The objective of the PEARL program in IRSN (Cadarache, France), within the Work-Package 5 (“Corium and debris coolability”) is the validation of numerical tools to predict the consequences of the reflooding of a severely damaged reactor core where a large part of the core has collapsed and formed a debris bed, i.e. prediction of debris coolability and steam production during quenching. A step–wise experimental approach has been adopted with a preliminary program (PRELUDE) to test the performance of the induction heating system on stainless steel particles simulating debris beds and to optimize the instrumentation in a two phase flow, for a better design of the PEARL facility. The PRELUDE facility includes: a water tank for reflooding with flow measurement, a test section containing a debris bed with thermocouples, an induction furnace (coils around test device, high frequency generator), and a downstream heated vertical tube to remove steam from test section, including a steam mass flow rate device.
(Prelude facility ©2009 IRSN)
Preliminary reflooding tests involved a debris bed of 4 mm particles inside a 110mm x 100mm section, investigating the effect of inlet water velocity, power (maintained or not during the reflooding phase), and initial temperatures (up to 330°C). Additional tests were performed to evaluate the power distribution inside a larger debris bed diameter (up to 280 mm) using stainless amagnetic steel particles (the Figure below illustrates the rather well uniform specific power). This campaign ended with a heating sequence of a debris bed up to 820°C before water injection. One can remark on the Figure below the difference between thermocouples inside and outside the beads: for a same location, cooling time of particle lasts few seconds more than in the void. It can be also noticed that the cooling of the thermocouples in the bottom part of the bed is much shorter than the cooling of the thermocouples in the upper part. Thermocouples inside the debris bed offer a fine illustration of different phases of reflooding.
The results obtained so far show that the chosen technology is able to deposit a sufficient power density during the reflooding phase. Moreover the level of 920°C is reached with induction system.
The injected water flow and the steam flow rate generated during reflooding were accurately measured with adapted sensors to reach a rather good water/steam balance. Tests will continue in 2010 to qualify the pressure measurement inside the debris bed. Reflooding experiments will be performed on a homogenous debris bed up to 1000°C with 1 to 2 mm diameter particles. In parallel, PEARL facility design has been completed; construction will start in the second half of 2010, qualification being planned at the beginning of 2011 to run experiments at pressure up to 10 bar.
Contacts: Georges Repetto, Philippe March