0()5(0 1-'1- I Iall)oratory for Fluid Flow and clleat Transport t'henomena Department of Nuclear Engineering The University of Michigan Ann Arbor, Michigan CAVITATION DAMAGE IN LIQUID METAL COOLED REACTOR POWERPLANTS THE UNIVERSITY OF MICHIGAN j ENGINEERING LIBRARY R. Garcia* F. G. Hammitt** Abstract Submitted to the American.Nuclear Society June 1967 Internal. Report No. 05031-14-I * Senior Engineer, Aerojet-General Corporation, Von Karman Center, Azusa, California **Professor of Nuclear Engineering and Director of the Laboratory for Fluid Flow and Heat Transport Phenomena, Department of Nuclear Engineering, The University of Michigan, Ann Arbor, Michigan Financial Support Provided by National Science Foundjtion (Grant G-22529) - THE UNIVERSITY. OF MICHIGAN

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CAVITATION DAMAGE IN IJQUID METAL COO1.,E REACTOR P'OWER'IdANTS* Pumping and handling of high-temperature liquid metals, wherein cavitationl is a problem, is highly important in the space program, particularly regarding liquid metal SNAP systems. Cavitation attack can occur in bear1 2 3,4 ings, close-clearance passages, pumps, etc. For minimum size and weight and maximum temperature, velocities are high and suppression heads low. Operation in a cavitating regime may be necessary, even though long unattended life is required. These problems are also important in conventional liquid 2 metal cooled nuclear powerplants. The cavitation resistance of various steels and refractory alloys has been measured in our laboratory in mercury at 70~F and 500~F and in leadbismuth alloy and lithium at 5000F and 1500~F utilizing a high-temperature 5,6,7,8 ultrasonic vibratory facility. Of materials tested, tantalum-base alloys (T-lll and T-222) were the most cavitation resistant, except for mer-'cury at 70~F, wherein stainless steel was best. As expected, all materials tested in lead-bismuth sustained greater damage at 1500~F than at 500~F. However, in lithium the damage at 1500~F was in general an order of magnitude less than at 5000F, due primarily to "thermodynamic effects." These are important also in other high-temperature liquid 9,10 metals, as sodium, and result from the effects of fluid vapor which become significant at higher temperature. When cavitation bubbles collapse, the heat of condensation from the condensing vapor within the bubble must be conducted into the surrounding fluid. If this does not occur sufficiently *Financial support provided under National Science Foundation Grant G-22529. 1

2 rapidly, as may be the case with higher vapor densities at higher temperature, the temperature and pressure of the uncondensed vapor are raised, arresting the bubble collapse, and decreasing collapse pressures and damage. Florschuetz and Chao have recently considered both thermodynamic and inertial factors in bubble collapse, defining a dimensionless parameter, Beff., which characterizes such collapses as being inertia controlled or heat transfer controlled. In the latter case, "thermodynamic effects" are said to be operative. For the present purpose:.f^ ('^^2 2 (NP-H) Beff.( L ) ( j(NPSH Figure I shows'our experimental data (type 304 stainless steel) in 9,10 mercury, lead-bismuth, and lithium, and data obtained elsewhere' in sodium, as a function of Beff. Nominal values of unity have been used for RO and NPSH. For large values of Beff. the bubble collapse is not effected by "thermodynamic effects" and the damage obtained is in agreement with that 8 expected on the basis of mechanical properties. However, for values of Beff less than about 1000, "thermodynamic effects" are significant, and the damage is considerably reduced. Figure 1 shows the resulting damage correction factor. This surprising reduction in damage may permit more aggressive design of high-temperature cavitating components.

3 Nomenclature B ff = Thermodynamic Parameter, dimensionless cff. = density, lbm./ft. C = specific heat, Btu/lbm.~F L = latent heat, Btu/lbm. T/ p = reciprocal slope of vapor pressure curve, 0F/(lbf./ft. ) = thermal diffusivity, ft. /hr. R0 = characteristic bubble radius, ft. NPSI = "net positive suction head", fluid head above vapor, ft.lbf./lbm. Subscripts: L = liquid v = vapor

-' LIQUID METALS l ~~~I l Pb-Bi (15000F). O L Hg (500) PB Li (500F) P (500F) 0 o oL ( I INo (500~F) Hg (700 F) LL -__ _.- I _ _ _ _. _ _ _ _. _ _ _ _. _ _ _ _. _ _ _ _._ _ _ _. _ _ _ w I I cH _ INERTIA CONTROLLED COLLAPS < Li (1500~ F) 4 / ___o / _ ______ HEAT TRANSFER CONTROLLED COLLAPSE Na (15000 F) -5 LOG B 2193 /-:3~0 3 6 12 18 30 36 42 48 54

REFERENCES 1. Decker, O., "Cavitation Erosion Experience in Liquid Mercury Lubricated Journal Bearings," First Annual Mercury Symposium, November, 1965, Atomics International, Canoga Park, California, p. 14. 2. Shoudy, A. A. and Allis, R. J., "Materials Selection for Fast Reactor Applications," Proc. of Michigan ANS Fast Reactor Topical Meeting, April, 1965, Detroit, Michigan. 3. Wood, G. M., Kulp, R. S. and Altieri, J. V., "Cavitation Damage Investigations in Mixed-Flow Liquid Metal Pumps," Cavitation in Fluid Machinery, ASME, November, 1965, pp. 196-214. 4. Smith, P. G., DeVan, J. H. and Grindell, A. G., "Cavitation Damage to Centrifugal Pump Impellers During Operation with Liquid Metals and Molten Salt at 1050-14000F," J. of Basic Eng., Trans. ASME, September, 1963, pp. 329-337. 5. Garcia, R. and Hammitt, F. G., "Ultrasonic-Induced Cavitation'in Liquid Metals at 1500-F-," Transactions of ANS, Vol. 8, No. 1, June, 1965, pp. 18-19. 6. Garcia, R. and Hammitt, F. G., "Ultrasonic-Induced Cavitation Studies in Lead-Bismuth Alloy, 500-1500~F," Corrosion, Vol. 22, No. 6, June, 1966, pp. 157-167. 7. Garcia, R., Nystrom, R. E. and Hammitt, F. G., "Comprehensive Cavitation Damage Data for Water, Mercury and Lead-Bismuth Alloy Including Correlations with Material and Fluid Properties," ASTM Symposium on Erosion by Cavitation or Impingement, Atlantic City, N.J., June, 1966. To be published Proc. ASTM. 8. Garcia, R., "Comprehensive Cavitation Damage Data for Water and Various Liquid Metals Including Correlations with Material and Fluid Properties," Ph.D. Thesis and ORA Technical Report No. 05031-6-T, Department of Nuclear Engineering, The University of Michigan, August, 1966. 9. Thiruvengadam, A., Preiser, H. S. and Rudy, S. L., "Cavitation Damage in Liquid Metals," Technical Progress Report 467-2 (NASA CR-54391) For the Period January 1, 1965 to March 31, 1965, Hydronautics, Inc., April 28, 1965. 10. Thiruvengadam, A., Preiser, H. S. and Rudy, S. L., "Cavitation Damage in Liquid Metals," Technical Progress Report 467-3 (NASA CR-54459) For the Period April 1, 1965 to May 31, 1965, Hydronautics, Inc., June 30, 1965. 11 Florschuetz, L. W. and Chao, B. T., "On the Mechanics of Vapor Bubble Collapse —A Theoretical and Experimental Investigation," Trans. ASME, J. Heat Transfer, C, 87, 1965, pp. 209-220.