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Neutron Kinetics for Reflected Compact Reactors on Short Periods

Description: The common seventh group approximation for treating the effect of neutron delay due to reflector slowing down and thermalization is presented. Modifications appropriate when reactivity changes are produced by reflector movements are introduced. An improved formulation, allowing distinctions between several different groups of slowing down and thermalizing neutrons, is presented. This formulation is shown to reduce to the seventh group approximation for the case of one atypical neutron group, providing the population and reaction rate of the group are small in comparison to the total neutron population and reaction rate. (auth)
Date: June 1, 1963
Creator: Miller, J.
Partner: UNT Libraries Government Documents Department


Description: The neutron and delayed neutron precursor contents and the temperature of a reactor are treated as random variables participating in a multiplicative stochastic process. It is shown that stationary fluctuations in these variables are moderated by the presence of delayed neutrons, a large neutron source, and a large negative temperature coefficient. Reactor instability with a positive temperature coefficient is discussed in terms of the non-existence of a stationary process. (auth)
Date: November 1, 1958
Creator: Harris, D.R.
Partner: UNT Libraries Government Documents Department

Thermal neutron imaging support with other laboratories BL06-IM-TNI

Description: The goals of this project are: (1) detect and locate a source of thermal neutrons; (2) distinguish a localized source from uniform background; (3) show shape and size of thermalizing material; (4) test thermal neutron imager in active interrogation environment; and (5) distinguish delayed neutrons from prompt neutrons.
Date: June 17, 2008
Creator: Vanier, P. E.
Partner: UNT Libraries Government Documents Department


Description: Many techniques have been developed and applied in the US and other countries for the control of the special nuclear materials (SNM) plutonium and uranium, but no standard methods exist for the determination of neptunium in bulk containers. Such methods are needed because the U.S. Department of Energy requires all Government-owned {sup 237}Np be treated as if it were SNM and the International Atomic Energy Agency is considering how to monitor this material. We present the results of the measurements of several samples of neptunium metal with a variety of techniques. Analysis of passive gamma-ray spectra uniquely identifies the material, provides isotopic ratios for contaminants, such as {sup 243}Am, and may provide information about the shielding, mass, and time since processing. Active neutron interrogation, using the delayed neutron technique in a package monitor, provides useful data even if the neptunium is shielded. The tomographic gamma scanner yields a map of the distribution of the neptunium and shielding in a container. Active photon interrogation with pulses from a 10-MeV linac produces delayed neutrons between pulses, even when the container is heavily shielded. Data from one or more of these techniques can be used to identify the material and estimate a mass in a bulk container.
Date: October 1, 2000
Creator: MOSS, C. & AL, ET
Partner: UNT Libraries Government Documents Department

High-efficiency He-3 proportional counter for the detection of delayed neutrons

Description: The present work examines a high-neutron efficiency detector used to measure delayed neutron techniques. The measurement of delayed neutrons requires a detector system that has high neutron efficiency and a low dead- time. The detection system must also have low gamma-ray sensitivity, and in addition must be insensitive to small sample displacement. The operating characteristics of the high-efficiency He-3 proportional counter used for the measurement of {beta}{sub i}-delayed neutrons is reported here.
Date: March 1, 1998
Creator: Loaiza, D.J.
Partner: UNT Libraries Government Documents Department

Seven surrogate precursors for modeling delayed neutron decay and predicting reactivity

Description: The use of a different set of group decay constants for each fissionable nuclide complicates analysis of the dynamic behavior of fast reactors. A fast reactor containing six principal fissioning nuclides of uranium and plutonium must, in effect, be described by 36 delayed neutron groups. Additionally, the use of group decay constants that depend on the neutron energy spectrum makes it difficult to select values that describe the dynamic response of epithermal systems because virtually all delayed neutron activity measurements have been performed for fast or thermal-neutron-induced fission. Clearly, it would be desirable to have a single set of group decay constants that could be applied to all fissionable nuclides. A set of seven fixed decay constants is proposed herein. Each of the proposed decay constants is associated with a specific, dominant delayed neutron precursor. In effect, each group is represented by a single surrogate precursor. Using recently measured delayed neutron activities for U-235 and Np-237, the proposed set of decay constants actually improved the goodness of fit to the data. For other fissionable nuclides lacking experimental data, a method has been devised to obtain yields consistent with the proposed set of decay constants from the traditional six-group parameters. This transformation is accomplished without altering the traditional inferred reactivity scale.
Date: December 31, 1997
Creator: Loaiza, D.J. & Haskin, F.E.
Partner: UNT Libraries Government Documents Department

The shift of prompt critical in reflected reactors and the limitations of the mean prompt-neutron lifetime model

Description: Prompt critical in a bare reactor is defined as the point at which the reactivity {rho} of the reactor is equal to the effective delayed neutron fraction {beta}. In a reflected reactor, however, it is shown that prompt critical will occur at a reactivity of {rho} = {beta}(1-f) where f is the fraction of core neutrons that return to the core region after having leaked into the reflector. Furthermore, it is also shown that the mean prompt-neutron lifetime model that has been traditionally used to characterize the dynamic response of reflected reactors may not always provide an adequate representation of the system for reactivities greater than 1$. And finally, the coupled, point-kinetic equations proposed by Avery and further developed by Cohn for simple reflected systems are recast into a more usable form that can be readily used to perform superprompt critical transient analyses.
Date: August 1, 1994
Creator: Spriggs, G. D. & Busch, R. D.
Partner: UNT Libraries Government Documents Department


Description: The results of instability studies suggest that the operational characteristics of the fully ribbed and rigid Mark III loading are governed by feedback processes that guarantee safe and stable operation under normal operating condiiions. No evidence of positive reactivity effects was noted for the fully-ribbed rigid core. Logical extrapolations of full-power full-flow test data indicate that the reactor could be brought into a resonant condition for power levels exceeding 1000 Mw. Strong nonlinearities were observed in power coefficients and were considered to pose no serious operational problems above 200 kw in the power range associated with the tests. An application of the Nyquist stability criterion to the extrapolated fully sheared data results in the conclusion that the reactor would attain resonance instability at full flow at - 11 Mw. Logical extrapolations of test data for one-third flow results in resonance instability at -10 Mw, a power level -20 times that designed for onethird flow. Rib shearing was shown to result in an unexpected and unexplained increase in the magnitude of the delayed structural power coefficient component. An empirical fit of feedback data to a model describing the dynamic and static behavior of the partially sheared core resulted in ihe values for the respective prompt negative, rod-bowing, and delayed structural power coefficient components of -2.21 x 10/sup -6/ +0.543 x 10/sup -6/ and -0.873 x 10/sup -6/4 delta /k/kw. The over all behavior of the Mark III core, whether fully ribbed and rigid, fully ribbed and loose, or even partially or fully sheared, is one of extreme stability. The inclusion of stabilizing ribs and a system of tightening rods in the Mark lII design elimuinated, or at least reduced to a point beyond detection, the prompt positive rod-bowing component that existed in the Mark II. (B.O.G.)
Date: December 1, 1960
Creator: Smith, R.R.; Boland, J.F.; McGinnis, F.D.; Novick, M. & Thalgott, F.W.
Partner: UNT Libraries Government Documents Department

Status of the Prototype Pulsed Photonuclear Assessment (PPA) Inspection System

Description: Prototype Photonuclear Inspection Technology – An Integrated Systems Approach* James L. Jonesa, Daren R. Normana, Kevin J. Haskella, James W. Sterbentza, Woo Y. Yoona, Scott M. Watsona, James T. Johnsona, John M. Zabriskiea, Calvin E. Mossb, Frank Harmonc a – Idaho National Laboratory, P.O. Box 1625-2802, Idaho Falls, Idaho 83415-2802 b – Los Alamos National Laboratory, P.O. Box 1663, MS B228, Los Alamos, New Mexico, 87585 c – Idaho State University, 1500 Alvin Ricken Dr., Pocatello, Idaho 83201 Active interrogation technologies are being pursued in order to address many of today’s challenging inspection requirements related to both nuclear and non-nuclear material detection. The Idaho National Laboratory, along with the Los Alamos National Laboratory and the Idaho State University’s Idaho Accelerator Center, continue to develop electron accelerator-based, photonuclear inspection technologies for the detection of shielded nuclear material within air-, rail-, and especially, maritime-cargo containers. This paper presents an overview and status of the prototype Pulsed Photonuclear Assessment (PPA) inspection system and its ability to detect shielded nuclear material by focusing on the integration of three major detection system components: delayed neutron measurement, delayed gamma-ray measurements, and a transmission, gray-scale mapping for shield material detection. Areas of future development and advancement within each detection component will be presented. *Supported in part by the Department of Homeland Security under DOE-ID Contract Number DE-AC07-99ID13727. POC: James L. Jones, 208-526-1730
Date: August 1, 2007
Creator: An, Prototype Photonuclear Inspection Technoloby -
Partner: UNT Libraries Government Documents Department

Beta-decay half-lives and beta-delayed neutron emisison probabilities of nuclei in the region A. 110, relevant for the r-process

Description: Measurements of the {beta}-decay properties of A {approx}< 110 r-process nuclei have been completed at the National Superconducting Cyclotron Laboratory, at Michigan State University. {beta}-decay half-lives for {sup 105}Y, {sup 106,107}Zr and {sup 108,111}Mo, along with ,B-delayed neutron emission probabilities of 104Y, 109,11OMo and upper limits for 105Y, 103-107Zr and 108,111 Mo have been measured for the first time. Studies on the basis of the quasi-random phase approximation are used to analyze the ground-state deformation of these nuclei.
Date: January 1, 2009
Creator: Moller, Peter; Pereira, J; Hennrich, S; Aprahamian, A; Arndt, O; Becerril, A et al.
Partner: UNT Libraries Government Documents Department


Description: The method of neutron activation analysis of U by delayed-neutron counting was investigated in order to ascertain if the method would be suitable for routine application to such analyses. It was shown that the method can be used extensively and routinely for the determination of U. Emphasis was placed on the determination of U in the types of sample materials encountered in nuclear technology. Determinations of U were made on such materials as ores, granite, sea sediments, biological tissue, graphite, and metal alloys. The method is based upon the fact that delayed neutrons are emitted from fission products from the interaction of neutrons with U/sup 235/. Since the U/sup 235/ component of U undergoes most of the fissions when a sample is in a neutron flux, the method is predominately one for the determination of U/sup 235/. The total U in a sample or the isotopic composition of the U in a sample can be determined provided there is a prior knowledge of one of these quantities. The U/sup 235/ content of a test sample is obtained by comparing its delayed-neutron count to that obtained with a comparator sample containing a known quantity of U/sup 235/. (auth)
Date: October 16, 1962
Creator: Dyer, F.F.; Emery, J.F. & Leddicotte, G.W.
Partner: UNT Libraries Government Documents Department


Description: An experimental determination of the reduced prompt neutron generation time LAMBDA / BETA in the Spert IV reactor utilizing a technique based on the statistical behavior of the neutron population is described. A mathematical model including the effects of delayed neutrons that relates the statistic variance-to-mean ratio of the count rate as a function of counting time'' to integral reactor parameters is derived. This model is used in conjunction with subcritical counting measurements from the Spert IV reactor to provide a value of LAMBDA / BETA that is in good agreement with an independent measurement obtained from super promptcritical excursion experiments. (auth)
Date: August 1, 1963
Creator: Johnson, R.L.
Partner: UNT Libraries Government Documents Department

Development of a Methodology for Analysis of Delayed-Neutron Signals

Description: Experimental and analytical techniques have been developed for analysis and characterization of delayed-neutron (DN) signals that can provide diagnostic information to augment data from cover-gas analyses in the detection and identification of breached elements in an LMFBR. Eleven flow-reduction tests have been run in EBR-II to provide base data support for predicting DN signal characteristics during exposed-fuel operation. Results from the tests demonstrate the feasibility and practicability of response-analysis techniques for determining (a) the transit time, for DN emitters traveling from the core to the detector and (b) the isotropic holdup time, of DN precursors in the fuel element.
Date: February 1980
Creator: Gross, K. C.; Strain, R. V. & Fryer, R. M.
Partner: UNT Libraries Government Documents Department

Measurements of delayed neutron emission from Np-237, Am-241, and Am-243

Description: Isotopes of transuranic elements are produced as a result of successive radiative capture reactions in the fuel of a nuclear reactor. Typically, these transuranic isotopes decay through long chains, have long half lives and dominate the long term toxicity of the spent reactor fuel. One of the options for waste management is to remove the transuranic from spent fuel by chemical processing, to load them into new special fuel elements, and to transmute them by neutron induced fission into shorter-lived fission fragments. Previous studies have shown the feasibility of actinide transmutation in either Light Water Reactors or Liquid Metal Fast Reactors. Due to the anticipated high transuranic loadings in the fuel of actinide burner reactors, the neutronic properties of the transuranic isotopes will have a significant effect on the operational and safety characteristics of such reactors. Experiments to determine delayed neutron group yields and decay constants for Np-237, Am-241, and Am-243 have been designed and carried out. The experiments were conducted at Texas A&M University TRIGA reactor using a very fast pneumatic transfer system.
Date: December 1995
Creator: Saleh, H. H.; Parish, T. A. & Raman, S.
Partner: UNT Libraries Government Documents Department


Description: >An experimental measurement of the effective delayed neutron fraction ( beta -bar) was made for a clean critical assembly by determining the asymptotic period associated with introduction of a known amount of reactivity. The "known amount" of reactivity was obtained by replacing, uniformly throughout the reactor, a small quantity of U/sup 235/ with an alloy of B/sup 10/ and Hf designed to match the absorption properties of U/sup 235/. The replacement was thus equivalent to a uniform reduction in nu , the number of neutrons emitted per fission from the fuel. Such a reduction introduces a reactivity change equal exactly to delta nu / nu /sub 0/. Two analyses of the experiment were made using different high energy cross sections in conjunction with four group, two dimensional diffusion theory. The measured value of beta lay between the results of these computations, the error spread (an average rms error of plus or minus 5.2%) being too great to permit any conclusion regarding the significance of the comparison. (auth)
Date: February 1, 1960
Creator: Kaplan, S. & Henry, A.F.
Partner: UNT Libraries Government Documents Department


Description: Calculations of critical size, reactivity coefficients, and delayed neutron fractions are described for mockups of a plutonium-fueled EBR-I (Mark IV) and five possible metal-fueled power reactors. The calculations for critical size were performed using the SNG transport-theory code. The reactivity coefficients were estimated by SNG calculations or by one-group perturbation- theory desk calculations. The delayed-neutron fractions were estimated by an approximate method, which starts with a calculation of beta for a bare core and then makes a correction for the small effect of the blanket. The reactivity effects studied were the effects of fuel-plate and whole-core expansion and control-rod worths. (auth)
Date: September 1, 1960
Creator: Baker, A.R.
Partner: UNT Libraries Government Documents Department


Description: A brief review of the theoretical water-boiler reactor-power transfer function is presented as background for the experimental determination of the ratio of effective prompt neutron lifetime to the effective fraction of delayed neutrons, 1/beta. The preparation and performance ot the experiment are discussed with special emphasis on equipment procedures, and measurement errors. The results, which strongly support a seven-delay-group model of the reactor, are presented and compared with theoretical six-and seven-group models. The experiment indicates qualitative values of the seventh-group constants, and it also indicates an 1/beta = 7.7 plus or minus 0.3 msec valid for all but short- period transients. (auth)
Date: December 1, 1960
Creator: Cordy, R.N.
Partner: UNT Libraries Government Documents Department

N-17, A Delayed Neutron Emitter

Description: The decay scheme of a 4.2 second neutron emitter has been investigated in detail. Chemical and physical evidence shows that it is N{sup 17}, which emits beta rays to a broad excited state of O{sup 17}, which then breaks up into a neutron plus O{sup 16}. The energy spectrum of the neutrons is determined by measuring the energies of the O{sup 16} recoils in a proportional counter. The neutrons have a most probable energy of 0.9 Mev, a 'half width' of less than .5 Mev, and an upper limit of about 2 Mev. {beta}-recoil coincidences are observed, as predicted by the Bohr-Wheeler theory, and the {beta}-ray energy is measured by absorption. The beta rays in coincidence with neutrons have an upper limit of 3.7 {+-} 0.2 Mev. Beta-rays directly to the ground stat of O{sup 17} are not observed because of high background effects, but should have an energy of 8.7 Mev. Some evidence is presented to show that energy is conserved in the {beta}-n transition through the broad excited state in O{sup 17}.
Date: November 5, 1948
Creator: Alvarez, L. W.
Partner: UNT Libraries Government Documents Department

Report on the workshop "Decay spectroscopy at CARIBU: advanced fuel cycle applications, nuclear structure and astrophysics". 14-16 April 2011, Argonne National Laboratory, USA.

Description: A workshop on 'Decay Spectroscopy at CARIBU: Advanced Fuel Cycle Applications, Nuclear Structure and Astrophysics' will be held at Argonne National Laboratory on April 14-16, 2011. The aim of the workshop is to discuss opportunities for decay studies at the Californium Rare Isotope Breeder Upgrade (CARIBU) of the ATLAS facility with emphasis on advanced fuel cycle (AFC) applications, nuclear structure and astrophysics research. The workshop will consist of review and contributed talks. Presentations by members of the local groups, outlining the status of relevant in-house projects and availabile equipment, will also be organized. time will also be set aside to discuss and develop working collaborations for future decay studies at CARIBU. Topics of interest include: (1) Decay data of relevance to AFC applications with emphasis on reactor decay heat; (2) Discrete high-resolution gamma-ray spectroscopy following radioactive decya and related topics; (3) Calorimetric studies of neutron-rich fission framgents using Total ABsorption Gamma-Ray Spectrometry (TAGS) technique; (4) Beta-delayed neutron emissions and related topics; and (5) Decay data needs for nuclear astrophysics.
Date: October 6, 2011
Creator: Kondev, F.; Carpenter, M.P.; Chowdhury, P.; Clark, J.A.; Lister, C.J.; Nichols, A.L. et al.
Partner: UNT Libraries Government Documents Department

Monte Carlo Simulation for LINAC Standoff Interrogation of Nuclear Material

Description: The development of new techniques for the interrogation of shielded nuclear materials relies on the use of Monte Carlo codes to accurately simulate the entire system, including the interrogation source, the fissile target and the detection environment. The objective of this modeling effort is to develop analysis tools and methods-based on a relevant scenario-which may be applied to the design of future systems for active interrogation at a standoff. For the specific scenario considered here, the analysis will focus on providing the information needed to determine the type and optimum position of the detectors. This report describes the results of simulations for a detection system employing gamma rays to interrogate fissile and nonfissile targets. The simulations were performed using specialized versions of the codes MCNPX and MCNP-PoliMi. Both prompt neutron and gamma ray and delayed neutron fluxes have been mapped in three dimensions. The time dependence of the prompt neutrons in the system has also been characterized For this particular scenario, the flux maps generated with the Monte Carlo model indicate that the detectors should be placed approximately 50 cm behind the exit of the accelerator, 40 cm away from the vehicle, and 150 cm above the ground. This position minimizes the number of neutrons coming from the accelerator structure and also receives the maximum flux of prompt neutrons coming from the source. The lead shielding around the accelerator minimizes the gamma-ray background from the accelerator in this area. The number of delayed neutrons emitted from the target is approximately seven orders of magnitude less than the prompt neutrons emitted from the system. Therefore, in order to possibly detect the delayed neutrons, the detectors should be active only after all prompt neutrons have scattered out of the system. Preliminary results have shown this time to be greater than 5 ?s ...
Date: June 1, 2007
Creator: Clarke, Shaun D; Flaska, Marek; Miller, Thomas Martin; Protopopescu, Vladimir A & Pozzi, Sara A
Partner: UNT Libraries Government Documents Department