Preface

Worldwide interest in nuclear reactors continues to increase and significant focus has been placed on advanced nuclear reactors intended to produce electricity and process heat. Somewhat absent from the broader discussion has been the importance of research reactors and certain specialized reactor analysis topics. This book attempts to fill this gap through three sections: "Nuclear Reactors for Spacecraft Propulsion", "Research Reactors", and "Select Reactor Analysis Techniques".

The first section of the book addresses the use of nuclear reactors for spacecraft propulsion. A detailed explanation is provided regarding the optimum approach for using a reactor as the heat source along with the basis for selecting hydrogen as the propulsion gas.

The second section of the book provides information about two landmark research reactors as well as a university reactor. The first research reactor discussed is the Transient Reactor Test Facility (TREAT) located in Idaho, USA. The TREAT reactor is an air-cooled graphite-moderated reactor used for testing new reactor fuel under extreme power transients. The TREAT reactor is capable of 18,000 MW power transients, which allows new fuel and material designs to be tested under severe accident conditions. The second research reactor discussed is the Experimental Breeder Reactor II (EBR II). EBR-II was a sodium-cooled fast-neutron-spectrum reactor that operated in Idaho, USA from 1964 to 1994. EBR-II provided comprehensive sodium-cooled fast reactor testing and operational experience. The most significant experiments conducted in EBR-II occurred in 1986 when the reactor was subjected to loss of flow and loss of heat sink, both without reactor SCRAM. In both experiments, the inherent safety properties of the reactor led to a safe shutdown without fuel damage, and no active engineered safety feature or operator action was required. The final reactor discussed is the Idaho State University AGN-201. This reactor has been operating for more than 50 years. The simple reactor design consists of UO2 dispersed in polyethylene along with a graphite reflector. The reactor operates at a very low power of 5 W and requires no active cooling, making it ideal for a university teaching setting where physics can be studied without the burden of numerous operational constraints.

The third section of the book includes a collection of interesting reactor analysis topics. It provides a detailed discussion of the Advanced Test Reactor (ATR) core reloading analysis. The ATR is in Idaho, USA, and is the largest test reactor operated by the US government and has been operating for more than 50 years. The very high neutron flux (greater than 1014 neutrons/cm2 s) in ATR necessitates frequent refueling but allows fuel and material testing to simulate years of reactor service in a matter of months. Additional reactor analysis topics discussed in this section include cyber-informed engineering for nuclear reactor digital instrumentation and control, a nuclear power plant case study focusing on instrumentation and control system reliability analysis, determining the plenum gas effect on fuel temperature, and finally, fault detection by signal reconstruction in nuclear power plants.

It is hoped that this collection of discussions on spacecraft nuclear reactor propulsion, research and university reactors, and various reactor analysis techniques will provide readers with valuable insights into important aspects of nuclear reactors that have not been well disseminated previously.

> **Chad L. Pope** Department of Nuclear Engineering, Idaho State University, Pocatello, USA

Section 1
