors adapt to electricity demand — called “load following” — by modifying the reactivity within the core. By doing so, power output is reduced, with a waste of potential energy. It also places a thermo-mechanical stress on the plant whenever the power regime is changed. Unlike gas-fueled power plants, there is not a relevant cost saving in operating a nuclear reactor at a lower power level due to the substantial fixed nature of nuclear costs.

In our research, we tested the idea of keeping the primary circuit at full power and following the load curve by using the power to cogenerate valuable by-products. Cogeneration is the use of a heat engine or power station to simultaneously generate electricity and other products.

We assessed the technical-economic feasibility of this approach when applied to Small Modular Reactors with two cogeneration technologies: algae-biofuel and desalinization.

Our results show that the power required by an algae-biofuel plant is not sufficient to justify the load following approach. However, it was viable in the case of desalination. Our successive economic analysis demonstrates the economic viability of the desalination approach in several scenarios. In conclusion, the coupling of SMRs with a desalination plant is a realistic solution to perform efficient load following in nuclear power generation.

Obstacles to more SMRs
If SMRs could make a valuable contribution to the energy supply then the next step would be to assess the legal feasibility to make this approach a reality.

This of course sounds simpler than it is! Locatelli, working with Tristano Sainati, one of his Ph.D. students at the University of Lincoln, concluded that the tailoring of the licensing process for SMRs, as part of a strong political commitment by several countries, is essential.

There is not a single international authority with power to make this happen and the various national regulatory bodies have limited ability to reshape their own licensing frameworks. A political commitment to SMRs would require a major set of legal reforms, deeply modifying the architecture and principles governing licensing processes. This is unlikely to happen in the short-term and represents one of the main obstacles preventing the widespread adoption of this promising technology.

— Read more in Tristano Sainati, Giorgio Locatelli, Naomi Brookes, “Small Modular Reactors: Licensing constraints and the way forward,” Energy82 (15 March 2015): 1092-95 (doi:10.1016/j.energy.2014.12.079); Giorgio Locatelli, Emanuele Palerma, Mauro Mancini, “Assessing the economics of large Energy Storage Plants with an optimisation methodology,” Energy83 (1 April 2015): 15–28 (doi:10.1016/j.energy.2015.01.050); Giorgio Locatelli, Sara Boarin, Francesco Pellegrino, Marco E. Ricotti, “Load following with Small Modular Reactors (SMR): A real options analysis,” Energy80 (1 February 2015): 41-54 (doi:10.1016/j.energy.2014.11.040)