摘要:

AbstractFlat-plate fuel-element surface temperatures in the Organic Moderated Reactor Experiment were monitored by 0.005-in. (0.013-cm)-diam chromel-alumel thermocouple wires, spot-welded to the stainless-steel fuel-plate surface. The thermocouple assembly, being exposed to the coolant stream, is subject to thermal-loading errors; as a result, thermocouple-calibration tests were performed in a forced-convection heat-transfer loop with Santowax O-M flowing over an electrically heated test plate containing typical thermocouple specimens. The tests were conducted under the following simulated reactor conditions: coolant temperatures from 300 to 600°F (149 to 316°C), coolant velocities from 10 to 20 ft/sec (3.1 to 6.1 m/sec), and heat fluxes ranging from 0.50×105to 1.6×105Btu/(h ft2) (15.77 to 50.46 W/cm2).Test results demonstrate that at reactor operating conditions, 600°F organic coolant flowing at 17.5 ft/sec (5.34 m/sec), the observed fuel-plate surface temperature is 700°F (371°C), while, in reality, the actual surface temperature is 750°F (399°C). The thermocouple thermal-loading errors were found to be a function of the coolant Reynolds and Prandtl numbers. Heat flux had no effect on the calibration. Excellent agreement was obtained between the experimental and predicted (Dittus-Boelter) heat-transfer coefficients for the organic coolant. Thermocouple-calibration factors for correction of observed surface temperatures over a wide range of operating conditions, are presented as a function of the organic-coolant heat-transfer coefficient on the fuel-plate surface.An electrical-analogue model of a thermocouple assembly on the surface of an OMRE fuel element was constructed to: a) verify experimental results; b) study the effect of a fouling film on surface-temperature measurements; and c) provide an inexpensive means of calibrating surface-attached thermocouples on fuel plates for future use. Prediction of thermal-loading errors associated with this type of surface-temperature measurement by the use of existing mathematical results is discussed. Good agreement was obtained between the electrical-analogue results, the analytical predictions, and the experimental data. Film formation on the fuel plate and the thermocouple wire was observed to reduce the thermocouple-calibration factor by as much as 45%.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21067

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractAn accurate heat-transfer analysis of reactor fuel elements requires an accounting of the axial heat-conduction effects. The exact treatment requires the solution of a boundary-value problem involving partial differential equations.In this paper, an approximate method is developed for determining the axial and transverse heat-flux distributions in reactor-fuel elements. The method is analogous to the Karman-Pohlhausen method of boundary-layer theory.When the results of the approximate method are compared with those of known exact solutions, the agreement is found to be excellent. Two examples are given in which the approximate method gives values that agree with the exact solutions to within about 2%.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21068

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractA high-pressure furnace that operates up to 2000°C in the pressure range of 100 atm to 10−5torr was designed and constructed to saturate UO2powder of 4-µm average particle size with4He. The powder was then dissolved in a fused salt in an induction chamber. The released4He was mixed with a known quantity of3He, and the mixture was analyzed with a mass spectrometer to determine the4He:3He ratio, hence the original mass of4He in the sample.The solubility of He in UO2at 1200 and 1300°C was found to be 6.71×10−4and 3.23×10−4cm3(STP)/(g atm), respectively. It was also found that the He-UO2system obeys Henry's law.From a plot of He concentration as a function of time, the diffusion coefficient at 1200°C was estimated to be 1.5×10−13cm2/sec.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21069

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractSmall crystals of NaI(TI) were exposed to (D, D) neutrons slowed down in a paraffin moderator. The crystals were either enclosed in cadmium or placed inside a small cadmium box filled with the moderator material. The activities induced in iodine at different positions were measured. Now let the normalized activities obtained with the detectors enclosed in cadmium beA1and let those obtained with the detectors placed inside the cadmium box beA2. It is assumed that the differenceA2−A1is proportional toq(0.5 eV)-the slowing down density at an energy of 0.5 eV-and from the measured quantitiesA2(r) andA1(r) the slowing down age has been determined. Bare crystals were also irradiated and the induced activities measured. Let these activities beA3. Then the differenceA3−A1will give a measure of the density of thermal neutrons and the migration area can be determined. With migration area and slowing down age known, the diffusion length of thermal neutrons could be determined too. The result obtained wasL= (2.86±0.16)cm compared to a calculated value of (2.60±0.01)cm. The discrepancy might indicate that the neutron temperature in the paraffin is about 400°K.Paraffin was used as moderator material because this greatly facilitated the experiment. It is never used as a reactor material and knowledge of the measured quantities may be of minor importance. The method, however, might possibly be of some interest.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21070

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThe use of series expansion methods in treating threshold-detector activation data has been analyzed. Normally the indiscriminate use of detectors having similar responses leads to unstable and ill-conditioned systems. The reasons for these deficiencies are determined and a new method for overcoming them is proposed. To make optimum use of the experimental data in obtaining a solution for the incident neutron spectrum, the series expansions coefficients are obtained through the Gauss method by solving a least-squares problem.A procedure, based on the Monte Carlo method, has been set up to statistically study the effect of experimental input errors on the solution obtained.The most important results indicate that:any set of threshold detectors can be used independent of their cross-section shapesthe reliability increases as the number of detectors increasesthe reliability decreases when the number of series expansion terms increases.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21071

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractThe production of defects by thermal neutrons in CdS results from the recoil of an energetic114Cd nucleus. The recoil results from prompt emission of 9 MeV of gamma energy following thermal-neutron capture by113Cd through the nuclear reaction:113Cd +nth→(114Cd)→114Cd +γ. The changes in the optical and electrical properties of CdS were measured to determine the effect of such recoils. A recombination center for the 7200A emission is produced and both the 4880A emission and edge emission are reduced. In addition, the conductivity of initially conducting CdS crystals is decreased by many orders of magnitude. The temperature dependence of the conductivity of thermal-neutron irradiated crystals indicates the production of a state about 0.5 eV below the conduction band.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21072

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractParameter measurements in a 1.3% enriched UO2lattice with H:U = 0.42 have been performed. These measurements are an extension of an experimental program in the TRX critical facility of the Bettis Atomic Power Laboratory. Earlier measurements were made for a wide range of water-to-uranium (H2O:U) volume ratios (1:1 to 8:1) using 4-ft (1.2-m)-high slightly enriched, 0.387-in. (0.98-cm)-diam uranium metal or oxide fuel rods clad with aluminum. The new data have been compared with current analytic techniques, using both P-1 and P-3 multigroup analysis in the epithermal neutron energy range and Monte Carlo multigroup methods for thermal neutrons. This extremely undermoderated lattice provides a very stringent test for both the computational methods and the neutron cross sections used. The quantities measured were: the ratio of epithermal-to-thermal radiative captures in U238(ρ28); the ratio of captures in U238to fissions in U235(the modified conversion ratio, CR*); the ratio of U238fisions to U235fissions (δ28); and the ratio of epithermal-to-thermal U235fissions (δ25). In addition, activations were obtained with thermal-neutron detectors of widely different spectral response.The results indicate that the calculational methods predict the parameters very well, except forδ28. The discrepancy inδ28may be due to inadequate U238inelastic scattering cross sections, but this conclusion requires additional study. Monte Carlo calculations of thermal-neutron detector activations show that use of either the Nelkin or Koppel kernel gives results that agree with the data.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21073

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractDoubleP/0diffusion theory is shown to be a sufficiently accurate representation for calculating resonance absorption and its temperature coefficient. The theory is formulated to allow for non-uniform temperature distributions and spatial variation of neutron cross sections. It is applied to uranium rods in graphite-moderated reactors, assuming a parabolic fuel-temperature distribution. Volume and surface temperature coefficients for absorption are defined. The energy distributions of these coefficients in strongly absorbing resonances are shown to differ significantly. It is found that the total volume coefficient exceeds the total surface coefficient by 15% at normal operating temperatures. At higher temperatures the total volume coefficient is larger by 5%. Rowlands' formula for the effective uniform temperature is shown to be reliable for calculating the resonance integral and the volume temperature coefficient, but not for the surface coefficient.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21074

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

摘要:

AbstractA theory of neutron transport which includes polarization effects is developed. We have in mind, in particular, the polarization of fast neutrons that results when they are scattered by unpolarized nuclei–an effect explained by a neutron-nucleus spin-orbit interaction. The polarization of neutrons is described by a quantum-mechanical polarization vector. We first examine the change of this vector in scattering and thence formulate a general transport theory in terms of two coupled transport (Boltzmann) equations for the scalar neutron flux and the vector polarization flux. For plane or spherical geometry we show that the polarization vector is always normal to the (r̂,Ω) plane and thus obtain two coupled scalar transport equations for the flux and this one component of the polarization flux. A spherical harmonics solution is developed wherein the neutron flux is expanded in Legendre polynomials and the polarization flux is expanded in associated Legendre functions of the first kind. In theP1approximation the effect of polarization on the neutron flux is obtained by simply increasing the transport cross section. The polarization flux is then proportional to the neutron current (as a function of position) times sinθwith cosθ= r̂·Ω, as usual. Higher-order spherical-harmonics values are found for the asymptotic diffusion length, and numerical results are calculated for neutrons scattered from uranium. We conclude that theP1theory can be used to obtain a reasonable estimate of the polarization effects and that the changes in diffusion length due to polarization are generally small, but may be a few percent for the energy range where thepwave scattering is important. The polarization of neutrons in a multiplying assembly should be experimentally observable.

ISSN:0029-5639    

DOI:10.13182/NSE65-A21075

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE65-A21076

出版商:Taylor&Francis    

年代:1965

数据来源: Taylor