Monday | May 15th
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Tuesday | May 16th
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Technical visit at KIT
The safety of light-water reactor (LWR) is since several years the principal topic of the NUSAFE program at Karlsruhe Institute of Technology (KIT). The Nuclear Safety Research Group is engaged in investigation of the accident relevant scenarios of LWR. KIT has a number of test facilities for research dedicated to nuclear reactor safety as well as to nuclear waste management, some of them are unique in Europe. Facilities for reactor safety include water test rigs for studies of relevant phenomena in light water reactors, a hydrogen experimental center, and large experimental facilities to investigate beyond-design basis accidents.
On May 20th, 2022, KIT offers the possibility to the participants to the ERMSAR 2022 meeting (max. 25 persons) to visit the following facilities:
The LIVE experimental platform is established to investigate the severe accident phenomena during a core melt accident in Gen- II, GEN-III and Gen-IV nuclear reactor pressure vessel (RPV). One of the Severe Accident Management (SAM) according to the Defense-in-depth strategy is to guarantee the melt retention inside the reactor vessel by flooding the vessel externally in case of a late-phase corium accident.
The investigated phenomena:
- Different patterns of corium arrival in the lower head;
- Transient behavior of debris meltdown and molten pool progression;
- Effects on combined or separated external cooling and top cooling;
- Heat transfer in a stratified melt pool;
- Influence of pool geometry on the thermos-hydraulic of the molten pool.
The experimental platform consists of melt preparation, heating supply and cooling system for three experimental facilities: LIVE3D, LIVE2D and LIVE core-catcher. Liquid simulant melt is prepared in a heating furnace, which melts solid particle and purify the liquid melt. By tilting the heating furnace, the melt is poured in one of the test vessel via a pouring spout. The whole system enables the flexibility in various melt pouring modes. Liquid melt can be extracted back to the heating furnace at the end of one experiment. All the test vessels are equipped with volumetrically distributed resistant heating system mimic the internal heat source of the core melt. The test vessels can be cooled with water externally and at the top surface.
LIVE3D and LIVE2D test vessels
One purpose of the two facilities is to investigate the influence of the geometry on the thermo-hydraulic and heat transfer at the top and wall boundary. Due to the different sidewall to the top surface area ratio between the two geometries, the relation of the heat transpfer rate at top surface to the wall boundary is shifted. This effect influence in return turbulent pattern, temperature distribution and heat flux distribution. A special purpose of LIVE2D facility is the direct observation of the turbulent pattern and the crust change of a stratified melt pool which has a high tendency on the heat flux focusing effect in the upper layer.
- Oxide liquid melt: eutectic KNO3-NaNO3 mixture with melting point at 222 °C; non-eutectic mixture of 20 mol. % NaNO3 – 80 mol. % KNO3 with liquidus temperature at 285 °C; Water
- Liquid metal in a stratified pool: a thermal oil with the operational temperature up to 240 °C
- Debris: nitrate particles, granite particles and ZrO2 rich ceramic beads
LIVE-Core Cather for SFR reactors
In-vessel Core-catcher design is implemented in many sodium fast reactors (SFR) to protect the reactor vessel and to distribute the liquid melt. The new test facility, ESFR-LIVE, is concepted explicitly to study the heat transfer of the melt and the dissolution of the refractory wall material in the core catcher. The new facility adopts the geometry of core-catcher sidewall design. The inner diameter of the vessel in the cylinder part is 1 m. The height of the truncated crone part is 8 cm with inclined angle of 20°, and the total height of the cylindrical upper part is 30 cm. The test vessel is made of 15 mm stainless steel. A cooling vessel encloses the test vessel and forms a cooling channel with 6 cm width at the bottom and at the side wall. An existing cooling lid is applied to the top surface cooling.
Four planes of heating elements inside the vessel provide maximum 112 kW simulating the internal heat source of core material. With this power density certain scenarios of debris dryout can be realized. The LIVE-Core catcher is flexibly in cavity height and geometry by means of:
- By shutdown the lower heating elements, bottom crust grows upwards and reduces the height of the liquid pool in the lower part
- The heating elements in the cylinder part can be removed, enabling top cooling lid at a lower position
- The heating system can also heat solely axial central region, and thus it is interesting to study a debris bed in conic form or cylinder form.
The melt is prepared in an external heating furnace designed to generate the simulant melt. The cylindrical furnace is 0.58 m in diameter and 1 m in height, and has a volume of 270 liter. The maximum temperature that can be reached to 900 °C. Solid nitrate particles are charged in at the top of the furnace, and are gradually melt and heated up to a designed melt pour temperature, which can be kept till a test begins. The impurities inside the solid nitrate salt are burnout during the heating process. The heating furnace is hold by a framework which can be driven in axial direction and be tilted. The pouring operation is started by tilting the heating furnace. Melt is discharged into the test vessel via a heated pouring spout. In addition, the heating furnace is equipped with a vacuum pump, so it is possible to extract the residual liquid melt out of the test vessel back into the heating furnace. The already purified melt can be reused for the next experiment. In addition, the crust inside the test vessel is uncovered after extraction of liquid melt, and is therefore available for the post-test measurement and analysis.