Target Curve with Maintenance Time in Optimal Xenon Shutdown Problems

A series of sparger tests have been conducted to investigate the performance of a steam sparger, which will be used in a Korean Advanced Power Reactor, APR1400. The tests have been conducted at the Blowdown and Condensation Loop in the Korea Atomic Energy Research Institute using a prototypic steam sparger. The major test parameters include amount of air mass and air temperature in the discharge line, valve opening time, steam mass flow rate, and water temperature and level in the In-Containment Refueling Water Storage Tank. The hydrodynamic loads induced by the air clearing phenomenon during typical operating conditions seem to be dependent on the valve opening time, steam mass flow rate, submergence of a sparger, and distance between the sparger and the structure. The effect of the amount of air mass in the discharge line and the water temperature to the peak load seems to be negligible for a given range of parameters. The hydrodynamic load induced by the prototypic steam sparger was less than those expected in a BWR and the steam sparger tested in this program can be used satisfactorily for the APR1400.     

喷洒器蒸汽浸没射流汽羽长度实验研究

以孔径分别为4、10、16 mm的侧开孔I型喷洒器为实验件,对质量流速为300~1100 kg·m?2·s?1的饱和蒸汽浸没在温度为35~65℃的过冷水中的直接接触式冷凝开展实验研究。结果表明:孔径不变时,汽羽贯穿长度基本随蒸汽质量流速和池水温度的升高而增大;大孔径喷洒器的汽羽长度与直管式喷嘴的汽羽长度接近,拟合值与实验值的偏差在±15%以内;小孔径喷洒器的汽羽长度明显低于直管式喷嘴,拟合值与实验值的偏差最高达80%;采用收缩喷管流量公式对蒸汽质量流速进行修正,拟合值与实验值的偏差在±20%以内,由实验值拟合的新关系式的预测误差在±10%以内。      

PWR safety/relief valve blowdown analysis experience

The paper describes the difficulties encountered in analyzing a PWR primary loop pressurizer safety relief valve and power operated relief valve discharge system, as well as their resolution. The experience is based on the use of RELAP5/MOD1 and TPIPE computer programs as the tools for fluid transient analysis and piping dynamic analysis, respectively.General approaches for generating forcing functions from thermalfluid analysis solution to be used in the dynamic analysis of piping are reviewed. The paper demonstrates that the “acceleration or wave force” method may have numerical difficulties leading to unrealistic, large amplitude, highly oscillatory forcing functions in the vicinity of severe flow area discontinuities or choking junctions when low temperature loop seal water is discharged. To avoid this problem, an alternate computational method based on the direct force method may be used. The simplicity and superiority in numerical stability of the forcing function computation method as well as its drawback are discussed.Additionally, RELAP modeling for piping, valve, reducer, and sparger is discussed. The effects of loop seal temperature on SRV and PORV discharge line blowdown forces, pressure and temperature distributions are examined. Finally, the effects of including support stiffness and support eccentricity in piping analysis models, method and modeling relief tank connections, minimization of tank nozzle loads, use of damping factors, and selection of solution time steps are discussed.     

Supercritical water heat transfer in vertical tubes: A look-up table

A new procedure for the prediction of wall temperatures in vertical tubes has been established in the framework of the development of the High Performance Light Water Reactor (HPLWR). The prediction of the wall temperature is accomplished by a look-up table for heat transfer in supercritical water. The look-up table lists the wall temperatures as a function of mass flux, heat flux, pressure, tube diameter, and bulk enthalpy. Based on an extended literature survey, experimental data for different conditions of upward flows in vertical smooth tubes are selected. To exclude data which exhibited local, buoyancy driven effects, a criterion of Jackson for deterioration of heat transfer is used to remove these data from further processing. An interpolation method is applied to assemble the tabulated grid points, based on published correlations for heat transfer in supercritical water. The look-up table covers a mass flux range of 700–3500 kg/m² s, a heat flux range of 300–1600 kW/m², a pressure range of 22.5–25 MPa, a diameter range of 8–20 mm and a bulk enthalpy range of 1200–2700 kJ/kg. Extreme combinations which required extrapolation of the data are excluded. The accuracy of the table in the vicinity of the pseudo-critical point is significantly higher than published correlations.     

CFD simulation of steam jet-induced thermal mixing in subcooled water pool

This study examined the IRWST thermal mixing phenomena induced by a steam jet in a subcooled water pool. Due to the limitation of the current CFD code to simulate condensation, the steam condensation region model was developed to evaluate the thermal mixing phenomena. Within this region, all the steam was condensed into water, and the steam mass and energy inputs were treated as the source. This calculation was treated using single-phase CFD methods. The benchmark calculation for a thermal mixing experiment in the water tank was performed to develop an optimized 3D evaluation methodology of the thermal-hydraulic behavior in APR1400 IRWST. Steam discharge through the sparger and condensation phenomenon was modeled with the choking flow and thermal mixing model in the quenching tank using CFX11.Three types of thermal mixing experiments, local phenomena test, thermal mixing tests in cylindrical water pool and annulus water pool, were designed to provide data representative of the behavior of the prototype for CFD simulations of the thermal-hydraulic behavior in IRWST. A comparison of the calculated and experimentally measured temperature profiles showed some disagreement particularly around the sparger. The main reason for this disagreement was caused by the difference in the test and simulating conditions at the tank wall. However, moving away from the sparger, the trends of the temperature rise became similar to that in the experiment. Despite these problems, this model is the best way of evaluating the thermal mixing phenomena caused by a steam jet in a subcooled water pool.     

Core concept of a passive-safety fast reactor “METAL-KAMADO” and reactivity coefficients

New concept of a passive-safety simple fast reactor “METAL-KAMADO” with metallic fuels is presented, which has same concept as a passive-safety thermal reactor “KAMADO”. A fuel element of the “METAL-KAMADO” consists of metallic fuel (U–10%Zr) and cooling holes of He gas flow. These fuel elements are located in a reactor water pool of atmospheric pressure (0.1 MPa) and low temperature (<60 °C). In case of LOF, decay heats of fuel elements are removed by natural heat transfer from surfaces of the fuel elements to the reactor water pool.

Preliminary neutronic calculations of the “METAL-KAMADO” show possibility of high burn-up of more than 120 GWd/t with 10% enriched U–Zr fuel. Reactivity coefficients of the core are also discussed.     

某核电止回阀开启过程中的瞬态流动与结构特征

为研究某核电止回阀在开启过程中的流动特征与部件的力学特征，采用商用计算流体动力学软件ANSYS Fluent和用户自定义函数（UDF），模拟了该阀门在高压工况下开启过程中的内部流动。在不同开度条件下采用流固耦合方法对阀门部件的力学行为进行了模拟，分析了阀体及阀芯的应力分布及变形情况。结果表明，随着阀门开度增大，过流断面的喉部与阀门出口出现高速区域；阀门入口段呈现较高的压力梯度；阀体上的最严重变形出现在喉部，变形量随开度变化呈现波动趋势；最大等效应力出现在阀门入口弯管处且最大等效应力随开度增加而减小；阀芯的最大变形量出现在靠近进口的一侧；最大等效应力出现在阀芯与弹簧接触区域，其随开度的增加呈现波动增长趋势。      

Mechanism of dynamic strain aging and characterization of its effect on the low-cycle fatigue behavior in type 316L stainless steel

Low-cycle fatigue tests were carried out in air in a wide temperature range from 20 to 650 °C with strain rates of 3.2 × 10⁻⁵–1 × 10⁻² s⁻¹ for type 316L stainless steel to investigate dynamic strain aging (DSA) effect on the fatigue resistance. The regime of DSA was evaluated using the anomalies associated with DSA and was in the temperature range of 250–550 °C at a strain rate of 1 × 10⁻⁴ s⁻¹, in 250–600 °C at 1 × 10⁻³ s⁻¹, and in 250–650 °C at 1 × 10⁻² s⁻¹. The activation energies for each type of serration were about 0.57–0.74 times those for lattice diffusion indicating that a mechanism other than lattice diffusion is involved. It seems to be reasonable to infer that DSA is caused by the pipe diffusion of solute atoms through the dislocation core. Dynamic strain aging reduced the crack initiation and propagation life by way of multiple crack initiation, which comes from the DSA-induced inhomogeneity of deformation, and rapid crack propagation due to the DSA-induced hardening, respectively.     

Experimental Investigation of the Steam Condensation Phenomena due to a Multi-hole Sparger

KAERI has performed a series of steam condensation tests to assess the performance of a unit cell sparger that will be used in the APR1400 reactor. A simplified I-sparger was used for the steady state steam condensation tests to study the characteristics of the condensation phenomena due to a multi-hole sparger and to provide test data for a code development and verification. A range of steam mass fluxes for the steady state condensation tests were selected to define the transition region from the condensation oscillation regime to the stable condensation regime. Condensation loads and a variation of the frequencies of the pressure waves due to a steam condensation are analyzed. In addition, the local temperature distribution near the sparger discharge holes is discussed and a condensation regime map for a multi-hole sparger has been suggested.     

百万千瓦级压水堆严重事故卸压阀高温瞬态分析

由于核电厂严重事故的恶劣工况,在卸压过程中严重事故卸压阀门可能会经历阀门无法承受的高温瞬态而导致不可用。本文在可能导致高压熔堆的事故序列中筛选出具有一定的包络性并包含各种典型严重事故现象的典型严重事故序列。针对该事故序列考虑严重事故管理中的开阀时间范围开展了高温瞬态计算,并针对重要的影响因素阀门开启时刻的稳压器水位开展分析。最终确定了百万千瓦级核电厂具备典型性及一定包络性的严重事故卸压阀工作条件,并得到了阀门开启前后阀门可能经历的最高流体温度及流体温度变化曲线,为严重事故卸压阀门的设备鉴定及功能应用提供了重要基础。      

An analytical study of the dynamics and stability of a spring loaded safety valve

Spring loaded self-actuating safety valves are employed as part of the overpressure protection systems in various industrial applications. In order to design and predict their performance it is necessary to study the dynamic behavior of the valve over a range of fluid and system conditions. A one-dimensional model has been developed to study the effects of different valve parameters such as the spring-mass characteristics, geometry of internal parts, adjustment ring settings, bellows etc. which influence the dynamic behavior and stability of the valve. Analytical results for steam flow conditions are presented to demonstrate the relative effects of these parameters on the valve opening time, maximum lift, blowdown (upstream pressure differential between the valve opening and closing) and any oscillations of the valve stem. If the valve is not properly backpressure compensated, it may become unstable as the stagnation pressure at the valve inlet decreases. Lowering of the guide adjustment ring position or raising the nozzle adjustment ring generally results in improved stability, shorter valve opening time, higher lift and longer blowdown. The effect of damping on the valve stability is also demonstrated. The model can be used to evaluate the design of safety valves and damping devices to eliminate unstable valve dynamic behavior.     

The effect of ageing temperature and time on the mechanical properties of Fe-NiCrMo alloys with different contents of δ ferrite

Laboratory cast alloys with 2–27% of δ ferrite were aged for up to 17,520 h in the temperature range 290–350 °C. Tensile and Charpy tests were performed at 22 and 290 °C on specimens aged for different times, and the microhardnesses of both constituents of the microstructure were determined for the alloy with 27% of δ ferrite. The effects of the content of δ ferrite, the ageing and testing temperature, and the ageing time on mechanical properties and notch toughness are presented and discussed.     

大型先进压水堆非能动冷却水箱关键热工水力特性研究综述

第3代大型先进压水堆设置非能动余热排出系统，包括大容积高位水箱及其内置的非能动余热排出热交换器(PRHR HX)和自动降压系统（ADS）喷洒器，在运行过程中呈现出复杂的气液两相热工水力现象和独特的传热、传质特性。近年来随着非能动安全系统工程需求和相关研究的兴起，国内外开展了一些针对大容积非能动冷却水箱及其内置关键部件热工水力特性的相关研究，本文对上述问题的研究现状进行综述。对于PRHR HX，评价特殊C型管束在单相自然对流、两相沸腾条件下的传热特性，分析经典传热模型及改进经验关联式的适用性；对于ADS 1~3级喷洒器高温高压蒸汽喷放冷凝过程，综合分析其喷放冷凝流型、特征参数、冷凝换热系数等关键传热、传质特性。以上研究大幅丰富了第3代大型先进压水堆大容积水箱的设计理论，并进行了实际工程应用。本文在此基础上，对相关研究未来发展方向进行展望。     

一种阀门排放分析验证方法的研究

以稳压器快速卸压截止阀为例，研究一种饱和蒸汽下阀门排放量的分析验证方法。将小开度、低压差下的阀门排放试验数值与理论计算数值对比，表明偏差在可接受范围内；将此试验数值带入推导公式，得到全开度、全压差下的阀门排放量；与ANSYS分析的全开度下排放量对比，发现实际推导排量与理论计算排量偏差为2.73%。研究结果表明，在试验能力不足情况下，可以采用小开度低压差的排放试验结合理论推导的方式分析阀门饱和蒸汽下的排量。      

A study on the boron injection initiation temperature curve of BWR

Boron injection initiation temperature (BIIT) provides important information for the safe shutdown of the reactor using boron injection system during anticipated transient without scram (ATWS). The purpose of this paper is to study BIIT curve of boiling water reactor owners’ group (BWROG). The unreasonable and non-conservative parts of BIIT are pointed out and suggested modifications are made. The starting reactor power of BIIT is increased in order to meet the actual application. The lower limit of suppression pool temperature of BIIT is revised for conservative operation during ATWS conditions. Analysis of the effects of maximum temperature capacity of the suppression chamber and concentration of boron in standby liquid control tank shows that BIIT is decreased by adopting a more conservative value of maximum temperature capacity of the suppression chamber. Consequently, early boron injection is anticipated. For system with automatic boron injection system, BIIT is not required.     

Temperature dependence of the chemical sputtering of amorphous hydrogenated carbon films by hydrogen

The temperature dependence of chemical erosion and chemical sputtering of amorphous hydrogenated carbon films due to exposure to hydrogen atoms (H⁰) alone and combined exposure to argon ions and H⁰ was measured in the temperature range from 110 to 950 K. The chemical erosion yield for H⁰ alone is below the detection limit for temperatures below about 340 K. It increases strongly with increasing temperature, goes through a maximum around 650–700 K and decreases again for higher temperatures. Combined exposure to Ar⁺ and H⁰ results in substantial chemical sputtering yields in the temperature range below 340 K. In this range the yield does not depend on temperature, but it increases with energy from about 1 (eroded carbon atoms per impinging Ar⁺ ion) to about 4 if the ion energy is increased from 50 to 800 eV. For temperatures above 340 K the measured erosion rates show the same temperature dependence as for the H⁰-only case, but they are higher than for H⁰-only. The difference between the Ar⁺ and H⁰ and the H⁰-only cases increases monotonically with increasing ion energy.     

A study of the effects of the location of flashing inception on maximum and minimum critical two-phase flow rates:: Part II: analysis and modelling

A general unified model is developed to predict one-component critical two-phase pipe flow. An extension of the Henry [Henry, R.E., 1970. The Two-Phase Critical Discharge of Initially Saturated or Subcooled Liquid. Nucl. Sci. Eng. 41, 336-342.] and Henry and Fauske [Henry, R.E., Fauske, H.K., 1970. The two-Phase critical Flow of One-Component Mixtures in Nozzles; Orifices and Short Tubes, ASME J. Heat Transfer, May 1970.] models to incorporate the effects of wall friction and the location of flashing inception is proposed. Modelling of the two-phase flow is accomplished by describing the evolution of the flow between the location of flashing inception and the exit (critical) plane. The model approximates the nonequilibrium phase change process via thermodynamic equilibrium paths. Included are the relative effects of varying the location of flashing inception, pipe geometry, fluid properties and length to diameter ratio. The model predicts that a range of critical mass fluxes exist and is bound by a maximum and minimum value for a given thermodynamic state. This range is more pronounced at lower subcooled stagnation states and can be attributed to the variation in the location of flashing inception. The model is based on the experimental study of critical two-phase flow rates of saturated and subcooled water through long tubes given in Part I of this work. In that study, the location of flashing inception was accurately controlled and adjusted through the use of a new device. The data obtained revealed that for fixed stagnation conditions, the maximum critical mass fluxes occurred with flashing inception located near the pipe exit; while minimum critical mass fluxes occurred with the flashing front located further upstream. The results of the present study, as well as available data since 1970 are compared with the model predictions. These data cover a wide range of conditions and include test section L/D ratios from 25 to 302 and a temperature and pressure range of 110-280°C and 0.16-6.9 Mpa, respectively. The predicted maximum and minimum critical mass fluxes show an excellent agreement with the range observed in the experimental data.     

The effect of impurities on TL emission wavelengths of NaCl crystals

We report emission spectra during thermoluminescence of NaCl crystals doped with Eu, Sr, Ca, Cr and Ni impurities. Crystals were irradiated at ambient temperature with X- or γ-rays prior to measurement. Isometric plots in the wavelength range 200–800 nm reveal only small differences in patterns of TL emission for pure samples and samples doped with Eu, Sr and Ca. However samples doped with Cr and Ni show significant variations characterized by suppressed emission between 390 nm and 520 nm. This is discussed in terms of the efficiency of colouration of the crystals and the state of aggregation of impurity–vacancy dipoles.     

Analysis of charge-exchanged neutral particles during IBW heating in the HT-7 tokamak

The charge-exchange neutral particles fluxes and energy distribution in IBW heated plasma were investigated in the HT-7 tokamak. The RF frequency was 30 MHz and with an injecting power up to 200 kW. It is observed that the plasma performance is obviously enhanced by IBW heating. The electron temperature was increased by 0.5 keV and the central line averaged electron density was doubled. The neutral particle fluxes of high-energy increased and the bulk ions were heated during IBW heating. The ion temperature was increased by 0.3 keV and the ion heating efficiency of (2–3) eV kW⁻¹ × 10¹³ cm⁻³ was achieved. The velocity distribution of charge-exchanged neutral particles appears to be Maxwellian without high-energy tail ions up to the maximum RF power.     

Pressure and Fluid Oscillations in Vent System due to Steam Condensation, (I)

Pressure and fluid oscillation in vent tubes and a header induced by steam condensation were measured with a test apparatus. Pressure oscillation consists of low-, middle- and high-frequency components. The frequencies measured in the present apparatus are around 2–8Hz, 15 Hz and 100–150 Hz for low, middle and high frequency respectively. The chugging phenomenon occurs in a certain range of steam flow rate. When the amplitude of fluid oscillation becomes maximum, the amplitude of pressure oscillation in the header also becomes maximum. High frequency component is predominant in the pressure oscillation in vent tubes. When the temperature of pool water becomes lower, the amplitude becomes larger. As the temperature of pool water gets higher, high-frequency component of pressure oscillation disappears, and middle, low frequency in order. Based on the experimental facts mentioned above, the theoretical analysis was conducted by considering the header as one volume and by modeling chugging as one-dimensional motion of water column in and out of vent tubes. As the result, the characteristics of chugging phenomenon got in the experiment coulbd well be simulated. Chugging phenomenon, accompanying back flow of water into vent tubes, is a kind of low-frequency oscillation which is predominant in the pressure oscillation in the header.