BASIC FEATURES AND SUSTAINABILITY POTENTIAL OF NUCLEAR ENERGY

Whatever the sociopolitical context for nuclear energy is at present, or may become in the future, it is important to recognize certain basic features of nuclear energy that define or even drive nuclear energy systems (NESs) to serve a sustainable energy future locally, regionally or globally. Nuclear energy holds 10⁶ more energy per unit mass of fuel (uranium or plutonium or thorium; in general, per unit mass of fertile/fissile material) than any fossil fuel and even more so for renewable energy resources. This very high energy density means that very little material needs to be included in the supply chain towards nuclear power plants compared to these other energy generating technologies and that, in principle, from a technical and logistics perspective, this very small amount of mass to be handled in the fuel cycle is a very big advantage, for example shipment of fuel materials in the nuclear fuel cycle are limited and of small size per TW·h and thus virtually represent zero environmental impact overall.

Nuclear energy is very capital intensive, requiring a high capital investment. However, as fuel costs are very low, the operational expenses for nuclear energy are also relatively low. This high capital intensity spreads over the whole period from initiating plans towards a nuclear plant, through the licensing process and the construction up to commercial operation, which altogether typically takes 15 years, resulting in additional expenses related to loan interest. This hints towards the economies of scale (or, alternatively, the economies of numbers when considering modular designs) for nuclear power plants to reduce the fixed costs per TW·h later on generated as much as possible. While the absolute capital investment becomes very high, and sometimes even beyond the abilities of smaller electricity utilities or investors, the high predictability and the virtually absent cost volatility in nuclear generation render nuclear energy very attractive, especially in view of the total independence of carbon tax impacts, when applicable.

To ensure faster return of large initial investments, nuclear power plants ideally operate at a constant load factor to deliver baseload electricity which, combined with the very low cost per TW·h generated, explains their typical baseload merit order in (national) electricity grids. Many members of the Organisation for Economic Co-operation and Development have well developed, interconnected electricity grids. Besides being well suited to large capacity baseload operation, these well interconnected grids have nowadays allowed, to a better degree than in other less interconnected regions, to incorporate a growing share of time stochastic (or intermittent) renewable energy resources, given important transmission capacity exists between (sub)regions within such interconnected grids [2.1–2.3].

Nuclear material only accounts only for a few per cent (typically 5%) in the overall generating cost for nuclear energy, and this indicates a high natural resource price independency strengthened by a natural uranium distribution across the world being different than the typical fossil fuel resource distributions [2.4]. All this contributes to a higher energy independency for those countries that would a significant nuclear energy fraction in their energy balance. In addition, some nuclear fuel cycle options involving reprocessing and recycling of uranium and plutonium further increase the available fissile resource and energy independence, while significantly reducing the natural uranium needs per TW·h. The present day nuclear power plants are being increasingly designed to operate with different fuel types, for example uranium oxide (UOX) and mixed oxide (MOX). Longer term innovative nuclear power plant designs, the so called Generation IV designs, often rely on fast neutron spectrum, adding additional fuel cycle flexibility potential. Next, the international nuclear fuel cycle, especially in the front end, has established itself as a competitive environment securing multiple supplier channels to many nuclear power plant operators. As such, in principle, nuclear fuel supply for nuclear energy is not an impediment to nuclear energy deployment, though local and regional options to secure such nuclear fuel supply may differ.

Nuclear energy, as any other industrial activity, produces waste which needs to be managed responsibly.

The amount of nuclear waste is very small per TW·h compared to the amount of waste produced by many other industries, especially fossil fuel based energy generation technologies. However, the fact that nuclear waste remains radioactive and radiotoxic over sometimes very long periods reaching hundreds of thousands or even millions of years combined with a sociopolitical ‘fear’ of radioactivity may result in a disproportionate ‘fear factor’ associated with nuclear waste. This fear stems from the fact that, different from other factors hazardous to human health

and environment, radioactivity is intangible and cannot be detected directly by common senses.¹ Long or very long lasting nature of radioactivity also complicates proving long term waste management solutions. For these reasons a virtually ‘stand-still’ situation with regard to deployment of any ultimate waste management solution proposed in the course of the previous four decades. This disproportionate fear of nuclear waste, despite the known waste management solutions, including those incorporating retrievability of storage facilities and repositories, has delayed full deployment of the ultimate waste management solution (i.e. geological disposal). In turn, this has impacted the deployment potential of nuclear energy, as public at large hesitates embracing nuclear energy for mostly this reason. Only about 5% of the used fuel discharged from nuclear power plants ultimately becomes waste to be disposed of, while a much larger part of used fuel is actually recyclable in today’s light water reactors (LWRs) (and heavy water reactors, HWRs) and increasingly in fast neutron spectrum reactors of the Generation IV type.

The physicochemical characteristics of the ultimate waste coming from the oxide fuel used in today’s nuclear power plants and envisaged to be used to meet the bulk of the projected nuclear energy demand within the present century fit well to final disposal in the reducing geological disposal conditions. Most, if not all, of the geological disposal solutions presently under investigation are of reducing nature (clay, salt and rock), under which the engineering barriers put in place would result in a virtually zero mobility of the radioactive content in ultimate nuclear waste and, therefore, in a very low, almost insignificant, radiological risk from such geological disposal sites. This would apply for sure when the ultimate waste stems from the reprocessing cycles where the bulk material, being uranium (~94%) and plutonium (~1%), are removed from the vitrified ultimate waste, which then contains only fission and activation products and minor actinides.

Further enhancement of the ultimate waste management could be considered by deploying separation/

partitioning and transmutation technologies envisaging the separation of some, if not all, of the minor actinides from the ultimate waste stream in order to transmute them in (mostly) fast neutron spectrum reactors in view of reducing their amount and their longevity, potentially resulting in a reduction of the decay heat and radiotoxicity of the then to be disposed ultimate waste. A variety of international and national studies [2.5] performed during the last few decades have shown that, in comparison to an all plutonium multi-recycling management scheme in fast reactors, partitioning and transmutation of all minor actinides can reduce the decay heat, resulting in a reduction of the high level waste section of a repository footprint by a factor up to 2.5 (if all minor actinides are transmuted and disposed of after 70 years of cooling) and by a factor of 5 to 8 for the same transmutation of all minor actinides, but after 120 years of cooling of the resulting ultimate high level waste. The radiotoxicity of the ultimate waste is reduced by a factor of 10 when only americium being transmuted and by a factor of up to 100 if all minor actinides are transmuted, again compared to an all plutonium multi-recycling scheme which on its own already reduces the radiotoxicity content of the ultimate waste by a factor 10 compared to a LWR once through fuel cycle. However, such advanced all minor actinide management schemes cannot be realized in the short or medium term and demand a significant amount of R&D and, if decided upon and considered overall technologically feasible, would require at least one century of continuous use of nuclear energy to start reducing the minor actinide inventory in geological repositories (while virtually requiring the indefinite continuation of nuclear energy use in increasingly specific or dedicated nuclear reactor systems). The latter would, in particular, apply when the last minor actinide-bearing reactor cores will need to be transmuted, which on itself would be almost a condition to be met in order to truly achieve the radiotoxicity reduction objective. That being said, care has to be taken that the advanced technologies and infrastructure deployed for the purposes of transmutation do not significantly increase overall costs.

It is important to note that, as such, radiological risk from the geological repositories would not be impacted by a reduction of radiotoxicity owing minor actinides transmutation, given the high required performance design and engineering of such repositories. This risk, owing to some long lived fission and activation products that cannot be transmuted, would always remain below the regulatory limits.

1 There are many chemical elements and compounds and biological agents that are highly stable in the environment that cause comparable or greater harm to human health than radiation. Many of these chemical and biological substances are more difficult to detect and measure than radiation, which can be detected at minute levels with comparably inexpensive and simple detectors. In fact, the ability to exquisitely detect radiation and radionuclides in minute quantities is associated with very significant public acceptance difficulties. The health effects of low dose radiation are unproven. The fear of low dose radiation is commonly linked psychologically with the origins of nuclear technology in military use and the drawing of a false equivalence between explosive and non-explosive technologies by the general public.

On an international level, nuclear energy cannot be considered without due attention to the inherently dual nature of the potential use of some of the fissile materials and nuclear knowledge required in overall nuclear energy use. The international safeguards regime ensuring a non-proliferation nature of civil nuclear energy use is essential in this respect. While all civil nuclear technologies are safeguardable in principle, as the last decennia have explicitly demonstrated, there is still a concern that the spread of nuclear technology and the advertent diversion of some of the fissile material from the civil nuclear energy installations may not be fully avoided when nuclear energy would become a globally deployed energy source. Some countries have therefore been prohibiting the domestic deployment of used fuel reprocessing and also encouraged other countries to follow this route. At the same time, piling up of the used fuel storages scattered over various reactor sites globally and the ‘self-protection’ by decay of the used fuel in these storages do not equate univocally to an improved non-proliferation status, especially when considering a worldwide growth in nuclear energy use. With this growth, sustainability of nuclear energy that is essentially driven by cost competitive paths towards reduced natural uranium use per TW·h and the reduced high level waste arising per TW·h may not be achieved without reprocessing and recycling of used fuel over time.

The majority of Generation IV NES concepts rely on one form or another of reprocessing and recycling.

During the past decade, multiple national and international studies have concluded that transitioning towards such NESs with enhanced sustainability will take time and needs to be addressed progressively [2.6–2.9]. Taking into account that safety and licensing are essential in nuclear energy, the transition to a closed nuclear fuel cycle should initially involve multi-recycling of plutonium in thermal or fast neutron spectrum reactors, before embarking on a more technologically challenging advanced NESs with some or all of minor actinides added to the nuclear fuel, as such advanced fuels would need performance qualification before ever used. A significant challenge will therefore emerge in the future related to, on the one hand, global deployment of nuclear energy to already address sustainable energy needs and resolve some of the geopolitical tensions a non-sustainable energy future might aggravate, and, on the other hand, the management of increasingly ‘closed’ nuclear fuel cycles involving fuel operations which are deemed today more proliferation risky than the less sustainable once through fuel cycle on a global level.

When revisiting the potential of nuclear energy to become a sustainable energy source for ‘all’ globally, it is necessary to recognize that not all of its users will be able to address, or capable of addressing, all sustainability objectives indigenously at once. Some may have to rely on imported ‘off the shelf’ nuclear technology in absence of a sufficiently developed domestic resource base while others may need low carbon energy rapidly and in massive amounts. In the latter case national nuclear deployment may be impacting the global nuclear energy scene. For example, global natural uranium demand may increase substantively with rapidly growing national nuclear energy deployment, such as planned in China and India in the near future, and this could indirectly hamper the domestic rapid nuclear deployment as well.

The pallet of nuclear energy options to countries embarking on, or moving forward with, nuclear energy as a low carbon energy source is rich and will increasingly demand international and regional cooperation among countries. This on itself is already an important step forward in seeking to ensure a globally sustainable deployment, while securing each country’s proper competitive, safe and proliferation resistant use of nuclear energy.

Can such sustainable nuclear energy deployment be undertaken in virtually the same way as done by a few countries during the 20th century, or is increasing collaboration² useful or even necessary to provide the path towards worldwide nuclear deployment? Essentially, this is the main question addressed by the Synergistic Nuclear Energy Regional Group Interactions Evaluated for Sustainability (SYNERGIES) collaborative project, which attempted to investigate synergies of the various kinds within and among NESs, geared towards facilitating the use and deployment of sustainable nuclear energy in a variety of countries across the world. This objective fits well with the path forward set out in President Dwight Eisenhower’s Atoms for Peace speech on 8 December 1953³.

2 Collaboration is understood here in a broader sense to include collaboration between technology holders and technology users in nuclear fuel cycle, joint ownership of facilities, and multilateral approaches to waste repositories, among other things.

3 President Eisenhower noted that: “The more important responsibility of this Atomic Energy Agency would be to devise methods whereby this fissionable material would be allocated to serve the peaceful pursuits of mankind. Experts would be mobilized to apply atomic energy to the needs of agriculture, medicine and other peaceful activities. A special purpose would be to provide abundant electrical energy in the power starved areas of the world. Thus, the contributing powers would be dedicating some of their strength to serve the needs, rather than the fears, of mankind.” A full transcript of the speech is available at www.iaea.org/about/history/

atoms-for-peace-speech

According to Article III of the IAEA Statute:

“B. In carrying out its functions, the Agency shall:

1. Conduct its activities in accordance with the purposes and principles of the United Nations to promote peace and international co-operation...”

Furthermore, according to A. Facilitating access to nuclear power of the IAEA Medium Term Strategy 2012–2017: “The Agency will facilitate and assist international research and development collaboration and partnership for beneficial uses of nuclear energy.”⁴

Synergies within the context of NESs are all actions that a country or a group of countries may undertake to facilitate (i.e. enable, accelerate and optimize) the deployment of an NES aiming at enhanced sustainability of such NESs. Synergies are those actions that make optimal use of a combination of technologies (i.e. synergies of intranuclear options) within the perimeter of a national or regional NES, as well as those that demand more increased cooperation among countries, each with their own NES, but where the cooperation brings benefits in achieving each country’s or collective sustainability objectives of an NES.

The introduction and use of nuclear energy demands a variety of resources ranging from competencies and expertise through education and training, to capacities such as R&D infrastructure and the necessary supply chain capacity which can, to varying degrees, be sourced from the international market. In this, a minimum set of resources is anyhow required in any country embarking or deploying nuclear energy to secure full compliance with safety, safeguards, security and overall operational performance of the nuclear energy as well as nuclear science and technology applications. The SYNERGIES collaborative project focused on synergies among NESs and typically among multiple countries each with its own nuclear energy programme, targeted at achieving long term NES sustainability and had not addressed explicitly the synergies that might exist in the area of nuclear science and technology, R&D infrastructure or education and training, as well as infrastructure issues associated with the deployment of a first nuclear power plant. The latter are addressed specifically in other available IAEA publications (see Refs [2.10, 2.11]). In this publication, the following two kinds of synergies are distinguished:

(a) Synergies in technology: Synergies among technologies with certain complementarity between fuel cycles of different reactors on a purely technical level.

(b) Synergies in collaboration: Synergistic collaboration among countries with different policies with regard to nuclear fuel cycles based on certain arrangements and aimed at bringing the benefits of innovation to all interested users.

The issue of NES sustainability has multiple dimensions [2.12–2.14] with some of the dimensions being directly or indirectly impacted by the nuclear fuel cycle. Indeed, while the local economic competitiveness of nuclear energy is essentially governed by the nuclear power reactor’s economic performance, the longer term sustainability of nuclear energy is essentially governed by the nuclear fuel cycle. The fissile resource and ultimate waste management issues, non-proliferation considerations, the resource and energy independence issue, and even the economic performance through assurance of stable low generation costs of energy are all driven or impacted by the fuel cycle considerations.

It should be noted that certain fuel cycle options are not possible without specific nuclear power plant developments that go hand in hand with the sustainability objectives, and a systems view on sustainable nuclear energy development is therefore essential. With more than two thirds of the life cycle cost of energy generation of nuclear energy defined by the financial settings for nuclear power plants (e.g. overnight capital costs, cost of financing and owners’ cost), these are the local or regional market conditions that would define the economic performance of an NES, and this becomes even more the case when enhanced sustainability oriented NES incorporating more advanced nuclear power plants, typically Generation IV plants, are being considered.

Competitive deployment of such systems would require international collaboration at least in R&D (already being accomplished through the Generation IV International Forum programmes) and even in industrial development and deployment.

4 See www.iaea.org/sites/default/files/mts2012_2017.pdf FIG. 2.1. INPRO concept of a sustainable nuclear energy system [2.15].