摘要:

A series of measurements of the conversion ratio of the PWR blanket has been performed. The experimental techniques and results are described, and a comparison of those results is made with theoretical calculations. The results indicate an average PWR blanket conversion ratio of approximately 1.15.

ISSN:0029-5639    

DOI:10.13182/NSE58-A25454

出版商:Taylor&Francis    

年代:1958

数据来源: Taylor

摘要:

Coupling a fast and thermal assembly in a power breeder reactor affords the possibility of obtaining the relatively long neutron lifetime characteristic of a thermal assembly and the high breeding ratio characteristic of a fast assembly. General properties of such mixed systems are discussed. A suggested design is discussed and compared with a prototype all-fast system. The coupled system considered consists of a 400-liter Pu239fueled, Na-cooled, fast core surrounded by a 10-cm inner blanket annulus containing natural U, Na coolant, and structural material, but no moderator. Outside the inner blanket is a 30-cm annulus of Be surrounded by an outer blanket consisting primarily of depleted U. The inner blanket serves as core for the thermal system, as barrier for low-energy neutrons between moderator and fast core, and as reflector for the fast core. Its construction is essentially the same as the first part of the blanket in a fast power breeder, so that the transition from an allfast system to the coupled system involves only the replacement of blanket material by moderator and the use of natural rather than depleted uranium in the inner blanket. The properties of the system described are thereby changed: neutron lifetime increases from∼1.5×10−7sec. to∼2×10−5sec; breeding ratio reduced∼10%; fast core critical mass decreased∼10%; multiplication constant of the system without the contribution of thermal fissions∼0.95; thermal fissions generate∼13% of total power; and the radial power distribution in fast core flattened, maximum to average ratio reduced from∼1.5 to∼1.3.

ISSN:0029-5639    

DOI:10.13182/NSE58-A25455

出版商:Taylor&Francis    

年代:1958

数据来源: Taylor

摘要:

Measurements have been made of the fast neutron cross sections for the production of N16and N17in the uranium rod cooling water of the NRX reactor by the reactions O16(np)N16and O17(np)N17. The N16and N17were detected by their gamma and fast neutron activities, respectively, in a continuously flowing sample of the effluent water from a uranium rod. The cross sections (fission neutron spectrum) for the reactions O16(np)N16and O17(np)N17are 1.85±0.15×10−2millibarns and 9.3±0.9×10−3millibarns, respectively.

ISSN:0029-5639    

DOI:10.13182/NSE58-A25456

出版商:Taylor&Francis    

年代:1958

数据来源: Taylor

摘要:

The degradation of neutron energies in a fast reactor is largely due to inelastic scattering. In a dilute fast system (large U238to U235atomic ratio) the neutron spectrum is then primarily determined by a fission spectrum distribution modified by inelastic scattering in U238. In this investigation a set of ten-group fast cross sections for U238have been prepared with the inelastic cross cross sections below about 1.35 Mev based upon levels at 45, 150, and 700 kev. The inelastic transfer contributions from unknown higher levels were chosen to be consistent with the gross measurements of Bethe, Beyster, and Carter, having the three-group energy division consisting of above 1.4 Mev. between 0.4 and 1.4 Mev, and below 0.4 Mev. The ten-group fast cross sections were tested by comparing the calculated equilibrium spectrum, diffusion length, and detector responses in natural uranium with reported experimental values found in the blanket of the Zephyr reactor and in the Snell experiments.

ISSN:0029-5639    

DOI:10.13182/NSE58-A25457

出版商:Taylor&Francis    

年代:1958

数据来源: Taylor

摘要:

The spatial moments,, andare calculated exactly for all energies below the source energy, for a point, isotropic source in an infinite, homogeneous medium in which there is no absorption and in which the scatterers scatter like hydrogen but with a 1/υcross section. For a monoenergetic source these moments are approximately consistent with a diffusion (Yukawa) radial distribution of the very low energy neutrons. Integration over a fission-like source spectrum,exp (−αE), gives moments consistent with a radial distribution of the very low energy neutrons of the form of a first collision density,r−2exp (−r/λ), but with a mean free pathλapproximately twice the mean free path at the average source energy. The results are compared with those given by the first collision approximation.

ISSN:0029-5639    

DOI:10.13182/NSE58-A25458

出版商:Taylor&Francis    

年代:1958

数据来源: Taylor

摘要:

Corrosion rates of sponge zirconium and Zircaloy-2 in dry air were measured at 500, 600, and 700°C (930, 1110, and 1290°F). The reaction proceeds in two stages: initially the rate decreases with exposure time, approximating a cubic relationship; after sufficient exposure, the rate becomes a linear function of time. The rate constants calculated from the data and expressed by the Arrhenius equation,k=Aexp (−Q/RT), are:Extrapolation of these data to lower temperatures shows that the service life of structures fabricated from these metals amounts to several years at temperatures below 400°C (750°F).

ISSN:0029-5639    

DOI:10.13182/NSE58-A25459

出版商:Taylor&Francis    

年代:1958

数据来源: Taylor

摘要:

A method for determining effective cross sections for geometrically thin absorbing regions in multigroup calculations is described. The effective absorption cross section in multigroup calculations provides a smooth transition from the usual diffusion theory cross section for low absorption slabs to theλtrextrapolated end-point condition for black slabs. In effect, the average flux between mesh points of the difference equation grid is related to the fluxes at the mesh points. Self-shielding effects are accounted for by material cross-section rather than difference equation modification. Application of the theory to lattice calculations is discussed, and comparisons are made with other methods for limiting cases.

ISSN:0029-5639    

DOI:10.13182/NSE58-A25460

出版商:Taylor&Francis    

年代:1958

数据来源: Taylor

摘要:

The failure to obtain agreement between the calculated and measured reflector savings in the Fast Exponential Experiment led to a study of the processes involved in obtaining spectral equilibrium in small, highly enriched systems. It was shown that the length of the equilibrium region was a sensitive function of the pedestal thickness and could be optimized for this assembly. Factors which were found to be significant are, as expected, the geometry and the spectrum of the source. Both the experimental results and the theoretically derived results are presented. The methods of collecting data and the methods of data analyses which proved most fruitful are also presented.

ISSN:0029-5639    

DOI:10.13182/NSE58-A25461

出版商:Taylor&Francis    

年代:1958

数据来源: Taylor