N. Todreas

Massachusetts Institute of Technology, Cambridge, MA, USA

1.1 Introduction

Just what are small modular reactors (SMRs)? This question is first answered simply along with a brief history of the evolution of this class of reactors. Subsequent sections detail the incentives and challenges to achieving successful commercial deployments, the different types of SMRs based on coolants employed, and, finally, the current status and future trends in the worldwide effort to develop and deploy this reactor type.

1.1.1 Defining SMRs

‘Small’ refers to the reactor power rating. While no definitive range exists, a power rating from approximately 10 to 300 MWe has generally been adopted. The minimum rating assures that the reactor delivers power suitable for the practical industrial application of interest. The maximum rating constrains these designs to power levels at which the expected advantages of serial production and incremental deployment as well as the match to electric grid siting opportunities and constraints can be realized.

‘Modular’ refers to the unit assembly of the nuclear steam supply system (NSSS) which, when coupled to a power conversion system or process heat supply system, delivers the desired energy product. The unit assembly can be assembled from one or several submodules. The desired power plant can then be created from one or several modules as necessary to deliver the desired power rating. Importantly the deployment of modules can also be sequenced over time both to match regional load growth and to levelize the timing of capital spending over a prescribed time horizon. Construction of the plant by assembly of factory-built elements or modules is the technique of modular construction. Although it is an integral part of the construction strategy envisioned for all SMRs, this technique is not uniquely applied to SMRs. Rather, it is now being employed for relevant construction elements of nuclear power plants of all power ratings, although the modules for large plants are considerably different in size, not typically amenable to rapid assembly as is being proposed for SMRs.

Handbook of Small Modular Nuclear Reactors. http://dx. doi. Org/10.1533/9780857098535.1.3

Copyright © 2015 Elsevier Ltd. All rights reserved.

‘Reactor’ is a term more broadly applied to vessels in which all manner of chemical processes are conducted. However, in our case, reactor refers to a system in which a controlled nuclear fission process is conducted.