Re-engineering the nuclear future

A new project led by Alexander Glaser explores the shapes of alternative nuclear futures looking in particular at emerging technologies that may be potential game changers. The first phase of the project focuses on Small Modular Reactors (SMR), reactor designs that have power levels of less than 300 MW, a fraction of the typical power level of reactors that have been constructed in the last two decades. Many consider SMR the most serious candidate technology in the nuclear area in the aftermath of the Fukushima accidents.

SMR are currently under development in the United States, Russia, China, France, Japan, and South Korea, and a wide variety of designs with distinct characteristics are under development. The project so far has focused on reviewing these designs and exploring different ways of classifying them, with the aim of creating a public database that would provide users with essential information about them. Further research will review and analyze proposed SMR designs and examine the implications of a large-scale deployment of this technology with a particular focus on economics, nuclear waste generation, and proliferation risk.

A second arena of work has been exploring how nuclear power would fit into a modern low-carbon energy system that may be more decentralized than today’s system and emphasize flexibility, energy efficiency, and small-scale solutions. As the first step, the project team has started working with the Global Change Assessment Model (GCAM), an Integrated Assessment Model that is widely used to project energy futures and associated greenhouse gas emissions, in order to improve the characterization of nuclear power in this model. Further analysis will explore the sensitivity of modeling results to the assumptions made about different types of nuclear technologies, including SMR (Figure 18).

Figure 18. Integrated Assessment Models (IAM) typically project very large increases in global nuclear power use for the second half of the 21st century. In the Policy Scenario shown here, global installed nuclear capacity approaches 2000 GW‐electric by 2060 (more than five‐times larger than today) and provides 23% of total projected electricity. This project aims to illuminate the sensitivity of IAM results to underlying assumptions about the nature of nuclear power technologies that may be available and to assess options for managing some of the risks associated with such large‐scale reliance on nuclear power.

Exploring prospects for direct capture of carbon dioxide from air

2011 saw the publication by the American Physical Society of a major technology assessment, Direct Air Capture of CO2 with Chemicals, which presents the results of a multi-year study led by Michael Desmond (bp) and Robert Socolow. Systems achieving direct air capture (DAC) are giant scrubbing devices (Figure 19), where ambient air flows over a chemical sorbent (either liquid or solid) that selectively removes the CO2. The CO2 is then released as a concentrated stream for disposal or reuse, while the sorbent is regenerated and the CO2-depleted air is returned to the atmosphere.

DAC is now included in discussions of long-term climate change policy because very large deployment might someday enable the world to lower the atmospheric CO2 concentration at a rate of perhaps one part per million per year (ppm/yr), gradually reducing the negative impacts of climate change. (Right now, the concentration is increasing two ppm/yr.) DAC may also eventually have a role to play in countering recalcitrant decentralized CO2 emissions, such as emissions from buildings and vehicles, which prove expensive to reduce by other means.

However, the message of the report is “first things first.” Aggressive deployment of DAC makes little sense until the world has largely eliminated centralized sources of CO2 emissions, especially at coal and natural gas power plants, either by substitution of non-fossil alternatives or by capture of nearly all of their CO2 emissions. It is much cheaper to capture the emissions of CO2 in the flue gas of a coal power plant than to remove CO2 from ambient air where it is 300 times more dilute.

Figure 19. Schematic representation of a facility for capturing 1 MtCO2/yr. The facility consists of five structures, each 10 meters high and 1 km long, and could collect 1 MtCO2/yr if air passed through at 2 m/s and 50% of the CO2 were collected. The structures are spaced 250 meters apart, and the footprint of the system is roughly 1.5 km2 . Approximately six of these systems would be required to compensate for the emissions of a 1 GW coal plant. Buildings not to scale

This is an interesting research frontier. Quoting from the press release: “A variety of science and engineering issues will determine the ultimate feasibility and competitiveness of DAC…[Needed are] alternative strategies for bringing air into contact with chemicals, new chemistries for sorption and regeneration, materials that can operate effectively and efficiently over thousands of consecutive cycles, and low-carbon energy sources for power and heat in order to avoid emitting more than one CO2 molecule into the atmosphere for each CO2 molecule captured.”

As a follow-up, in May 2011 Socolow and CMI researcher Massimo Tavoni organized a meeting in Venice on “negative emissions,” a state of the world where more CO2 is removed from the atmosphere than added to it. DAC might be a contributor to such a world, and so might biological strategies on land or in the ocean. The meeting sought to improve communication between modelers of century-scale mitigation of climate change (who are already including negative emissions trajectories in their models) and experts on various negative emissions strategies. The talks presented will appear in a special issue of Climatic Change edited by Tavoni and Socolow.