Karlsruhe Institute of Technology (KIT)

1QUENCH (Large-scale tests on the early and late phases of core degradation)
Bundle experiments in the QUENCH facility are designed to study the early and late phases of core degradation in prototypic geometry for different reactor designs and different cladding alloys for a proper assessment of the risk posed by quenching of degraded core to full-scale power plants. The QUENCH program aims not only to determine the amount of hydrogen released during reflood of a test bundle with genuine core materials as cladding and spacer grids, but also to investigate the related high-temperature interactions of the core materials providing comprehensive data for model development and subsequent implementation into Severe Fuel Damage (SFD) computer codes.
The main component of the QUENCH test facility is the test section with the test bundle. The facility can be operated in two modes: a forced-convection mode (typical for most QUENCH experiments) and a boil-off mode. The system pressure in the test section is around 0.2 MPa absolute. The test section has separate inlets at the bottom to inject water for reflood (bottom quenching) and synthetic air (80% N2 and 20% O2) during air ingress phase. The argon, the steam not consumed, and the hydrogen produced in the zirconium-steam reaction flow from the bundle outlet at the top through a water-cooled off-gas pipe to the condenser where the steam is separated from the non-condensable gases. The water cooling circuits for bundle head and off-gas pipe are temperature-controlled to guarantee that the steam/gas temperature is high enough so that condensation at the test section outlet and inside the off-gas pipe is avoided.
The test bundle is ~2.5 m long and is made up of 21 fuel rod simulators and four corner rods. The fuel rod simulators are held in position by five grid spacers, four are made of Zircaloy-4 and the one at the bottom of Inconel 718. Except the central one all rods are heated. Heating is electric by 6 mm diameter tungsten heaters of length 1024 mm installed in the rod centre. Electrodes of molybdenum and copper are connected to the tungsten heaters at one end and to the cable leading to the DC electrical power supply at the other end. The tungsten heaters are surrounded by annular ZrO2-TZP pellets. The rod cladding of the heated and unheated fuel rod simulators is Zircaloy-4.
The test bundle is surrounded by a shroud of Zirconium-702 with ZrO2fiber insulation extending from the bottom to the upper end of the heated zone and a double-walled cooling jacket of Inconel (inner tube) and stainless steel (outer tube) over the entire length.
The off-gas including Ar, H2 and steam is analysed by a state-of-the-art mass spectrometer Balzers “GAM300” located at the off-gas pipe.
The test bundle, shroud, and cooling jacket are extensively equipped with sheathed thermocouples at different elevations with an axial step of 100 mm. There are 40 high-temperature (W/Re) thermocouples in the upper hot bundle region and 32 low-temperature (NiCr/Ni) thermocouples in the lower “cold” bundle. Other bundle thermocouples are attached to the outer surface of the rod cladding. The shroud thermocouples are mounted at the outer surface of Zircaloy-4 shroud. Additionally the test section incorporates pressure gauges, flow meters, and a water level detector.
2LIVE (Large-scale tests on behaviour of the corium melt pool)
The LIVE test facility concentrates on the investigation of the whole evolution of the in-vessel late phase of a severe accident, including e.g. formation and growth of the in-core melt pool, characteristics of corium arrival in the lower head, and molten pool behaviour after the debris re-melting in large scale 3D geometry with emphasis on the transient behaviour.
The main part of the LIVE-3D test facility is a 1:5 scaled semi-spherical lower head of the typical pressurized water reactor. The diameter of the test vessel is 1 meter. The top area of the test vessel can be covered by an insulated or a cooled lid. The test vessel is enclosed in a cooling vessel to simulate the external cooling.
The melt is prepared in an external heating furnace designed to generate 220 l of the simulant melt. The maximum temperature that can be reached in the heating furnace is limited to 1100 °C. In addition, the heating furnace is equipped with a vacuum pump; so it is possible to extract the residual melt out of the test vessel back into the heating furnace.
The volumetric decay heat is simulated by means of 6 heating planes in the test vessel. Each heating plane consists of a spirally formed heating element with a distance of ~40 mm between each winding. The heating elements are shrouded electrical resistance wires and are located in a special cage to ensure the correct positioning. To realize a homogeneous heating of the melt, each plane can be controlled separately. In the case of homogeneous heat distribution the maximum heating power is limited to ~18 kW. The maximum temperature of the heating system is limited to 1100 °C. To investigate both the transient and the steady state behaviour of the simulated corium melt, an extensive instrumentation of the test vessel is realized. The temperatures of the vessel wall inner surface and outer surface are measured to be able to calculate heat flux distributions. Additionally, up to 80 thermocouples are positioned within the vessel to measure the temperature distribution in the melt pool and in the crust. To get detailed information about the crust formation three thermocouple trees are installed at the vessel wall at different heights. A precise crust detection lance can detect the crust front and measure the crust/melt boundary temperature as well as the melt pool vertical temperature profile. Two video cameras and one infrared camera are used to visualize the convection of the melt pool.
Binary melts of KNO3–NaNO3 are selected as simulant melts for the experiments both in non-eutectic mixture of 80 mole% KNO3–20 mole% NaNO3 and in eutectic mixture of 50 mole% KNO3–50 mole% NaNO3 (eutectic temperature is 225 °C). These melts can be used in a temperature range from 220 °C (solidification) to 380 °C (chemical decomposition). Due to its solubility for water the applicability of such melts is restricted to dry conditions inside the test vessel.

3)DISCO (Large-scale tests on melt dispersion and on direct containment heating)

The DISCO experiments are designed to investigate the fluid-dynamic, thermal and chemical processes during melt ejection out of a breach in the lower head of a PWR pressure vessel at pressures below 2 MPa with an iron-alumina melt and steam. In the frame of these investigations the following issues are addressed: final location of corium debris, loads on the reactor pit and the containment in respect to pressure and temperature, and the amount of hydrogen produced and burned.
The main components of the facility are scaled about 1:18 linearly to a large PWR. The model of the containment pressure vessel has a height of 5.80 m and a total volume of 14 m³. The volumes of the reactor cooling system (RCS) and the reactor pressure vessel (RPV) are modelled by a vertical pipe. A disk holding 8 pipes (46 mm I.D., 255 mm length) separates the two partial volumes. This arrangement models the main cooling lines with respect to the flow constriction between RCS and RPV. The RPV model, mounted at the lower end of the pipe, serves as crucible for the generation of melt by a thermite reaction between iron oxide and aluminium. The total volume of the RCS/RPV vessel is 0.08 m³.The breach in the lower head is modelled by a graphite annulus at the bottom, which is closed with a brass plate. This plate melts when the thermite reaction reaches the bottom. The reactor pit is made of concrete and is installed inside a strong steel vessel. The main cooling lines are modelled by eight horizontal steel cylinders with a scaled annular space around each of them, modelling the flow path leading into the equipment rooms. The equipment rooms are modelled according to the reactor design being investigated.
The containment vessel is closed at atmospheric pressure and room temperature. In most experiments a containment atmosphere was aimed at, as it can be expected during a core melt accident, with steam and a certain hydrogen content.
The accumulator is pressurized with steam to around twice the planned initial blow down pressure. The model of the RPV contains the aluminium-iron oxide thermite. The experiment is started by igniting the thermite electro-chemically at the upper surface of the compacted thermite powder. When the pressure raise in the RPV-RCS vessel verifies that the thermite reaction has started, the valve in the line connected to the steam accumulator is opened and steam enters the RCS vessel, which is preheated to the saturation temperature of the planned burst pressure. About 3 to 6 seconds after ignition the brass plug at the bottom of the RPV vessel is melted by the 2100 °C hot iron-alumina mixture. That initiates the melt ejection. The melt is driven out of the breach by the steam and is dispersed into the cavity and beyond.
Standard test results are: pressure and temperature history in the RPV, the cavity, the reactor compartments and the containment vessel, post-test melt fractions in all locations with size distribution of the debris, video film in the sub-compartments and containment and pre- and post-test gas analysis in the cavity and the containment. The gas analysis allows determining the amount of produced, burned and remaining hydrogen.

4)HYKA((Hydrogen safety test site HYKA at the Karlsruhe Institute of Technology)

In order to investigate main consequences of ex-vessel scenario of the MCCI accident a set of facilities has been fabricated and then assembled at IKET KIT: Hydrogen Test Chamber (PZ); Safety-Vessels A1, A2, A3, A6, A8; Explosion Chambers (EC) and Shock Tubes (ST). Four Control Rooms (CR) were equipped with gas filling and data acquisition systems. The experimental facilities constituting the hydrogen test site HYKA are among the largest available in Europe. In a combination with the highest static and dynamic operating pressures, the experimental facilities are designed for unique hydrogen/steam dispersion and explosion experiments in confined and semi-confined geometries, active and passive ventilation experiments and structural analysis. Several experimental programs were performed within European, national German and international projects in collaboration with American, Korean, Chinese and Japanese participants.
Main research areas of the HYKA KIT infrastructure: Hydrogen/steam dispersion, hydrogen explosion, high pressure hydrogen releases, laminar flame velocity, flammability and self-ignition limits for hydrogen-air mixtures, structural response and integrity of metal structures to pressure loads, ventilation system efficiency.

4.1 HYKA-A2 Facility (Large Scale Hydrogen/Steam Distribution/Explosion Chamber)

The largest safety vessel A2 with main dimensions of 6 m id and 9 m height provides an empty test volume of about 220 m3. It is designed for fire and explosion tests with an operating over-pressure from -1 to 10 bar. Depending on the purpose, large specimens can be tested inside them, or the whole vessel can be used as a test volume. The vessel may be evacuated by vacuum pump or filled with inert atmosphere of nitrogen or steam and may be heated up to 150 oC. The vessel is equipped with many vents and ports for experiment and measurement set-ups as well as with windows for visual observations. It has 3 vents of 2000 mm id, 4 vents of 700 mm id, 5 vents of 400 mm id and about 40 vents of smaller inner diameters (50-250 mm). The measuring system consists of thermocouples array (gas temperature, flame arrival time); piezoelectric and piezoresistive gauges (initial pressure, explosion pressure); gas analyzer and mass spectrometer (to control mixture composition); sonic hydrogen sensors, photodiodes and ion probes (flame arrival time, flame speed), strain gauges (deformations). The data acquisition system is based on multi-channel (64) ADC with a sampling rate of 1 MHz. The vessel was successfully tested within the LACOMECO project using 2 large scale combustion experiments of hydrogen-steam-air mixture (10:25:75 = H2:H2O:air) at 1.5 bar of initial pressure and 90 oC temperature. The maximum combustion pressure was about 5 bar. Dynamics of combustion process was controlled by Background Oriented Schlieren (BOS) method combined with high speed cameras.
Main research area(s) of the infrastructure unit: Turbulent hydrogen combustion in uniform and nonuniform gas mixtures at different initial pressures and temperatures; effect of venting on flame propagation regimes; high pressure hydrogen releases, experiments on hydrogen distribution in closed volume, structural response of piping structures to internal pressure loads, bon fire testing of high pressure tanks, integrity of high pressure tanks under external and internal pressure loads.
 

4.2 HYKA-A1 Facility (Horizontal Large Scale Hydrogen Distribution/Explosion Chamber)

The vessel A1 has main dimensions of 3.5 m id and 12 m length with a volume of 100 m3. It was certified at maximum static pressure of 100 bar. The vessel may also be used as a safety vessel or filled itself with a hydrogen-air mixture at ambient conditions. A rectangular sub-compartment of 9 x 3 x 0.6 m3 may be used to study a combustion and detonation in a horizontal semi-confined layer of hydrogen air mixture. The vessel is equipped with measuring ports and windows for visual observations. The existing gas-filling system allows creating a layer of hydrogen-air mixtures with a linear vertical concentration gradient from 0.1 to 1.1 %H2/cm. It has a semi-spherical cover to open/close whole cross-section of the vessel. Combined with vessel A3, it can be used for combustion propagation tests in a multi-compartment geometry. The measuring system consists of thermocouples array (gas temperature, flame arrival time); piezoelectric and piezoresistive gauges (initial pressure, explosion pressure); gas analyzer and mass spectrometer (to control mixture composition); sonic hydrogen sensors, photodiodes and ion probes (flame arrival time, flame speed), strain gauges (deformations). The data acquisition system is based on multi-channel (64) ADC with a sampling rate of 1 MHz. The vessel was successfully tested within European LACOMECO, German GRS and Radiolysis Gas Projects even for detonation of 16 m3 of stoichiometric hydrogen-air mixture at ambient pressure and temperature.
Main research areas of the infrastructure unit: Dynamics of hydrogen stratification, turbulent hydrogen combustion in uniform and nonuniform gas mixtures at ambient conditions; flame acceleration and detonation experiments in confined and semi-confined geometries, effect of venting on flame propagation regimes; high pressure hydrogen releases, experiments on hydrogen distribution, structural response of piping structures to internal pressure loads, integrity of high pressure tanks under external and internal pressure loads, to use as a safety vessel.
      

4.3 HYKA-A3 Facility (Vertical Large Scale Hydrogen Explosion Chamber)

The vessel A3 has main dimensions of 2.5 m id and 8 m height with a volume of 33 m3. It was certified at maximum static pressure of 60 bar. The vessel may be evacuated or filled with a hydrogen-air mixture at different pressures from sub-atmospheric to several bar of initial pressure. Having a sub-volume of 11 m3 together with a system of obstructions it can be used for combustion propagation tests in a multi-compartment geometry. The existing gas-filling system allows creating nonuniform hydrogen-air mixtures with a “positive” or “negative” (related to the gravity) vertical concentration gradient from 0.1 to 1.0 %H2/m. The vessel is equipped with measuring ports and windows for visual observations. The measuring system consists of thermocouples array (gas temperature, flame arrival time); piezoelectric and piezoresistive gauges (initial pressure, explosion pressure); gas analyzer and mass spectrometer (to control mixture composition); photodiodes and ion probes (flame arrival time, flame speed). Within LACOMECO project, the vessel was successfully tested for deflagration of 33 m3 of 13% hydrogen-air mixture at ambient pressure and temperature. Effect of stratification on hydrogen deflagration was also investigated.

4.4 HYKA-A8 Facility (Middle Scale Vacuum/High Pressure Chamber)

The vessel A8 has main dimensions of 1.8 m id and 3.7 m length with a volume of 8.8 m3. It was certified at maximum static pressure of 120 bar. The vessel may also be used as a safety vessel or filled itself with a hydrogen-air mixture at different pressures from 1 mbar to 120 bar of absolute pressure. It has a semi-spherical cover to open/close whole cross-section of the vessel. Different installations and specimens as pipelines, valves and high-pressure hydrogen tanks can be put inside the vessel for testing. The vessel is equipped with measuring ports and windows for visual observations. The existing gas-filling system allows creating either inert atmosphere or hydrogen-air mixtures at different concentrations and pressures. Hydrogen, nitrogen or air injection into the evacuated or pressurized vessel may also be investigated. The measuring system consists of thermocouples array (gas temperature, flame arrival time), piezoelectric and piezoresistive gauges (initial pressure, explosion pressure), gas analyzer and mass spectrometer (to control mixture composition), photodiodes and ion probes (flame arrival time, flame speed), strain gauges (deformations). Within the F4E Fusion program, the vessel was successfully tested for air ingress into a hydrogen atmosphere and combustion at sub-atmospheric pressure of 200-800 mbar.
Main research areas of the infrastructure unit: Turbulent hydrogen combustion in uniform and nonuniform gas mixtures at different pressures; effect of venting on flame propagation regimes; high pressure hydrogen releases, experiments on hydrogen distribution, hydrogen jet combustion, structural response of piping structures, integrity of high pressure tanks under pressure loads, to use as a safety vessel for small hydrogen inventory facilities.

4.5 HYKA-PZ Facility (Ventilated Large Scale Test Chamber)

The hydrogen test chamber consists of three floors and is located in a larger building on the hydrogen test site HYKA. The ground floor contains the concrete footing of the cell floor, the second floor is the test chamber itself and the third floor houses its active ventilation system. The test chamber has an internal volume of approx. 160 m3 (8.53 m x 5.5 m x 3.3 m), so the powerful venting system that produces air flows of up to 24.000 m3/h allows exchanging its internal atmosphere two times within one minute. The air flow can be arranged to circulate around samples and both supply- and exhaust-air-system to the ambience are explosion proof. High pressure hydrogen jet release and hydrogen jet development, its ignition in a stagnant atmosphere or in presence of active ventilation is the main purpose of this facility. The integrity of the test chamber was proven in detonation experiments with up to 16 g H2, even larger amount of hydrogen (up to 64 g H2) is possible in the case of slow deflagration regime. A series of experiments on hydrogen jet fire, hydrogen vented deflagration and hydrogen releases and dispersion was performed within European Hysafe, Hyindoor, GermanIcefuel and BG Bahn projects.
Main research areas of the infrastructure unit: high pressure hydrogen releases, hydrogen dispersion, ventilation system efficiency, cryogenic hydrogen releases, combustion of hydrogen jets, vented deflagration, laminar flame velocity, flammability and self-ignition limits for hydrogen-air mixtures, structural analysis.
 

4.6 HYKA-ST (a set of shock tubes)

Several explosion tubes available at the hydrogen test site HYKA: a detonation tube with a length of 12 m and 350 mm id, a tube with a length of 8 m and 50 mm id, a tube with a length of 4 m and 25 mm id, a tube with a length of 12.2 m and 520 mm id. The last one 12.2-m tube, for instance, was delivered directly from KernkraftwerkPhilippsburg (Germany) as a real exhaust pipe for testing of the tube integrity in case of radiolysis gas explosion. Each of tubes is equipped with a gas filling system and a large number of sensor ports. The HYKA explosion tubes allow basic combustion experiments on flame acceleration and detonation transition with uniform mixtures at different initial pressures up to 1500 bar and temperatures up to 300 oC. Pipeline specimens may also be fabricated and tested with respect to integrity of pipelines under internal detonation pressure loads. The tubes in this case may be additionally equipped with strain gauges to monitor a mechanical response of the tube. The measuring system consists of thermocouples array (gas temperature, flame arrival time), piezoelectric and piezoresistive gauges (initial pressure, explosion pressure), gas analyzer and mass flow rate controller (to control mixture composition), photodiodes (flame arrival time, flame speed), strain gauges (deformations).
Main research area(s) of the infrastructure units: Hydrogen combustion and detonation, critical conditions for flame acceleration and detonation initiation in a tube geometry, mechanical response of pipelines under internal pressure loads