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Research Papers: Operations, Applications and Components

Microporous Coatings and Enhanced Critical Heat Flux for Downward Facing Boiling During Passive Emergency Reactor Cooling

[+] Author and Article Information
Albert E. Segall

Department of Engineering Science
and Mechanics,
The Pennsylvania State University,
University Park, PA 16803
e-mail: aesegall@psu.edu

Faruk A. Sohag, Faith R. Beck, Lokanath Mohanta, Fan-Bill Cheung

Department of Mechanical and
Nuclear Engineering,
The Pennsylvania State University,
University Park, PA 16803

Timothy J. Eden, John Potter

Applied Research Laboratory,
The Pennsylvania State University,
University Park, PA 16803

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received November 9, 2016; final manuscript received June 1, 2017; published online August 1, 2017. Assoc. Editor: Allen C. Smith.

J. Pressure Vessel Technol 139(5), 051601 (Aug 01, 2017) (9 pages) Paper No: PVT-16-1208; doi: 10.1115/1.4037001 History: Received November 09, 2016; Revised June 01, 2017

During a reaction-initiated accident (RIA) or loss of coolant accident (LOCA), passive external-cooling of the reactor lower head is a viable approach for the in-vessel retention (IVR) of Corium; while this concept can certainly be applied to new constructions, it may also be viable for operational systems with existing cavities below the reactor. However, a boiling crisis will inevitably develop on the reactor lower head owing to the occurrence of critical heat flux (CHF) that could reduce the decay heat removal capability as the vapor phase impedes continuous boiling. Fortunately, this effect can be minimized for both new and existing reactors through the use of a cold-spray-delivered, microporous coating that facilitates the formation of vapor microjets from the reactor surface. The microporous coatings were created by first spraying a binary mixture with the sacrificial material then removed via etching. Subsequent quenching experiments on uncoated and coated hemispherical surfaces showed that local CHF values for the coated vessel were consistently higher relative to the bare surface. Moreover, it was observed for both coated and uncoated surfaces that the local rate of boiling and local CHF limit varied appreciably along the outer surface. Nevertheless, the results of this intriguing study clearly show that the use of cold spray coatings could enhance the local CHF limit for downward facing boiling by more than 88%. Moreover, the cold-spray process is amenable to coating the lower heads of operating reactors.

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Figures

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Fig. 1

Schematic of the quenching system in the SBLB test facility

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Fig. 2

Schematic of the test vessel being preheated by the customized heating mantle

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Fig. 3

Schematic of the cold spray system used to deposit microporous coatings

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Fig. 4

(a) Microporous-coated test vessel and (b) microscopic image of the coating at 100×

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Fig. 5

Quenching phenomena observed for the bare vessel

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Fig. 6

Quenching phenomena observed for the coated vessel

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Fig. 7

Local boiling curves measured during quenching (a) bare vessel and (b) coated vessel

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Fig. 8

Boiling curves at different angular locations for (a) bare and (b) coated test vessel

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Fig. 9

Comparison of the boiling curves between bare and coated vessel at the 14 deg location

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Fig. 10

Variations of the local CHF limits on the vessel outer surface

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