摘要:

AbstractA mechanism believed responsible for the explosive vapor growth observed in Armstrong’s experiment with LMFBR materials (liquid sodium injected into molten UO2) is discussed. Basically, liquid sodium globules can be entrained and wet the liquid UO2surfaces. The lack of nucleation sites in the liquid-liquid-like system results in the overheating of the liquid sodium until homogeneous nucleation occurs. When the superheat limit is reached, vaporization is rapid enough to produce shock waves.The validity of the proposed entrainment-wetting-superheat mechanism to explain the observed UO2-Na explosions has been demonstrated by above surface injection of liquid Freon-11 (normal boiling point 23.8°C) into hot water (70 to 90°C). This liquid-liquid system is believed to simulate Armstrong’s UO2-Na system, since in the latter, the transition from film boiling to nucleate boiling based upon Henry’s film boiling correlation will take place at a temperature well above the melting temperature of UO2.Based upon this mechanism, large-scale coherent UO2-Na vapor explosions would appear impossible in a reactor environment. In a real reactor system, fission gases and fragments, as well as solid materials and gas bubbles entrained in the liquid sodium, would be present and would promote boiling prior to reaching the threshold for homogeneous nucleation in sodium, therefore resulting in mild interactions of the type observed in the TREAT in-pile experiments.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26584

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractExperiments have been performed which give further insight into the so-called“in-and-down”scattering problem. Experimental ceiling attenuation factors have been developed and compared with previously published results of radiation attenuation in basement ceilings.The experiments were performed on a full-scale structure with basement ceiling mass thicknesses of 12 and 0 psf at several solid angle fractions. Additional experiments were performed for several ceiling mass thicknesses at a solid angle fraction near unity. Generally, the experiments showed that previously published ceiling attenuation factors appear inadequate for large solid angle fractions and large overhead mass thicknesses. For small mass thicknesses and solid angle fractions below≍0.8, the agreement between experiment and previously published results is reasonable. It is clear that ceiling attenuation factors should demonstrate a solid angle fraction dependence as well as a mass thickness dependence. However, these experiments show that there is no reason to believe that in the limit as the solid angle fraction approaches unity, the ceiling attenuation factor should approach old formulations which had no solid angle fraction dependence.It has also been shown in this work that ceiling attenuation factors may be experimentally determined solely from finite field data. There is no need to estimate far-field contributions or skyshine contributions in the determination of ceiling attenuation factors.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26585

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractHigh energy gamma-ray spectra from the radiative capture of 14-MeV neutrons in copper, zirconium, and antimony have been measured with a coincidence-anticoincidence telescope pair spectrometer. These spectra are compared with predictions from calculations using the semidirect (collective) capture model. The parameter values used were derived from other types of experiments and from nuclear models. Agreement is found both in shape and in magnitude without further adjustment of parameters. Partial radiative capture cross sections, obtained by integrating the gamma-ray spectra for gamma energies in excess of 14 MeV, are compared with values from other measurements.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26586

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractNeutron resonance energies have been obtained for a number of selected well-isolated resonances in several elements and isotopes. The energy parameters were mainly obtained at Columbia University’s 200-m time-of-flight spectrometer with high precision. These energy calibration points are important for a number of experiments in neutron and reactor physics.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26587

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe fission cross-section ratio241pu:235U has been measured in the neutron energy range from 5 keV to 1.2 MeV with an accuracy between 3 and 4%. The neutron energy was determined by the time-of-flight method. Two identical gas scintillation chambers were used to detect the fission events. The present measurements were carried out at sufficiently fine energy intervals to show for the first time the detailed shape of the fission cross-section ratio. In contrast to the results of other authors, a distinct structure was found. A comparison with an evaluation by Davey of previous data shows a systematic difference in shape up to 10% between 30 and 400 keV. At higher energies the evaluation generally agrees with the new data except in the region between 900 and 1000 keV, where the values of this work indicate a significant dip in the cross-section ratio.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26588

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractNeutron-induced fission cross sections of233U,235U,239Pu, and241Pu have been measured up to 30 keV. These measurements were performed with samples cooled down to liquid nitrogen temperature and with a nominal resolution of 1 nsec/m, using the 60-MeV Saclay LINAC as a pulsed-neutron source. The agreement with previously published results is within 3% for235U in the energy range 60 eV to 10 keV, and 6% for233U below 1220 eV. For239Pu and for241Pu in the energy ranges 0.7 to 7 keV and 10 to 20 keV, the agreement is also within 6%. Total errors are a function of target material and incident neutron energies and hence are estimated to lie between 3 and 7%. The existence of an intermediate structure is demonstrated in the fission cross section of239Pu.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26589

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe finite element method is applied to the one-dimensional neutron transport equation. Piecewise bilinear or trilinear polynomials that are continuous in the space-angle phase space are utilized in an even-parity functional for the angular flux to establish linear simultaneous sets of algebraic equations. Both inhomo-geneous and eigenvalue problems in slab, spherical, and cylindrical geometries are treated. The application of the finite element method to problems with anisotropic scattering and material interfaces is also demonstrated. In all cases, the accuracy of the finite element results is an improvement over that obtained from standardSNcalculations using comparable numbers of simultaneous equations.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26590

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe previous transfer matrix formulation of exact one-speed neutron transport with isotropic scattering in slab geometry is extended to arbitrary anisotropic scattering and to azimuthally dependent problems. Explicit comparison is made with results obtained by Case’s method, and some new relations expressing reciprocity are derived. The special case of no absorption is considered separately.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26591

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractThe problem treated in Part I in terms of a continuousµ-variable is here treated in the double-PNapproximation for azimuthally symmetric situations. Exqplicit representations for basic matrices are derived. The transfer matrix equations were solved on the CDC-6600. Results are presented for two problems of interest—transmission and reflection from thick slabs and the finite reflector critical problem. Anisotropic scattering is considered in both cases. Tables of typical computing times are presented.

ISSN:0029-5639    

DOI:10.13182/NSE73-A26592

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor

摘要:

AbstractA higher order perturbation formula for calculating changes in the reactivity up to a desired order in concise form is given; the formula uses the iterative technique well known in quantum mechanics and in the neutron life-cycle method. This procedure is possible only when the adjoint flux in the unperturbed system is used as the weighting function. The higher order perturbation formula contains the interaction between the perturbation inserted and its surrounding medium, but it consists only of the integration over the perturbed region. Numerical calculations up to the third-order perturbation show that the first-order perturbation technique gives a low value for the reactivity worths of fission, absorption, and scattering materials; further, then’th-order perturbation is proportional to then’th power of the concentration of an inserted perturbation.

ISSN:0029-5639    

DOI:10.13182/NSE51-180

出版商:Taylor&Francis    

年代:1973

数据来源: Taylor