A practical tool

Nuclear Corrosion Modeling focuses on the formation, release, transport and deposition of corrosion products in the primary coolant circuit of pressurized water reactors. This book takes an interesting perspective on the behaviour of crud in reactor coolant circuits. Unlike a typical text, Castelli approaches the problem from an engineering perspective and specifically, from that of a reactor coolant chemist’s perspective. His goal is to develop a practical tool for tracking corrosion products throughout the primary circuit to address important operational issues such as; the impact of structural materials selection on crud deposition, optimizing or designing a coolant purification system, determining the interaction between crud deposition and axial power shape (and processes such as axial offset anomaly), and the relationship between oxidation product behaviour and radiological exposure during maintenance.

Castelli begins with a short introduction on the origin of corrosion products in the primary system and the corrosion of iron- and nickel-based alloys. The discussion includes identification of plant components that are responsible for corrosion products, specific corrosion product forms, the influence of surface finish and other important variables. He then defines seven key processes such as corrosion growth, corrosion release, particulate deposition, particulate crystallization and dissolution, etc. Because the transport of radioactive corrosion products is central to the objective, he identifies the five most important isotopes of the key elements involved in the relevant processes. The result is a definition of dependent variables, which are essentially the five important isotopes and their occurrence in four primary states: oxide sub layer, oxide surface layer, in the coolant as particulates or in the coolant as dissolved ions.

The middle section of the book (chapters 3-6) builds on what Castelli refers to as equation sets. The general equation set consists of 31 partial differential equations describing the time rate of change of the mass of each of the five isotopes in oxide sublayers or surface layers, and their concentrations as particulates or dissolved ions by the processes listed earlier. The media equation set refers to 20 equations that describe the time rate of change of the mass of the five isotopes in an ion exchanger and a filter, and the time rate of change of the concentrations of the five isotopes in particulate and soluble form by the processes listed earlier.

The next several chapters (7-9) address the solution algorithm for the general and media equation sets, input architecture, programme architecture and graphical user interfaces for visualization of the output of the code. The last chapter discusses specific design applications of the resultant code, dubbed NOC (nature of crud).

It is clear to the reader that the development of a code to model the behaviour of corrosion products throughout the primary circuit is a massive undertaking. It is also clear that the value of such a tool is also huge since the behaviour of materials in the primary coolant circuit is vital to the safe and economical operation of commercial pressurized water reactors.

Unfortunately, the reader is left wondering whether the model is indeed, finished and whether its promise has been realized. The book ends rather abruptly without discussion of results of test cases, benchmarking trials, sensitivity analyses, accuracy tests and case history examples. This information is generally provided in the validation of large computational models of complex physical phenomena. Adding to the uncertainty is Castelli’s revelation in chapter 10 that the project is only 75% complete. The reader is left to wonder whether the tool really exists.

Nevertheless, this book should have much value to engineers interested in the formation, transport and deposition of oxidation products around the primary circuit. It is essentially a manual or guide to the modeling of corrosion product transport. The general strategy of how to treat the problem is well laid out and the solution algorithm is explained in appropriate detail. I would recommend this book as a guide for those interested in learning about corrosion product transport in pressurized water reactor primary circuits.

Author Info:

Gary Was, is a professor in the department of nuclear engineering at the University of Michigan’s materials science and engineering department

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