Thla report waa prepared a1 an account of work tponaorod by tht Unlttd Stattl Government. Neither the Unlttd Stattl nor tho Enorgy Ro10arch and Otvtlopmont Admlnlatratlon, nor the Nuclear Regulatory Comml11lon, nor any of their employee~, nor any of their contractor•, aubcontractora, or their employee~, makoa any warranty, expreaa or Implied, or aaaumea any legal liability or reaponalblllty for the accuracy, completene11 or uaefuln111 of any Information, apparatus, product or proce11 dlacloaed, or repreaenta that Ita uae would not Infringe privately owned rlghta.

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The objective of this work is to understand how the size of an arc on the electrode of an magnetohydrodynamic (MHD) generator or accelerator depends on operating parameters such as boundary-layer shape and current density. Arc size has an important bearing on device lifetime and performance. A boundary layer in an MHD device is a region of exceedingly steep gradients including, in particular, the gradient of electrical conductivity. A theory relating arc size to the characteristics of these gradients is developed and compared with behavior observed in various MHD devices, most recently that in the Component Development and Integration Facility in Butte, Montana. Nomenclature A = sublayer thickness B = magnetic flux density, (T) Cf = friction coefficient C p = specific heat at constant P D -arc-column diameter E -electric field strength F c = contraction factor h = arc enthalpy-ambient enthalpy / = arc current j = current density A/cm 2 k = Boltzmann's constant k s -effective roughness height t = mixing length m = molecular weight n e = electron number density P = pressure Pr -Prandtl number R = universal gas constant Re x -Reynolds number R k = roughness Reynolds number r 0 = arc-column radius T = temperature u = velocity V = voltage, (V) y = distance from electrode wall y 0 -a distance related to roughness a = recombination coefficient /3 = Hall parameter d = velocity thickness c = ionization energy, turbulent diffusivity K = thermal conductivity /* = viscosity p = gas density, p a , in arc colomn a = electrical conductivity T = shear stress, recombination time Subscripts a = arc column = core flow or arc-column region = edge of arc column = region of uniform current flow = spreading region = top of arc column = wall = x component = y component

This report[a] describes the results of the first scoping test in the Irradiation Effects Test Series conducted by the Thermal Fuels Behavior Program, which is part of the Water Reactor Research Program of EG&G Idaho, Inc. The research is sponsored by the United States Nuclear Regulatory Commission. This test used an unirradiated, three-foot-long, PWR-type fuel rod. The' objective of this test was to thoroughly evaluate the remote fabrication procedures to be used for irradiated rods in future tests, handling plans, and reactor• opet'ations. Additionally, selected fuel behavior data were obtain~d. The fuel r~J was subjee~ed to a series of preconditioning power cycles_followed by a power increase which brought the fuel rod power to about 20.4 kW/ft peak l~near heat rating at a coolant mass flux of 1.83 x 10 6 lb/hr-ft 2. Film boiling occurred for a period of 4.8 minutes following flow reductions to 9.6 x 10 5 and 7.5 x 10 5 lb/hr-ft 2. The test fuel rod failed following reactor shutdown as a result of heavy internal •and external cladding oxidation and embrittlement which occurred during the film boiling operation. [a] This report was previously published (TFBP-TR-110, January,"l976) with a limited internal distribution. This publication is made under the distribution selected for final reports on tests in the NRC Fuel Behavior Program;

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