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Studies of axial-leakage simulations for homogeneous and heterogeneous EBR-II core configurations

Description: When calculations of flux are done in less than three dimensions, leakage-absorption cross sections are normally used to model leakages (flows) in the dimensions for which the flux is not calculated. Since the neutron flux is axially dependent, the leakages, and hence the leakage-absorption cross sections, are also axially dependent. Therefore, to obtain axial flux profiles (or reaction rates) for individual subassemblies, an XY-geometry calculation delineating each subassembly has to be done at several axial heights with space- and energy-dependent leakage-absorption cross sections that are appropriate for each height. This report discusses homogeneous and heterogeneous XY-geometry calculations at various axial locations and using several differing assumptions for the calculation of the leakage-absorption cross section. The positive (outward) leakage-absorption cross sections are modeled as actual leakage absorptions, but the negative (inward) leakage-absorption cross sections are modeled as either negative leakage absorptions (+-B/sup 2/ method) or positive downscatter cross sections (the ..sigma../sub s/(1 ..-->.. g) method). 3 refs., 52 figs., 10 tabs.
Date: August 1, 1985
Creator: Grimm, K.N. & Meneghetti, D.
Partner: UNT Libraries Government Documents Department

Evidence of fast non-linear feedback in EBR-II rod-drop measurements

Description: Feedback reactivities determine the time dependence of a reactor during and after a transient initiating event. Recent analysis of control-rod drops in the Experimental Breeder Reactor II (EBR-II) Reactor has indicated that some relatively fast feedback may exist which cannot be accounted for by the linear feedback mechanisms. The linear and deduced non-linear feedback reactivities from a control-rod drop in EBR-II run 93A using detailed temperature coefficients of reactivity in the EROS kinetics code have been reported. The transient analyses have now been examined in more detail for times close to the drop to ascertain if additional positive reactivity is being built-in early in the drop which could be gradually released later in the drop.
Date: June 1, 1987
Creator: Grimm, K.N. & Meneghetti, D.
Partner: UNT Libraries Government Documents Department

Use of additional fission sources or scattering sources to model inward axial leakages in fast-reactor analysis

Description: When calculations of flux are done in less than three dimensions, bucklings are normally used to model leakages (flows) in the dimensions for which the flux is not calculated. If the net leakage for a given energy group is outward (positive), the buckling is positive, and buckling methods work well. However, if the new leakage for a given energy group is inward (negative), the buckling is negative and can lead to numerical instabilities (oscillations in the iterative flux calculation). This report discusses two equivalent nonbuckling methods to model inward leakages. One method (the chi/sub g/ method) models these incoming neutrons by additional fission sources. The other method (the ..sigma../sub s/(1 ..-->.. g) method) models them by increased downscatter sources. The derivation of the two methods is shown, and the flux spectra obtained by their use are compared with those obtained from two-dimensional (RZ) calculations.
Date: October 1, 1981
Creator: Grimm, K.N. & Meneghetti, D.
Partner: UNT Libraries Government Documents Department

Comparisons of power transfer functions and flow transfer functions

Description: Transfer functions may be used to calculate component feedbacks or temperature increments by convolution of the transfer function with the appropriate fractional change in system-quantity. Power-change transfer functions have been reported. The corresponding flow transfer functions for this case, and comparison with the power transfer functions, are reported here. Results of feedback simulation of ramped flow transients using flow transfer functions are also described.
Date: November 15, 1987
Creator: Grimm, K.N. & Meneghetti, D.
Partner: UNT Libraries Government Documents Department

Midplane and off-midplane axial leakage simulation of heterogeneous subassemblies in EBR-II

Description: Generally EBR-II XY geometry and one-dimensional (1D) cylindrical neutron flux calculations using transport theory analysis assume energy independent DB/sup 2/-type absorptions to simulate effects of axial leakages. This assumption, while generally resulting in satisfactory eigenvalues and high- and intermediate-energy flux spectra, gives large errors in the low-energy flux spectra where the flux levels are smaller. These midplane errors, and more importantly the off-midplane errors, can be reduced by using a more realistic leakage model: space and energy dependent leakage absorption cross sections. Analyses have been reported in which transport theory methods using row-wise azimuthally-homogeneous RZ-geometry boundary angular fluxes to calculate space and energy dependent leakage absorptions which were then used in subsequent 1D cylindrical simulations of RZ calculations. The present paper extends the study to include heterogeneous core loading configurations. This study contains modeling of heterogeneous XYZ loadings using heterogeneous XY geometry and space and energy dependent leakage absorptions. Because of the complexities arising from the three-dimensional analysis, the results presented here use diffusion theory. Although the actual negative leakage absorption values can be used in the CITATION diffusion theory code, it was found that the ..sigma../sub s/(1..-->..g) method gave better results in the core region of these studies.
Date: January 1, 1984
Creator: Grimm, K.N. & Meneghetti, D.
Partner: UNT Libraries Government Documents Department

Comparison of measured and calculated composition of irradiated EBR-II blanket assemblies.

Description: In anticipation of processing irradiated EBR-II depleted uranium blanket subassemblies in the Fuel Conditioning Facility (FCF) at ANL-West, it has been possible to obtain a limited set of destructive chemical analyses of samples from a single EBR-II blanket subassembly. Comparison of calculated values with these measurements is being used to validate a depletion methodology based on a limited number of generic models of EBR-II to simulate the irradiation history of these subassemblies. Initial comparisons indicate these methods are adequate to meet the operations and material control and accountancy (MC and A) requirements for the FCF, but also indicate several shortcomings which may be corrected or improved.
Date: July 13, 1998
Creator: Grimm, K. N.
Partner: UNT Libraries Government Documents Department

Time constants and transfer functions for a homogeneous 900 MWt metallic fueled LMR

Description: Nodal transfer functions are calculated for a 900 MWt U10Zr-fueled sodium cooled reactor. From the transfer functions the time constants, feedback reactivity transfer function coefficients, and power coefficients can be determined. These quantities are calculated for core fuel, upper and lower axial reflector steel, radial blanket fuel, radial reflector steel, and B/sub 4/C rod shaft expansion effect. The quantities are compared to the analogous quantities of a 60 MWt metallic-fueled sodium cooled Experimental Breeder Reactor II configuration. 8 refs., 2 figs., 6 tabs.
Date: January 1, 1988
Creator: Grimm, K.N. & Meneghetti, D.
Partner: UNT Libraries Government Documents Department

ZPPR-20 phase D : a cylindrical assembly of polyethylene moderated U metal reflected by beryllium oxide and polyethylene.

Description: The Zero Power Physics Reactor (ZPPR) fast critical facility was built at the Argonne National Laboratory-West (ANL-W) site in Idaho in 1969 to obtain neutron physics information necessary for the design of fast breeder reactors. The ZPPR-20D Benchmark Assembly was part of a series of cores built in Assembly 20 (References 1 through 3) of the ZPPR facility to provide data for developing a nuclear power source for space applications (SP-100). The assemblies were beryllium oxide reflected and had core fuel compositions containing enriched uranium fuel, niobium and rhenium. ZPPR-20 Phase C (HEU-MET-FAST-075) was built as the reference flight configuration. Two other configurations, Phases D and E, simulated accident scenarios. Phase D modeled the water immersion scenario during a launch accident, and Phase E (SUB-HEU-MET-FAST-001) modeled the earth burial scenario during a launch accident. Two configurations were recorded for the simulated water immersion accident scenario (Phase D); the critical configuration, documented here, and the subcritical configuration (SUB-HEU-MET-MIXED-001). Experiments in Assembly 20 Phases 20A through 20F were performed in 1988. The reference water immersion configuration for the ZPPR-20D assembly was obtained as reactor loading 129 on October 7, 1988 with a fissile mass of 167.477 kg and a reactivity of -4.626 {+-} 0.044{cents} (k {approx} 0.9997). The SP-100 core was to be constructed of highly enriched uranium nitride, niobium, rhenium and depleted lithium. The core design called for two enrichment zones with niobium-1% zirconium alloy fuel cladding and core structure. Rhenium was to be used as a fuel pin liner to provide shut down in the event of water immersion and flooding. The core coolant was to be depleted lithium metal ({sup 7}Li). The core was to be surrounded radially with a niobium reactor vessel and bypass which would carry the lithium coolant to the forward inlet plenum. Immediately inside the ...
Date: September 30, 2006
Creator: Lell, R.; Grimm, K.; McKnight, R.; Shaefer, R.; Division, Nuclear Engineering & INL
Partner: UNT Libraries Government Documents Department

An evaluation of waste radiotoxicity reduction for a fast burner reactor closed fuel cycle: NEA benchmark results

Description: As part of a program proposed by the OECD/NEA Working Party on Physics of Plutonium Recycling (WPPR) to evaluate different scenarios for the use of plutonium, fast reactor physics benchmarks were developed. In this paper, the fuel cycle performance of the metal-fueled benchmark is evaluated in detail. Benchmark results assess the reactor performance and toxicity behavior in a closed nuclear fuel cycle for a parametric variation of the conversion ratio between 0.5 and 1.0. Results indicate that a fast burner reactor closed fuel cycle can be utilized to significantly reduce the radiotoxicity destined for ultimate disposal.
Date: December 1, 1995
Creator: Grimm, K.N.; Hill, R.N. & Wase, D.C.
Partner: UNT Libraries Government Documents Department

Studies of Axial-Leakage Simulations for Homogeneous and Heterogeneous EBR-II Core Configurations

Description: When calculations of flux are done in less than three dimensions, leakage-absorption cross sections are normally used to model leakages (flows) in the dimensions for which the flux is not calculated. Since the neutron flux is axially dependent, the leakages, and hence the leakage-absorption cross sections, are also axially dependent. Therefore, to obtain axial flux profiles (or reaction rates) for individual subassemblies, an XY-geometry calculation delineating each subassembly has to be done at several axial heights with space- and energy-dependent leakage-absorption cross sections that are appropriate for each height. This report discusses homogeneous and heterogeneous XY-geometry calculations at various axial locations and using several differing assumptions for the calculation of the leakage-absorption cross section. The positive (outward) leakage-absorption cross sections are modeled as actual leakage absorptions, but the negative (inward) leakage-absorption cross sections are modeled as either negative leakage absorptions (+-B² method) or positive downscatter cross sections (the ..sigma../sub s/(1 ..-->.. g) method).
Date: August 1985
Creator: Grimm, K. N. & Meneghetti, D.
Partner: UNT Libraries Government Documents Department

Use of Additional Fission Sources or Scattering Sources to Model Inward Axial Leakages in Fast-Reactor Analysis

Description: When calculations of flux are done in less than three dimensions, bucklings are normally used to model leakages (flows) in the dimensions for which the flux is not calculated. If the net leakage for a given energy group is outward (positive), the buckling is positive, and buckling methods work well. However, if the new leakage for a given energy group is inward (negative), the buckling is negative and can lead to numerical instabilities (oscillations in the iterative flux calculation). This report discusses two equivalent non-buckling methods to model inward leakages. One method (the chi/sub g/ method) models these incoming neutrons by additional fission sources. The other method (the sigma/sub s/(1 --> g) method) models them by increased down-scatter sources. The derivation of the two methods is shown, and the flux spectra obtained by their use are compared with those obtained from two-dimensional (RZ) calculations.
Date: October 1981
Creator: Grimm, K. N. & Meneghetti, D.
Partner: UNT Libraries Government Documents Department

Approximations of Gamma Cross Sections for Fast Nuclear Reactors

Description: The report shows a method to approximate a P₁ scattering solution for the flux in a fast reactor, using an isotropic, but not a diagonal-transport-approximation scattering matrix. Presented are flux errors relative to a P₁ solution for different levels of transport approximation in an EBR-II type of core surrounded by a stainless steel reflector. Problems associated with the use of the method are also presented.
Date: 1978?
Creator: Grimm, K. N. & Meneghetti, D.
Partner: UNT Libraries Government Documents Department

First Determination of the Weak Charge of the Proton

Description: The Qweak experiment has measured the parity-violating asymmetry in polarized e-p elastic scattering at Q^2 = 0.025(GeV/c)^2, employing 145 microamps of 89% longitudinally polarized electrons on a 34.4cm long liquid hydrogen target at Jefferson Lab. The results of the experiment's commissioning run are reported here, constituting approximately 4% of the data collected in the experiment. From these initial results the measured asymmetry is A_e_p = -279 +- 35 (statistics) +- 31 (systematics) ppb, which is the smallest and most precise asymmetry ever measured in polarized e-p scattering. The small Q^2 of this experiment has made possible the first determination of the weak charge of the proton, Q^p_W, by incorporating earlier parity-violating electron scattering (PVES) data at higher Q^2 to constrain hadronic corrections. The value of Q^p_W obtained in this way is Q^p_W(PVES) = 0.064 +- 0.012, in good agreement with the Standard Model prediction of Q^p_W(SM) = 0.0710 +- 0.0007. When this result is further combined with the Cs atomic parity violation (APV) measurement, significant constraints on the weak charges of the up and down quarks can also be extracted. That PVES+APV analysis reveals the neutron's weak charge to be Q^n_W(PVES+APV) = -0.975 +- 0.010.
Date: October 1, 2013
Creator: Androic, D; Armstrong, D S; Asaturyan, A; Averett, T; Balewski, J; Beaufait, J et al.
Partner: UNT Libraries Government Documents Department