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Critical mass experiment using U-235 foils and lucite plates

Description: The main objective of this experiment was to show how the multiplication of the system increases as moderated material is placed between highly enriched uranium foils. In addition, this experiment served to demonstrate the hand-stacking techniques, and approach to criticality by remote operation. This experiment was designed by Tom McLaughlin in the mid seventies as part of the criticality safety course that is taught at Los Alamos Critical Experiment Facility (LACEF). The W-U-235 ratio for this experiment was 215 which is where the minimum critical mass for this configuration occurs.
Date: May 1, 1998
Creator: Sanchez, R.; Butterfield, K.; Kimpland, R. & Jaegers, P.
Partner: UNT Libraries Government Documents Department

A keff Search Capability in MC21

Description: The MC21 Monte Carlo code is required to permit an individual geometric component or groups of components to be tagged as ''movable'' within some permissible range. Typical examples of such movable components would be control devices such as translating rods or rotating drums. Given this geometric information, a target multiplication factor (k{sub eff}), and a convergence criterion, MC21 will iterate on movable component positions and return a final position that reflects a k{sub eff} close to the target value. An initial version of this capability is demonstrated through modifications to MC21 that sets the geometry data structures for the movable components, calls the main Fortran-95 solver to compute k{sub eff}, and converges on the final position. This approach uses an adaptive batching algorithm that continually increases the accuracy of each successive MC21 k{sub eff} result as the movable geometry approaches the converged position.
Date: January 9, 2007
Creator: Morrow RE, Trumbull TH, Donovan TJ, Sutton TM
Partner: UNT Libraries Government Documents Department


Description: Neutron multiplication measurements were made on tamped and untamped cylindrical assemblies. The assemblies consisted of plutonium metal sheet mcderated with Plexiglas. Experiments were performed to evaluate the effects of inhomogeneity. This work is a continuation of RFP-178. (auth)
Date: April 1, 1960
Creator: Bidinger, G.H.; Schuske, C.L. & Smith, D.F.
Partner: UNT Libraries Government Documents Department

Implementation of nodal equivalence parameters in DIF3D-VARIANT for core analysis of prismatic Very High Temperature Reactor (VHTR).

Description: The VARIANT module of the DIF3D code has been upgraded to utilize surface-dependent discontinuity factors. The performance of the new capability is verified using two-dimensional core cases with control rods in reflector and fuel blocks. Cross sections for VHTR components were generated using the DRAGON and HELIOS codes. For rodded block cross sections, the DRAGON calculations used a single-block model or the multi-block models combined with MCNP4C flux solutions, whereas the HELIOS calculations utilized multi-block models. Results from core calculations indicate that multiplication factor, block power, and control rod worth are significantly improved by using surface-dependent discontinuity factors.
Date: March 15, 2007
Creator: Lee, C. H.; Joo, H. K.; Yang, W. S. & Taiwo, T. A.
Partner: UNT Libraries Government Documents Department

Review of Subcritical Source-Driven Noise Analysis Measurements

Description: Subcritical source-driven noise measurements are simultaneous Rossia and randomly pulsed neutron measurements that provide measured quantities that can be related to the subcritical neutron multiplication factor. In fact, subcritical source-driven noise measurements should be performed in lieu of Rossia measurements because of the additional information that is obtained from noise measurements such as the spectral ratio and the coherence functions. The basic understanding of source-driven noise analysis measurements can be developed from a point reactor kinetics model to demonstrate how the measured quantities relate to the subcritical neutron multiplication factor.
Date: November 1, 1999
Creator: Valentine, T.E.
Partner: UNT Libraries Government Documents Department

Relationship between k{sub eff} and the fraction of critical mass

Description: It is not universally understood that k{sub eff} and fractional critical mass are related in a non linear fashion. For example, a neutronic system with a k{sub eff} = 0. 95 is NOT at 95% of its critical mass. What is striking is just how non-linear the relationship between k{sub eff} and critical mass really is. This relationship is investigated and documented below for both unfavorable (i.e., very reactive) and favorable (less reactive) geometries. The implications of this non-linearity for criticality safety regulation will also be discussed.
Date: May 1, 1997
Creator: O`Dell, R.D. & Parsons, D.K.
Partner: UNT Libraries Government Documents Department

The equivalent, fundamental-mode source

Description: In 1960, Hansen analyzed the problem of assembling fissionable material in the presence of a weak neutron source. Using point kinetics, he derived the weak source condition and analyzed the consequences of delayed initiation during ramp reactivity additions. Although not clearly stated in Hansen`s work, the neutron source strength that appears in the weak source condition actually corresponds to the equivalent, fundamental-mode source. In this work, they describe the concept of an equivalent, fundamental-mode source and they derive a deterministic expression for a factor, g*, that converts any arbitrary source distribution to an equivalent, fundamental-mode source. They also demonstrate a simplified method for calculating g* in subcritical systems. And finally, they present a new experimental method that can be employed to measure the equivalent, fundamental-mode source strength in a multiplying assembly. They demonstrate the method on the zero-power, XIX-1 assembly at the Fast Critical Assembly (FCA) Facility, Japan Atomic Energy Research Institute (JAERI).
Date: December 24, 1996
Creator: Spriggs, G.D.; Busch, R.D.; Sakurai, Takeshi & Okajima, Shigeaki
Partner: UNT Libraries Government Documents Department

Subcritical measurements with a cylindrical tank of Pu-U nitrate

Description: This series of measurements with a mixed Pu-U nitrate solution (280 g Pu/liter, 180 g U/liter) in a 35.54-cm-diam cylindrical tank provides a wide variety of experimental data for subcritical configurations that can be used to verify calculational methods and nuclear data. The Pu contained 7.85 wt% {sup 240}Pu and the uranium was natural uranium. The measurements performed were: inverse count rate, prompt neutron decay constants, inverse kinetics, and frequency analysis by the {sup 252}Cf source driven method. These data are presented in sufficient detail that the results of the experiments can be calculated directly. For purposes of extrapolating to the delayed critical height the ratio of spectral densities was linear with height and thus provided the best estimate of critical height.
Date: April 1, 1997
Creator: Mihalczo, J.T.; Valentine, T.E. & King, W.T.
Partner: UNT Libraries Government Documents Department

Determination of the multiplication factor and its bias by the {sup 252}Cf-source technique: A method for code benchmarking with subcritical configurations

Description: A brief discussion of the Cf-252 source driven method for subcritical measurements serves as an introduction to the concept and use of the spectral ratio, {Gamma}. It has also been shown that the Monte Carlo calculation of spectral densities and effective multiplication factors have as a common denominator the transport propagator. This commonality follows from the fact that the Neumann series expansion of the propagator lends itself to the Monte Carlo method. On this basis a linear relationship between the spectral ratio and the effective multiplication factor has been shown. This relationship demonstrates the ability of subcritical measurements of the ratio of spectral densities to validate transport theory methods and cross sections.
Date: August 1, 1997
Creator: Perez, R.B.; Valentine, T.E.; Mihalczo, J.T. & Mattingly, J.K.
Partner: UNT Libraries Government Documents Department

MCNP{sup TM} criticality primer and training experiences

Description: With the closure of many experimental facilities, the nuclear criticality safety analyst is increasingly required to rely on computer calculations to identify safe limits for the handling and storage of fissile materials. However, the analyst may have little experience with the specific codes available at his or her facility. Usually, the codes are quite complex, black boxes capable of analyzing numerous problems with a myriad of input options. Documentation for these codes is designed to cover all the possible configurations and types of analyses but does not give much detail on any particular type of analysis. For criticality calculations, the user of a code is primarily interested in the value of the effective multiplication factor for a system (k{sub eff}). Most codes will provide this, and truckloads of other information that may be less pertinent to criticality calculations. Based on discussions with code users in the nuclear criticality safety community, it was decided that a simple document discussing the ins and outs of criticality calculations with specific codes would be quite useful. The Transport Methods Group, XTM, at Los Alamos National Laboratory (LANL) decided to develop a primer for criticality calculations with their Monte Carlo code, MCNP. This was a joint task between LANL with a knowledge and understanding of the nuances and capabilities of MCNP and the University of New Mexico with a knowledge and understanding of nuclear criticality safety calculations and educating first time users of neutronics calculations. The initial problem was that the MCNP manual just contained too much information. Almost everything one needs to know about MCNP can be found in the manual; the problem is that there is more information than a user requires to do a simple k{sub eff} calculation. The basic concept of the primer was to distill the manual to create a ...
Date: September 1, 1995
Creator: Briesmeister, J.; Forster, R.A. & Busch, R.
Partner: UNT Libraries Government Documents Department

Stationarity and source convergence in monte carlo criticality calculation.

Description: In Monte Carlo (MC) criticality calculations, source error propagation through the stationary cycles and source convergcnce in the settling (inactive) cycles are both dominated by the dominance ratio (DR) of fission kernels, Le., the ratio of the second largest to largest eigenvalues. For symmetric two fissile component systems with DR close to unity, the extinction of fission source sites can occur in one of the components even when the initial source is symmetric and the number of histories per cycle is larger than one thousand. When such a system is made slightly asymmetric, the neutron effective multiplication factor (kern) at the inactive cycles does not reflect the convergence to stationary source distribution. To overcome this problem, relative entropy (Kullback Leibler distance) is applied to a slightly asymmetric two fissile component problem with a dominance ratio of 0.9925. Numerical results show that relative entropy is effective as a posterior diagnostic tool.
Date: January 1, 2002
Creator: Ueki, T. (Taro) & Brown, F. B. (Forrest B.)
Partner: UNT Libraries Government Documents Department


Description: Neutron multiplication measurements and theoretical calculations were made on cylindrical assemblies of graphite and plutonium disks. (auth)
Date: September 29, 1958
Creator: Goodwin, A. Jr. & Schuske, C.L.
Partner: UNT Libraries Government Documents Department

Intact and Degraded Component Criticality Calculations of N Reactors Spent Nuclear Fuel

Description: The objective of this calculation is to perform intact and degraded mode criticality evaluations of the Department of Energy's (DOE) N Reactor Spent Nuclear Fuel codisposed in a 2-Defense High-Level Waste (2-DHLW)/2-Multi-Canister Overpack (MCO) Waste Package (WP) and emplaced in a monitored geologic repository (MGR) (see Attachment I). The scope of this calculation is limited to the determination of the effective neutron multiplication factor (k{sub eff}) for both intact and degraded mode internal configurations of the codisposal waste package. This calculation will support the analysis that will be performed to demonstrate the technical viability for disposing of U-metal (N Reactor) spent nuclear fuel in the potential MGR.
Date: January 31, 2001
Creator: Angers, L.
Partner: UNT Libraries Government Documents Department

Criticality Potential of Waste Packages Containing DOE SNF Affected by Igneous Intrusion

Description: The Department of Energy (DOE) is currently preparing an application to submit to the U.S. Nuclear Regulatory Commission for a construction authorization for a monitored geologic repository. The repository will contain spent nuclear fuel (SNF) and defense high-level waste (DHLW) in waste packages placed in underground tunnels, or drifts. The primary objective of this paper is to perform a criticality analysis for waste packages containing DOE SNF affected by a disruptive igneous intrusion event in the emplacement drifts. The waste packages feature one DOE SNF canister placed in the center and surrounded by five High-Level Waste (HLW) glass canisters. The effective neutron multiplication factor (k{sub eff}) is determined for potential configurations of the waste package during and after an intrusive igneous event. Due to the complexity of the potential scenarios following an igneous intrusion, finding conservative and bounding configurations with respect to criticality requires some additional considerations. In particular, the geometry of a slumped and damaged waste package must be examined, drift conditions must be modeled over a range of parameters, and the chemical degradation of DOE SNF and waste package materials must be considered for the expected high temperatures. The secondary intent of this calculation is to present a method for selecting conservative and bounding configurations for a wide range of end conditions.
Date: February 7, 2006
Creator: Kimball, D.S. & Sanders, C.E.
Partner: UNT Libraries Government Documents Department


Description: The net multiplication effect of beryllium oxide, which is due to the (n,2n) reaction, was calculated using an essentially exact calculation of the neutron spectrum as a function of energy. The upper limit of the (n,2n) cross section curve gives the unpoisoned value epsilon /sup +/ = 1.047 and the lower limit gives epsilon /sup -/ = 1,027. The behavior of the Li/sup 6/poisoned fast multiplication effect as a function of the number of collisions was studied for both beryllium and beryllium oxide. (auth)
Date: December 14, 1959
Creator: Hafele, W. & Tsagaris, M.
Partner: UNT Libraries Government Documents Department

Plutonium Plexiglas Assemblies

Description: Neutron multiplication measurements were made on tamped and untamped cylindrical assemblies. The assemblies consisted of Pu metal sheet moderated with Plexiglas, Experiments were performed to evaluate the effects of inhomogeneity. (auth)
Date: January 20, 1960
Creator: Schuske, C. L.; Bidinger, G. H.; Goodwin, A., Jr. & Smith, D. F.
Partner: UNT Libraries Government Documents Department