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On Vapor/Steam Explosion Analysis THE NUCLEAR NEWS INTERVIEW Fauske and Henry: On vapor/steam explosion analysis Vapor explosions are an integral part of reactor safety evaluations when accident conditions could lead to molten fuel coming in contact with liquid coolant. he book Experimental Technical Bases for Evalu- involving these types of explosions must be evaluated ating Vapor/Steam Explosions in Nuclear Reactor in a manner consistent with the available experimen- TSafety was recently published by the American tal technical bases. Their new book, they say, provides a Nuclear Society. The authors, Hans Fauske and Robert common reference that includes the total experimental Henry, say that the possibility of vapor/steam explo- database for vapor/steam explosions, as well as informa- sions occurring at nuclear power plants is an important tion directly related to molten materials and the coolant consideration for safety assessments of events wherein a of interest. high-temperature molten mass could come into contact Early in his career, Fauske joined Argonne National with a liquid coolant. Laboratory, where he focused on reactor safety evalua- The authors stress that potential accident conditions tions for both fast and light-water reactors. Vapor explo- sions were a key element of the safety evaluations for the Fast Flux Test Fa- cility and the Clinch River Breeder Reactor designs, and steam explo- sions were an important part of the safety assessments for water-cooled reactors. Fauske left ANL in 1980 to establish, with Robert Henry and Michael Grolmes, Fauske & Associ- ates. In 2011, Fauske stepped away from management responsibilities at the company to spend more time on engineering evaluations and writing. Henry also worked at ANL, under Fauske: “We wrote the book to provide Henry: “Vapor explosions in general a convenient, common reference for are an integral part of reactor safety Fauske’s direction, on both fast reactor experimentalists or analysts.” evaluations.” and LWR safety. In March 1979, the August 2017 • Nuclear News • 29 Three Mile Island-2 accident occurred, Through the years, Fauske & Associates and during the following summer and has been deeply involved in nuclear and fall, Henry was on loan from ANL to the chemical reactor safety evaluations. The Nuclear Safety Analysis Center, which company developed the Modular Acci- was established by the Electric Power dent Analysis Program (MAAP), a com- Research Institute to study the data ob- puter code that runs faster than real time tained from the accident. By that winter and can evaluate the response of boiling he was part of an ANL group that worked water reactors and pressurized water re- with Commonwealth Edison to conduct actors for a broad spectrum of accident a near-term study on the implications of sequences. Steam explosion modeling is the TMI-2 accident for the Zion reactor, an important component of the MAAP located north of Chicago, Ill. The issue of evaluations. steam explosions was a major component Rick Michal, director of ANS’s Depart- of the Zion study. Henry also authored TMI-2: An Event ment of Scientific Publications and Standards, conducted in Accident Management for Light-Water–Moderated Re- this interview with Fauske and Henry, whose new book actors, published by ANS in 2011. is available through ANS and at Amazon.com. Why did you write this book? describing the test facilities and pro- in Chapter 2) that are completely consis- Henry: The book is needed by the nucle- viding a summary of the experimental tent with the experimental bases lead to a ar community. Let me begin by explaining results. Equally important, the 19 pages set of requirements for a large- scale vapor that a steam explosion is referred to as a of references in our book tell the readers explosion that could not be satisfied un- vapor explosion when water is the volatile where they can find more details on these der accident conditions. For commercial liquid that is vaporized. Vapor explosions experiments should they have a desire to water- cooled nuclear reactors with oxid- in general are an integral part of reactor read the original documents. ic fuel and zirconium alloy fuel pin clad- safety evaluations if accident conditions Fauske: A second but related reason ding, the experimental bases (discussed could lead to high- temperature molten for the book is that we have observed that in Chapters 3 and 4) that are derived fuel coming into contact with the liquid many of the original experiments don’t from numerous experiments throughout coolant. Both Hans and I have been active seem to be referenced in some of the more the world show only very weak events, for more than four decades in developing recent papers, even when comparable re- and these can be characterized in a sim- the understanding of vapor explosions for sults have been obtained. This can be for ple, bounding manner for severe accident different types of reactor designs. During many reasons, such as that the authors analyses. Chapters 5 and 6 discuss those this time we have had the opportunity to may not be aware of some of the original experiments that are related to the role know and work with many talented, ded- experiments, the original documents have of aluminum in water- cooled reactors icated engineers and scientists who have been difficult to find, or the authors docu- such as were observed in the BORAX- I touched on one or more of the numerous menting some of the more current works and SPERT- I tests, as well as the accident facets that comprise this phenomenon. In didn’t have time to develop an in- depth that occurred in the SL- 1 reactor. High- addition, we have had the opportunity to understanding of the original documents. temperature molten aluminum is a very perform experiments, observe other ex- Whatever the reason, this experimental reactive metal in the presence of steam. periments, and examine the relevant data database is too broad and too important These components of the experimental that has been gained from programs con- to reactor accident evaluations and se- databases address the mechanisms and ducted all over the world. vere accident management guidelines to the necessary conditions for a steam ex- It has always been our conviction that be minimized. As a result, we wrote the plosion to transition into a chemical ex- any evaluation of vapor explosions for book to provide a convenient, common plosion. These are particularly relevant to potential reactor accident conditions reference for experimentalists or analysts special- purpose reactors that differ greatly must be consistent with the entire ex- to ensure that they are consistent with the from those just mentioned but neverthe- perimental database that has been de- broad experimental technical bases given less have aluminum structures in a water- veloped. To quote W. Edwards Deming, in the book when they are planning their cooled reactor. Consequently, these need “Without data you are just a person with respective approaches to vapor explosion to be considered in light of the possibility an opinion.” The relevant data associated experiments or models and when they are of a steam explosion alone, as well as the with vapor explosions now spans at least documenting their results. possibility, or lack thereof, for an explosive five decades, and some of the original Henry: A third reason for this book is chemical reaction to be initiated. papers, reports, conference proceedings, that we have found through this growing and other source materials are somewhat experimental basis that the major obser- Is the book intended to address the severe difficult to find, while some old reports vations have consistently demonstrated a accident analysis for all liquid- cooled reac- exist only as copies that are virtually few important behaviors that have differ- tors and not just commercial nuclear power unreadable. Therefore, our first reason ent characters, depending on the reactor reactors? for writing the book was to define the design in question. For the liquid sodium– Henry: Yes. Severe accident analyses technical bases by listing the key exper- cooled fast reactors, the general behavior must consider those conditions that could iments, from our perspective, and then principles for a vapor explosion (explained cause the reactor fuel to become molten, 30 • Nuclear News • August 2017 www.ans.org/nn Interview: Fauske and Henry which generally means very high tempera- plosion to occur, there must be nucle- throughout the world. Can you give some tures, and then come into direct contact ation of liquid to vapor and rapid energy examples of the extent of the experimental with the liquid coolant. This applies to all transfer to generate vapor faster than the database for the key principles mentioned reactors with a liquid coolant in which ac- surrounding medium can respond to the previously? cident conditions could result in very high rapidly increasing steam volume. Of these, Henry: The importance of the interface fuel temperatures and includes water- the method of vapor nucleation from the temperature principle is clearly illustrated cooled commercial power reactors, liquid liquid state is the most important. It differs by experiments performed at Argonne Na- metal–cooled fast reactors, and special- by orders of magnitude from the normal tional Laboratory using simulant materi- purpose reactors. boiling processes that experience nucle- als. These are further supported by the ex- ation at imperfections—for example, crev- periments where high- temperature solids Could you list the conditions or require- ices, scratches, and pits—in the solid sur- dropped into water did not produce a steam ments that could lead to a vapor/steam face for a liquid- solid boundary, such as a explosion. In addition, the experimental explosion? pot of water on a stove or a fuel rod surface database includes numerous in- reactor Fauske: First, there must be a liquid- transferring energy to the water coolant.
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