摘要:

AbstractThe pulsed photon activation (PPA) technique for nonintrusive measurements of single and two-phase flows in a horizontal pipe is developed. The advantages of PPA over pulsed neutron activation are discussed. Fluid velocity determinations using such a technique are carried out. An interesting subregion of the horizontal annular flow regime is found to have twin peak PPA time profiles. It is confirmed that these twin peaks are associated with the film flows on the upper and lower parts of the horizontal pipe, using the directionality of the PPA bremsstrahlung tagging beam. Film thickness measurements around the circumference of horizontal annular flows are also carried out using a resistivity needle probe, and analytical models involving droplet exchange and secondary vapor flow pattern are compared with the experimental data.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17301

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractLiterature describing natural-circulation analyses, experiments, and plant operation have been obtained from the Nuclear Regulatory Commission, reactor vendors, utility-sponsored research groups, utilities, national laboratories, and foreign sources. These have been reviewed and significant results and conclusions identified. Three modes of natural-circulation cooling are covered: singlephase, two-phase, and reflux condensation. Single-phase natural circulation is amply verified by plant operational data, test data from scaled experimental facilities, and analysis with assessed computer codes. Ample evidence also exists that two-phase natural circulation can successfully cool pressurized water reactors. This mode occurs during certain events such as small-break loss-of-coolant accidents. The data base for reflux condensation is primarily from tests in scaled experimental facilities. There are no plant operational data and only limited assessment of thermal-hydraulic systems codes has been performed. Further work is needed before this mode of natural circulation can be confidently used.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17302

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA method to predict the probabilistic distribution of channel coolant flow rate was developed for a boiling-water-cooled, pressure-tube-type reactor. This method deals with the probabilistic deviation of core flow distribution and total coolant flow rate based on the characteristics of the correlation between two-phase pressure drop of a primary core cooling system and the characteristics of the recirculation pump Q-H. The effect of local and global uncertainties on the probabilistic variation of channel coolant flow rate is discussed in terms of coolant flow correlation among all of the pressure tube channels. The probabilistic deviation of channel coolant flow rate due to uncertainties in fabrication tolerances, experimental data, and physical properties has been evaluated for various operating conditions of the FUGEN reactor. Predicted channel flow deviations were in good agreement with the deviation of actual measured data in the FUGEN reactor.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17303

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA simple and accurate analytic method for calculating pressure vessel neutron damage>1-MeV fluence has been derived. The method employs asymptotic expressions for the one-speed neutron transport Green's function, together with an effective removal cross section, to propagate the neutron source from the core out to the pressure vessel. The spatial integration over the core neutron source is performed using a multipole expansion of the transport Green's function. The analytic method reproduces detailed (DOT) numerical calculations in both (r,θ) and (r,z) geometries to within⪝5%, and similar accuracy is expected in three dimensions.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17304

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractAn analysis of the Oklo natural reactor, a self-sustaining and self-regulating critical assembly that existed some 2 billion years ago in Gabon, Africa, is presented. Nonlinear continuous differential and nonlinear discrete iterative formulations are established and selected parameter characterizations identified. Conceivable power oscillations are calculated and discussed. Some implications of nonlinear mappings for nuclear simulation are suggested.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17305

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA standard assumption used in unit-cell interface-current codes is that neutrons enter each spatial region with an isotropic angular distribution. The physical interpretation of this assumption is discussed, and the magnitude of the error introduced by it is shown for a range of practical unit-cell geometries. An improvement on the calculation of first-flight transmission probabilities for one-dimensional unit cells based on limiting the neutron source angular distribution to physically possible neutron flight directions is then presented. For three-region problems, one additional calculation of a revised outer region transmission probability is sufficient for determining all the revised transmission probabilities of interest. Calculation of the revised transmission probabilities requires only minor coding changes and eliminates the improper angular redistribution of neutrons at the region boundaries.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17306

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractMeasurements of the energy spectra of delayed neutrons for the isotope-separated, fission product precursors93-97Rb and143-145Cs, over the energy region from∼10 to∼1300 keV, are reported. These data were obtained at the TRISTAN ISOL facility using gas-filled proton-recoil proportional counters. The data for each of the rubidium and cesium isotopes show good qualitative agreement with the existing3He ionization chamber data at energies above∼200 keV. In addition, they provide definitive spectral information down to∼10 keV. Of particular note is the observation of line structure below∼200 keV with energy resolution much better than that obtained using3He ionization chambers.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17307

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractA set of multigroup Legendre coefficients is derived that can be used to implement the diamond difference scheme for the continuous slowing down operator in standard (unmodified) Sncodes. Calculations are performed that demonstrate the validity of these coefficients, and the superior accuracy of the diamond difference scheme relative to the standard first-order multigroup method.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17308

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe skyshine dose distributions of neutron and secondary gamma rays were calculated systematically using the Monte Carlo method for distances up to 2 km from the source. The energy of source neutrons ranged from thermal to 400 MeV; their emission angle from 0 to 90 deg from the vertical was treated with a distribution of the direction cosine containing five equal intervals.Calculated dose distributionsD(r) were fitted to the formula;D(r) =Qexp(−r/λ)/r. The values ofQandλare slowly varied functions of energy. This formula was applied to the benchmark problems of neutron skyshine from fission, fusion, and accelerator facilities, and good agreement was achieved. This formula will be quite useful for shielding designs of various nuclear facilities.

ISSN:0029-5639    

DOI:10.13182/NSE85-A17309

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor

摘要:

AbstractThe Creare one-fifth-scale Phase II experiments, which model fluid and thermal mixing of relatively cold high-pressure injection water into a cold leg of a full-scale pressurized water reactor having loop flow, are analyzed. It is found that they cannot achieve complete similarity with respect to characteristic Reynolds and Froude numbers and developing hydrodynamic entry length. Several analyses show that these experiments fall into two distinct regimes of mixing: momentum and gravity controlled (stratification).

ISSN:0029-5639    

DOI:10.13182/NSE85-A17310

出版商:Taylor&Francis    

年代:1985

数据来源: Taylor