Download or read book Evaluation and Application of Delayed Neutron Precursor Data written by Michaele Clarice Brady and published by . This book was released on 1988 with total page 564 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Evaluated Delayed Neutron Precursor Data written by and published by . This book was released on 1987 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Based on energetics, approx. 270 fission products should be delayed neutron precursors. Of these, approx. 85 have measured and evaluated emission probabilities (Pn's) and approx. 34 have measured spectra data; the latter account for 80% or more of the total anti .nu./sub d/. Although the measurements are probably adequate for most reactor applications, complete data sets are needed for ENDF/B and for fission product yield evaluations. This paper briefly describes the use of systematics and nuclear models used to produce a complete set of data for 272 precursors and presents aggregate summation calculations needed to produce the conventional six time-group approximations. 10 refs., 2 figs.
Download or read book Delayed Neutron Spectra and Intensities from Evaluated Precursor Data written by and published by . This book was released on 1985 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently evaluated and model estimated precursor data are used with preliminary ENDF/B-VI fission yields to calculate total and time-group anti nu/sub d/ and spectra. 8 refs.
Download or read book Delayed Neutron Spectra Decay Group for Fissioning Systems from 227Th Through 255Fm written by and published by . This book was released on 1988 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Most applications of delayed neutrons use an approximate temporal group representation of measured aggregate data. Such data have been limited to the few fissioning nuclides that have aggregate measurements, and even these have inadequate or no spectral measurements. Improvements in the experimental techniques of isotope separation and neutron spectroscopy have made the study of delayed neutron emission from individual precursor nuclides more practical and productive over the past fifteen or so years. The quantity and quality of the delayed neutron emission probabilities and particularly the neutron emission spectra for the individual nuclides have been greatly improved. This paper will briefly review a recently completed evaluation of precursor data that comprises the largest single set of such data to date, and will also describe how the precursor data has been used to produced delayed neutron yields, halflives, and spectra in the classical six-group representation for 43 fissioning systems from 227Th to 225Fm. Comments and observations made concerning the use of more than six time groups will also be included. The application of the data in both its explicit and reduced (six temporal group representation) forms in the point reactor kinetics equations will also be discussed. Results from beta-effective calculations in a simple Godiva-type system will be presented, but the paper will concentrate on the data base and its few-group representations. 17 refs., 1 fig., 1 tab.
Download or read book Delayed Neutron Spectra by Decay Group for Fissioning Systems from 227Th Through 255Fm written by and published by . This book was released on 1988 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The quality and quantity of delayed neutron precursor data has greatly improved over the past approximately 15 years. Supplementation of the data with model calculations and the use of models to extend the number of precursors to 271 is now practical. These data, along with improved fission-product parameters, permit direct calculations of aggregate behavior for many fissioning nuclides. The results can even be approximated using a few (usually six) temporal groups. This paper summarizes an extensive four-year effort to provide a complete set of evaluated data and emphasizes its use to generate the temporal approximations; precursor data and group values are intended for inclusion in ENDF/B-VI. 19 refs., 8 figs., 1 tab.
Download or read book Delayed Neutrons from Fissionable Isotopes of Uranium Plutonium and Thorium written by George Robert Keepin and published by . This book was released on 1957 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Evaluation of Delayed neutron Data and Associated Covariances written by Daniela Foligno and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the context of nuclear reactor physics, one of the main issues is the control of the chain reaction. After a fission event has occurred, around three prompt neutrons are immediately emitted. Luckily, a small fraction of neutrons - less than 1% - appears with a certain delay with respect to the fission event. Delayed neutrons (DN) are an easy way out from the uncontrollable prompt-neutron driven chain reaction because they slow down the response of the reactor to a change in reactivity. Quantifying the fraction of such neutrons as well as their kinetic behavior is essential to design a safe reactor. The main consequence of a lack of accurate DN data is the conservatism in the design of a reactor. Nowadays, the discrepancy between the reactivity simulated using different international databases, rises up to 16% for LWRs, and the uncertainties associated with the recommended parameters are still too large for the needs of the industry. The DN parameters are generally estimated through a calculation or an integral measurement. This Ph.D. aims at producing a new set of DN parameters by performing both calculations and measurements, and by exploiting the two through the Bayesian inference, with the aim of reducing the uncertainties and creating the associated covariance matrices.The results for 235U, together with the calculated values for 238U, have been tested in three benchmarks, giving satisfying solutions with respect to the effective delayed neutron fraction. The main achievement of this work is the great improvement in the predicted reactivity, especially for negative periods, which is accompanied by an extremely good precision, never exceeding 2.2%.
Download or read book Delayed Neutrons from Fission written by and published by . This book was released on 1972 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Delayed Neutron Data written by and published by . This book was released on 1974 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: BS>The status of delayed neutron measurements is reviewed. Emphasis is placed on the absolute yield va the energy of the neutrons cauging fission, group yields and periods, and in the delayed neutron spectra. Systematics are discussed; and an evaluated data set, based both on available measurements and on systematics arguments, is suggested for inclusion in ENDF/B-IV. Areas of delayed neutron studies which require additional measurements are outlined. (18 figures, 18 tables) (auth).
Download or read book Delayed Neutrons written by George Robert Keepin and published by . This book was released on 1955 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive review is given of existing measurements as of October 1955 on the properties of delayed neutrons from various fissionable isotopes. The relation of these measurements to current theory and practice is discussed.
Download or read book Delayed Neutrons Form Fission written by L. Tomlinson and published by . This book was released on 1972 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Uncertainty Evaluation of Delayed Neutron Decay Parameters written by Jinkai Wang and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In a nuclear reactor, delayed neutrons play a critical role in sustaining a controllable chain reaction. Delayed neutron's relative yields and decay constants are very important for modeling reactivity control and have been studied for decades. Researchers have tried different experimental and numerical methods to assess these delayed neutron parameters. The reported parameter values vary widely, much more than the small statistical errors reported with these parameters. Interestingly, the reported parameters fit their individual measurement data well in spite of these differences. This dissertation focuses on evaluation of the errors and methods of delayed neutron relative yields and decay constants for thermal fission of U-235. Various numerical methods used to extract the delayed neutron parameter from the measured data, including Matrix Inverse, Levenberg-Marquardt, and Quasi-Newton methods, were studied extensively using simulated delayed neutron data. This simulated data was Poisson distributed around Keepin's theoretical data. The extraction methods produced totally different results for the same data set, and some of the above numerical methods could not even find solutions for some data sets. Further investigation found that ill-conditioned matrices in the objective function were the reason for the inconsistent results. To find a reasonable solution with small variation, a regularization parameter was introduced using a numerical method called Ridge Regression. The results from the Ridge Regression method, in terms of goodness of fit to the data, were good and often better than the other methods. Due to the introduction of a regularization number in the algorithm, the fitted result contains a small additional bias, but this method can guarantee convergence no matter how large the coefficient matrix condition number. Both saturation and pulse modes were simulated to focus on different groups. Some of the factors that affect the solution stability were investigated including initial count rate, sample flight time, initial guess values. Finally, because comparing reported delayed neutron parameters among different experiments is useless to determine if their data actually differs, methods are proposed that can be used to compare the delayed neutron data sets.
Download or read book Technique for the Identification of Dominant Delayed Neutron Precursors written by and published by . This book was released on 2001 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: A technique for the identification of delayed neutron precursors has been developed based on the product of cumulative yield and probability of neutron emission. The motivation behind this work is to fix the decay constants of delayed neutrons to those of the dominant delayed neutron precursors. The desirability of identifying a single set of decay constants that would apply to all fissionable isotopes and be independent of the neutron energy spectrum has been addressed by several authors. The main advantages of a fixed-decay constant representation are simplifying the analysis of epithemal and fast reactors with multiple fissioning isotopes, and improving the fit to experimental data while preserving the inferred positive reactivity scale associated with the original six-group representation. It is well known that 27 1 delayed neutron precursors exist, but only a select number of those precursors contribute significantly to the decay of delayed neutron. Using data compiled by England and Rider, which lists fission yield and probability of neutron emission values for the 27 1 known delayed neutron precursors in 32 fissioning systems, thirteen precursors were identified that are consistently dominant for alI fissioning systems.
Download or read book Validation of Aggregate Delayed Neutron Spectra Calculated from Precursor Data written by and published by . This book was released on 1989 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: An extensive reference library of delayed neutron data has been compiled which contains fission yields and branchings, delayed neutron emission probabilities, and spectra for 271 precursors. These data have been used to calculate the aggregate behavior of delayed neutrons following a fission event in 43 fissioning systems. Least-squares techniques were used to produce fitted decay constants and abundances in the conventional six-group formalism from these calculated activity curves. A consistent set of six-group spectra have also been calculated for each of the fissioning systems. Recent measurements at the University of Lowell have produced measured energy spectra for delayed neutrons following the thermal fission (T) of 235U and 239Pu, and the fast fission (F) of 238U. These measured spectra provide data that may be used to validate the precursor data base and the fitted six-group data. This summary presents results of this validation effort. Both the individual precursor data and the six-group data have been used to calculate aggregate equilibrium spectra for 235U(T), 238U(F), and 239Pu(T) via summation techniques. The important precursors in each case are identified, and the status of their data reviewed. 8 refs., 3 figs., 3 tabs.
Download or read book Few group Representation of the Energy Spectra of Delayed Neutrons written by and published by . This book was released on 1987 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The importance of delayed neutrons in reactor calculations has been well established. A recent evaluation of delayed neutron data has resulted in the compilation of a reference library containing emission probabilities, Pn's, and energy spectra for approx. 272 individual precursor nuclides. The library may be used to calculate aggregate spectra and total delayed neutron yields. 10 refs., 1 fig., 1 tab.
Download or read book Energy Research Abstracts written by and published by . This book was released on 1994-04 with total page 526 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Delayed Neutron Data for the Major Actinides written by G. Rudstam and published by . This book was released on 2002 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt:
