S. Bragg-Sitton

Idaho National Laboratory, Idaho Falls, ID, USA

Notice: This manuscript has been authored by Battelle Energy Alliance, LLC under Contract No. DE-AC07-05ID14517 with the U. S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

13.1 Introduction

Large-scale nuclear reactors are traditionally operated for a singular purpose: steady- state production of dispatchable baseload electricity that is distributed broadly on the electric grid. While this implementation is key to a sustainable, reliable energy grid, small modular reactors (SMRs) offer new opportunities for increased use of clean nuclear energy for both electric and thermal ap plications in more locations — while still accommodating the desire to support renewable production sources. There are several questions that a potential investor or utility must ask before making the decision to build a power plant, followed by the decision on where to site that plant:

• What is the specific energy requirement that needs to be met? Is it primarily thermal or electrical, or a mix of both? Could a single integrated energy system meet both needs?

• Does the energy demand vary over short or long time frames (e. g. hourly, daily or seasonal)?

• What resources are available in the region (water, land, carbon feedstock, etc.)? Are these resources necessary to the operation of a proposed energy system? Can they be used to enhance the operation of an integrated energy system?

• Is renewable generation an attractive option in the region? Are renewables presently in use (wind, solar, hydro, geothermal, biomass, etc.)?

• Will the proposed power plant be integrated on a small or large electricity grid, or will it be operated independently to support a specific industrial need?

The answers to these and related questions provide the framework for a multi-purpose implementation of nuclear energy systems that could integrate multiple resources to produce multiple output products. Co-generation systems (single input systems,

Handbook of Small Modular Nuclear Reactors. http://dx. doi. Org/10.1533/9780857098535.3.319
providing both thermal and electrical output) and multi-input, multi-output nuclear hybrid energy systems (NHESs) can be designed to operate flexibly based on thermal and/or electrical energy demands while accommodating multiple input streams. Those input streams could be several independent reactor units or a combination of resources such as nuclear reactors, windmills, solar panels, biofuels and fossil fuels.

Given the strong public (and, hence, political) desire to support non-carbon-emitting sources, electricity produced by renewable sources is often treated as ‘must-take’ on the grid. This scenario can mean that the baseload provider is required to ramp down production when the wind is blowing or the sun is shining, or sell electricity at a loss. The intermittency of renewable plants, such as wind and solar, occurs on a relatively short timescale. This intermittency places significant demands on the dispatchable, baseload plants that also supply the grid because they are then required to vary relatively large fractions of their load over a short time. A recent report by the Organisation for Economic Co-Operation and Development (OECD) Nuclear Energy Agency (NEA) states that the substantial amount of renewables that have been introduced on the grid in Germany has ‘repeatedly led to prices below the marginal costs of nuclear, including several instances of negative prices’ [1]. These scenarios are not attractive economically, nor does load-following by ramping reactor power up and down look good from the perspective of plant operations and maintenance. In these cases the renewables are connected directly to the grid, resulting in loosely coupled generation sources. This chapter considers an alternate scenario in which renewable generation would be tightly coupled with the nuclear generation source — behind the grid — to meet the grid demand as an integrated energy system while simultaneously producing other commodities with the available thermal energy.

Increasing the penetration of clean, affordable, reliable, secure, and resilient energy sources on electrical grids around the world can be accomplished by progressively establishing tightly coupled systems of distributed, dispatchable power generation assets that include a high penetration of intermittent renewable resources and energy storage or buffering units. Optimization and integration of these more complex and interactive power systems will require new technology with new approaches to deliver the optimized energy services across local, regional and national boundaries. Recent advances in control systems, energy management systems, advanced informatics and forecasting enable innovations in integrated plant design.