Neutronic Aspects Research Articles

Seventh summer school on neutron scattering held in ZUOZ

The almost 40 poster presentations by the participants were an essential input to the program of the school. The posters were discussed in a dedicated session as well as in six seminars devoted to particular aspects of neutron scattering. The excursion day featured a bus trip to southern Germany to see the total solar eclipse. For those who preferred to stay in the Engadine valley, a hiking tour, a visit to the Swiss National Park and river rafting were the alternatives. During the final banquet our indefatigable secretary, Renate Bercher, was promoted to “Angel of Zuoz,” for taking care of everything around the school. We also celebrated the 60th birthday of Walter Fischer who was the initiator of the Zuoz summer schools on neutron scattering and who has been the school chairman since the beginning in 1993. A miraculous rocket show over the midnight heaven of Zuoz capped off this celebration.

Neutronics aspects of a DHCE experiment

Abstract The DHCE (dynamic helium charging experiment) irradiation experiment was conceived to simulate fusion-relevant helium production in a fission reactor irradiation. The main objective is to maintain the helium-to-dpa ratio at, roughly, the same level as expected in a fusion environment. The problem in fission reactor irradiation is that helium production is very low, because the fission neutrons, for basically all structural materials relevant for fusion applications, do not have enough energy to trigger the helium producing reactions. A DHCE experiment involves the decay of tritium to He-3 to produce the required helium during irradiation. This paper describes an analysis of the most important aspects of a DHCE experiment and compares different types of fission reactors and their suitability for performing such an experiment. It is concluded that DHCE experiments are feasible in a certain class of mixed-spectrum fission reactors, but a careful and detailed evaluation, for each facility and condition, must be performed to ensure the success of the experiment.

“New perspectives in neutron and muon science” meets in abingdon

The second “New Perspectives in Neutron and Muon Science” meeting was held at Cosener's House in Abingdon from September 23–24, 1998. The objective of this meeting, organized by the Neutron Scattering Group of the Institute of Physics and The Royal Society of Chemistry, and co'sponsored by ISIS and EPSRC, was to provide Ph.D. students and young postdoctoral researchers with an opportunity to present their work in an informal atmosphere. This year, the meeting was divided into four sessions entitled “Structure, Including Surfaces and Interfaces,” “Excitations and Vibrations,” “Large Scale Structures,” and “Disordered Materials and Muons.” Three keynote lectures by Paul Attfield (Cambridge), Andrew Boothroyd (Oxford), and Colin Bain (Oxford) provided an excellent overview of the current state of neutron science. Fifteen contributed talks were presented, all of a uniformly high standard, covering many aspects of neutron scattering and muon spectrosCOPY.

Design of the Centerpost for a Spherical Torus Volumetric Neutron Source

Mechanical, thermal and neutronics design aspects of the toroidal field coil centerpost (CP) for a spherical torus based volumetric neutron source (ST-VNS) are presented. It is being investigated with support of a DOE-SBIR under the direction of TSI Research Inc. of Solana Beach, CA. The ST-VNS is to provide a test bed for developing nuclear technologies, as well as qualifying blanket designs for future fusion reactors. The device is scoped to be capable of staged operation with a neutron wall loading range of 0.5–4.0 MW/m2 as the physics and engineering design assumptions are raised from modest to aggressive levels. Margins in the design are ensured, since operation at 2 MW/m2 neutron wall loading will satisfy the mission of the VNS. The device has a naturally diverted plasma with a major radius of 1.1m, a minor radius of 0.78 m for an aspect ratio of 1.4, an elongation of 3, a triangularity of 0.6 and can be driven with neutral beams (NB) or radio frequency (RF). It utilizes a single turn; unshielded normal conducting CP made of dispersion strengthened (DS) Cu that is 15.5 m long and has a diameter of 0.55 m at the midplane. Resistive heating at the start of operation is 153 MW and increases to 178 MW after three full power years. The effect of transmutation in the Cu causes an increase in the resistivity, producing a shift in the CP current towards the center. The results of this shift on power distribution are reported.

On optical interaction of neutrons with magnetic media

New fundamental aspects of spin-dependent neutron scattering from magnetic media may be revealed when the Born approximation fails.

Preliminary Neutronics Investigation of the Delayed Neutron Nondestructive Assay of an Integral Fast Reactor Waste Canister

An innovative liquid-metal reactor, the Integral Fast Reactor (IFR), is being developed at Argonne National Laboratory. One characteristic of the IFR is the fuel cycle closure. Fissile material bred and fissionable material produced in the reactor are recycled back into the reactor. Waste generated during fuel reprocessing will be packaged into special waste canisters and will be shipped to a repository for final disposal. Prior to its removal from the facility, a measurements of the fissile content will be necessary as a part of an overall fissile material inventory accountability system. A particular form of nondestructive assay called delayed neutron nondestructive assay (DNNDA) is being developed to assist in the establishment of an accountability system. A preliminary neutronics investigation for the current DNNDA has been made to assist and verify the characteristics of the design from a neutronic aspect. A 10[sup 11] n/s, 14-MeV neutron source would provide adequate counting statistics for fissile material at the milligram to gram level.

Comprehensive Analysis of Passive Safety Test Phase IIB in the Fast Flux Test Facility

Power Reactor and Nuclear Fuel Development Corporation (PNC), using computer codes developed and/or modified at PNC, has analyzed the Phase IIB passive safety test (PST) proposed for the Fast Flux Test Facility (FFTF). Major interests of PST are understanding core bowing and mitigating extremely low probability accidents. It is confirmed that the PNC code system is applicable to all aspects of the FFTF Phase IIB PST program. Results of the pretest analysis indicate that the proposed Phase IIB PST in FFTF can be devised to provide very useful data for validation of the analytical models that treat reactivity feedback effects due to core bowing. Recommendations to the test program are also made. With those analytical tools, future fast breeder reactor concepts will incorporate to a greater degree than earlier designs passive safety features on neutronic aspects as well as on thermohydraulic aspects.

Neutronics Aspects of ARIES-II and ARIES-IV Fusion Power Reactors

The ARIES study investigates the potential of tokamaks as fusion power reactors and focuses on improving the economic and safety features of fusion by integrating the environmental constraints into the design from the beginning. The ARIES-II and ARIES-IV designs incorporate advanced physics and technologies that would be available over the next 5–20 years. The two designs have the same plasma physics but different fusion-power-core designs.1 ARIES-II uses liquid Li as a coolant/breeder with V alloy structure while ARIES-IV employs solid breeder with He coolant and SiC/SiC composite structure. Low activation materials were utilized in the design to reduce the radioactive inventory. A variety of blanket/shield options was examined for both designs and the relative merits of the various materials as a function of blanket/shield thickness were demonstrated. The lifetime of the structural components was determined based on the radiation-induced damage in V and SiC. In this paper, a comparison between the two designs based on detailed neutronics analysis is presented.

Inelastic neutron scattering analysis of low-frequency motions in proteins: Harmonic and damped harmonic models of bovine pancreatic tryspin inhibitor

Inelastic neutron scattering spectra are calculated from harmonic and damped harmonic models of the internal dynamics of a small protein, the bovine pancreatic trypsin inhibitor (BPTI). Numerical Fourier transformation of the intermediate scattering function Fvibinc (q, t) is used to calculate the inelastic scattering. This permits the inclusion of multiphonon scattering and frictional damping effects. Although for a typical experimental configuration, the multiphonon contribution does not significantly alter the form of the scattering at frequencies below about 30 cm−1, it does have a significant effect on the scattering intensity at higher frequencies. Frictional damping is introduced into the harmonic model by assuming that each mode acts as an independent damped Langevin oscillator. With this model and the assumption that the lowest frequency modes are overdamped while the higher frequency modes are underdamped, improved agreement with the experimental BPTI powder results is obtained. The measured scattering from BPTI in solution shows increased intensity at frequencies below 50 cm−1 relative to the powder results. The solution scattering profile can be reproduced approximately by the addition of overdamped Langevin oscillator normal modes to the dynamic model in best agreement with the powder data. Several other aspects of neutron scattering from proteins are examined. Anisotropy in the harmonic resolution broadened scattering is demonstrated. Spectra calculated assuming classical equations of motion are shown to agree with those calculated with the full quantum-mechanical dynamical model. Translational diffusion broadening is found to be small compared to the instrumental resolution broadening for the range of scattering wave vectors of interest. The contribution of the coherent scattering to the measured intensity is calculated for the case of a partially hydrated protein. Under typical experimental conditions, the measured cross sections are dominated by the incoherent scattering and the self part of the coherent scattering, a result that justifies the comparison of experimental data with calculated incoherent scattering spectra.

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Scientific opportunities with advanced facilities for neutron scattering: Summary of a workshop held at Shelter Island, New York, USA October 23–26, 1984

This article presents a summary of a Workshop held in October 1984 to discuss scientific opportunities in the field of neutron scattering. Introductory material summarizes both the goals of the Workshop and makes a case for more intense sources of neutrons. This section is followed by the recommendations of the Workshop. None of this material requires a detailed knowledge of neutron scattering. The technical part of the paper follows and consists of ten brief reports reflecting various aspects of neutron scattering, and the new opportunities that would be available if more intense sources were constructed. Each report also compares the opportunities with a new 5 × 10 15 n cm −2 s −1 steady state source and with a new 10 17 n cm −2 s −1 peak flux spallation source. Such comparisons are made across all fields of science in which neutron scattering is applied.

Neutronics Activities for Next Generation Devices

Neutronics activities for the next generation devices are the subject of this paper. The main activities include TFCX and FPD blanket/shield studies, neutronics aspects of ETR/INTOR critical issues, and neutronics computational modules for the tokamak system code and tandem mirror reactor system code. Trade-off analyses, optimization studies, design problem investigations and computational models development for reactor parametric studies carried out for these activities are summarized.

Nuclear design of a heliotron-H fusion power reactor

Nuclear analysis was carried out for the heliotron-H fusion power reactor employing anl=2 helical heliotron field. The neutronics aspects examined were (a) tritium breeding capability, (b) shielding effectiveness for the superconducting magnet (SCM), and (c) induced activity after shutdown. In this reactor design of the heliotron-H, the space available for the blanket and shield is limited due to the reactor geometry. Thus, some parametric survey calculations were performed to satisfy the design requirements. The nucleonic design features of the heliotron-H are as follows. An adequate tritium breeding ratio of 1.17 is obtained when a 10-cm thick Pb neutron multiplier and a 40-cm thick Li2O breeding blanket are used. In this case, the total nuclear energy deposition is 16.10 MeV per 14.06 MeV incident neutron. The performance of the SCM is assured during ∼2 yr of continuous operation using a 20-cm thick tungsten shield. Biological dose rate behind the SCM at 1 day after shutdown is too high for hands-on maintenance.

Description of breeding blanket test modules for TASKA-M

Abstract TASKA-M is a conceptual design of a low power, low cost test reactor based on a tandem mirror without thermal barriers utilizing physics which is presently in hand, or which should be available by 1985. The main purpose of the reactor is to study plasma engineering and provide a reasonable cost test bed for qualifying materials and investigating different blanket concepts. The central cell which is nominally 4.25 m long is divided into five zones: a liquid metal test module, a solid breeder test module, two material test modules and a central cell shield insert. This paper describes the structural, thermal hydraulics and neutronic aspects of the breeding test modules. Two liquid metal test blanket modules, one using Li 17 Pb 83 and the other elemental Li are designed to fit into the same slot within the central cell and will, therefore, be tested consecutively. The solid breeder test module is designed to test all kinds of breeding materials rather than as a reactor prototypical module with a high breeding ratio. The main emphasis is on fast, easy insertion and withdrawal of the solid breeder material samples. A breeding ball blanket concept has been developed, where the Li-ceramic is contained in spherical stainless steel shells which are inserted into pressure tubes coiled around the plasma.

(Deuterium-Deuterium)-Driven Experimental Hybrid Blankets and Their Neutronic Analyses

The impressive progress made so far toward the achievement of the physics goal of ignited fusion fuel of deuterium-tritium (D-T) is stirring the scientific community to look back and work for the earliest possible introduction of advanced fusion fuel based reactors with the ultimate objective of very clean, safe, and limitless fusion power. As the introduction of advanced fuel fusion drivers is expected to be in phases due to energetics considerations, it is quite instructive to examine the neutronic aspects of deuterium-deuterium (D-D) neutron driven hybrid blankets. The neutronics investigations of some compact hybrid blankets that could be tested experimentally are presented. The blanket designs are selected to conform to a rather small experimental chamber of the LOTUS fusionfission hybrid facility. The parallelepiped-shaped blankets are driven by a (D-D) neutron source from one side. The fertile fuel is either ThO/sub 2/, natural UO/sub 2/, or LOTUS UO/sub 2/. The tritium breeders are chosen from lithium, LiAlO/sub 2/, or Li/sub 2/O. The relative performances of different fertile fuels and tritium breeders are compared. The performance characteristics of ThO/sub 2/ blankets driven by (D-T) and (D-D) neutrons are compared. The improvement in performance characteristics obtained by the introduction of actinides as multipliersmore » with ThO/sub 2/ hybrid blankets is also investigated.« less

Plate vs rod fuel elements in a tight-lattice water reactor

Abstract In this paper, the possibility of using plate fuel elements in tight-lattice water reactors instead of rod fuel elements is explored. For this purpose we compared the thermal-hydraulic and neutronic aspects of plates with those of rod fuel elements. Because of the fact that plates have a higher mechanical strength than rods with equal dimensions, it is possible to reduce the thickness of the plates and thus reduce the centerline temperature. This fact and other thermal-hydraulic considerations demonstrate that plate fuel elements are safer than rods with respect to their resistance to LOCA. Preliminary neutronic calculations indicate that plates and rods have about the same neutronic characteristics.

Requirements of Position-Sensitive Detectors for Neutron Scattering Experiments

Neutron scattering is a very important tool in the understanding of the structure, dynamics, and magnetic properties of condensed matter, and the performance of neutron scattering instruments is heavily dependent on both the quality and quantity of neutron detectors which can be provided. This paper sets forth those detector characteristics which are important in various aspects of neutron scattering instrument performance. Current technology for standard and position-sensitive detectors is primarily based on gas proportional counters, and is adequate to meet current instrumentation requirements for many of these characteristics. However, a number of areas can be pointed out where immediate detector improvements are desirable or even essential. Development of new, more powerful neutron sources is leading to the development of new instrumentation with new requirements for detectors, which are not adequately met by; current detector technology. A great deal of innovation and development will be required if neutron detector performance is not to severely limit the potential capabilities of some current and of most future neutron scattering instruments.

Some time dependent aspects of fast neutron induced atomic cascades

Abstract Analytical results are obtained for the time-energy distribution of neutrons and the associated displaced atoms slowing down in an amorphous medium according to a general force law. Explicit results are given for the inverse power law, and applications to hard-sphere and Coulomb scattering are discussed. Complete results are obtained for the steady state energy distribution of particles arising from a primary knock-on, and from a neutron initiated cascade. The speed of the slowing down process is assessed by calculating the slowing down time of particles. Two different concepts of slowing down time are discussed, one based upon a density average and the other on a slowing down density average. It is shown that the latter definition is physically more realistic and mathematically simpler.

An Introduction to On-Line Computers

"An Introduction to On-Line Computers." Nuclear Science and Engineering, 50(4), p. 404 Additional informationNotes on contributorsMelvin TobiasAbout the Reviewer: Melvin L. Tobias has been in the Reactor Division of Oak Ridge National Laboratory since 1950. He has been concerned with heat transfer research, the measurement of physical properties of reactor materials, reactor analysis, and the development of neutron diffusion and cross-section preparation codes. Currently, he is working on the neutronics aspects of fusion reactor technology.

Theory of Thermal Neutron Scattering – the Use of Neutrons for the Investigation of Condensed Matter

W Marshall and S W Lovesay Oxford: University Press 1971 pp xxiii + 599 price £12 This is a very important addition to the literature of solid state physics. Although, as the title implies, most aspects of thermal neutron scattering by solids, liquids and gases are covered, the book is mainly devoted to a wide ranging account of the theory of those magnetic properties of solids which can be studied with neutrons.