Soluble and particulate species present in the coolant of light water nuclear reactors can deposit on the surfaces of fuel rods, due to a phenomenon known as sub-cooled boiling. These deposits, known as 'CRUD' (a technical term), can lead to three major problems in reactors: an axial power shift, accelerated corrosion of the fuel cladding, and increased worker dose. The power shift can lead to a mandatory derating of the plant. A new model, MAMBA-BDM, is being developed to study how CRUD forms using a multiphysics, multiscale, fully coupled approach, where no approximations or 'fudge factors' are used to understand how CRUD forms from first-principles.
The deposition of corrosion products (see CRUD above) is a serious problem in areas that require high heat transfer and fluid flow to keep cool. These include reactor fuel rods, steam generators, and compact heat exchanger designs like printed circuit heat exchangers (PCHEs). Synergistic atomistic simulations, multiphysics models, and experiments are being proposed to find ways to impart deposition resistance to these surfaces. It is believed that the electronic structure of the surface is the key, and techniques such as plasma ion implantation, gas ion nitriding, and electro-implantation are being studied to stop deposition products from forming altogether.
The era when a single alloy or material can solve all the problems related to strength, ductility, corrosion resistance, and radiation resistance in some extreme environments is ending. New reactor concepts push the outlet temperatures, the material dose, and the lifetimes of reactor materials to extremes beyond the reach of single alloys. A composite approach is therefore necessary, to combine the best properties of each constituent material without degrading the system as a whole or at its interfaces. Steel composites have been developed at MIT to achieve both high strength and corrosion resistance in liquid lead-bismuth up to 715C, and similar efforts are underway for liquid sodium.
Provisional Patent Application #61/600,128: “Method for Improving Deposition (CRUD) Resistance of Nuclear Fuel Cladding and Components” (filed 2012)
P. V. Kumar, M. P. Short, S. Yip, B. Yildiz, J. C. Grossman. “First-Principles Assessment of the Reactions of Boric Acid on NiO (001) and ZrO2 (-111) Surfaces.” Accepted (DOI:10.1021/jp301607h), J. P. Chem. C (2012).
M. P. Short, R. G. Ballinger. “A Functionally Graded Composite for Service in High-Temperature Lead- and Lead-Bismuth-Cooled Nuclear Reactors – I: Design" Nuclear Technology, 177(3):366-381 (2012).
M. P. Short, R. G. Ballinger, H. Hänninen. “Corrosion resistance of alloys F91 and Fe-12Cr-2Si in lead-bismuth eutectic up to 715C." Under Review, Journal of Nuclear Materials (2012).
J. Deshon, D. Hussey, B. Kendrick, J. McGurk, J. Secker, M. P. Short. “Pressurized Water Reactor Fuel Crud and Corrosion Modeling." August 2011, Journal of the Minerals, Metals & Materials Society (JOM), 63(8):68-76 (2011).
M. P. Short, S. Morton, S. E. Ferry and R. G. Ballinger. “Diffusional stability of ferritic–martensitic steel composite for service in advanced LBE cooled nuclear reactors. International Heat Treatment and Surface Engineering, 4(2):74-80 (2010).