Release of Al from SiC targets used for radioactive ion beam production

On-line targets of silicon carbide have been used to produce radioactive ion beams (RIB) at TRIUMF’s ISAC facility. Surface ionized beams of Li, Na and Al from SiC targets have been delivered to a variety of experiments. While yields of Li and Na radionuclide beams have been high enough to meet experimental requirements, the yields of radio-aluminums have been very low in comparison to in-target production estimates. The properties of SiC relevant to radioactive Al ion beam production are reviewed and on-line measurements of radiogenic Li, Na and Al from SiC are presented. Diffusion, effusion and formation of stable phases are found to strongly affect the release of radio-aluminum from SiC, greatly reducing overall Al RIB production efficiency. In comparison, the production of radio-sodium beams from SiC is found to be relatively efficient.     

Accelerator mass spectrometry II: Background reduction with a Wien (velocity) filter; 10Be contents of Central American basalts

Our limit of detection for ¹⁰Be by accelerator mass spectrometry has been lowered to a few million atoms by the installation of a Wien filter which screens out co-transmitted ⁹Be. Analyses of six Central American basalts gave ¹⁰Be contents ranging from 1 × 10⁶ to 60 × 10⁶ atom/g. The sample richest in ¹⁰Be has been contaminated by sediments. The other samples have ¹⁰Be contents in the range reported in the literature by Brown and co-workers.     

Fusion technology for a magnetic fusion production reactor

The tandem mirror and tokamak are being considered as candidate fusion drivers for a materials production reactor that could be implemented in the 1990s. This report considers, in detail, the required performance characteristics of the fusion plasma and the major technological subsystems for each fusion driver. These performance characteristics are compared with the present state of the art, corresponding development needs are identified, and technology program requirements, in addition to those now being supported by the Department of Energy, are pointed out. The tandem mirror and tokamak fusion drivers are also compared with regard to their required advancements in plasma performance and technology development.This paper represents work carried out from 1980 to 1982 and was in draft form in 1982. It was received for publication with only minor editing of its 1982 version, explaining the fact that some of the material is dated.     

Screener3D:a gaseous time projection chamber for ultra-low radioactive material screening

In experiments searching for rare signals,back-ground events from the detector itself are some of the major factors limiting search sensitivity.Screening for ultra-low radioactive detector materials is becoming ever more essential.We propose to develop a gaseous time projection chamber(TPC)with a Micromegas readout for radio screening.The TPC records three-dimensional tra-jectories of charged particles emitted from a flat sample placed in the active volume of the detector.The detector can distinguish the origin of an event and identify the particle types with information from trajectories,which significantly increases the screening sensitivity.For a particles from the sample surface,we observe that our proposed detector can reach a sensitivity higher than 100 p Bq m-2 within two days.     

Selection of a toroidal fusion reactor concept for a magnetic fusion production reactor

The basic fusion driver requirements of a toroidal materials production reactor are considered. The tokamak, stellarator, bumpy torus, and reversed-field pinch are compared with regard to their demonstrated performance, probable near-term development, and potential advantages and disadvantages if used as reactors for materials production. Of the candidate fusion drivers, the tokamak is determined to be the most viable for a near-term production reactor. Four tokamak reactor concepts (TORFA/FED-R, AFTR/ZEPHYR, Riggatron, and Superconducting Coil) of approximately 500-MW fusion power are compared with regard to their demands on plasma performance, required fusion technology development, and blanket configuration characteristics. Because of its relatively moderate requirements on fusion plasma physics and technology development, as well as its superior configuration of production blankets, the TORFA/FED-R type of reactor operating with a fusion power gain of about 3 is found to be the most suitable tokamak candidate for implementation as a near-term production reactor.This paper represents work carried out from 1980 to 1982 and was in draft form in 1982. It was received for publication with only minor editing from its 1982 version (except for Tables II and III and Fig. 1), explaining the fact that some of the material is dated.     

Radiation effects in Be and Al for a magnetic fusion production reactor

Estimates of the expected performance of beryllium and several aluminum alloy structural components of the breeding blanket of a magnetic fusion production reactor are made based on the known behavior and properties of these materials in fission reactor applications. Comparisons of the irradiation damage effects resulting from the fission reactor neutron spectra and the fusion reactor blanket spectra indicate that beryllium will perform well in the breeding blanket for at least one year and the aluminum alloy 5052 will retain structural integrity for about 5 years.This paper represents work carried out from 1980 to 1982 and was in draft form in 1982. It was received for publication with only minor editing of its 1982 version, explaining the fact that some of the material is dated.     

Finite element and reliability: a method for compound variables—application on a cracked heating system

Nuclear engineering systems are designed to ensure safety criteria. To predict the behavior of mechanical systems, the finite element analysis (FEA) is actually the main tool for numerical analysis of mechanical problems. In order to design a system under data variability considerations, performance functions have to be defined by the relationship between the action effects and the material strengths. Then a certain level of safety should be satisfied with sufficiently high probability. This is the subject of the reliability theory. Controlling a FEA software in order to carry out the reliability analysis, it is to define a ‘combination method’. This paper proposes a general method for the reliability analysis combined with FEA codes. The method is efficient for independent, correlated and compound random variables. The proposed method is illustrated by numerical example of a cracked membrane exposed to thermal shortening. The risk to evaluate is represented by the crack propagation in the material.     

Probabilistic seismic hazard analysis—lessons learned: a regulator's perspective

Probabilistic seismic hazard analysis is a powerful, rational and attractive tool for decision-making. It is capable of absorbing and integrating a wide range of information and judgement and their associated uncertainties into a flexible framework that permits the application of societal goals and priorities. Unfortunately, its highly integrative nature can obscure those elements which drive the results, its highly quantitative nature can lead to false impressions of accuracy, and its open embrace of uncertainty can make decision-making difficult. Addressing these problems can only help to increase its use and make it more palatable to those who need to assess seismic hazard and utilize the results.     

Chromium-molybdenum steels for fusion reactor first walls — a review

Chromium-molybdenum steels have recently become of interest as a first wall and blanket structural material for fusion reactors. This application will be assessed, and possible approaches on how Cr---Mo alloys may be further developed for this application will be proposed.Generally, the Cr---Mo steels can be divided into two categories: unmodified, basically Cr---Mo---C steels and Cr---Mo---C steels modified by the addition of carbide-forming elements. Extensive research and development efforts have been conducted on the unmodified steels, especially Cr-1 Mo and 12 Cr---Mo steels. Considerable work has also been done on 12 Cr---Mo steels modified with additions of V, Nb, Ti and W. In recent years much of the research effort on this type of alloy has been directed at developing modified Cr---Mo steels with less than 12% Cr (generally 9%) for applications where the “stainless” properties imparted by chromium additions of at least 12% are not needed.We will examine the unmodified and modified steels in terms of hardenability, precipitation processes (stability at elevated temperatures), strength, and toughness. Where possible, we will discuss the effects of irradiation on these properties. Such a study leads to the types of tradeoffs that may be necessary between the well-researched unmodified Cr-1 Mo steel and a high-chromium modified steel.     

COMPBRN IIIe—a computer code for probabilistic fire risk analysis

The COMPBRN code has been used extensively to predict deterministically the time-to-damage of critical components in nuclear power plant fire risk analyses. Because there is a significant amount of uncertainties in the input parameters used in room fire simulations, the assessment of the damage time of the specified components must be performed probabilistically. This paper presents an updated version of the code, called COMPBRN IIIe, which emphasizes the importance of parameter uncertainty propagation by incorporating capabilities to provide probability distributions for component damage times. COMPBRN IIIe eliminates several errors from its previous versions and incorporates a user-friendly environment to assist users in preparing input files. With these improvements, the code can significantly reduce the time and effort required in the performance of a probabilistic fire risk assessment. A compartment fire simulation is also provided to demonstrate the application of the code.     

System for high-level radioactive waste using microchannel chip — extraction behavior of metal ions from aqueous phase to organic phase in microchannel

In order to clarify the extraction behavior of U(VI) from aqueous phase to organic one in microchannel, we have carried out extraction experiments of U(VI) from HNO₃ aqueous solution of 3 M (M = mol/dm³) to 30% or 100% TBP phase in microchannel. From the results of extraction experiments, it was found that the extraction of U(VI) in microchannel could be performed in a short time for approximately 1 s with a good extractability in both organic phases of 30% and 100% TBP, and suggested that the other nuclides could be extracted with high extraction efficiency in microchannel. Furthermore, it is expected that the innovative and sophisticated nuclide separation systems can be developed by using microchannel extraction with selective extractants for specific nuclide.     

Approximate fracture methods for pipes — Part II: Applications

In the part I paper entitled “Approximate fracture methods for pipes — Part I, Theory” [4], five different J-estimation schemes for through-wall cracked pipes were presented. The (i) GE.EPRI method utilizes a compilation of finite-element solutions. The (ii) Paris/Tada and (iii) LBB.NRC methods utilize an interpolation between the linear elastic and rigid plastic solutions, (iv) the LBB.GE method also uses numerical solutions, and (v) the LBB.ENG uses an equivalent area method to estimate J. All five methods are very simple to use and all five give reasonable predictions of crack growth and failure in pipes. The present paper provides a comparison of some of the methods to full-scale finite-element analyses. In addition, predictions for actual pipe experiments compared to experimental data are also provided.     

LISA — a European project for FEM-based limit and shakedown analysis

The load-carrying capacity or the safety against plastic limit states are the central questions in the design of structures and passive components in the apparatus engineering. A precise answer is most simply given by limit and shakedown analysis. These methods can be based on static and kinematic theorems for lower and upper bound analysis. Both may be formulated as optimization problems for finite element discretizations of structures. The problems of large-scale analysis and the extension towards realistic material modelling will be solved in a European research project. Limit and shakedown analyses are briefly demonstrated with illustrative examples.     

Numerical weld modeling — a method for calculating weld-induced residual stresses

In the past, weld-induced residual stresses caused damage to numerous (power) plant parts, components and systems (Erve, M., Wesseling, U., Kilian, R., Hardt, R., Brümmer, G., Maier, V., Ilg, U., 1994. Cracking in Stabilized Austenitic Stainless Steel Piping of German Boiling Water Reactors — Characteristic Features and Root Causes. 20. MPA-Seminar 1994, vol. 2, paper 29, pp.29.1–29.21). In the case of BWR nuclear power plants, this damage can be caused by the mechanism of intergranular stress corrosion cracking in austenitic piping or the core shroud in the reactor pressure vessel and is triggered chiefly by weld-induced residual stresses. One solution of this problem that has been used in the past involves experimental measurements of residual stresses in conjunction with weld optimization testing. However, the experimental analysis of all relevant parameters is an extremely tedious process. Numerical simulation using the finite element method (FEM) not only supplements this method but, in view of modern computer capacities, is also an equally valid alternative in its own right. This paper will demonstrate that the technique developed for numerical simulation of the welding process has not only been properly verified and validated on austenitic pipe welds, but that it also permits making selective statements on improvements to the welding process. For instance, numerical simulation can provide information on the starting point of welding for every weld bead, the effect of interpass cooling as far as a possible sensitization of the heat affected zone (HAZ) is concerned, the effect of gap width on the resultant weld residual stresses, or the effect of the ‘last pass heat sink welding’ (welding of the final passes while simultaneously cooling the inner surface with water) producing compressive stresses in the root area of a circumferential weld in an austenitic pipe. The computer program (finite element residual stress analysis) was based on a commercially available code (Hibbitt, Karlsson, Sorensen, Inc, 1997. user's manual, version 5.6), and can be used as a 2-D or 3-D FEM analysis; depending on task definition it can provide a starting point for a fracture mechanics safety analysis with acceptable computing times.     

AC operation of large titanium sublimation pumps in a magnetic field: Results of the test stand for the W7-X neutral beam injectors

A neutral beam injection (NBI) system is being built for the Stellarator experiment Wendelstein 7-X (W7-X) currently under construction at IPP Greifswald. The NBI system consists of two injectors which are essentially a replica of the system present in the Tokamak experiment ASDEX-Upgrade at IPP Garching. A vacuum system with high pumping speed and large capacity is required to ensure proper vacuum conditions in the neutral beam line. For this purpose, large titanium sublimation pumps (TSP) are installed inside the NBI boxes, consisting of 4 m long hanging wires containing Ti and the surrounding condensation walls. The wires are DC ohmically heated up with 142 A to Ti sublimation temperature. A TSP system has been operated since many years in the AUG-NBI system, sublimating Ti in the pauses between the plasma discharges, when no magnetic field is present. However, at W7-X the superconducting coils generate a magnetic field permanently during experimental campaigns, whose stray B field with a maximum of 30 mT, affects the TSPs. Operated with DC, the wires would be deflected against the surrounding panels due to the Lorentz force. A simple possible solution is heating with AC, which reduces the wire deflection amplitude, inducing a risky wire oscillation. The feasibility of the AC operation in an equivalently strong B field such as the stray B field around W7-X has been demonstrated in a test stand for different AC waveforms and frequencies. Several test campaigns have shown no qualitative difference in the pumping properties between AC and DC operation of the TSP and no critical dynamic behaviour of the wires.     

CASSPERR: A γ–γ cascade detector for resonant nuclear reaction analysis

Resonant nuclear reaction analysis (RNRA) is sometimes the only technique able to quantify elements in a matrix containing other elements. Background due to cosmic rays and natural radioactivity has limited traditional RNRA to samples with relatively high concentrations of the measured element, or to facilities with large amounts of passive shielding. Many nuclear reactions of interest in RNRA produce excited states in the resulting nuclei that then de-excite by product-specific sequences of photon emissions. The CAScade SPEctrometer for Resonant Reactions (CASSPERR) selects only events that match the desired combination of photon emissions. Rejection of other events greatly reduces the background, thus improving the signal to noise ratio (SNR). Since it is constructed from available commercial components, CASSPERR opens RNRA to typical ion beam analysis facilities. The design, operation and evaluation of CASSPERR with applications to materials science are currently under investigation.