Patent Number: 050842293
Section: description

DETAILED DESCRIPTION OF THE INVENTION An apparatus, FIG. 1, for testing fuel element specimens and corrosion coupons at high temperature transients is provided. The apparatus raises a specimen to its critical heat temperature by electrical flux induction. This critical heat flux (CHF) test apparatus is located in a hot cell so that highly irradiated specimens, i.e. fuel elements, can be tested in situ. All operations are performed remotely within a hot cell using a slave manipulator or robot 107. A specimen 11 is placed within a quartz tube 13 which has one upper heating portion where induction wires 15 are coiled around its exterior surface. The lower end of specimen 11 is attached to a riser clamp 17. This specimen riser clamp 17 rests upon a movable metal pin 19 which supports the specimen 11 while it is in the heating portion of the quartz tube 13 (the region of the induction coil 15). Below the heating portion of the tube 13 is a cooling portion or quench chamber 23. The base of this cooling portion 23 is provided with a shock absorbing spring 103. The coolant 25, usually water, fills the quench chamber 23 and is supplied to this quench chamber 23 from a reservoir 27 connected to the chamber 23 by a pipe having a flow control valve 29. At the base of the quench chamber 23 is a coolant return valve, circulation valve 31. The system valves 29 and 31 can be solenoid operated or motor position (servo motor) controlled from a remotely located valve control 65. Control signal lines connect this valve control 65 and the valves 29 and 31. The coolant circulation valve 31 connects the quench chamber 23 to a reservoir 27 through piping 37. A circulation pump 35 positioned in this piping 37 forces the water coolant from a lower level below the quench chamber 23 to an upper level where the reservoir 27 is positioned. The reservoir 27 is high enough to gravity pressure feed the quench chamber 23 through piping containing the valve 29. The quartz tube 13 is connected to a moisture trap 39 by an evacuation tube 41 attached at a coupling 85, which KOVAR transition coupling 47 is connected to the quartz tube 13. Access through the tube 41 is controlled by a valve 43 in the tube 41. The coupling 47 meets the tube in the region of the movable metal pin 19 below the region of the induction heating coils 15. The evacuation tube 41 and moisture trap 39 is connected to the vacuum system of the fission gas collection apparatus 81 exterior to the hot cell by a connector 83. A pair of vent pipes 44a and 44b connect into the evacuation tube 41 between the coupling 47 and the valve 43. A system vent valve 45 is connected to the lower vent pipe 44b of the evacuation tube 41. This vent valve 45 is closed during testing, i.e., during the heating and cooling of the specimen 11 and opened before the CHF apparatus is opened to remove the specimen 11. Also connected to the evacuation tube 41 at the upper vent pipe 44a is a pressure gauge 49 for monitoring the CHF apparatus pressure while it is in operation. The CHF apparatus is closed with a furnace cap 51 placed over the open top of quartz tube 13. A thermocouple 87 is welded onto the specimen 11. Coiled wires 53 are welded to the thermocouple 87 and extend from the weld junction through the furnace cap 51 and to a first cell plug 55 through the hot cell wall 57. These wires 53 are connected through that cell plug 55 to a thermocouple temperature recorder 59. Power cables from a radio frequency generator 69 located outside the hot cell pass through a second cell plug 67 and extend across the hot cell to power the induction coils 15. A third cell plug 71 is used as a passageway through the cell wall 57 for signal wires from an external pump control 73 to the coolant pump 35. Power cables 93 from a resistance welder power supply 75 are also passed through this cell plug 71 to a welder 91 located in the hot cell. A fourth cell plug 79 is used to pass a pipe 84 to a fission gas apparatus 81 from the moisture trap 39. This pipe 84 is provided with an adapter union connector 83 to interface with the fission gas vacuum system 81. The remotely powered welder 91 within the hot cell has a base 92 which rests on the hot cell floor and holds the specimen 11 with a vise member 94. A vertical arm 96 holds the resistance welder tip 98 on a dual link pivoted positioning arm 102. A small grinding tool 109 is positioned within the hot cell adjacent the welder 91. This grinder 109 is used to prepare the surface of the specimen 11 prior to welding the thermocouple in place. The furnace cap 51 mates with the quartz tube 13 with a spherical socket. The thermocouple wire 53 extends through the furnace cap 51. The top of the furnace cap 51 has a KOVAR seal 95 and KOVAR cap 97. The thermocouple wires 53 extend through KOVAR seal 95, the KOVAR cap 97 and are surrounded by a solder and epoxy seal. These thermocouple wires 53 extend to an electrical coupling 101 and then through the first cell plug 55 to the thermocouple temperature recorder device 59 which is located outside the cell wall 57. A specimen 11 is prepared, FIG. 2, in the hot cell, by grinding away its corrosion film in the weld area. A previously prepared thermocouple 87 is welded to the specimen 11, at a point near its top so that the specimen hangs straight from the wire 53 attached to the thermocouple 87. The wires 53 are braided and coiled to allow vertical displacement when dropped into the quench chamber and may be a chromel-alumel combination. The thermocouple junction 87 is Heliarc welded to prevent oxidation. The specimen 11 and thermocouple assembly 87 are attached to a specimen riser clamp 17. The purpose of the clamp 17 is to position specimen 11 within the induction coil 15. A special holder 99, FIG. 3, is used to test multiple corrosion coupons without damaging the corrosion films. It has a top holder portion 111 and a base 113. The base 113 of this special holder 111 has a cross shaped cross section. This holder 99, top portion 111, FIG. 3a, has three rectangular depressions 115, 117, 119 for holding individual coupon specimens. Separating the three depression regions 115, 117, 119 are flat portions, elevated to a height above the depression regions 115, 117, 119. Extending from the center of each of the flat portions is a projection 123. A cover 121 is adapted to fit over the depression containing the top portion and is provided with openings through which the projections 123 extend. Three separate compartments are formed from the three depressions 115, 117, 119. It is within these compartments that corrosion film individual coupon specimens are placed for testing. The coupon in the top position is then welded with a thermocouple and the holder is placed in the CHF apparatus in the same manner in which the specimen 11 was prepared and placed in the CHF apparatus. The CHF apparatus is closed when the furnace cap 51 is placed atop the quartz tube 13. The system vent valve 45 is closed and the valve 43 to the evacuation tube 41 opened so that the CHF apparatus is evacuated. Thereafter, the system is sealed by closing the valves. Maximum power is applied to the induction coil 15 by the radio frequency generator 69 to achieve the initial heat up rate. Power is decreased to hold the specimen 11 at a predetermined dwell temperature and time. The apparatus can heat a specimen 11, such as a fuel element, to 1300 degrees F. (704 degrees C.) at rates up to 120 degrees F./sec (49 degrees C./sec). Each specimen has a different temperature at which its substructure will be permanently altered. This temperature is a function of the critical heat of the element. This apparatus is designed to quickly raise the temperature of the specimen and then rapidly cool it, so the effects of exposure to a high temperature for a predetermined time can be studied dimensionally, by metallography and by examination of the by-products driven off of the element and collected by the vacuum apparatus. In this way, the various stages and changes in the structure of a specimen, i.e., phase transformations, can be plotted over time and temperature and the order and manner in which the structural changes occur studied. When power to the coil 15 is turned off, the metal support pin 19 is remotely removed by a magnet device 105 causing the specimen 11 to drop into the lower quench chamber 23 of the apparatus. As the specimen 11 is cooled, the system is monitored for potential fission gas release, that is, the gas released if the integrity of the specimen is compromised. The specimen is cooled at rates up to 300 degrees F./sec (149 degrees C./sec). Any gases released are collected through the evacuation tube 41. After a test, the system is vented by opening the vent valve 45 and the specimen 11 withdrawn by a slave manipulator 107 which removes the cap 51 and which grasps the thermocouple wires 53 attached to the specimen 11. This procedure can be repeated immediately if it is so desired or the specimen may be transferred to another station for examination. This CHF apparatus is particularly adapted to perform rapidly repeatable heat transient tests on model fuel elements and can be modified to permit testing of a variety of other materials, both irradiated and non-irradiated. Modifications can be made to the above-described invention without departing from the intent and scope thereof. Accordingly, it is intended that the scope of the invention is not to be limited by the foregoing description. The above description is to be considered as illustrative of the invention.