Co-generation: Nuclear Energy’s untapped potential in aiming for Net Zero

  • 2 December 2020
  • Environment
  • Dr Dame Sue Ion

The role nuclear power has in providing low-carbon electricity is gaining greater awareness and not before time! However, its significant potential in providing a solution to the more challenging aspects of the goal to achieve Net Zero has yet to receive the attention it deserves. Nuclear power offers so much more than low carbon electricity. It is vital this is acknowledged and built into the required system level thinking for meeting our future energy demands. 

There are two key issues that impact on the utility of current nuclear power plants: they are most economic when run at high output, and 65% of the energy generated is lost as waste heat. This waste heat which would otherwise be discharged to the environment and ‘lost’can be actually be tapped, not only from the more advanced systems such as High Temperature Reactors (HTRs), but also light water Small Modular Reactors (SMRs). This major opportunity from LWR SMRs has been less emphasized historically but should now be given much greater scrutiny given the advantages it would give nuclear power over other low carbon energy sources.

Nuclear power today contributes 17% of the UK’s total electricity consumption on an annual basis. At its peak in the early 1990’s it provided ~30% of the UK’s electricity requirements. Capacity will drop to ~3% as most of the UK’s existing fleet retires this decade. It is worth remembering that electricity requirements are going to increase not decrease. For Net Zero to stand any chance of being achieved, future nuclear power must work with a generating system dominated by intermittent renewable energy. The gap between intermittent generation and electricity demand is currently accommodated using gas fired generation which produces carbon dioxide. The introduction of more intermittent renewable generation, coupled with the need to reduce gas fired generation, demands greater flexibility and greater utility from nuclear generation as it continues to play an important part in our low carbon energy mix though deployment of newer modern systems. It is this greater utility and generally unrecognized benefit from the heat as well as electricity offered by nuclear energy compared with other sources of low carbon energy which delivers real advantage provided it is driven forward to deployment.

Much has been made of the potential for hydrogen to be the energy vector of choice to replace gas for space heating and potentially in the transport sector but this is only beneficial if the hydrogen is generated cleanly. This is not the case currently. There is no doubt of the potential for renewable energy sources such as wind and solar, to make a contribution to wider aspects of the Net Zero challenge via for instance at times of low demand and excess availability producing hydrogen via the electrolysis of water. Nuclear energy can use its heat output as well as electricity to do so much more economically. 

The recent report from the Royal Society highlighted the potential for LWR SMRs to produce hydrogen cleanly.  It also emphasized their potential in district heating and the possibility of SMRs designs enabling the thermal output from the reactor to be matched to the thermal/electrical requirements of a single or cluster of industrial processes. It is absolutely vital that the UK grasps the opportunity it has with an indigenous SMR technology and nuclear power system to really capitalize not only on the benefits it would bring within the UK but also the very significant export opportunities it could generate. 

Developing cogeneration technologies is one way to improve the flexibility, competitiveness and utilization of the energy generated by nuclear reactors and also to enhance the productivity of this primary source of low-carbon energy. Other cogeneration options range from the manufacture of synthetic fuels and ammonia to medical isotopes. The development of a cogeneration capability that includes isotope production represents an additional commercial opportunity due to a global shortage of key radioisotopes. Further, there is potential to use nuclear to power direct air capture of carbon dioxide.

The heat generated by civil nuclear reactors can be extracted at two points. Higher temperature heat can be accessed before the turbine generator in the secondary cooling circuit. Lower temperature ‘waste’ heat can be extracted from the steam turbine exhaust. With nuclear cogeneration, high-temperature heat can be used to drive a turbine generator to create electricity, supply heat to industry or be stored for later use. Low-temperature heat can be used by industry or used to heat homes. In both situations, the reactor can be used to generate electricity and supply heat, or to switch between electricity and heat in order to provide very a flexible response to grid requirements. Nuclear power stations thus offer one of the largest reliable sources of both electricity and flexible low-carbon heat. 

All reactor types (Generation II, III (including SMRs), IV, and Fusion) can provide relatively low-temperature post turbine steam for applications such as district heating and desalination. For cogeneration applications requiring higher temperature steam, certain Generation IV reactors may be better suited as they are designed to operate at considerably higher temperatures (above 600°C) so could provide heat assistance for key industrial processes such as iron and steel manufacture, glass and concrete making. The availability of high-temperature process heat can be used to facilitate the production of other chemicals. These include single molecule feedstocks such as ammonia, and more complex molecules, for example synthetic fuels. In this way, nuclear energy could be used to produce ammonia and synthetic fuels to  store energy for later use and to decarbonise difficult to electrify transport modes, such as shipping, aircraft, and heavy goods vehicles. The UK already has a significant expertise and experience base with its historic role in HTR technology at its inception globally, through participation in the South African Pebble Bed project at the turn of the millennium and more recently through the initiative led by Urenco to develop its U-Battery off grid micro rector. 

As well as maximizing the potential for SMRs on an early timescale, every opportunity must be taken to move HTR technology forward synergistically with the sectors of industry likely to benefit from its heat output.

In conclusion nuclear energy must be viewed through a new lens - one which recognizes and capitalizes on its potential to help the UK to achieve net-zero carbon emissions by 2050- not only through the generation of low-carbon electricity but by more fully utilising the heat generated as it produces electricity. This heat can be used to address difficult to decarbonise energy demands. UK companies and their supply chains stand to benefit hugely if this whole systems approach is taken for future energy production.

If you enjoyed this blog post, and would like to learn more about the topic, register for our free event "Nuclear Cogeneration and Net Zero" at 6pm on Wednesday 9th December 2020. 

Dame Sue Ion, FREng, FRS, FIoM3, FNucI is currently Hon President of the National Skills Academy for Nuclear and is a member of the UK Nuclear Regulator’s Independent Advisory Panel.  She was Chairman of the UK Government’s Nuclear Innovation Research Advisory Board which operated from January 2014- March 2016. Dame Sue was BNFL’s Chief Technology Officer from 1992-2006 and since then has served on a number of advisory committees associated with the UK’s energy requirements

She holds honorary or visiting professorships at the University of Manchester and Imperial College London and currently serves as a member of Board of Governors of the University of Central Lancashire. Dame Sue is a Fellow of both the Royal Academy of Engineering and the Royal Society, where she chairs or serves on a number of standing committees.