Molten Fuel-coolant Interaction Research Articles

The particle size distribution of solidified melt debris from molten fuel-coolant interaction experiments

The statistical distribution of debris from molten fuel-coolant interactions (MFCIs) is examined. It is shown that a wide range of fragmentation processes, including MFCIs, produce debris which has an upper limit lognormal (ULLN) distribution. Fitted distributions are presented for 20 experiments using 24 kg of uranium dioxide/molybdenum melt quenched in water.

Molten fuel-coolant interaction phenomena with application to carbide fuel safety

This paper reviews the major phases occurring during an energetic molten fuel/coolant interaction (MFCI), the categories of interaction and modes of contact between molten fuel and liquid coolant, the film boiling destabilization and collapse mechanisms, and the important fragmentation mechanisms of the melt. Two major models that describe the processes involved in an MFCI event are discussed: the spontaneous nucleation model and the pressure detonation model. Finally, the MFCI experiments involving carbide fuel and liquid sodium are reviewed and the potential for an energetic interaction between molten carbide fuel and liquid sodium is discussed. Recommendations are given for future work on MFCI phenomena relative to the carbide fuel/sodium system.

Failure Behavior of Stainless Steel Clad Fuel Rod under Simulated Reactivity Initiated Accident Condition

In-reactor experiments were performed in Nuclear Safety Research Reactor of Japan Atomic Energy Research Institute to study the failure behavior of stainless steel clad fuel rods under a simulated reactivity initiated accident (RIA) condition. A single test fuel rod with stainless steel cladding was contained in a capsule filled with water at room temperature and atmospheric pressure and irradiated by pulsing power simulating an RIA. It was revealed through the experiments that the failure mechanism of the stainless steel clad fuel rod was cladding melting, which was different from oxygen-induced embrittlement observed in the Zircaloy clad fuel rod in the same test condition, and the failure threshold energy was determined to be about 240cal/g·UO2 (–1,000 kJ/kg·UO2), which was about 20 cal/g·UO2 (–85 kJ/kg·UO2) lower than that of the Zircaloy clad fuel rod. It was also found that the mechanical energy was generated by explosive vaporization of coolant due to molten fuel-coolant interaction as a consequence of the fuel rod failure accompanying fuel pellet fragmentation at an energy deposition of nearly 380 cal/g·UO2 (–1,600 kJ/kg·UO2) or more.

State-of-the-art review on the mechanical response of fast reactor sub-assemblies in local accident conditions

A review of work on the mechanical response of fast reactor sub-assemblies (SAs) in local accident conditions has been made. The review deals with the consequences of a supposed molten fuel-coolant interaction in one SA. It covers work done in France, Germany, Italy, UK, USA and at JRC Ispra. The topics reviewed are SA design data, material properties, single SA response to internal and external loads and the response of the array of SAs surrounding the incident one. Results of static and dynamic tests on single SAs and arrays of SAs are summarised. A comparison of the predictions of theoretical methods with these test results is made. The adequacy of existing data and methods is evaluated and recommendations for further work are made.

Failure behavior of stainless steel clad fuel rod under simulated reactivity initiated accident condition.

In-reactor experiments were performed in Nuclear Safety Research Reactor of Japan Atomic Energy Research Institute to study the failure behavior of stainless steel clad fuel rods under a simulated reactivity initiated accident (RIA) condition. A single test fuel rod with stainless steel cladding was contained in a capsule filled with water at room temperature and atmospheric pressure and irradiated by pulsing power simulating an RIA. It was revealed through the experiments that the failure mechanism of the stainless steel clad fuel rod was cladding melting, which was different from oxygen-induced embrittlement observed in the Zircaloy clad fuel rod in the same test condition, and the failure threshold energy was determined to be about 240cal/g·UO2 (–1,000 kJ/kg·UO2), which was about 20 cal/g·UO2 (–85 kJ/kg·UO2) lower than that of the Zircaloy clad fuel rod. It was also found that the mechanical energy was generated by explosive vaporization of coolant due to molten fuel-coolant interaction as a consequence of the fuel rod failure accompanying fuel pellet fragmentation at an energy deposition of nearly 380 cal/g·UO2 (–1,600 kJ/kg·UO2) or more.

Fuel fragmentation and mechanical energy conversion ratio at rapid deposition of high energy in LWR fuels.

The fuel fragmentation is one of the important subjects in the field of molten fuel-coolant interaction (MFCI) since it is one of basic processes of the MFCI, and it has not yet been made clear enough. Accordingly, U02 fuel fragmentation was studied in a postulated reactivity initiated accident (RIA) condition by the Nuclear Safety Research Reactor (NSRR). The distribution of the size of fuel fragments was obtained through the experiments and the mechanism of fuel fragmentation was studied. Also, the relation between the conversion ratio of the mechanical energy to the thermal and the degree of fuel fragmentation was obtained experimentally. It was revealed that the distribution of fuel fragments was well described in the form of logarithmic Rosin-Rammler's distribution law. The fuel fragmentation was found to be explained by the Weber-type hydraulic instability model and the internal pressurization model. It was also shown that the mechanical energy conversion ratio was inversely proportional to the volu...

A description of a fuel-coolant thermal interaction model with application in the interpretation of experimental results

A coherent thermo- and hydrodynamic model to explain molten fuel-coolant interactions in the CORECT II experimental facility is described. The effects of heat losses to the surroundings, mass entrainment, two-phase frictional losses and non-condensable gases are taken into account for the coolant modelization, while a solidification-controlled fragmentation model is proposed for the fuel behavior. Interpretation of two significant experiments in the CORECT II facility permit verification of the consistency of the formulation for the behavior of the fuel-coolant couple. The interpretations allow a generalized interaction scenario in this facility to be proposed, illustrate the importance of understanding the mechanisms underlying the prefragmentation and mixing phase preceding the thermal interaction, and confirms the hypothesis that the process of solidification in the fuel is a major factor governing fuel fragmentation.

Observation of Liquid Droplet Deformation due to Liquid Jet Impact as Possible Mechanism of Molten Fuel Coolant Interaction

Observation of Liquid Droplet Deformation due to Liquid Jet Impact as Possible Mechanism of Molten Fuel Coolant Interaction

Fragmentation of molten debris during a molten fuel-coolant interaction

The potential for an energetic molten fuel-coolant interaction (MFCI) during a hypothetical core meltdown accident is of concern in nuclear safety analysis. An important aspect of a MFCI is the fine fragmentation and intermixing of molten core debris with the core coolant. The fragmentation characteristics of the molten debris (a mixture of UO 2 and zircaloy cladding) particles produced during a recent high-energy in-pile experiment are analyzed. The experimental results suggest that two mechanisms contributed to the fragmentation of the molten debris in this experiment, in which an MFCI occured. Phenomenological modelling of these two mechanisms and the effects of the governing parameters are presented.

On the primary system type of geometrical constraint in molten fuel-coolant interaction studies

On the primary system type of geometrical constraint in molten fuel-coolant interaction studies

Molten fuel-coolant interaction during a reactivity initiated accident experiment

The results of a reactivity-initiated accident experiment, designated RIA-ST-4, are discussed and analyzed with regard to molten fuel-coolant interaction (MFCI). In this experiment, extensive amounts of molten UO 2 fuel and zircaloy cladding were produced and fragmented upon mixing with the coolant. Coolant pressurization up to 35 MPa and coolant overheating in excess of 940 K occurred after fuel rod failure. The initial coolant conditions were similar to those in boiling water reactors during a hot startup (that is, coolant pressure of 6.45 MPa, coolant temperature of 538 K, and coolant flow rate of 85 cm 3/s). It is concluded that the high coolant pressure recorded in the RIA-ST-4 experiment was caused by an MFCI and was not due to gas release from the test rod at failure, Zr/water reaction, of UO 2 fuel vapor pressure. The high coolant temperature indicated the presence of superheated steam, which may have formed during the expansion of the working fluid back to the initial coolant pressure; yet, the thermal-to-mechanical energy conversion ratio is estimated to be only about 0.3%.

A quasi transient heat conduction model of heat transfer in fuel-coolant interaction in LMFBRs

In this paper, we have studied the effect of fuel temperature profile, that builds up in the fuel particles during the transient heat conduction from fuel to the coolant in the mixing zone of molten fuel-coolant interaction (MFCI) in LMFBRs, on the thermal to mechanical work energy conversion efficiency. The results have been compared with the transient heat conduction model of Cho, Ivins and Wright who assumed a linear fuel temperature profile over the fuel particles during the transient. It has been found that whereas the linear fuel temperature profile model of Cho et al. and the present model give almost similar results for smaller fuel particles with radius less than 10 μ, the results of these two models differ for bigger fuel particles. Hence, the present model of quasi-transient heat conduction which is an improvement over the linear temperature profile approximation of Cho et al. may be used when the fuel particles interacting with the cold sodium are coarse size.

Transient deformation of LMFBR cores due to local failure: Experimental and theoretical investigation

Abstract This paper describes an effort to predict the mechanical core deformation caused by local failure within an LMFBR core. These activities are intended to cover all the potential core damage possibilities currently under discussion and analysis. In particular it is shown that the reactor can be scrammed in time under pessimistic-realistic pressure transients and that the damage does not exceed tolerable limits. A special gas generator technique to simulate a fuel coolant explosion has been developed at AWRE Foulness. This has been used to perform the explosion tests needed to demonstrate the safety of the SNR 300 core. A molten fuel—coolant interaction (MFCI) experimental facility, and a drop tower to carry out sub-assembly crushing tests are described. Theoretical studies are presented which use mass-spring-dashpot, lumped parameter-hinge or micro-rigid-lumped-mass models. They simulate the crushing and bending of a single sub-assembly interacting with the coolant as well as the behaviour of a multirow “spoke” model. For the core analysis only preliminary computational results are presently available which can be compared with the full scale tests in which the fluid pressure did not exceed a “threshold” of about 100 bar. Parameter studies show the influence of pulse shape, material properties as well as the time integrator. Some of the unanswered question concern the dydrodynamic feedback of the deformations on the pressure distribution in space and time. Also the behaviour of the highly irradiation-embrittled cores is poorly understood today. Finally, an enhanced energy release package to describe the MFCI must still be added to the reactivity calculation module of a future fast reactor dynamics code.

Molten Fuel-Coolant Interaction during Hypothetical Accidents in Light Water Reactors

Molten Fuel-Coolant Interaction during Hypothetical Accidents in Light Water Reactors

Pressure waves in sodium during a fast reactor accident

The release of acoustic energy by molten fuelcoolant interaction in a fast reactor accident is described on the basis of an analytical evalutation of plane pressure waves profiles. The possibility of application and extension to curved geometries is discussed. Simple analytical expressions and graphical representations for the most important wave parameters (vaporization time, wave length, peak pressure, momentum and acoustic energy release) are given as functions of the accident conditions.

Reactor structural response to molten fuel-coolant interactions

In order to realistically determine the structural response of a liquid metal fast breeder reactor to a molten fuel-coolant interaction (MFCI), an MFCI region was incorporated into the two-dimensional, hydrodynamic containment code, REXCO-H. In this way, it is possible to account for the two-dimensional hydrodynamic response, as well as for the effect of vessels and plates, upon the expansion process in the MFCI region. The MFCI model has been extended in order to increase the usefulness of the code under a variety of conditions. The sodium equation of state has been improved using basic thermodynamic relations and recent data to incorporate temperature dependent properties. Heat transfer models available to describe the MFCI include not only a quasi-steady-state model, but also a parametric model, including the fuel heat of fusion. Nonhomogenous MFCI regions can be treated by assigning different parameters to each zone within a region, including volume fractions of fuel, sodium, steel, and void, as well as initial fuel and coolant temperatures and fraction of molten fuel. Several cases have been studied in order to delineate the effect of various parameters on the peak pressures generated in the MFCI zones. These include effect of initial fuel and coolant temperatures, void fraction, amount of molten fuel and/or vessel wall compliance. The response of a typical reactor configuration is evaluated for a given set of initial conditions.