摘要:

AbstractThe fission cross section of243Am was measured in the neutron energy range from 1 eV to 10 MeV. Several methods of neutron production were employed using the Van de Graaff accelerator and the electron linear accelerator of the Central Bureau of Nuclear Measurements. The energy averaged fission cross section measured at the Geel electron linear accelerator (GELINA) above 100 eV and the fission cross sections measured at the Van de Graaff above 350 keV were determined relative to the235U(n,f) cross section. The detailed neutron cross sections measured at GELINA in the 1-eV to 30-keV range were measured relative to the6Li(n, t)4He cross-section shape and were normalized to the known fission integral of235U between 7.8 and 11 eV. The present data provide unique new information between 1 and 50 eV. In this energy range, fission areas from 31 resonances were determined. In the subthreshold region above 100 eV, the present results demand drastic corrections of the evaluated data files by factors up to 6. Between the first and second chance fission threshold, the present experiment supports the ZEBRA integral experiment, which suggested a reduction of the fission cross section of243Am in this region by 12% with respect to an earlier data set.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23540

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractThe longer term response of oxide- and metal-fueled liquid-metal-cooled reactors to unscrammed loss-of-flow and loss-of-heat-sink failures is investigated. The investigation consists of a review of numerical transient calculations performed by the Argonne National Laboratory Reactor Analysis and Safety Division, and of analytical analyses of semiasymptotic states. The emphasis is on the identification and evaluation of an inherent shutdown state for metal fuel, with its high heat conductivity, as an alternative to the familiar low-power asymptotic critical state. Design implications for retaining the inherently effected shutdown for a sufficiently long period are discussed and quantitatively evaluated. In addition, the effect of uncertainties of reactivity coefficients on predictions for such unscrammed transients is investigated. It is shown how measurements during a preoperational safety demonstration phase can validate and possibly correct those predictions.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23541

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractThe source of correlation for the signals from detectors in the presence of a stochastic neutron field is analyzed for a variety of circumstances. A general methodology, based on a master equation approach, is compared with the Langevin/Schottky method with the result that there is consistency if the detection process is included in detail. For cases where the detector removes the detected neutron, the only sources of correlation are elementary processes that produce more than one neutron; consequently, the Schottky prescription for the noise equivalent source must be corrected accordingly. An additional term because of the finite electronic resolution is also found and added to the noise equivalent source. Because of the relevance of the subject to the theory of the252Cf source noise method to measure reactivities, the general results are applied to interpret a recently performed experiment with this type of source.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23542

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractA vectorized source algorithm was developed for the Electric Power Research Institute light water reactor core nodal code SIMULA TE-E. The existing line successive displacement scheme was replaced by configuring the source for all nodes in a given plane as a single vector that could be computed simultaneously. Power distributions and eigenvalues for all test problems agreed exactly with the original scalar code. A factor of 2 to 7 reduction in execution time was achieved for typical pressurized water reactor problems on the CYBER 205.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23543

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractAxial distributions of fissions and of fertile-to-fissile conversions in thick depleted uranium and thorium targets bombarded by 800-MeV protons have been measured. The amounts of239Pu and233U produced were determined by measuring the yields of239Np and233Pa, respectively. The number of fissions was deduced from fission product mass-yield curves. Integration of the axial distributions gave the total number of conversions and fissions occurring in the targets. For the uranium target, experimental results were 5.90±0.25 fissions and 3.81±0.01 atoms of239Pu produced per incident proton. Corresponding calculated results were 6.14±0.04 and 3.88±0.03. In the thorium target, 1.56±0.25 fissions and 1.25±0.01 atoms of233U per incident proton were measured; the calculated values were 1.54±0 0.01 fissions and 1.27±0.01 atom/proton.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23544

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractThe mathematical derivation and application of two deterministic sensitivity analysis methods, the direct approach of sensitivity (DAS) and the adjoint sensitivity method (ASM), are presented for two-phase flow problems. The physical problems investigated are formulated by the transient onedimensional two-phase flow diffusion model, which consists of a system of four coupled quasi-linear first-order partial differential equations. The DAS method provides the sensitivity coefficients of all primary dependent variables at each time and space location with respect to a single input parameter. On the other hand, the ASM provides the sensitivity coefficients of a single response function at a specified time and space location with respect to all input parameters.The systems of governing equations of both sensitivity methods developed possess the same characteristic directions as those of the original physical model. Therefore, the same numerical methods for the solution of these equations have been selected as for the solution of the physical problem, i.e., Turner scheme and modified Turner (NAIAD) scheme. Special techniques to incorporate the boundary conditions of the ASM governing equations for each numerical scheme have been developed. The sensitivity coefficients computed by both methods have been verified against results from standard parametric studies. Two sample problems are thoroughly investigated. The first problem considers the transient fluid behavior in a uniformly heated channel subjected to an inlet flow decay. The second problem considers the transient fluid response within the same channel when a pressure step change at the channel inlet is imposed. Both methods predict satisfactorily the sensitivity coefficient behavior in space and time in comparison with parametric studies, even when a moving boiling boundary exists within the flow field. Certain coefficients in the thermodynamic correlations of the liquid density and the liquid saturation enthalpy, as well as the boundary conditions of the problems, were found to be the most“sensitive”input parameters in both problems investigated. Some input parameters of minor significance in the steady-state conditions were found to be very“influential”during the transient and vice versa. The behavior of most of the sensitivity coefficients, in space and time, cannot be estimated without a systematic sensitivity analysis method.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23545

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

摘要:

AbstractA procedure has been developed for preparing 3- to 9-ℓvolumes of air under natural conditions with a known concentration of222Rn to be used for calibrating radon systems. Air is passed into a plastic bag through a standard226Ra solution (prepared by the U.S. National Bureau of Standards) contained in an emanation flask. This plastic bag retains222Rn with little loss into or through the bag walls. The mean ratios of the222Rn in the air at 2 and 7 days after filling to that immediately after filling were 0.992±0.006 and 0.969±0.008, which suggests a rate of radon loss into the bag of 0.4±0.1%/day. The air from the bag was used to calibrate six Lucas chambers. Each chamber was calibrated 11 times with an average fractional standard error of the mean of 0.5%. This value is greater than the 0.2% expected from counting errors alone and suggests that the entire calibration procedure plus the counting system introduces a systematic standard deviation of 1.4% for each individual calibration and counting procedure. The bag and calibrated counters can also be used to determine the226Ra and the222Rn content of water. In addition, by replacing the air with other flush gases, calibration factors for gas mixtures other than air can be determined. The accuracy of these calibrations was verified by comparison with four methods, three of which are completely independent. The results by all four methods agree within±1%.

ISSN:0029-5639    

DOI:10.13182/NSE88-A23546

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE88-A23547

出版商:Taylor&Francis    

年代:1988

数据来源: Taylor