Fluid Fuel Reactors: Molten Salt Reactors, Aqueous Homogeneous Reactors, Fluoride Reactors, Chloride Reactors, Liquid Metal Reactors and Why Liquid Fission

by James A. Lane, H.G. MacPherson, Frank Maslan

A landmark book written at Oak Ridge National Laboratory under the auspices of the Atomic Energy Commission as part of its Atoms for Peace program. FLUID FUEL REACTORS approaches to the subject of nuclear power from a chemical standpoint, rather than from the point of view of mechanical engineering. Today, the value of this approach has (finally) been recognized by venture capitalists such as Peter Thiel, philanthropists such as Bill Gates, and policy makers in Washington who have recently been passing advanced-reactor friendly legislation year after year. China's Navy is funding the Chinese Academy of Science Thorium Molten Salt Reactor program. The DoE (through GAIN) has funded essential Molten Salt research in the United States. Canada has funded Molten Salt research, and is currently conducting a pre-licensing vendor review. Dr. Anil Kokodkar, the former-head of India's nuclear program has stated, given a do-over he'd have pursued a liquid fuel (as opposed to a conventional solid fuel) approach to advanced nuclear. Molten Salt Reactor startups are flourishing, and typically, a single copy of FLUID FUEL REACTORS can be found in their head-office. The founders of these startups are driven to provide clean energy to developing nations, and replace today's polluting energy options which power western industry and prosperity. First printed in 1958, FLUID FUEL REACTORS continues to be cited as a useful reference by ORNL engineers, MSR startup employees, and those in academia. Alvin Weinberg suggested people should re-examine "dusty old books" such as FLUID FUEL REACTORS in his last recorded public interview (2 years before his death) at the University of Tennessee on 2004. Used physical copies have sold online for well over $1,000. 60 years after FLUID FUEL REACTORS was first published, it can now, for the first time, be enjoyed on digital reading devices, in a manner that supports adjustable font sizes and easy-to-read formatting... as opposed to looking at a series of bitmap images of words, like an animal.

1581 pages, Kindle Edition

Published December 5, 2018

About the author

James A.^^Lane

Reviews

[Rodney Harvill · Rating 4 out of 5]

The power reactors currently operating in the U.S. are light water reactors (LWRs), in which demineralized water is circulated through a reactor core consisting of fuel assemblies, with the uranium dioxide fuel pellets confined to the interior of zircaloy fuel pins. In the 1950s, however, a wide variety of reactor types were under consideration before the nation settled on LWRs. One such reactor type was the fluid fuel reactor, in which the uranium fuel is dissolved in the reactor coolant. Fission power is generated only in the core because that is where the dissolved fuel achieves a critical configuration. This book is a survey of the knowledge base associated with fluid fuel reactors as of 1958. Because of the subsequent focus on LWRs, work on fluid fuel reactors after this time was limited, and this book represents much of the available knowledge associated with a reactor concept that in recent years appears to be experiencing a revival of interest.

Among fluid fuel reactor types, there are three discussed in this book:

• Aqueous homogeneous reactors
• Molten salt reactors
• Liquid-metal fuel reactors

In aqueous homogenous reactors, uranium compounds are dissolved in water. Because of the high temperatures necessary to boil water in a steam generator, these reactors are essentially pressurized water reactors, the primary difference being the fuel dissolved in the coolant. In addition to experimental reactors operated at Oak Ridge National Laboratory and Los Alamos National Laboratory during the 1950s, the book describes at least one proposed commercial pilot plant.

In molten salt reactors, uranium compounds are dissolved in molten salt coolant, molten because it is in solid form at room temperature. Such reactors typically operate with a cover gas that is pressurized slightly above atmospheric pressure. The molten salt reactor described in the book is the aircraft reactor experiment at Oak Ridge. During the 1960s, after this book was written, Oak Ridge built and operated the Molten Salt Reactor Experiment (MSRE), at first with U-235 fuel and subsequently with U-233 fuel. MSRE operating experience is discussed in the following report

• ORNL-TM-3039, MSRE Systems and Components Performance

The available design and operations reports for the MSRE are:

• ORNL-TM-728, MSRE Design and Operations Report, Part I, Description of Reactor Design
• ORNL-TM-729, MSRE Design and Operations Report, Part IIA, Nuclear and Process Instrumentation
• ORNL-TM-730, MSRE Design and Operations Report, Part III, Nuclear Analysis
• ORNL-TM-732, MSRE Design and Operations Report, Part V, Reactor Safety Analysis Report
• ORNL-TM-733, MSRE Design and Operations Report, Part VI, Operating Safety Limits for the Molten-Salt Reactor Experiment
• ORNL-TM-907, MSRE Design and Operations Report, Part VII, Fuel Handling and Processing Plant
• ORNL-TM-908, MSRE Design and Operations Report, Part VIII, Operating Procedures
• ORNL-TM-909, MSRE Design and Operations Report, Part IX, Safety Procedures and Emergency Plans
• ORNL-TM-910, MSRE Design and Operations Report, Part X, Maintenance Equipment and Procedures
• ORNL-TM-911, MSRE Design and Operations Report, Part XI, Test Program
• ORNL-TM-2111, MSRE Design and Operations Report, Part V-A, Safety Analysis of Operation with 233U
• ORNL-TM-2304, MSRE Design and Operations Report, Part XI-A, Test Program for 233U Operation

Per OSTI.gov, one design and operations report was never issued and is, therefore, unavailable.

• ORNL-TM-731, MSRE Design and Operations Report, Part IV, Chemistry and Materials

I refer to these reports because the book would have summarized data from such reports had they been available when it was written.

In liquid-metal fuel reactors, uranium compounds are dissolved in molten metal. The book describes the design of a proposed experimental reactor at Brookhaven National Laboratory in which molten bismuth is used.

Here are a few observations about these reactors.

• The LWRs in use today are best operated as base load units, at full power or as close to full power as possible because refueling requires replacing fuel assemblies during scheduled refueling outages. Because only a portion of the core is replaced each outage, the replacement fuel is designed based on an assumed burnup window for the previous core. In the nuclear industry, we think of burnup in terms of megawatt days per metric ton of uranium (MWD/MTU), but the Navy's burnup term, effective full power days (EFPD) may make more sense to the uninitiated. Having the burnup window coincide with a scheduled refueling outage requires consistent full power operation. However, the growing use of renewable power such as solar and wind, which operates intermittently, militates against base load nuclear units. A fluid fuel reactor, in which new fuel is added merely by dissolving more uranium in the coolant, eliminating the problem of burnup windows, could load follow in response to changes in power demand without adverse effects on fuel economy.
• A downside of a fluid fuel reactor is the fission products in the coolant. In a LWR, operations and maintenance personnel can perform work near the reactor coolant piping at low power or shutdown conditions because the fission products are confined to the core, which is behind a biological shield typically consisting of several feet of concrete. In a fluid fuel reactor, decay of the fission products would produce lethal radiation levels around the reactor coolant piping. As a result, remote maintenance techniques are required. Given the tremendous advances in robotics, maintenance of such a reactor is likely much more feasible today than several decades ago.
• Fluid fuel reactors offer the potential for removing fission products from the system during power operation. Because their decay, adds heat to the coolant that can be turned into electric output, I don't consider it advisable to remove most of the fission products. However, some fission products, such as Xe-135 and Sm-149, adversely affect neutron economy and should be removed. The section on molten salt reactors doesn't address fission product removal, but the section on liquid-metal fuel reactors does. Interestingly enough, some of the proposed mechanisms included molten salt carrier agents. Given that some advanced reactor designs are molten salt, I have to wonder if such fission product removal systems might work with them. I am a nuclear engineer, not a radiochemist; so I don't know the answer here.

The Kindle version of the book that I read has some formatting issues, including some captions without associated figures, some equation numbers without associated equations and numerous spelling errors attributable to the OCR scan. Regardless, I found the information in the book to be quite enlightening.