Experimental study on combustion characteristics of sodium fire in a columnar flow

In the operation of the sodium-cooled fast reactor, the accident caused by the leakage and combustion of liquid sodium is common and frequent in sodium-related facilities. This paper is based on an experimental study of sodium fire in a columnar flow, which was carried out to focus on the burning characteristics by analyzing the temperature fields in the burner. The injection of 200 °C liquid sodium with the flux of 0.5 m³/h was poured into a 7.9 m³ volume stainless steel cylindrical burner to shape a sodium fire, and the data of temperature fields in the burner have been collected by dozens of thermocouples which are laid in the combustion space and sodium collection plate. These results show that the sodium fire in a columnar flow is composed of the foregoing centered columnar fire, the subsequent spray fire caused by atomization and the pool fire on the collection plate. The temperature close to the burning sodium flow maximally reaches up to 950 °C. The radial temperatures apart from the sodium flow are relatively low and generally about 200 °C, and maximally just 300 °C even when close to the sodium collection plate. The maximum temperature of the burning sodium dropping on the collection plate rises in the center of plate, about 528 °C. This study is helpful to evaluate the combustion characteristics, formation process and composing forms of the sodium fire in the sodium-related facilities.     

Experimental study on characteristics of sodium fire in a columnar flow with discontinuous injections

In the operation of the sodium-cooled fast reactor, the accident caused by the leakage and combustion of liquid sodium is common and frequent in sodium-related facilities. In this paper, an experiment Harbin Engineering University-Sodium Columnar Fire 4 (HEU-SCF4) is carried out to focus on the combustion characteristics in a discontinuous columnar flow. Liquid sodium (250°C) with the flux of about 1.0 m³/h was injected into a 7.9 m³ stainless steel cylindrical test chamber twice to shape the sodium fire in a columnar flow with discontinuous injections. The temperature, pressure data, and heat release rate in the test chamber were acquired and analyzed. It is found that each injection would cause a peak of space temperature, and it takes much shorter time to reach temperature peak in the second injection than the first injection. The peaks of pressure and heat release rate caused by the second injection are much higher than those caused by the first injection. This study is promising to evaluate the combustion characteristics of sodium fire in a columnar flow with different injection forms in the sodium-related facilities.     

Potential results of spray and pool fires

The studies on sodium pool inflammation have been conducted in a 3161 vessel, and those on sodium pool fires in three facilities: 4, 22 and 400 m³. The influence of the following parameters has been studied: sodium temperature, combustion area, humidity in the atmosphere and oxygen concentration. The experimental results have been used to validate the FEUNA code. The experimental studies on sodium spray fires have been conducted in a 3.7 m³ vessel. The experimental results have been used to validate a sodium spray fire computer code: PULSAR.     

Numerical prediction of fire extinguishment characteristics of sodium leak collection tray in a fast breeder reactor

Sodium leak collection tray (LCT) is an efficient passive device used for the extinguishment of liquid sodium fire in case of an accidental leakage from the secondary circuit of a fast breeder reactor. The LCT essentially isolates the leaking sodium into closed containers where the resulting fire is extinguished due to limited availability of oxygen. The current work aims to highlight the combustion extinguishment characteristics of LCT through a lumped formulation by conserving the mass and energy of liquid sodium and constituent gases in various parts of the LCT. Here, the complex hydrodynamics of liquid sodium is emulated through a semi-analytical draining/sloshing model and its burning rates are predicted through a three-dimensional open pool combustion model for the tray region and a closed pool combustion model for the holdup vessel. These simulations evaluate the burning rates at discrete levels of liquid sodium which are subsequently interpolated to establish correlations involving instantaneous liquid levels and oxygen concentration. Using the correlations obtained from the draining and combustion models, the overall lumped formulation directly predicts the un-burnt sodium recoverable after the extinguishment of fire in the LCT. The predicted results of this model compare well with the available experimental data.     

钠冷快堆中池式钠火的计算分析

文章论述了根据池式钠火的特点建立了理论模型 ,编制了SPOOL程序。该程序模拟钠燃烧过程中钠和氧气的化学反应 ,钠燃烧热在各种介质中不同方式的传递 ,钠气溶胶的产生、沉积 ,以及在各种通风条件下多种介质的质量和能量交换等瞬态过程 ,描述了钠燃烧过程中各种特征参数随时间的变化。其主要的计算参数包括房间内气体的压力和温度、房间建筑结构的温度、钠气溶胶质量浓度等等。用俄罗斯别洛雅尔斯克核电站实验和法国卡桑德拉 3号实验的数据 ,对SPOOL程序进行验证的结果表明 ,该程序的计算结果可信。该程序为国内钠冷快堆中池式钠火事故的安全分析提供了分析方法     

雾状钠火钠滴燃烧比率的模拟及应用

将雾状钠火中钠滴的燃烧分成预燃阶段和燃烧阶段,利用雾状钠火程序计算得到钠滴燃烧比率和时间的关系曲线,分别用幂函数、指数函数和线性函数对曲线进行拟合,拟合效果较好。拟合函数中包含钠滴下落时间和钠滴最大燃烧比率等参数,这些参数可通过钠滴下落燃烧试验或雾状钠火程序计算得到。通过推导得到了雾状钠火燃烧和单个钠滴燃烧的关系,钠滴燃烧比率的拟合函数被用来模拟雾状钠火燃烧的过程,包括用于计算已燃烧的钠质量、空气中未燃烧的钠质量、进入钠池的钠质量和雾状钠火的燃烧速率。当雾状钠火燃烧过程中钠泄漏流量恒定不变时,空气中未燃烧的钠质量和钠泄漏流量呈正比,雾状钠火的燃烧速率和钠泄漏流量呈正比。雾状钠火的燃烧速率和钠火造成的事故工艺间内的温度与压力变化直接相关。雾状钠火的燃烧速率被用来求解钠气溶胶的生成速率、钠燃烧火焰层和空气之间的传热、钠燃烧火焰层和墙壁之间的传热。总之,使用简单的函数模拟钠滴的燃烧比率曲线,将雾状钠火燃烧当成事故工艺间的热源和钠气溶胶源作为输入,便可模拟雾状钠火的整个燃烧过程,计算得到工艺间温度、压力和钠气溶胶浓度的变化。钠滴的燃烧比率曲线、雾状钠火的燃烧速率曲线还可与试验数据进行对比验证后作为雾状钠火模拟的输入,这种模拟方法可用于钠火事故安全分析中雾状钠火的模拟。     

Validation study of computer code sphincs for sodium fire safety evaluation of fast reactor

A computer code sphincs solves coupled phenomena of thermal hydraulics and sodium fire based on a multi-zone model. It deals with an arbitrary number of rooms, each of which is connected mutually by doorways and penetrations. With regard to the combustion phenomena, a flame sheet model and a liquid droplet combustion model are used for pool and spray fires, respectively, with the chemical equilibrium model based on the Gibbs free energy minimization method. The chemical reaction and mass and heat transfer are solved interactively. A specific feature of sphincs is detailed representation of thermalhydraulics of a sodium pool and a steel liner, which is placed on the floor to prevent sodium-concrete contact. The authors analyzed a series of pool combustion experiments, in which gas and liner temperatures are measured in detail. It has been found that good agreement is obtained and the sphincs code has been validated with regard to pool combustion phenomena. Further research needs are identified for pool spreading modeling considering thermal deformation of steel liner and measurement of pool fluidity property as a mixture of liquid sodium and reaction products. The sphincs code is to be used mainly in the safety evaluation of the consequence of a sodium fire accident in a liquid metal cooled fast reactor as well as fire safety analysis in general.     

池式钠火事故下燃烧产物气溶胶行为研究

在钠冷快堆的安全评估中,分析钠泄露导致的池式钠火事故下燃烧产物的气溶胶行为尤为重要。本文采用将池式钠火燃烧模型与气溶胶动力学模型耦合的方式,开发了池式钠火事故下燃烧产物气溶胶行为分析程序REBAC-SFR,基于该程序模拟了SAPFIRE-D1和ABCOVE池式钠火实验,并与实验数据进行了对比。结果表明,本文开发的程序具有良好的可靠性和正确性,可为钠工艺间内池式钠火事故下燃烧产物气溶胶行为分析研究提供理论工具。      

基于FDS程序的钠火事故情景模拟技术研究

钠火是钠冷快堆的典型事故,钠火事故情景计算机模拟仿真是对钠火事故风险评价的有力工具。本文以常规火灾三维计算流体力学软件FDS为平台,增加钠火燃烧模型,包括燃烧热模型、燃烧速率模型、喷射液钠粒径分布模型等,完成了钠火情景模型的开发,并通过与SPHINCS钠火试验和计算结果的温度分布与氧气含量对比,验证了模拟技术和模型开发方案的可行性。本文的研究成果能为后续钠火仿真模拟程序的开发提供研究基础和经验参考。     

Sodium Fire Accident Scenario Simulation Technology Study Based on FDS Code

Sodium fire is a typical accident of sodium-cooled fast reactor. Simulation of sodium fire accident scenario by software is a powerful tool for risk assessment of sodium fire accident. In this paper, the conventional fire three-dimensional computational fluid dynamics software FDS was used as a platform to add a sodium fire combustion model, including combustion heat model, combustion rate model, spray liquid sodium particle size distribution model, etc., and complete the development of sodium fire scenario modeling analysis program. And through the comparison with SPHINCS sodium fire test and calculation results, the feasibility of the method and development plan was verified. The research results of this paper can provide the research basis and experience reference for the development of the subsequent sodium fire simulation program.     

钠滴氧化燃烧特性的实验研究

液态钠泄漏和燃烧是钠冷快堆在运行中一多发的常见事故。本文主要针对液态钠滴在不同初始温度(140~370℃)和氧浓度(4%~21%)条件下的氧化燃烧行为进行实验研究。实验通过1套钠滴燃烧装置和高速摄像机使钠滴的氧化燃烧行为可视化。实验结果表明:钠滴的初始温度和氧浓度越低,钠滴表面产生的柱状氧化物越长;在相同氧浓度条件下,钠滴初始温度越高,越易着火燃烧;钠滴初始温度在200℃以下时很难点燃,当有扰动破坏了表面的氧化层结构时,钠滴也会逐渐燃烧;钠滴初始温度在140~370℃的条件下,氧浓度≥12%时,钠滴能燃烧充分,最高温度基本可升至600~800℃;氧浓度12%时,燃烧并不充分,燃烧的最高温度均在600℃以下。这些结果对柱状流及雾状钠火的研究有重要的指导意义。     

Effect of ventilation procedures on the behaviour of a fire compartment scenario

This contribution presents a study on the consequences of applying ventilation procedures during a fire scenario involving a TPH/TBP pool fire in a ventilated enclosure. This research is addressed to fire safety in the nuclear industry in which ventilated enclosures remain a configuration frequently encountered. This work presents experiments comprising a 300 kW liquid pool fire in a 400 m³ vessel connected to an industrial ventilation system featuring one inlet and one exhaust branch. The investigated ventilation procedures consist in closing the inlet branch only or closing both inlet and exhaust branches. The analysis compares fire behaviour with and without the implementation of a ventilation procedure and points out the effects of said procedures on the combustion rate, fire duration and gas temperature within the vessel. It highlights pressure variations within the vessel when both the inlet and exhaust ventilation branches are closed. Conclusions provide practical answers that would be useful when designing appropriate ventilation strategies limiting fire hazards.     

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.     

A numerical study of radiation heat transfer in sodium pool combustion and response surface modeling of luminous flame emissivity

A response surface model of the luminous flame emissivity of sodium pool fire has been proposed for use in safety analysis computer codes of a liquid metal fast reactor. The liquid sodium burns in air resulting in not only heat generation but also release of sodium oxide aerosols of sub-micron diameters. Aerosols levitating in air are radiative and they influence the allocation of combustion heat from the flame to atmospheric gas or sodium pool. The emissivity of the flame needs to be quantified, as it is one of user-specified parameters of the computer codes for the sodium fire analysis. The response surface model of the flame emissivity is developed based on numerical experiments on the physics of mass and heat transfer and behavior of the aerosol. Thermal-hydraulic equations have been solved coupled with aerosol dynamics and chemical reaction. Three influential variables on the emissivity are identified as pool temperature, gas temperature and oxygen molar fraction in the air. It has been found that the emissivity is calculated reasonably as a function of the three variables. The proposed response surface model can be easily employed in the sodium fire analysis codes because it is a simple quadratic expression. For the safety evaluation of the sodium fire, combined use is recommended of the proposed model and the lumped-mass zone model code.     

Response Surface Modeling of Aerosol Release Fraction in Sodium Pool Combustion

A response surface model has been proposed to evaluate an aerosol release fraction during sodium pool fire in a liquid metal fast reactor (LMFR). Air containing aerosols are radiative and they influence the allocation of combustion heat from the flame to atmospheric gas or sodium pool. Hence, the aerosol release fraction needs to be quantified based on the behavior of the aerosols and physics of mass and heat transfer. However, the aerosol release fraction is one of user-specified parameters of computer codes for the sodium fire safety analysis of the LMFR. In the present study, a response surface model of the aerosol release fraction has been developed based on numerical experiments of aerosol dynamics. For developing the model, aerosol dynamic equation has been solved coupled with thermal-hydraulics and chemical reaction. The authors obtained good agreement of the aerosol release fraction between the numerical experiments and the past experiments. Therefore, the aerosol behavior model has been validated with regard to the pool combustion phenomena and is reasonably applicable to the numerical experiment. Three influential variables on the release fraction are identified as pool temperature, gas temperature and oxygen molar fraction in the air. The proposed response surface model is a quadratic expression of the influential variables and can be easily employed in the sodium fire analysis code.     

钠冷快堆混合钠火程序开发

钠管道泄漏继而发生钠的燃烧为钠冷快堆特有的事故。在喷雾钠火模型和池式钠火模型基础上,将钠喷雾燃烧和池式燃烧进行了耦合,并针对钠冷快堆钠工艺间的结构特点,最终开发了混合钠火计算程序COMSFIRE。使用该程序计算了FAUNA喷雾钠火试验和CADARACHE池式钠火试验,并与试验结果和部分程序计算结果进行了对比。同时设计了混合燃烧算例,并使用该程序与CONTAIN-LMR程序进行了对比。通过计算结果的对比和分析,初步验证了程序的正确性。     

CONTAIN-LMR程序中池式钠火事故分析计算模型的验证

CONTAIN-LMR是针对以液态钠为冷却剂的反应堆而开发的安全壳事故一体化分析程序。我国目前的CONTAIN-LMR程序版本为2000年左右从法国引进,还未进行过面向工程设计的系统性地程序开发和验证。本文主要针对CONTAIN-LMR程序中模拟池式钠火事故的分析模型进行详细分析,并采用国际上的池式钠火实验进行验证,实验验证结果表明CONTAIN-LMR程序可以较准确地模拟池式钠火事故造成的钠工艺间内的温度、压力升高及放射性钠气溶胶行为。本文的研究结果初步表明CONTAIN-LMR程序可用于钠冷快堆的钠火事故分析。     

Development of Sodium-cooled Fast Reactor Sodium Combined Fire Code

Sodium fire caused by sodium pipe leakage is the specific accident for sodium-cooled fast reactor. Based on the sodium spray fire model and sodium pool fire model, sodium spray fire and sodium pool fire were coupled together. A sodium combined fire code COMSFIRE was finally developed based on the structure characteristic of sodium technology room in sodium-cooled fast reactor. FAUNA sodium spray fire experiment and CADARACHE sodium pool fire experiment were calculated with the developed COMSFIRE code, the results of which were compared with the experiments results and some other code results. A combined fire case was designed, and the results were compared with CONTAIN-LMR code. The correctness of the COMSFIRE code was primarily proved through the comparison and analysis.     

Combustion of wood equipping package shock absorbers: after regulatory fire test

According to IAEA regulation, type B packages are designed to withstand a fire test following the mechanical tests, simulating accident conditions during transport. The wood of the shock absorber located near the damage zones produced by these tests may ignite and the conditions of air accessibility inside the absorber could mean that wood smouldering persists during the cooling period. IRSN has conducted an experimental study in which a real scale shock absorber specimen has been exposed to a large scale heptane pool fire test. A dedicated facility makes it possible to simulate the thermal power of the package contents and to measure in real time the heat transfer at the rear surface of the absorber. After a pool fire of 35 min duration, wood combustion continued for four days. Significant values were measured on the contact surface between lid and shock absorber for heat flux (up to 8 kW m^?2) and temperatures (reaching 460°C). The impact of wood smouldering induced heat fluxes on typical lid gaskets has also been evaluated.     

Validation study of computer code for sodium fire safety evaluation of fast reactor

A computer code solves coupled phenomena of thermal hydraulics and sodium fire based on a multi-zone model. It deals with an arbitrary number of rooms, each of which is connected mutually by doorways and penetrations. With regard to the combustion phenomena, a flame sheet model and a liquid droplet combustion model are used for pool and spray fires, respectively, with the chemical equilibrium model based on the Gibbs free energy minimization method. The chemical reaction and mass and heat transfer are solved interactively. A specific feature of is detailed representation of thermalhydraulics of a sodium pool and a steel liner, which is placed on the floor to prevent sodium–concrete contact. The authors analyzed a series of pool combustion experiments, in which gas and liner temperatures are measured in detail. It has been found that good agreement is obtained and the code has been validated with regard to pool combustion phenomena. Further research needs are identified for pool spreading modeling considering thermal deformation of steel liner and measurement of pool fluidity property as a mixture of liquid sodium and reaction products. The code is to be used mainly in the safety evaluation of the consequence of a sodium fire accident in a liquid metal cooled fast reactor as well as fire safety analysis in general.