DOUBLE RUBBLE: FLECHT Run 9573, December 11, 1970
FLEC—500 — Facility Operation
The final FLECHT test (Bundle Z-lO) was completed on December 11, 1970. The test was run with flooding of 1 in/sec. beginning at 2000 degrees F. Several heaters failed approximately 18 seconds after flooding when the peak indicated midplane temperature was 2325 degrees F. Heater failure at this temperature is unlikely, particularly under conditions of decay heat and increasing temperature. The steam probe thermocouple located one foot above midplane in close proximity to a Zircaloy grid indicated an extremely rapid rate of temperature rise (over 3OO F/sec.)_beginning approximately 12 seconds after flooding and reached 2450 degrees F by 16 seconds after flooding. It appears likely that ignition of the Zircaloy grids led to high rates of heat input* at the elevation one foot above (and below) midplane and this caused overtemperature and failure of the heaters. Test results are currently being studied.
The temperature measuring system in FLECHT was the object of a complete audit by Idaho Nuclear Corporation prior to the final FLECHT test. The audit was very thorough and required approximately seven days. IdahoNuclear Corporation found that the total temperature measurement system was highly reliable and the final Zircaloy test was run with no changes to the system.
*The ratio of surface area to heat capacity for a Zircaloy grid is approximately 15 times that of a heater rod, hence Zircaloy-steam reactions can lead to steeper temperature ramps in the vicinity of a Zircaloy grid.
NUCLEAR ENERGY SYSTEMS
Test Engineering
R. H. Leyse
The original copy of this report is below.
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