D. Cummins

Rock Creek Technologies, LLC, Loudon, TN, USA

6.1 Introduction

Integral pressurized-water reactors (iPWRs), Small modular reactors (SMRs) of the light pressurized-water kind, are the wave of the future. Other chapters have detailed the advantages of iPWR modular designs in meeting the needs of small metropolitan centers or developing countries where the electrical grid infrastructure is not present, as well as the needs of normal power plants with the modular ability to add units. The ‘smallness’ and the ‘modularity’ of the new iPWR designs present several advantages to the nuclear power community.

Some of the common architecture features of an iPWR are:

• small capsule-like design;

• below grade installation;

• steam generators inside the reactor pressure vessel;

• small on-site crew manning for operations and maintenance (more automation);

• a multi-unit control room;

• modularity and grow-ability (ability to add more modules to increase the power output for a small additional increase in infrastructure);

• more passive cooling techniques;

• less accident or safety cases;

• more built-in fail-safe features;

• more prognostic and diagnostic capabilities;

• low or no maintenance instrumentation for cycle to cycle runs;

• incorporation of lessons learned from large PWR experiences.

With these features come challenges for the instrumentation and controls (I&C) design. iPWRs will have more automation, more redundancy, more cyber security, more fail­safe features, more fault-tolerant designs, more prognostic and diagnostic capability, and different measurement methods. With these design challenges it is important to focus on I&C development early in the overall reactor design/development phase in order that solutions, possibly unique solutions, can be developed and qualified early. Just as the mechanical/electrical design requires I&C compatibility, the I&C design requires mechanical/electrical modifications. This give-and-take between the I&C design and the mechanical/electrical design is a necessity in these new builds

Handbook of Small Modular Nuclear Reactors. http://dx. doi. Org/10.1533/9780857098535.2.123

Copyright © 2015 Elsevier Ltd. All rights reserved.

and requires a high level of communication and coordination between functional divisions.

New technologies offer solutions and abilities that the old 1970s and 1980s technology did not have. The advent of digital designs and wireless communications are technological advances that should be considered in every new design. The extent to which an iPWR incorporates these technological advances will determine the amount of safeguards that may need to be built in to the design and the license application. In the case of microprocessor-based digital technology, a detailed defense of common cause and common mode failures must be developed. In the case of hardwired logic-based digital design, such as field programmable gate arrays (FPGAs), common cause and common mode failures are not as much of an issue, but a detailed diversity and defense in depth must still be developed. In the case of digital or wireless communications, cyber security threats and electromagnetic interference/radio frequency interference (EMI/RFI) must be considered.

Traditional measurement methods may not be applicable in the new designs. New environments, submerged vessels, lack of traditional piping and new geometries all play a part in the need for new measurement devices and methods. The traditional devices offer the safety qualification pedigree that a nuclear plant requires, but the traditional devices are designed for a traditional plant and may not be qualified or designed for the new harsher environment and/or the new smaller geometries involved. There is an emerging need for radiation-hardened, high pressure and temperature qualified, submergible, smaller sensors with remote processing electronics. Although the technology is developed, the application of this technology to the new iPWR environment has not been accomplished in many cases; especially the cases of primary vessel level and flow. New qualification programs will need to be developed for the new sensor technologies.

In summary, the maturation of iPWR design is bringing about a paradigm shift in instrumentation design and methodology. What used to work for large light — water PWRs will not necessarily work in the iPWR environment. The new smaller dimensions, differing geometries, and harsher environments will necessitate new instrumentation solutions. This chapter highlights the requirements, challenges, and potential solutions for this new I&C world.