15 Matching Results

Search Results

Advanced search parameters have been applied.

Activation of Air and Utilities in the National Ignition Facility

Description: Detailed 3-D modeling of the NIF facility is developed to accurately simulate the radiation environment within the NIF. Neutrons streaming outside the NIF Target Chamber will activate the air present inside the Target Bay and the Ar gas inside the laser tubes. Smaller levels of activity are also generated in the Switchyard air and in the Ar portion of the SY laser beam path. The impact of neutron activation of utilities located inside the Target Bay is analyzed for variety of shot types. The impact of activating TB utilities on dose received by maintenance personnel post-shot is analyzed. The current NIF facility model includes all important features of the Target Chamber, shielding system, and building configuration. Flow of activated air from the Target Bay is controlled by the HVAC system. The amount of activated Target Bay air released through the stack is very small and does not pose significant hazard to personnel or the environment. Activation of Switchyard air is negligible. Activation of Target Bay utilities result in a manageable dose rate environment post high yield (20 MJ) shots. The levels of activation generated in air and utilities during D-D and THD shots are small and do not impact work planning post shots.
Date: April 8, 2010
Creator: Khater, H; Pohl, B & Brererton, S
Partner: UNT Libraries Government Documents Department

Neutron and Photon Transport in Sea-Going Cargo Containers

Description: Factors affecting sensing of small quantities of fissionable material in large sea-going cargo containers by neutron interrogation and detection of {beta}-delayed photons are explored. The propagation of variable-energy neutrons in cargos, subsequent fission of hidden nuclear material and production of the {beta}-delayed photons, and the propagation of these photons to an external detector are considered explicitly. Detailed results of Monte Carlo simulations of these stages in representative cargos are presented. Analytical models are developed both as a basis for a quantitative understanding of the interrogation process and as a tool to allow ready extrapolation of the results to cases not specifically considered here.
Date: February 9, 2005
Creator: Pruet, J; Descalle, M; Hall, J; Pohl, B & Prussin, S G
Partner: UNT Libraries Government Documents Department

Criticality experiments with mixed plutonium and uranium nitrate solution at a plutonium fraction of 0.4 in slab geometry

Description: R. C. Lloyd of PNL has completed and published a series of critical experiments with mixed plutonium- uranium nitrate solutions (Reference 1). This series of critical experiments was part of an extensive program jointly sponsored by the U. S. Department of Energy (DOE) and the Power Reactor and Nuclear Fuel Development Corporation (PNC) of Japan and was carried out in the mid-1980`s. The experiments evaluated here (published as Report PNL-6327) were performed with mixed plutonium- uranium nitrate solution in a variable thickness slab tank with two 106.7 cm square sides and a width that could be varied from 7.6 to 22.8 cm. The objective of these experiments was to obtain experimental data to permit the validation of computer codes for criticality calculations and of cross-section data to minimize the uncertainties inherent therein, so that facility safety, efficiency, and reliability could be enhanced. The concentrations of the solution were about 105, 293, and 435 g(Pu+U)/liter with a ratio of plutonium to total heavy metal (plutonium plus uranium) of about 0. 40 for all eight experiments. Four measurements were made with a water reflector, and four with no reflector. Following the publication of the initial PNL reports, considerable effort was devoted to an extensive reevaluation of this series of experiments by a collaboration of researchers from ORNL, PNL, and PNC (Reference 2). Their work resulted in a more accurate description of the ``as built`` hardware configuration and the materials specifications. For the evaluations in this report, the data published in Reference 2 by Smolen et al. is selected to supersede the original PNL report. Eight experiments have been evaluated and seven (063, 064, 071, 072, 074, 075, and 076) provide benchmark criticality data. Experiment 073 could not achieve criticality within vessel height limitations.
Date: September 1, 1997
Creator: Pohl, B.A. & Keeton, S.C.
Partner: UNT Libraries Government Documents Department

Emission of. gamma. rays from various materials pulsed with 14-MeV neutrons

Description: We have performed a number of experiments at LLNL recently to investigate the leakage of gamma rays from spheres of selected materials pulsed centrally with 14-MeV neutrons. Such spectral information may be carefully compared to calculational results to validate the transport models, particularly the nuclear cross section data base. In the present case, the TART code and SANDYL codes are used to explicitly calculate the observable, the recoil electron spectrum. The materials studied were H/sub 2/O, /sup 6/LiD, Be, C, /sup 14/N, CF/sub 2/, Al, Si, Ti, Fe, Cu, Ta, W, Au, Pb, Th, and /sup 238/U. Generally, agreement was good between experiment and calculation. However, for some, the calculations significantly underestimated or overestimated experiment. For oxygen (i.e., H/sub 2/O), the ENDL cross section set led to a sizeable calculational overestimate. Re-examination led to a large improvement. For tungsten, the calculated output was approx.30% below experiment. A re-evaluation led to closer agreement. 16 refs., 10 figs., 1 tab.
Date: October 1, 1987
Creator: Goldberg, E.; Hansen, L.F.; Howerton, R.J.; Komoto, T.T. & Pohl, B.A.
Partner: UNT Libraries Government Documents Department

HOTSPUR: gamma ray emission from spheres pulsed with D-T neutrons. I. Calibration of improved NE213 detector assembly. II. Comparison of TART/SANDYL electron recoil spectra to experiment; preliminary results

Description: The NE213 scintillator detector was modified so that the pulse height would be linear with electron energy over the full range of interest - up to 7.1 MeV. Absolute calibration was done with four different calibrated gamma sources. An average correction factor is obtained which normalizes SANDYL calculations with respect to the calibration experiments. The procedure for calculating neutron-induced gamma-ray output and electron recoil spectra is described, and experimental data from a number of spherical assemblies are given and compared to TART/SANDYL calculations. (LEW)
Date: September 1, 1986
Creator: Goldberg, E.; Hansen, L.F.; Komoto, T.T. & Pohl, B.A.
Partner: UNT Libraries Government Documents Department

Neutron scattering cross sections for /sup 232/Th and /sup 238/U inferred from proton scattering and charge exchange measurements. [7 MeV, 26 and 27 MeV]

Description: Differential cross sections for the (p,n) reactions to the isobaric analog states (IAS) of /sup 232/Th and /sup 238/U targets were measured at 26 and 27 MeV. The analysis of the data was done in conjunction with the proton elastic and inelastic (2/sup +/, 4/sup +/, 6/sup +/) differential cross sections measured at 26 MeV. Because collective effects are important in this mass region, deformed coupled-channels calculations were carried out for the simultaneous analysis of the proton and neutron outgoing channels. The sensitivity of the calculations was studied with respect to the optical model parameters used in the calculations, the shape of the nuclear charge distribution, the type of coupling scheme assumed among the levels, the magnitude of the deformation parameters, and the magnitude of the isovector potentials, V/sub 1/ and W/sub 1/. A Lane model-consistent analysis of the data was used to infer optical potential parameters for 6- to 7-MeV neutrons. The neutron elastic differential cross sections obtained from these calculations are compared with measurements available in the literature, and with results obtained using neutron parameters from global sets reported at these energies. 7 figures, 3 tables.
Date: January 1, 1980
Creator: Hansen, L.F.; Grimes, S.M.; Pohl, B.A.; Poppe, C.H. & Wong, C.
Partner: UNT Libraries Government Documents Department


Description: A detailed model of the Target Bay (TB) at the National Ignition Facility (NIF) has been developed to estimate the post-shot radiation environment inside the facility. The model includes large number of structures and diagnostic instruments present inside the TB. These structures and instruments are activated by the few nanosecond pulse of neutrons generated during a shot and the resultant gamma dose rates are estimated at various decay times following the shot. The results presented in this paper are based on a low-yield D-T shot of 10{sup 16} neutrons. General environment dose rates drop to below 3 mrem/h within three hours following a shot with higher dose rates observed at contact with some of the components. Dose rate maps of the different TB levels were generated to aid in estimating worker stay-out times following a shot before entry is permitted into the TB.
Date: October 29, 2010
Creator: Sitaraman, S; Brereton, S; Dauffy, L; Hall, J; Hansen, L; Khater, H et al.
Partner: UNT Libraries Government Documents Department

A Proposal for High-resolution X-ray Imaging of Intermodal Cargo Containers for Fissionable Materials

Description: The sensitivity for identification of high-Z objects in elemental form in the massive cargo of intermodal containers with continuous bremsstrahlung radiation depends critically on discriminating the weak signal from uncollided photons from the very intense flux of scattered radiations that penetrate the cargo. We propose that this might be accomplished by rejection of detected events with E {le} 2-3 MeV that contain the majority of multiply-scattered photons along with a correction for single-scattered photons at higher energies. Monte Carlo simulations of radiographs with a 9-MeV bremsstrahlung spectrum demonstrate that rejection of detected events with E {le} 3 MeV removes the majority of signals from scattered photons emerging through cargo with Z {le} 30 and areal densities of at least 145 g cm{sup -2}. With analytical estimates of the single-scattered intensity at higher energies, accurate estimates of linear attenuation coefficients for shielded and unshielded uranium spheres with masses as small as 0.08 kg are found. The estimated maximum dose is generally so low that reasonable order tomography of interesting portions of a container should be possible.
Date: July 5, 2007
Creator: Quiter, B J; Prussin, S G; Pohl, B; Hall, J; Trebes, J; Stone, G et al.
Partner: UNT Libraries Government Documents Department


Description: A set of computational tools was developed to help estimate and minimize potential radiation exposure to workers from material activation in the National Ignition Facility (NIF). AAMI (Automated ALARA-MCNP Interface) provides an efficient, automated mechanism to perform the series of calculations required to create dose rate maps for the entire facility with minimal manual user input. NEET (NIF Exposure Estimation Tool) is a web application that combines the information computed by AAMI with a given shot schedule to compute and display the dose rate maps as a function of time. AAMI and NEET are currently used as work planning tools to determine stay-out times for workers following a given shot or set of shots, and to help in estimating integrated doses associated with performing various maintenance activities inside the target bay. Dose rate maps of the target bay were generated following a low-yield 10{sup 16} D-T shot and will be presented in this paper.
Date: October 22, 2010
Creator: Verbeke, J; Young, M; Brereton, S; Dauffy, L; Hall, J; Hansen, L et al.
Partner: UNT Libraries Government Documents Department

Gamma-ray identification of nuclear weapon materials

Description: There has been an accelerating national interest in countering nuclear smuggling. This has caused a corresponding expansion of interest in the use of gamma-ray spectrometers for checkpoint monitoring, nuclear search, and within networks of nuclear and collateral sensors. All of these are fieldable instruments--ranging from large, fixed portal monitors to hand-held and remote monitoring equipment. For operational reasons, detectors with widely varying energy resolution and detection efficiency will be employed. In many instances, such instruments must be sensitive to weak signals, always capable of recognizing the gamma-ray signatures from nuclear weapons materials (NWM), often largely insensitive to spectral alteration by radiation transport through intervening materials, capable of real-time implementation, and able to discriminate against signals from commonly encountered legitimate gamma-ray sources, such as radiopharmaceuticals. Several decades of experience in classified programs have shown that all of these properties are not easily achieved and successful approaches were of limited scope--such as the detection of plutonium only. This project was originally planned as a two-year LDRD-ER. Since funding for 1997 was not sustained, this is a report of the first year's progress.
Date: February 3, 1997
Creator: Gosnell, T. B., LLNL; Hall, J. M.; Jam, C. L.; Knapp, D. A.; Koenig, Z. M.; Luke, S. J. et al.
Partner: UNT Libraries Government Documents Department

Detection of radioactive materials at Astrakhan

Description: Astrakhan is the major Russian port on the Caspian Sea. Consequently, it is the node for significant river traffic up the Volga, as well as shipments to and from other seaports on the Caspian Sea. The majority of this latter trade across the Caspian Sea is with Iran. The Second Line of Defense and RF SCC identified Astrakhan as one of the top priorities for upgrading with modern radiation detection equipment. The purpose of the cooperative effort between RF SCC and DOE at Astrakhan is to provide the capability through equipment and training to monitor and detect illegal shipments of nuclear materials through Astrakhan. The first facility was equipped with vehicle and rail portal monitoring systems. The second facility was equipped with pedestrian, vehicle and rail portal monitoring systems. A second phase of this project will complete the equipping of Astrakhan by providing additional rail and handheld systems, along with completion of video systems. Associated with both phases is the necessary equipment and procedural training to ensure successful operation of the equipment in order to detect and deter illegal trafficking in nuclear materials. The presentation will described this project and its overall relationship to the Second Line of Defense Program.
Date: July 1, 1999
Creator: Cantut, L; Dougan, A; Hemberger, P; Kravenchenko, Gromov, A; Martin, D; Pohl, B et al.
Partner: UNT Libraries Government Documents Department

A Monte Carlo Model for Interrogation of Thick Cargos for Clandestine Fissionable Materials; Tests with 14-MeV Neutrons

Description: A Monte Carlo model has been developed for interrogation of fissionable material embedded in thick cargos when high-energy {beta}-delayed {gamma} rays are detected following neutron-induced fission. The model includes the principal structural components of the laboratory, the neutron source and collimator assembly in which it resides, the assembly that represents cargo of given characteristics, a target of highly-enriched uranium (HEU) and large external plastic scintillators for photon detection. The ability of this model to reproduce experimental measurements was tested by comparing simulations with measurements of the number of induced fissions and the number of detected photons when the HUE target was irradiated with 14.25-MeV neutrons in the absence of any cargo and while embedded in assemblies of plywood and iron pipes. The simulations agreed with experimental measurements within a factor of about 2 for irradiation of the bare target and when the areal density of intervening cargo was 33 g cm{sup -2} (wood) and 61 g cm{sup -2} (steel pipes). This suggests that the model can permit exploration of a large range in parameter space with reasonable fidelity.
Date: June 8, 2006
Creator: Prussin, S; Descalle, M; Hall, J; Pruet, J; Slaughter, D; Accatino, M et al.
Partner: UNT Libraries Government Documents Department

Early results utilizing high-energy fission product (gamma) rays to detect fissionable material in cargo

Description: A concept for detecting the presence of special nuclear material ({sup 235}U or {sup 239}Pu) concealed in intermodal cargo containers is described. It is based on interrogation with a pulsed beam of 7 MeV neutrons that produce fission events and their {beta}-delayed neutron emission or {beta}-delayed high-energy {gamma}-radiation between beam pulses provide the detection signature. Fission product {beta}-delayed {gamma}-rays above 3 MeV are nearly ten times more abundant than {beta}-delayed neutrons and are distinct from natural radioactivity and from nearly all of the induced activity in a normal cargo. Detector backgrounds and potential interferences with the fission signature radiation have been identified and quantified. An important goal in the US is the detection of nuclear weapons or special nuclear material (SNM) concealed in intermodal cargo containers. This must be done with high detection probability, low false alarm rates, and without impeding commerce, i.e. about one minute for an inspection. The concept for inspection has been described before and its components are now being evaluated. While normal radiations emitted from plutonium may allow its detection, the majority of {sup 235}U {gamma} ray emission is at 186 keV, is readily attenuated by cargo, and thus not a reliable detection signature for passive detection. Delayed neutron detection following a neutron or photon beam pulse has been used successfully to detect lightly or unshielded SNM targets. While delayed neutrons can be easily distinguished from beam neutrons they have relatively low yield in fission, approximately 0.008 per fission in {sup 239}Pu and 0.017 per fission in {sup 235}U, and are rapidly attenuated in hydrogenous materials making that technique unreliable when challenged by thick hydrogenous cargo overburden. They propose detection of {beta}-delayed high-energy {gamma} radiation as a more robust signature characteristic of SNM.
Date: September 30, 2004
Creator: Slaughter, D R; Accatino, M R; Bernstein, A; Church, J A; Descalle, M A; Gosnell, T B et al.
Partner: UNT Libraries Government Documents Department