Clogging of industrial pleated high efficiency particulate air (HEPA) filters in the event of fire

The IRSN and AREVA NC are currently conducting a common interest fire research programme with the aim, among other things, of improving knowledge of clogging of high efficiency particulate air (HEPA) filters and developing an empirical model for clogging of such filters by combustion aerosols. This model must - insofar as possible - be independent of the nature of the fuel and be able to be integrated in a calculation code covering the interaction between the ventilation and the fire. This paper discusses the influence of various “direct” factors such as the filtration velocity, the mass of deposited aerosol per filter area, the diameter and morphology of the combustion particles, the condensate content of the aerosols, and “indirect” factors such as the air flow feeding the fire and its oxygen content, which influence the evolution of the aeraulic resistance of a clogged filter.     

钠冷快堆钠雾火事故三维数值模拟

针对钠冷快堆可能发生的钠雾火事故,开发和研制了一套用于钠火事故分析,能求解发生钠雾火事故后,事故空间3维的气体温度分布和化学成份分布的程序。本文详细介绍了分析求解钠雾火的燃烧模型和热传输模型,以及计算空间流场采用的计算方法和步骤,并将计算结果与试验值进行了比较：结果表明,二者符合较好。     

The ignition and burning behaviour of sodium metal in air

A review has been made of the ignition and combustion of sodium, both in terms of the fundamental chemistry and also with reference to its use as the heat transfer fluid of a fast breeder reactor. In the discussions of both the combustion chemistry and the scientific mechanisms of possible fire extinguishants comparisons are made with the burning of hydrocarbon fluids. A large part of the review is devoted to the considerable amount of quantitative data produced by various agencies in the world in their pursuit of commercial fast reactor technology. Both practical and theoretical studies have been carried out, some on a large scale, mainly in the field of spray fires and pool fires. Vapour combustion is briefly discussed as is the subject of passive and active fire extinction and possible corrosion damage to structures. Some suggestions are made as to which areas are adequately understood and which areas need significant further work in the context of sodium cooled fast reactors.     

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.     

Performance of High Efficiency Particulate Air Filters

To examine the performance of the high efficiency particulate air (HEPA) filter, demonstration tests were done in various conditions, such as; normal condition, high temperature and earthquake condition, using conventional deep-pleat filters, 610- × 610- × 292-mm in size.

The authors found that the HEPA filter acted efficiently enough in various conditions supposed in the air purification system of a nuclear plant. Some empirical formulae were proposed to express the performance of the filter.

The test results were summarized from these three points: (1) decontamination factor (DF) of intact filters, (2) mechanical strength and (3) pinholes, because these three points are important criteria in evaluating the performance of HEPA filter systems.     

Spent fuel transportation risk assessment: cask fire analyses

Abstract

The US Nuclear Regulatory Commission has recently completed an updated Spent Fuel Transportation Risk Assessment, NUREG-2125. This assessment considered the response of three certified casks to a range of fire accidents in order to determine whether or not they would lose their ability to contain the spent fuel or maintain effective shielding. The casks consisted of a lead shielded rail cask that can be transported either with or without an inner welded canister, an all steel rail cask that is transported with an inner welded canister, and a DU shielded truck cask that is transported with directly loaded fuel. For the two rail casks, large pool fires that were concentric (fully engulfing), offset from the casks by 3 m, and offset from the cask by 18 m were analysed using the computational fluid dynamics CAFE-3D fire modelling code coupled with the finite element analysis PATRAN-Thermal heat transfer code. All of the fires were assumed to last for 3 h. In addition to these extraregulatory fires, the regulatory 30 min fire was analysed using both the regulatory uniform 800°C boundary condition and the more realistic CAFE-3D fire modelling code. For the truck cask, only the engulfing fire case was analysed using a 1 h fire duration. In all of the fire analyses, the seal region of the cask stayed below the failure temperature; therefore, there would be no release of radioactive material. In addition, the temperature of the fuel rods stayed below their burst rupture temperature, providing another barrier to release. For the lead shielded cask, very severe fires cause some of the lead to melt. There is no leak path for this molten lead to exit the shield region, but its expansion during the melting and subsequent contraction due to solidification during cool down results in a reduction in gamma shielding effectiveness.     

Certification test for Safety of New Fuel Transport Package (Fire Test)

Abstract

Fire tests of actual transport systems for both BWR type and PWR type new fuel assemblies were carried out to clarify their safety margin, create a public perception of the transport programme and offer a data base to verify analytical codes. The supposed scenario of traffic accidents was considered by first reviewing them to select the plan of this work. Next, heating tests of simulated fuel rod elements and fuel assemblies of 1 m length were conducted in an electric furnace to examine their deformation and oxidisation behaviour under high temperature conditions. An analytical code including a simple model was verified by comparison with data obtained in a furnace test simulating a fire accident. Furthermore, simulated fuel assemblies and actual containers of both BWR and PWR types were manufactured. Actual 11 ton trucks carrying them were put in a burn pit 5 m in width, 11·5 m in length and 0·5 m in depth. The fire tests were carried out by burning kerosene for 30 min. These experimental results were analysed by the code.     

钠冷快堆中喷雾钠火的计算分析

根据钠冷快堆中喷雾钠火的特点建立了理论模型，编制了SSPRAY程序。该程序模拟钠喷雾燃料过程中钠滴的运动、钠和氧气的燃烧反应、热量传递和质量传递等瞬态过程。用该程序计算了气体和墙壁温度、气体压力、氧气摩尔份额、喷雾流燃烧速率和热量热递速率等主要参数。利用AI实验数据和美国SPRAY－3A的计算结果对程序进行了验证，结果符合较好。     

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。     

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.     

核通风净化系统泄漏率检测试剂替代研究现状

概述了核通风净化系统中的高效过滤器和碘吸附器泄漏率检测所用DOP和R-11试剂的替代研究及应用状况,并对国内展开此方面研究提出了建议。     

The aerosol release factor for Pu as a consequence of an ion exchange resin fire in the process cell of a fuel reprocessing plant

One of the upper limit accidents usually considered in the safety analysis of a fuel reprocessing plant is an accidental explosion, followed by a fire, of an ion exchange column containing resin loaded with large quantities of plutonium. In such accidents, a certain fraction (release factor) of Pu is released in the form of an aerosol into the ventilation system, and finally to the environment through HEPA filters and the stack. The present study was undertaken to determine the aerosol release factor for Pu in the process cell of a typical fuel reprocessing plant.Geometrically similar scaled-down models of three different sizes were built, and suitably scaled-down quantities of resin loaded with thorium in nitric acid medium were burnt in these model cells. Thorium was used in place of Pu because of its physical and chemical similarities with Pu. The release factor was obtained by comparing the amount of Th in air with the total. The study also dealt with aerosol characteristics and kinematics of process of fire.The aerosol release factors for the three models were found to lie in the range 0.01–0.07%, and varied non-monotonically with model size. The analysis of scaled down results in conjunction with simplified aerosol modelling yielded the release factor for the actual cell conditions as 0.012% with an upper limit value of 0.1%. The particle size analysis based on Th-radioactivity and particle-mass indicated nonuniform tagging of Th to aerosol particles. These particles were irregularly shaped, but not as long chain-like aggregates.The study proposes, with a reasonable degree of conservatism, the release factor of 0.1% for such fires, and aerosol parameters, AMAD and σ_g, as 2 μm and 2 respectively. However, for situations significantly different from the present one, the release factor of 1% recommended by the American National Standards Institute may be used with a greater degree of confidence in the light of the present work.     

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.     

Investigating the burning characteristics of electric cables used in the nuclear power plant by way of 3-D transient FDS code

Burning characteristics of electrical cables are one of the key parameters for the fire hazard assessment of nuclear power plants (NPPs) since the cables are the essential sources of fire in the plants. A three-dimensional (3-D) transient computational fluid dynamics (CFD) code_FDS is adopted in this paper to simulate these characteristics related to the cable burning. Being one of the NRC licensing fire codes, the FDS includes the thermal-hydraulic equations, the turbulence model and the chemical combustion model, etc. In order to assess the CFD fire models used in this code, a burning test using the control cable with the outer jacket of polyvinylchloride (PVC) and the inner insulation of cross-linked polyethylene (XLPE) is conducted. The measured parameters associated with the burning characteristics include the heat release rate (HRR), O₂ depletion, and CO and CO₂ production, etc. Except the amount of O₂ consumption, the predicted transient behaviors of other parameters can reproduce the measured data. Based on the chemical combustion model in the FDS code, this discrepancy may be essentially resulted from the default value of hydrogen fraction (H_frac) contained in the soot since the soot yield for the burning of PVC material is high enough that the uncertainty in the H_frac value has a prominent effect on the amount of O₂ consumption. This explanation can be confirmed by a benchmark calculation for simulating a burning test with the polymethylmethacrylate (PMMA) fuel of low-soot yield. The present simulation works can provide the useful information for the plant staff or the researcher as they would perform the fire hazard analysis in the NPPs using the FDS code.     

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     

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.     

An investigation of containment pressurization by sodium spray fires

An investigation of the sodium spray burning phase of LMFBR hypothetical low probability core disruptive accidents (HCDAs) has been undertaken in order to test the response of various containment designs. The HCDAs are produced by arbitrarily inserting unrealistically large amounts of reactivity in a short period of time. The spray fires result from a HCDA which causes head failure due to high-velocity impact by the sodium pool followed by rotating plug jump, loss of rotating plug seals, control rod ejection, failure of instrument tubes, or breach of in-vessel transfer machine ports. Head failure can in principle lead to the injection of significant amounts of sodium into the reactor containment building by residual pressure of the HCDA gas bubble, which forces the upper plenum sodium through the interstitial spaces (e.g., rotating plug gaps, control rod housings, etc.) in the breached head structure.Calculations were made of the hydraulic behavior of the sodium under various injection scenarios for both pool and loop reactor systems. In the case of plug jump, although massive amounts of sodium can be injected into the containment building, the injection will be primarily in a radial direction, and the major consequences could be a low-intensity pool fire rather than a high-intensity sodium spray fire. However, if the bearing housing on the rotating plug fails, a 20 atm initial HCDA residual bubble pressure has the potential for injecting a sodium stream through the rotating plug gaps which could potentially impact the containment building ceiling. Sodium discharges through broken control rod housings could also impact the ceiling and become widely dispersed.The SOMIX-1 sodium spray fire code was used to calculate the energy releases corresponding to a variety of head failure scenarios corresponding to the cases where a high velocity jet impinges on the ceiling of the containment building. The calculated maximum pressure rise was about 2.1 atm. The analysis showed that containment building pressures do not always increase with increasing sodium injection rates since the oxygen concentration can be reduced to a level where the spray begins to cool rather than heat the gas.     

钠雾火试验结果及与雾火程序计算的比较分析

钠雾火试验在一个体积为2.4 m~3的封闭容器内进行,用于分析雾状钠火的热动力学后果。250℃的液态钠在电磁泵的驱动下经过直径为2.4mm的喷头呈液滴喷出形成雾状钠火,喷头与容器底部的距离为1.35m,钠喷射流量约14.85g/s,喷射持续78s,试验测得容器内的气体在78s时达到最高压力41kPa,113s时达到最高温度190℃。将试验数据和利用基于雾状钠火计算程序(NACOM)编制的计算程序计算得到的数据进行了对比和分析。结果表明:当将钠喷射的流量修正为3.83g/s、容器壁的总传热系数修正为9.6 W/(m~2·K)时,钠喷射期间,计算压力大于试验压力,钠喷射结束后,计算的压力变化曲线和试验所得的压力变化曲线吻合较好;而计算所得的温度曲线和试验测得的温度曲线有较大差异,理论上容器内的温度在第78s时达到最大值303℃,分析认为是因为热电偶测量的温度存在滞后现象。