Sodium Fire Research Articles

F134 ナトリウム燃焼で発生したエアロゾル雰囲気中での 3 次元透過解析

A method to estimate optical properties of sodium oxide aerosol is developed. They are used to solve the radiative heat transfer problems in a system with aerosol generated by sodium fire. For the purpose, three-dimensional radiative transfer in an absorbing-scattering media is solved by the Monte Carlo method. The Mie's scattering theory is used to handle particle scattering during the analysis. By comparing the experimental results of the intensity and the angular distribution of the transmitted energy with the analyzed results obtained by assuming the complex index of refraction, it is shown that the value if the complex refractive index can be estimated.

815 高速炉における複合現象の数値実験技術開発 : (2) ナトリウム・酸素燃焼反応と伝熱流動

Numerical methodology for sodium combustion has been developed for the safety evaluation of a liquid metal cooled fast reactor. The methodology includes fast-running zone model computer program, field model program for multi-dimensional thermalhydraulics, chemical reaction analysis program based on chemical equilibrium theory, and so forth. Phenomenological scale in sodium fire varies widely and it is impossible to deal with all the scales in one simulation. Therefore, multi-level modeling and detailed-level simulations develop numerical correlations that can be used in the zone model or field model codes. Simulations using numerically-derived correlations are effective way of safety analysis. Although the sodium combustion is a complex phenomenon, use of these computer programs gives better understanding of the coupled thermalhydraulics and chemical reaction.

545 Na火災時のエアロゾル雰囲気中の1次元ふく射伝熱解析(OS26 火炉内の伝熱・燃焼シミュレーション)(OS26 火炉内の伝熱・燃焼シミュレーション)

545 Na火災時のエアロゾル雰囲気中の1次元ふく射伝熱解析(OS26 火炉内の伝熱・燃焼シミュレーション)(OS26 火炉内の伝熱・燃焼シミュレーション)

ナトリウム燃焼実験と火災事故例の概観および安全防護への考察

Summaries are described on the sodium combustion experiments conducted by HEDL (F1, F2, F4, F5), KfK, Cadarashe (IGNA 402 & 2002, IGNA 3602 & 3604), the former PNC, etc. The sodium fires of Almeria Solar Plant and ILONA Test Facility are taken up as the examples of large-scale accidents. Fast breeder reactor (FBR) safety considerations are discussed, with attentions paid to the integrity of steel liner and sodium-concrete reaction, in relation to the secondary sodium leakage of MONJU. The author suggests that injection of nitrogen gas is an effective measure against sodium fires, suppressing the temperature rises, chemical reactions and also surely excluding a hydrogen explosion in case of sodium-concrete reaction.

An Empirical Model For Upward Flame Spread Over Vertical Flat And Corner Walls

Ignition and extinguishment of sodium fires was investigated in air diluted by nitrogen using a coaxial burner. Oxygen concentration and temperature were changed from 0.5% to 21% and from 110oC to 700 oC, respectively. In undiluted air, ignition occurred near the crust of sodium oxides at temperatures below 600oC. At temperatures higher than 625oC, ignition was observed in a vapour layer and a conical diffusion flame appeared on a sodium pool at 700oC. The flame was observed for only one second after the ignition before a dense cloud from burning sodium obscured vision. In this study, the lowest ignition temperature of sodium was 115oC under an air flow rate of 5 L/min. There were extinguishing limits of oxygen concentrations for burning sodium. The limits decreased linearly with increasing sodium temperature up to a temperature of 700oC. Anomalous ignition was found in a region of oxygen concentrations lower than the limits. One example was an observed ignition occurring in the region of oxygen concentrations below 3% and temperatures above 400oC. The ignition was observed on the crust of sodium oxides after relatively long induction periods, but no stable combustion followed. Another anomaly was re-ignition of a cooled combustion residue exposed to fresh air. Such ignition was even observed below 50oC. The oxidized sodium prepared in a low oxygen atmosphere also ignited at the same temperature. Both types of anomalous ignition were attributed to production of sodium peroxide. Thus, the extinguishment of sodium fires by nitrogen requires consideration of methods to block the production of sodium peroxides.

Sodium Fire Code SFIRE1C for Pool Fire Characteristics

Sodium pool fire code, SOFIRE II, written for the constant value of stoichiometric combustion ratio and heat of reaction is used to compute the buildup of pressure and temperature in a containment. In the SOFIRE II model, for the formation of a mixture of Na2O and Na2O2 in the sodium pool, the input stoichiometric combustion ratio and heat of formation values need to be varied to corresponding values admissible for the mixture. In the present work, the SOFIRE II one-cell model is revised and the present version SFIRE1C (Sodium FIRE 1 Cell model) accounts for the formation of Na2O in an early stage of the fire and shifts to the formation of Na2O2 at a later stage. Thus SFIRE1C computes in a more realistic manner the reaction products which are formed in the pool. The model for sodium oxide aerosol release is also modified in this version, by incorporating a more appropriate aerosol release rate equation. The calculated values using the SFIRE1C one-cell model are compared with sodium pool fire experimental results.

Sodium Fire Code SFIRE1C for Pool Fire Characteristics.

Sodium pool fire code, SOFIRE II, written for the constant value of stoichiometric combustion ratio and heat of reaction is used to compute the buildup of pressure and temperature in a containment. In the SOFIRE II model, for the formation of a mixture of Na2O and Na2O2 in the sodium pool, the input stoichiometric combustion ratio and heat of formation values need to be varied to corresponding values admissible for the mixture. In the present work, the SOFIRE II one-cell model is revised and the present version SFIRE1C (Sodium FIRE 1 Cell model) accounts for the formation of Na2O in an early stage of the fire and shifts to the formation of Na2O2 at a later stage. Thus SFIRE1C computes in a more realistic manner the reaction products which are formed in the pool. The model for sodium oxide aerosol release is also modified in this version, by incorporating a more appropriate aerosol release rate equation. The calculated values using the SFIRE1C one-cell model are compared with sodium pool fire experimental ...

Sodium Pool Combustion Codes for Evaluation of Fast Breeder Reactor Safety

For the evaluation of thermal consequences of a sodium leak accident in the auxiliary buildings of the LMFBRs, the sodium pool combustion codes SOFIRE-MII, ASSCOPS and SPM have been developed. In SOFIRE-MII and ASSCOPS, assumptions are made that the combustion occurs at a pool surface, and the process is controlled solely by the turbulent oxygen transfer from atmospheric gas to the pool surface. Combustion heat is dissipated by turbulent and radiation heat transfers to the gas and surrounding walls. On the contrary, a flame over the pool is modeled in SPM, in which the combustion is controlled by sodium vapor and oxygen supplies by the diffusion from the pool surface and the turbulent mass transfer from the atmospheric gas, respectively. These codes were validated using experimental results obtained in the large-scale sodium fire test facilities; SAPFIRE (PNC, Japan) and FAUNA (KfK, Federal Republic of Germany). The comparison revealed that agreements between the codes and the test results are reasonably well.

Turbidimetric determination of caesium in contaminated sodium fire residue

A rapid and accurate method with high reproducibility for the turbidimetric determination of caesium in contaminated sodium fire residue, with use of an ultraviolet-visible spectrophotometer, has been developed. In this method, sodium tetraphenylborate was used as an analytical reagent to produce stable turbidity arising from the formation of caesium tetraphenylborate, which has very low solubility. In order to standardise the test conditions, various parameters affecting the analytical scheme were investigated.

Fast breeder reactor building, severe accident loading and ultimate capacity

The accident loading of the SNR-300 containment is different from that of an LWR due to the different containment concept, • - sodium as coolant, which can cause energetic reactions • - additional design measures against loads resulting from an HCDA Accidental release of sodium, radioactive materials and/or decay heat result in pressure and temperature rise in the containment. Due to the temperature rise of the concrete structures stress and deformation analysis is often necessary. Heated concrete releases water or steam which has to be separated from the Na-leakage by a steel lining and by a relief system to avoid chemical reactions with additional energy and gas release. The additional assumption of safety system failures as the core catcher, the steel lining, the reventing system, the energy supply, the barriers between inner and outer containment alone or still in combination for risk analysis can lead to physical and chemical phenomena as sodium fires, water release from heated concrete, sodium—water reactions, sodium boiling, core concrete interactions or sodium—concrete interactions. An acceptable best estimate evaluation of the resulting loads and consequences can only be realized by application of computer codes as CONTAIN or CACECO, which mostly respect the coupling of all involved phenomena.

Morphological analysis and evaluation of dynamic shape factor of particles produced in a real scale sodium fire

Morphological analysis and evaluation of dynamic shape factor of particles produced in a real scale sodium fire

Thermal degradation behaviour of sodium fire extinguishant powder

Although liquid sodium has proved to be a technologically superior and economically viable coolant in the heat-exchange circuits of fast reactors, it is fraught with the serious problems of fire hazards in the event of accidental leakages into the ambient air. For the rapid and effective suppression of sodium fires, sodium bicarbonate has emerged as a potential extinguishant. This paper attempts a description of the thermal decomposition behaviour of sodium bicarbonate fine powder in vacuum on the basis of thermogravimetry and differential thermal analysis. The analog percentage mass change data, transformed into dimensionless extents of reaction and calculated rates of reaction, are then analysed by a generalized computational technique. The results indicate that the most probable rate-controlling step is a process of three-dimensional contraction of the bicarbonate particle surface, with activation energyE=82.94 kJ mol−1 and frequency factorA=34.73×106 s−1. The decomposition temperature of sodium bicarbonate shows an upward trend with increasing heating rate.

Sodium Aerosol Behavior in Liquid-Metal Fast Breeder Reactor Containments

A tripartite consortium DEBENE (Deutschland-Belgium-Netherlands), Japan, and France studied the sodium evaporation process of aerosols in a sodium fire. In an inert atmosphere, experimental and theoretical condensation rates were compared and indicated sodium hydride (NaH) to be the foreign nucleus for mist formation. In a normal atmosphere, the physicochemical characteristics of the aerosols produced by a sodium fire and their evolution in containment or in the environment were determined; models enabling the various countries to achieve harmonious results were derived. The proper functioning of the components, guaranteeing perfect operation during and after a sodium fire accident, was tested.

Consideration of turbulent deposition in aerosol behaviour modelling with the contain code and comparison of the computations with the fauna 2 sodium fire experiment

Consideration of turbulent deposition in aerosol behaviour modelling with the contain code and comparison of the computations with the fauna 2 sodium fire experiment

Experimental determination of the dynamic shape factor of the primary sodium peroxide aerosol

A hypothetical accident in a fast breeder reactor could cause aerosols to be generated in a sodium fire. The computer codes relating to the modelization of these accidents make it necessary to use various input parameters, among which is the dynamic shape factor κ of the aerosols produced. This study concerns the shape factor of sodium peroxide; the divergence of the values of this parameter given in the literature justifies the usefulness of our work. We have tried to use the simplest method possible for this experiment. The dynamic shape factor is proportional to the ratio of the equivalent volume diameter to the aerodynamic diameter for a given particle. Therefore, these two quantities must be determined. A centrifuge enables classification of the particles as a function of their aerodynamic diameter; the equivalent volume diameter of the particle thus selected can then be determined by assessing the mass (neutron activation) and the number (electron microscope) on the same sample of particles. Our results show that the dynamic shape factor of the sodium peroxide submicronic particles generated by a fire is nearly 1 and that the values of this parameter increase with the size of the particles.

Development of Analytical Model for Sodium Pool Combustion

An analytical model for sodium pool combustion has been developed and verified by experiments. The model can be used to analyze sodium fire accidents in LMFBRs. It features a layer of sodium vapor between the flame and the sodium pool surface which functions to resist heat transfer. Results obtained with the model show: combustion rate increases with oxygen concentration, sodium pool temperature and gas pressure, but it decreases with in-creases in gas temperature. Calculated combustion rates agree within 15% of the experimental results.

Development of analytical model for sodium pool combustion.

An analytical model for sodium pool combustion has been developed and verified by experiments. The model can be used to analyze sodium fire accidents in LMFBRs. It features a layer of sodium vapor between the flame and the sodium pool surface which functions to resist heat transfer. Results obtained with the model show: combustion rate increases with oxygen concentration, sodium pool temperature and gas pressure, but it decreases with in-creases in gas temperature. Calculated combustion rates agree within 15% of the experimental results.

Sodium fires and aerosols. Behavior of radioiodine.

Release of 131I associated with burning of contaminated Na, decay of airborne concentration of the released 131I and the size distribution of aerosols referred to radioiodine are investigated in experimental runs conducted on laboratory scale. These investigations are carried out in conjunction with similar investigations for the Na matrix. An experimental chamber (5.4 m3) is used for burning a small pool of Na (–50 g) containing spiked 131I (40–500 μCi). Values of the specific activity ratio, viz. the ratio of the concentration of 131I in the aerosol Na to that in pool Na lay in the range of 0.9×10−2—5.7×10−2 at pool temperatures of about 300°C. The concentration decay half-time and the aerosol size distribution characteristics referred to 131I remain similar to those applicable to the Na content of the aerosols. Surface concentrations of 131I in the residues examined differ from the bulk concentrations (calculated) in the pool and are lower by a factor of −20. The concentrations of 131I in the aerosols released are further lower than the surface concentrations in the residues by a factor of −2.

Investigation of a commercially available chemical powder for extinguishing liquid metal pool fires

Commercially available dry chemical powder (sodium bicarbonate based) was tested exhaustively on deep pool and medium scale pool fires. The efficacy of this powder was evaluated by comparing the quantity of powder required per unit weight of sodium and the quantity of powder required per unit surface area of sodium fire. Carbon monoxide levels were also measured. These investigations conclusively indicate the potential of this powder.

Characterization of sodium fire aerosols in the aerodynamic range by means of an inertial spectrometer

Characterization of sodium fire aerosols in the aerodynamic range by means of an inertial spectrometer