Past Events - April 7 1998

Randy Fong, a materials research engineer from the Chalk River Laboratories of AECL, visited Whiteshell Laboratories April 7 - 9 1998 to witness a test in the program studying the thermal behaviour of an improved calandria tube design for CANDU reactors. While here in Manitoba, Randy presented his paper on this program:

External Glass Peening of Zircaloy Calandria Tubes To Increase The Critical Heat Flux

by

R.W.L. Fong1, C.E. Coleman1, T. Nitheanandan2, V.D. Kroeger2,
R.G. Moyer2, D.B. Sanderson2, J.H. Root3 and R.B. Rogge3

Abstract

Glass-peening the outside surfaces of Zircaloy calandria tubes increases the nucleation sites available for boiling heat transfer and has been demonstrated to enhance the critical heat flux (CHF) in pool-boiling experiments. The objective of this study is to optimise the heat-transfer enhancement by glass peening while ensuring that the microstructure of the peened tube is acceptable for reactor use. Pool-boiling tests were done using small Zircaloy tubes with as-received ("smooth") surfaces and variously-peened surfaces, to evaluate two peening parameters, glass-bead size and the coverage of peened surface. Our results showed that the maximum enhancement of CHF (by 60% compared with as-received tubes) was obtained using a glass-bead size of 90-125 m with a coverage of 100%. The CHF enhancement was found to be insensitive to glass-bead size over a wide range (from 60-90 m to 125-180 m). Using a fixed glass-bead size of 125-180 m to evaluate the influence of peening coverage, the maximum effect on the CHF response was obtained with a coverage of 100%. The microstructures of the peened tubes were evaluated using light microscopy, X-ray and neutron diffraction, and mechanical tests. After peening, the microstructure in the sub-surface layer (~30 mm) consisted of deformed a-Zr grains, and the crystallographic texture of the grains changed slightly. After stress-relieving at 500C for 1 h, some recrystallisation had occurred and the residual strains remaining in the tube were low. The tensile and burst properties of glass-peened and stress-relieved tubes were similar to those of as-received tubes. The microstructures introduced by peening and stress-relieving were judged to have little effect on creep and growth behaviour. Since there are no deleterious consequences of the glass-peening treatment, the peened and stress-relieved tubes are found to be acceptable for reactor use.

To be presented at the 11th Pacific Basin Nuclear Conference 1998 May 3-7, Banff, Alberta, Canada

1 AECL Chalk River Laboratories, Chalk River, Ontario, Canada K0J 1J0
2 AECL Whiteshell Laboratories, Pinawa, Manitoba, Canada R0E 1L0
3 National Research Council Canada, Chalk River Laboratories, Chalk River, Ontario, Canada K0J 1J0

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