一维特征线法中子输运程序开发及验证

为探讨两维/一维综合法堆芯分析方法,本文基于特征线法研制了一维中子输运程序--PEACH-1D.不同于通常的平源近似特征线方法,PEACH-1D可对子区的中子源项作线性近似;程序运用指数函数插值表和渐近源外推技术来加速计算过程.相关数值结果表明,PEACH-1D具有很高的计算精度和效率,线性源近似的特征线法具备处理较粗网格的能力,值得推广.     

Small break loch experiments and verification of CANAC-II code

Scaled experiments on small break, loss-of-coolant accidents have been conducted. The tests simulated loss-of-coolant accidents (LOCAs) resulting from a 0.53% and a 0.13% communicative break in the cold leg and the pressurizer power operated relief valve (PORV). The thermal-hydraulic behavior such as natural circulation and reflux condensation cooling during a small break LOCA has been investigated.

A new computer program CANAC-II (a Computer Analysis Program of Natural Circulation for multi-loop systems) has been developed and verified based upon comprehensive tests. A drift flux model was applied for two-phase flow in CANAC-II. It also has a shorter computer running time than the real time.     

Vectorization and parallelization of a production reactor assembly code

In order to efficiently use new features of supercomputers, production codes, usually written 10 – 20 years ago, must be tailored for modern computer architectures. We have chosen to optimize the CPM-2 code, a production reactor assembly code based on the collision probability transport method. Substantional speedups in the execution times were obtained with the parallel/vector version of the CPM-2 code. In addition, we have developed a new transfer probability method, which removes some of the modelling limitations of the collision probability method encoded in the CPM-2 code, and can fully utilize parallel/vector architecture of a multiprocessor IBM 3090.     

Vectorization and parallelization of a production reactor assembly code

In order to efficiently use new features of supercomputers, production codes, usually written 10 – 20 years ago, must be tailored for modern computer architectures. We have chosen to optimize the CPM-2 code, a production reactor assembly code based on the collision probability transport method. Substantional speedups in the execution times were obtained with the parallel/vector version of the CPM-2 code. In addition, we have developed a new transfer probability method, which removes some of the modelling limitations of the collision probability method encoded in the CPM-2 code, and can fully utilize parallel/vector architecture of a multiprocessor IBM 3090.     

Development of efficient Krylov preconditioning techniques for multi-dimensional method of characteristics

Two techniques are proposed in the preconditioning for the Krylov sub-space method called the Generalized Minimal RESidual (GMRES) method to accelerate inner iterations based on the method of characteristics (MOC). The GMRES method is an iterative method to solve a linear algebraic system byminimizing the norm of the residual vector. The proposed preconditioning technique is based on the first flight collision probability which is efficiently made by the multi-dimensional MOC code. To simplify the preconditioner, slight couplings among regions are ignored by considering the mean free path. And another proposed technique makes simplified preconditioner by the scaling matrix which can homogenize and de-homogenize the fuel region and the cladding region. The scaling technique reduces the size of the matrix and also reduces the calculation time of inverse matrix. Numerical results show that the preconditioner simplified by the mean free path efficiently reduces the number of iterations for the GMRES algorithm. And the scaling technique keeps the efficiency of preconditioner even in the multi-dimensional geometry. The total calculation time is found to be reduced when these techniques are employed.     

二维MOC的CMFD加速计算模块开发与验证

DRAGON程序中的二维特征线法(MOC)计算模块包含多种加速方法,但加速效率很高的粗网有限差分(CMFD)加速算法并未得到应用。为提高DRAGON程序中现有的二维MOC计算模块的计算效率,开发了CMFD加速计算模块并探究其收敛稳定性。运用C5G7-2D基准题验证所开发的CMFD加速计算模块,验证结果表明,所开发的CMFD加速计算模块与DRAGON程序中原有的加速模块相比具有很高的计算效率,较同类计算程序OpenMOC有更好的收敛稳定性。     

Improvement of HYCA3D code and experimental verification in rectangular geometry

Concerns about the local hydrogen behavior in a nuclear power plant (NPP) containment during severe accidents have increased with the 10CFR50.34(f) regulation after TMI accident. Consequently, investigations on the local hydrogen behaviors under severe accident conditions were required. An analytical model named HYCA3D was developed at Seoul National University (SNU) to predict the thermodynamics and the three dimensional behavior of a hydrogen/steam mixture, within a subdivided containment volume following hydrogen generation during a severe accident in NPPs. In this study, the HYCA3D code was improved with a steam condensation and spray model, and verified with hydrogen mixing experiments executed in a SNU rectangular mixing facility. Helium was used to simulate hydrogen in both the calculations and the experiments. The calculation results show good agreement with the experimental data.     

基于GPU并行的二维时空中子动力学MOC程序开发及验证

目前特征线方法（MOC）被广泛应用于反应堆精细中子输运计算。为提高基于MOC方法的时空中子动力学输运计算效率,本文开发了ALPHA程序的动力学计算模块,实现了基于GPU并行的二维精细动力学输运计算。同时,实现了基于GPU并行的CMFD加速计算,并对TWIGL基准题和MINI-CORE基准题进行验证。数值结果显示,基于GPU并行的中子动力学计算方法能保证良好的计算精度,且具有明显的加速效果。     

Development of multicomponent vaporization/condensation model for a reactor safety analysis code SIMMER-III: Theoretical modeling and basic verification

It is believed that the numerical simulation of thermal-hydraulic phenomena of multiphase, multicomponent flows in a reactor core is essential to investigate core disruptive accidents (CDAs) of liquid-metal fast reactors. A new multicomponent vaporization/condensation (V/C) model was developed to provide a generalized model for a fast reactor safety analysis code SIMMER-III, which analyzes relatively short-time-scale phenomena relevant to accident sequences of CDAs. The model characterizes the V/C process associated with phase transition through heat-transfer and mass-diffusion limited models to follow the time evolution of the reactor core under CDA conditions. The heat-transfer limited model describes the nonequilibrium phase-transition processes occurring at interfaces, while the mass-diffusion limited model is employed to represent effects of noncondensable gases and multicomponent mixture on V/C processes. Verification of the model and method employed in the multicomponent V/C model of SIMMER-III was performed successfully by analyzing a series of multicomponent phase-transition experiments.     

Development of a novel 1D coupled neutronics/thermal-hydraulics code and its verification on PWR rod ejection accident benchmark

This paper presents a new 1D Neutronics/Thermal-hydraulics code ATAC-1D based on the advanced Jacobian-Free Newton-Krylov (JFNK) method and the low dimensional equivalent strategy. Conventional operator-splitting (OS) strategies are used to maintain its accuracy with small time steps and linearization of the nonlinear problem, which leads to slow computation speed and linearization error. The JFNK method solves the troubles in the coupled neutronics/thermal-hydraulics problems mentioned above. Furthermore, a core-wide three dimension to one dimension equivalent method has been developed to provide variable few-group parameters. Finally, the performance of the coupled neutronics/thermal-hydraulics code ATAC-1D is studied by simulating four OECD/NEA CRP PWR rod ejection benchmark problems. The simulation results are compared to the reference ones, which proves that the developed 1D code has a good accuracy and practicability in nuclear reactor transient calculation.     

PRTHRUST-J1 code for calculation of blowdown thrust force and its experimental verification

This paper presents an outline of the PRTHRUST-J1 code for calculating blowdown thrust force and gives two numerical examples to show the effectiveness of this code. One numerical example is the problem of saturated steam blowdown. The blowdown thrust forces obtained from the PRTHRUST-J1 code were compared with those of the simplified method of Moody. Fairly good agreement was found between these two results. The other numerical example is the problem of jet discharging tests with stop valve performed in Japan Atomic Energy Research Institute. Analysis was carried out by varying the discharge coefficient. The analytical blowdown thrust force and pressure in the discharging nozzle were compared with experimental results. Qualitative agreement was found between the analytical and experimental results of the blowdown thrust force. Generally speaking, the blowdown thrust forces obtained from the experiment were between the analytical results for discharge coefficients of 1.0 and 0.6.     

Development of an MCNP-tally based burnup code and validation through PWR benchmark exercises

The aim of this study is to evaluate the capabilities of a newly developed burnup code called BUCAL1. The code provides the full capabilities of the Monte Carlo code MCNP5, through the use of the MCNP tally information. BUCAL1 uses the fourth order Runge Kutta method with the predictor–corrector approach as the integration method to determine the fuel composition at a desired burnup step. Validation of BUCAL1 was done by code vs. code comparison. Results of two different kinds of codes are employed. The first one is CASMO-4, a deterministic multi-group two-dimensional transport code. The second kind is MCODE and MOCUP, a link MCNP–ORIGEN codes. These codes use different burnup algorithms to solve the depletion equations system. Eigenvalue and isotope concentrations were compared for two PWR uranium and thorium benchmark exercises at cold (300 K) and hot (900 K) conditions, respectively. The eigenvalue comparison between BUCAL1 and the aforementioned two kinds of codes shows a good prediction of the systems’ k-inf values during the entire burnup history, and the maximum difference is within 2%. The differences between the BUCAL1 isotope concentrations and the predictions of CASMO-4, MCODE and MOCUP are generally better, and only for a few sets of isotopes these differences exceed 10%.     

六角形组件均匀化参数计算程序TPFAP-HEX的验证及其对WWER反应堆的应用

利用IAEA及文献提供的俄罗斯WWER-1000反应堆燃料组件计算的基准问题,对我国研制的压水堆六角形组件均匀化参数计算软件TPFAP-HEX进行了校核计算。通过和CASMO-HEX以及俄罗斯库尔恰托夫研究院等国外研究机构在组件k_∞、栅元的功率分布以及各种反应性效应等方面的比较,可以初步得出结论:TPFAP-HEX软件的研制是成功的,它基本达到了工程计算的功能和精度要求。     

先进中子学栅格程序KYLIN-2中特征线方法模块的开发与验证

针对先进核反应堆中结构复杂的燃料组件,基于特征线中子输运计算方法,在先进栅格计算程序KYLIN-2中开发能够满足各类燃料组件中子学数值模拟的输运计算模块。分别利用循环射线布置和射线反向延长追踪技术处理特定和任意边界条件问题,同时采用广义粗网格有限差分加速方法(GCMFD)来加速中子输运求解流程。数值结果表明,开发的特征线方法模块具有较高的计算精度,满足未来工程使用的需求。     

Study on the tritium behaviors in the VHTR system. Part 1. Development of tritium analysis code for VHTR and verification

A tritium permeation analyses code (TPAC) has been developed at Idaho National Laboratory (INL) by using MATLAB SIMULINK package for analysis of tritium behaviors in the VHTR integrated with hydrogen production and process heat application systems. The modeling is based on the mass balance of tritium-containing species and hydrogen (i.e., HT, H₂, HTO, HTSO₄, and TI) coupled with a variety of tritium source, sink, and permeation models. The code includes: (1) tritium sources from ternary fission and neutron reactions with ⁶Li, ⁷Li ¹⁰B, and ³He; (2) tritium purification system; (3) leakage of tritium with coolant; (4) permeation through pipes, vessels, and heat exchangers; (5) electrolyzer for high temperature steam electrolysis (HTSE); and (6) isotope exchange for SI process. Verification of the code has been performed by comparisons with the analytical solutions, the experimental data, and the benchmark code results based on the Peach Bottom reactor design. The results showed that all the governing equations are well implemented into the code and correctly solved. This paper summarizes all the background, the theory, the code structures, and some verification results related to the TPAC code development at INL.     

Stochastic techniques for the control and surveillance of a modular pebble bed reactor

This paper represents the first of a series of publications describing work in progress on the research, design and testing of a control and surveillance system for a Modular Pebble Bed Reactor.

The scope of the project involves the design of a simple state of the art control system for the reactor and a surveillance system based on smart instrumentation and expert system logic. It is noted that there are some physical and experimental problems unique to the MPBR family. These problems are connected with long neutron lifetimes, the need for a new evaluation of kinetic parameters and reactivity effects, and the need for very high sensitivity counting channels.     

Development of multicomponent vaporization/condensation model for a reactor safety analysis code SIMMER-III: Extended verification using multi-bubble condensation experiment

Complex phenomena such as phase transitions and heat transfers in multiphase, multicomponent flows were modeled in the fluid-dynamics portion of SIMMER-III, which was developed to appropriately assess core disruptive accidents (CDAs) in liquid–metal fast reactors (LMFRs). A new multicomponent vaporization/condensation (V/C) model was developed and introduced to SIMMER-III by the authors. In the present study, a new series of multi-bubble condensation experiments was performed to demonstrate that SIMMER-III with the present V/C model is practically applicable to multicomponent, multiphase flow systems with phase transition. In the experiments, bubble diameters and void fractions were quantified from visualization images using original image-processing techniques. Comparing SIMMER-III predictions with experimental data, it was confirmed that SIMMER-III with the proposed V/C model could suitably represent the effects of noncondensable components on the condensation process in multi-bubble systems. This work has improved the reliability of SIMMER-III with regard to multicomponent phase-transition phenomena.