摘要:

AbstractBoth theoretical and numerical results on the relationships between the magnitude of the interphase drag coefficients, the mesh size, and the stability of the semi-implicit method used in RELAP5 are presented. It is shown that the numerical solutions are both stable and convergent on meshes with a characteristic ratio (ratio of mesh size-to-hydraulic diameter) that is not too small, that the code is capable of simulating physical instabilities on coarse meshes, and that unphysical instabilities will occur only at small mesh size even for problems that admit physical instabilities. Good transition from pre-critical heat flux (CHF) to post-CHF, however, is necessary to improve the accuracy of certain calculations.

ISSN:0029-5639    

DOI:10.13182/NSE94-A18984

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractAn integral, fast-running computational model is developed to simulate the thermal-hydraulic and melt progression behavior in a nuclear reactor rod bundle under severe fuel damage conditions. This consists of the submodels for calculating steaming from the core, hydrogen formation, heat transfer in and out of the core, cooling from core spray or injection, and, most importantly, fuel melting, relocation, and freezing with chemical interactions taking place among the material constituents in a degrading core. The integral model is applied to three German severe fuel damage tests to analyze the core thermal and melt behavior: CORA-16 (18-rod bundle and slow cooling), CORA-17 (18-rod bundle and quenching), and CORA-18 (48-rod bundle and slow cooling). Results of the temperature response of the fuel rods, the channel box, and the absorber blade; hydrogen generation from the fuel rod and the channel box; and core material eutectic formation, melt relocation, and blockage formation are discussed. Reasonable agreement is observed for component temperatures at midelevation where prediction and measurement uncertainties are minimal. However, discrepancies or uncertainties are noticed for hydrogen generation and core-melt progression. The experimentally observed peak generation of hydrogen upon reflooding is not able to be reproduced, and the total amount generated is generally underpredicted primarily because of the early relocation of the Zircaloy fuel channel box and cladding. Also, difficulties are encountered in the process of assessing the core-melt formation and the relocation model because of either modeling uncertainties or a lack of definitive metallurgical data as a function of time throughout the transient.

ISSN:0029-5639    

DOI:10.13182/NSE94-A18985

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe performance of seven computer platforms is evaluated with the widely used and internationally available MCNP4A Monte Carlo radiation transport code. All results are reproducible and are presented in such a way as to enable comparison with computer platforms not in the study. We observe that the HP/9000–735 workstation runs MCNP 50% faster than the Cray YMP 8/64. Compared with the Cray YMP 8/64, the IBM RS/6000–560 is 68% as fast, the Sun Sparc10 is 66% as fast, the Silicon Graphics ONYX is 90% as fast, the Gateway 2000 model 4DX2–66V personal computer is 27% as fast, and the Sun Sparc2 is 24% as fast. In addition to comparing the timing performance of the seven platforms, we observe that changes in compilers and software over the past 2 yr have resulted in only modest performance improvements, hardware improvements have enhanced performance by less than a factor of∼3, timing studies are very problem dependent, MCNP4A runs about as fast as MCNP4.

ISSN:0029-5639    

DOI:10.13182/NSE94-A18986

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractFor the first time, spectra in the range of 34 MeV down to 0.4 eV for neutrons that penetrated through iron and concrete shields were measured with the use of quasi-monoenergetic sources generated from anatLi(p,n)Be reaction.

ISSN:0029-5639    

DOI:10.13182/NSE94-A18987

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractAn approximate evaluation procedure is derived for a second-order theory of coupled nucleon transport in one dimension. An analytical solution with a simplified interaction model is used to determine quadrature parameters to minimize truncation error. Effects of the improved method on transport solutions with the BRYNTRN data base are evaluated. Comparisons with Monte Carlo benchmarks are given. Using different shield materials, the computational procedure is used to study the physics of space protons. A transition effect occurs in tissue near the shield interface and is most important in shields of high atomic number.

ISSN:0029-5639    

DOI:10.13182/NSE94-A18988

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractNew core-reflector boundary conditions designed to replace the explicit representation of the reflector in nodal computations are developed taking into account the transverse leakage in the reflector region. Two approximations are introduced for the transverse leakage in the reflector region: exponential approximation for the slab reflector and quadratic polynomial and exponential approximation for the L-shaped reflector. Core-reflector boundary conditions that relate net current with flux at the core-reflector interfaces are then derived by solving the transverse integrated neutron diffusion equation with transverse leakage approximations in the reflector region. To test the usefulness of new core-reflector boundary conditions, nodal expansion method computations with and without explicit representation of reflectors are performed for the core power distribution and criticality of Zion-1 and YGN-1 pressurized water reactors. It is demonstrated that core power and criticality computations with new boundary conditions agree very well with those with the reflector included explicitly in computational nodes.

ISSN:0029-5639    

DOI:10.13182/NSE94-A18989

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractAn artificial neural network (ANN)-based diagnostic adviser capable of identifying the operating status of a nuclear power plant is described. A dynamic node architecture scheme is used to optimize the architectures of the two backpropagation ANNs that embody the adviser. The first or root network is used to determine whether or not the plant is in a normal operating condition. If the plant is not in a normal condition, the second or classifier network is used to recognize the particular off-normal condition or transient taking place. These networks are developed using simulated plant behavior during both normal and abnormal conditions. The adviser is effective at diagnosing 27 distinct transients based on 43 scenarios simulated at various severities that contain up to 3% noise.

ISSN:0029-5639    

DOI:10.13182/NSE94-A18990

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor