摘要:

In postulated loss-of-coolant accidents in water-cooled reactors, it is possible for an increase in Zircaloy clad temperature, coupled with reactor depressurization, to give significant local clad strain, and hence reduced area for coolant flow. This paper establishes a simple method of calculating the effect of consequent impairment of local heat-removal capability.An existing flow model, due to Gambill, has been used to estimate the local reduction in the heat transfer coefficient due to clad ballooning. By formulating an energy balance for the fuel pins, temperature transient curves for the distorted cladding are derived from those for undistorted fuel.To analyze the complicated two-phase phenomena, several simplifying assumptions are contained in the flow model. Results, therefore, are given for a range of flow and blockage assumptions, and are shown to be in reasonable accord with an analysis using large and complex computer codes and with all available experimental data.The model can be applied to all types of water-cooled reactors, including pressure tube reactors, by a suitable evaluation of the resistance to bypass flow.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26763

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

A previous single-bubble model describing the coolant motion within an oxide fuel subassembly of a liquid-metal fast breeder reactor due to rapid gas release from multiple pin failure has been extended to include the description of coolant motion following the release of fission gas into the exit coolant plenum. The present model supplements the previous model in that it follows the motion of the lower gas-liquid interface by allowing for the expansion of gas in the exit plenum in the form of a spherical bubble, and by allowing it to detach and form another bubble in its place. The model assumes that the motion of the liquid surrounding the expanding bubble can be described by potential flow theory and that the motion of lower liquid slug in the subassembly can be described by one-dimensional continuity and momentum equations for incompressible flow model. The model also considers the translation of the center of the plenum bubble during its expansion. It is demonstrated that the behavior of the first bubble (i.e., when the difference between bubble pressure and the pressure of the surroundings is large) is analogous to that of the high-pressure bubble formed under large depths of water,and the behavior of those bubbles formed subsequently resembles that of the bubbles due to orifice bubbling above a gas chamber of finite volume. The sample calculations for a Fast Flux Test Facility reactor subassembly indicate that the recovery of coolant flow, even with a nearly simultaneous breach of all 217 pins in the sub-assembly, is very rapid, and the total transient time is not long enough to cause any significant overheating of the coolant and the cladding.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26764

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

The results of two integral experiments on carbon, performed at the Oak Ridge National Laboratory (ORNL) and at Intelcom Radiation Technology were compared with Monte Carlo calculations to test evaluated carbon neutron and gamma-ray production data sets. In both experiments NE-213 detectors were used to measure the angular dependence of neutron scattering and gamma-ray production from thick (1-mfp) carbon samples in the energy range from 0.5 to 20 MeV. Additional measurements from the ORNL experiment also provided angular-dependent energy distributions of the scattered neutrons. Multigroup Monte Carlo calculations modeling the two experimental arrangements were made to compare with the measured data. Both ENDF/B-III and ENDF/B-IV carbon data were used in the computations. The results indicate that such experiments are adequate for testing processed neutron scattering and gamma-ray production data (both integral and double differential) to within 10 to 20% over a wide range of incident neutron energies (1 to 15 MeV). Also, on the whole, calculations with the carbon ENDF/B-IV data compared favorably with the measured results over the energy range, tested. The only notable exceptions were the disagreements in the neutron result comparisons above 9 MeV, which were attributed for the most part to errors in the evaluated C(n, n’)3αand elastic angular distribution cross sections in this range.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26765

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

Calculations of the Doppler effect on resonance absorption, which assume equivalence, are shown to underestimate the effect in thin lumped absorbers where the mean chord length is of the order of the resonance-neutron mean-free-path. This error results from the deviation of Wigner’s rational approximation, both the original and as modified by Otter, from the exact escape probability in this region. Results for238U using the computer programs ZUT (with exact escape probabilities) and TRIX (assuming equivalence) are compared. A new temperature-dependent modification to Wigner’s rational approximation is developed and shown to improve agreement between calculations using equivalence and those using exact escape probabilities. Calculations are made for thin238U metal and oxide slabs in the surface area-to-mass range of 1 to 40 cm2/g and at temperatures up to 2000°C.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26766

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

Activation measurements of the Doppler effect in a 1/E slowing-down spectrum for thin238U-metal foils, of surface area to mass ratio between 8 and 25 cm2/g, have been made at temperatures up to 1000 K. The activation technique was modified to remove the dependence on flux monitor foils by rotating both a heated and a reference foil. The results show consistently higher Doppler ratios than those predicted by flat-flux models using either exact numerical solutions or the assumption of equivalence.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26767

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractIn this paper an improved degenerate kernel is obtained and subsequently used instead of the exact thermalization kernel for the calculation of thermal-neutron densities in a heterogeneous reactor lattice.The degenerate kernel is composed of a number of functions, some of which are obtained by conserving speed moments of the kernel while the remaining functions are chosen so as to reproduce scattering probabilities involving epithermal energies.The degenerate kernel satisfies the detailed balance strictly and, as opposed to conventional degenerate kernels, shows the desirable feature of improved accuracy when the number of terms in the degenerate kernel is increased.This degenerate kernel is employed to compute thermal-neutron spectra in cylindricized unit cells by solving the integral transport equation for the scalar neutron density. For this purpose the DESMOS code was developed. The results of these calculations are compared with the analogous THERMOS code results. DESMOS proves to be accurate and its speed of execution compares favorably with that of THERMOS.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26768

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractCalculations taking into account the influence of grain structure on the effective resonance integral of high-temperature reactor fuel assemblies caused by the use of coated particles are checked by measurements of such fuel assemblies with a lead spectrometer. The effect is quite remarkable and can be clearly seen from the measurements. Calculations show good agreement with our measurements.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26769

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractThe effects of the presence of a central cavity on the space- and time-dependent neutron energy spectrum in a fast-neutron multiplying system are analyzed as a fundamental time eigenvalue problem by use of the telegrapher’s equation. The computational results show that the cavity cooling occurs in the fast235U system with a fundamental time eigenvalue. The results of the telegrapher’s equation are compared with those from the time-dependent Snmethod.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26770

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

摘要:

AbstractWith the help of the generalized function theory, the macroscopic treatment of neutrons slowing down in a homogeneous medium is investigated. As a result, it is found that the balance equation for neutron flux is exactly expressed byfor a monoenergetic source as well as a fission source, where the moderating parameter is defined as the ratio of slowing down density to collision integralSource dependence of this parameter,(u), is also examined analytically and numerically. In the transient region the difference of(u)’s for a monoenergetic source and a fission source is shown to be remarkable. For a monoenergetic source the asymptotic valueis found to be a monotonically decreasing function of the absorbing ratio, a, while theof fission neutrons is also a decreasing function for the smaller absorbing ratio than a certain critical absorbing ratio and for large a it has the constant value.

ISSN:0029-5639    

DOI:10.13182/NSE75-A26771

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE75-A26773

出版商:Taylor&Francis    

年代:1975

数据来源: Taylor