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Description: A description of the TREAT facility is presented. The static characteristics of the reactor which pertain to its dynamic behavior, such as temperature coefficient and prompt-neutron lifetime, are discussed. Also considered are other phenomena, the analyses of which provide some measure of the general adequacy of the calculational techniques employed. The correlation and analysts of transientexperiment results on this clean-geometry reactor are examined in considerable detail. In addition, an extrapolation of the reactor's performance beyond the present low design limitation of 400 deg C maximum local temperatare is included. (auth)
Date: September 1, 1960
Creator: Okrent, D.; Dickerman, C. E.; Gasidlo, J.; O'Shea, D. M. & Schoeberle, D. F.
Partner: UNT Libraries Government Documents Department


Description: The prompt neutron lifetime of the SRE was measured by both the oscillation and random noise techniques. Measurement by use of the oscillation technique gave a prompt neutron lifetime of (5 25 plus or minus 0 35) x 10/sup - 4/ sec for a calculated beta of 7 x 10/sup -3/. The measured noise response indicated a lifetime of (5.25 plus or minus 0.7) x 10/sup -4/ sec. Both measured values are in agreement with the calculated value of 5 x 10/sup -4/ sec. Four experiments utilizing the noise analysis technique were performed to determine the prompt neutron lifetime of the KEWB. All four experiments gave results which agreed within 3%, For an estimated beta of 8 x 10/sup -3/, the measured value obtained was (7.8 plus or minus 0.3) x 10/sup -5/ sec. This is in reasonable agreement with both the energy independert calculated value of 6.6 x 10/sup -5/ see and the value of 6.2 x 10/sup -5/ sec obtained from the experimental inhour equation The oscillation technique has been found to be better suited for lifetime determinations in reactors where the prompt neutron break frequency is less than 5 cps. Reactor noise analysis is more suitable for reactors which have prompt neutron lifetime break frequencies above 20 cps. (auth)
Date: October 15, 1959
Creator: Griffin, C.W. & Lundholm, J.G. Jr.
Partner: UNT Libraries Government Documents Department

Experiments with the Dragon Machine

Description: The basic characteristics of a self-sustaining chain reaction were demonstrated with the Chicago Pile in 1943, but it was not until early 1945 that sufficient enriched material became available to experimentally verify fast-neutron cross-sections and the kinetic characteristics of a nuclear chain reaction sustained with prompt neutrons alone. However, the demands of wartime and the rapid decline in effort following the cessation of hostilities often resulted in the failure to fully document the experiments or in the loss of documentation as personnel returned to civilian pursuits. When documented, the results were often highly classified. Even when eventually declassified, the data were often not approved for public release until years later.2 Even after declassification and approval for public release, the records are sometimes difficult to find. Through a fortuitous discovery, a set of handwritten notes by ''ORF July 1945'' entitled ''Dragon - Research with a Pulsed Fission Reactor'' was found by William L. Myers in an old storage safe at Pajarito Site of the Los Alamos National Laboratory3. Of course, ORF was identified as Otto R. Frisch. The document was attached to a page in a nondescript spiral bound notebook labeled ''494 Book'' that bore the signatures of Louis Slotin and P. Morrison. The notes also reference an ''Idea LS'' that can only be Louis Slotin. The discovery of the notes led to a search of Laboratory Archives, the negative files of the photo lab, and the Report Library for additional details of the experiments with the Dragon machine that were conducted between January and July 1945. The assembly machine and the experiments were carefully conceived and skillfully executed. The analyses--without the crutch of computers--display real insight into the characteristics of the nuclear chain reaction. The information presented here provides what is believed to be a complete collection of the original ...
Date: August 12, 2005
Creator: Malenfant, R.E.
Partner: UNT Libraries Government Documents Department

Event-by-Event Fission with FREYA

Description: The recently developed code FREYA (Fission Reaction Event Yield Algorithm) generates large samples of complete fission events, consisting of two receding product nuclei as well as a number of neutrons and photons, all with complete kinematic information. Thus it is possible to calculate arbitrary correlation observables whose behavior may provide unique insight into the fission process. The presentation first discusses the present status of FREYA, which has now been extended up to energies where pre-equilibrium emission becomes significant and one or more neutrons may be emitted prior to fission. Concentrating on {sup 239}Pu(n,f), we discuss the neutron multiplicity correlations, the dependence of the neutron energy spectrum on the neutron multiplicity, and the relationship between the fragment kinetic energy and the number of neutrons and their energies. We also briefly suggest novel fission observables that could be measured with modern detectors.
Date: November 9, 2010
Creator: Randrup, J. & Vogt, R.
Partner: UNT Libraries Government Documents Department

Calculation of 239Pu fission observables in an event-by-event simulation

Description: The increased interest in more exclusive fission observables has demanded more detailed models. We describe a new computational model, FREYA, that aims to meet this need by producing large samples of complete fission events from which any observable of interest can then be extracted consistently, including any interesting correlations. The various model assumptions are described and the potential utility of the model is illustrated. As a concrete example, we use formal statistical methods, experimental data on neutron production in neutron-induced fission of {sup 239}Pu, along with FREYA, to develop quantitative insights into the relation between reaction observables and detailed microscopic aspects of fission. Current measurements of the mean number of prompt neutrons emitted in fission taken together with less accurate current measurements for the prompt post-fission neutron energy spectrum, up to the threshold for multi-chance fission, place remarkably fine constraints on microscopic theories.
Date: March 31, 2010
Creator: Vogt, R; Randrup, J; Pruet, J & Younes, W
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

Comparison of neutron lifetimes as predicted by MCNP and DANTSYS

Description: The prompt removal lifetime algorithm used in the latest version of MCNP was modified to conform with the neutron-balance definitions described by Spriggs et al. In accordance with the neutron-balance theory, the non-adjoint-weighted removal lifetime is given by where {Phi} is the angular neutron flux, v is the neutron velocity, {Sigma}{sub a} is the macroscopic absorption cross section, E is neutron energy, {Omega} is angle, and r is a spatial vector. The numerator in this expression represents the total neutron population in the system, N, and the denominator represents the total loss rate due to leakage and absorption.
Date: January 22, 1997
Creator: Hendricks, J.S.; Parsons, D.K. & Spriggs, G.D.
Partner: UNT Libraries Government Documents Department

Prompt neutron decay for an unreflected and unmoderated uranium (HEU) metal sphere

Description: Prompt neutron decay constants were measured for a delayed critical, unmoderated and unreflected U metal sphere at the Oak Ridge Critical Experiments Facility. Prompt neutron decay constant was 1.1095{+-}0.0013 {mu}s{sup -1}. This can be used to verify calculational methods, both deterministic and Monte Carlo neutron transport methods. This value is in agreement with the value from GODIVA I data corrected for effects of support structure (1.10{+-}0.01 {mu}s{sup -1}) but has a much smaller error as a result of the large number (167) of the measurements here and the high degree of sphericity of the sphere.
Date: August 1, 1996
Creator: Mihalczo, J.T.
Partner: UNT Libraries Government Documents Department

Theory of neutron emission in fission

Description: A survey of theoretical representations of two of the observables in neutron emission in fission is given, namely, the prompt fission neutron spectrum N(E) and the average prompt neutron multiplicity {bar {nu}}{sub p}. Early representations of the two observables are presented and their deficiencies are discussed. This is followed by summaries and some examples of recent theoretical models for the calculation of these quantities. Emphasis is placed upon the predictability and accuracy of the recent models. In particular, the dependencies of N(E) and {bar {nu}}{sub p} upon the fissioning nucleus and its excitation energy are treated in detail for the Los Alamos model. Recent work in the calculation of the prompt fission neutron spectrum matrix N(E, E{sub n}), where E{sub n} is the energy of the neutron inducing fission, is then discussed. Concluding remarks address the current status of the ability to calculate these observables with confidence, the direction of future theoretical efforts, and limitations to current (and future) approaches. This paper is an extension of a similar paper presented at the International Centre for Theoretical Physics in 1996.
Date: August 1998
Creator: Madland, D. G.
Partner: UNT Libraries Government Documents Department

Design of an Ogive-Shaped Beamstop

Description: This paper addresses the evolution, design, and development of a novel approach for stopping cw (continuous-wave), non-rastered proton beams. Capturing the beam in vacuo within a long, axisymmetric surface of revolution has the advantages of spreading the deposited energy over a large area while minimizing prompt neutron backstreaming and reducing shield size and mass. Evolving from a cylinder/cone concept, the ogive shape avoids abrupt changes in geometry that produce sharp thermal transitions, allowing the beam energy to be deposited gracefully along its surface. Thermal management at modest temperature levels is provided with a simple, one-pass countercurrent forced-convection water passage outside the ogive. Hydrophone boiling sensors provide overtemperature protection. The concept has been demonstrated under beam conditions in the CRITS (Chalk River Injector Test Stand) facility.
Date: August 23, 1998
Creator: Van Hagan, T.H.; Doll, D.W.; Schneider, J.D. & Spinos, F.R.
Partner: UNT Libraries Government Documents Department

Preliminary results of GODIVA-IV prompt burst modeling

Description: The dynamic computer model developed to simulate GODIVA-IV prompt bursts adequately predicts the magnitude of power bursts. Also, it demonstrates the characteristic features of prompt bursts in metal assemblies, such as the change in shape of power pulses and the ringing of fuel surfaces at the onset of inertial effects. The model will be used to test more sophisticated reactivity feedback coefficients and neutronic-hydrodynamic coupling schemes. It will also be used for a more detailed analysis of inertial effects.
Date: June 1, 1996
Creator: Kimpland, R.
Partner: UNT Libraries Government Documents Department


Description: Calculations were made of thc effect of prompt neutrons on the deflection and time of flight of fission fragments. This was done as an aid to the analysis of data from fission experiments using time-of-flight techniques. Assuming that the energy distribution function of prompt neutrons is that given by Watt, an expression is obtained for the probability distribution in the angle between the final velocities of the two fragments as a function of the number of prompt neutrons emitted and the masses of the fragments. Under the same assumption, it is shown that the probability distribution for the flight time of a given fragment over a given flight path is very nearly Gaussian. This distribution is (to a close approximation) centeicd about the flight time for no neutron emission with a variance which depends on the number of neutrons emitted and the mass of the fragment. (auth)
Date: October 1, 1962
Creator: Lide, R.W.
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


Description: Taking advantage of the neutron source of the LANCSE, it has been possible to obtain a measure of the velocity distribution and the number of prompt-neutrons emitted in the neutron-induced fission of {sup 238}U and {sup 237}Np over a broad incident neutron energy range. The mean kinetic energy was extracted and is shown as the function of the incident-neutron energy. We confirm here the observation, for both reactions, of a dip around the second chance fission which is explained by the lower kinetic energy of the pre-fission neutrons. Such a observation is reproduced by Los Alamos model as implemented at Bruyeres le Chatel and by the Maslov model. As far as the neutron multiplicity is concerned, a similar dip is observed. However, such a behavior is not present in data measured by other groups.
Date: June 28, 2007
Partner: UNT Libraries Government Documents Department

Event-by-Event Study of Prompt Neutrons from 239Pu

Description: Employing a recently developed Monte Carlo model, we study the fission of {sup 240}Pu induced by neutrons with energies from thermal to just below the threshold for second chance fission. Current measurements of the mean number of prompt neutrons emitted in fission, together with less accurate measurements of the neutron energy spectra, place remarkably fine constraints on predictions of microscopic calculations. In particular, the total excitation energy of the nascent fragments must be specified to within 1 MeV to avoid disagreement with measurements of the mean neutron multiplicity. The combination of the Monte Carlo fission model with a statistical likelihood analysis also presents a powerful tool for the evaluation of fission neutron data. Of particular importance is the fission spectrum, which plays a key role in determining reactor criticality. We show that our approach can be used to develop an estimate of the fission spectrum with uncertainties several times smaller than current experimental uncertainties for outgoing neutron energies of less than 2 MeV.
Date: January 15, 2010
Creator: Vogt, R; Randrup, J; Pruet, J & Younes, W
Partner: UNT Libraries Government Documents Department

Covariance Spectroscopy for Fissile Material Detection

Description: Nuclear fission produces multiple prompt neutrons and gammas at each fission event. The resulting daughter nuclei continue to emit delayed radiation as neutrons boil off, beta decay occurs, etc. All of the radiations are causally connected, and therefore correlated. The correlations are generally positive, but when different decay channels compete, so that some radiations tend to exclude others, negative correlations could also be observed. A similar problem of reduced complexity is that of cascades radiation, whereby a simple radioactive decay produces two or more correlated gamma rays at each decay. Covariance is the usual means for measuring correlation, and techniques of covariance mapping may be useful to produce distinct signatures of special nuclear materials (SNM). A covariance measurement can also be used to filter data streams because uncorrelated signals are largely rejected. The technique is generally more effective than a coincidence measurement. In this poster, we concentrate on cascades and the covariance filtering problem.
Date: June 2, 2009
Creator: Rusty Trainham, Jim Tinsley, Paul Hurley, Ray Keegan
Partner: UNT Libraries Government Documents Department

FREYA-a new Monte Carlo code for improved modeling of fission chains

Description: A new simulation capability for modeling of individual fission events and chains and the transport of fission products in materials is presented. FREYA ( Fission Yield Event Yield Algorithm ) is a Monte Carlo code for generating fission events providing correlated kinematic information for prompt neutrons, gammas, and fragments. As a standalone code, FREYA calculates quantities such as multiplicity-energy, angular, and gamma-neutron energy sharing correlations. To study materials with multiplication, shielding effects, and detectors, we have integrated FREYA into the general purpose Monte Carlo code MCNP. This new tool will allow more accurate modeling of detector responses including correlations and the development of SNM detectors with increased sensitivity.
Date: June 12, 2012
Creator: Hagmann, C A; Randrup, J & Vogt, R L
Partner: UNT Libraries Government Documents Department

Sampling the Number of Neutrons Emitted per Fission

Description: I define in detail the model used to sample the number of prompt neutrons emitted in fission; this description is based on publications defining the model [1] as well as publications comparing the model to experimental measurements [2]. The model described in these publications is exactly what the TART [3] Monte Carlo transport code uses. Based on comparisons between TART [3] and MCNPX [4], it is obvious that at the time this report was published these two computer codes are not using the same model, and the results significantly differ. It is my hope that this report will contribute toward better understanding of this model, and hopefully eventually to agreement between TART and MCNPX results. Partial success has already been achieved in the sense that based upon reading a preliminary version of this report, John Hendrichs [5], one author of MCNPX, acknowledged that the sources of differences as described in this report demonstrate an error in MCNPX (John even offered me the traditional $20 reward for reporting an error in MCNPX; I declined to accept). John is presently updating MCNPX to eliminate these sources of differences; hopefully in the not too distant future this correction will be available in MCNPX, and we will obtain agreement between TART and MCNPX, which is the ultimate objective of this report.
Date: June 29, 2006
Creator: Cullen, D E
Partner: UNT Libraries Government Documents Department


Description: Experimental parameters of ZPR-HI fast reactor assemblies were compared with those calculated through use of a cross-section set derived from that of Yiftah, Okrent, and Moldauer, and initially used for a study of the critical sizes of ZPR-III assemblies. This cross-section set waa also used to study central fission ratios in ZPR-III assemblies. The analysis was extended to prompt neutron lifetimes and the relative reactivity effects of the substitution of materials at the reactor centers. The results of the work were examined in conjunction with those of the critical size and fission ratio studies. (auth)
Date: June 1, 1963
Creator: Davey, W.G.
Partner: UNT Libraries Government Documents Department


Description: A calculation, coded for a fast computer, is discussed that can fairly accurately match the experimental resuIts obtained from the LASL Lady Godiva prompt burst program. In particular, the code can predict the reactivity where the burst yield deviates from a linear dependence on reactivity and commences to rise much more rapidly. The burst width and maximum rates can be predictcd with reasonable accuracy. The calculation is applied to other simple systems, with the result that there appear to be general rules that one can use to relate the bursts of thcse systems. The calculation can predict what fraction of the energy of the system is converted into kinetic energy. It appears that step-function increases of reactivity of about 1O cents or less in homogeneous metal systems develop only a trivial explosive energy. The method was extended to hypothetical accidents in very idealized reactors. Two general models of reactor cores were considered. These are (1) a core of low density in which the characteristic o a threshold is important, and (2) a model in which the spherical shells are alternately normal density and void. The numbers quoted should be regarded only as establishing upper and lower limits. (auth)
Date: January 1, 1957
Creator: Stratton, W.R. & Colvin, T.H.
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

Definition of neutron lifespan and neutron lifetime in MCNP4B

Description: MCNP4B was released in early 1997. In this new version, several major changes were made to the underlying theory used to estimate the non-adjoint-weighted removal, fission, capture, and escape prompt-neutron lifetimes. These four lifetimes are now being calculated in accordance to the neutron-balance theory described by Spriggs et al. in which the non-adjoint-weighted lifetime for a particular type of reaction (i.e., fission, capture, escape, removal, etc.) is defined as the total neutron population in the system divided by that reaction rate.
Date: January 15, 1997
Creator: Busch, R. D.; Spriggs, G. D. & Hendricks, J. S.
Partner: UNT Libraries Government Documents Department