Detailed measurement of axial pressure profiles is often required to optimize the design of nuclear fuel assemblies. The classic method of using drilled pressure taps at predetermined locations in the test section has limited practicality and resolution. In addition, it cannot be used to test actual assemblies whose integrity must be preserved.This paper describes an alternative technique that can be applied to complex geometries. The method includes the use of a slender tube with a static hole near one end, which is introduced through slider seals into the test piece and moved to the desired locations. When signal-averaging is applied to the measurement, the technique is powerful in resolving pressure losses due to small subcomponents, such as fuel-element spacers. This technique was applied to the fuel design for a new research reactor, allowing the design to be optimized with confidence from the standpoint of pressure loss. (C) Elsevier Science Inc., 1997.

AECL is currently demonstrating the use of pool-type reactors of up to 10 MW output to produce hot water at about 90°C. The initial focus for the development is the provision of a source of hot water for institutional and municipal heating networks. Ongoing developments are designed to broaden the applications to electricity generation and industrial processes such as desalination and agricultural needs. The reactor concept is based on the Slowpoke-2 research reactor, eight of which are successfully operating in Canada and abroad. The primary-circuit flow is driven by natural convection, with the heated water, produced by the reactor core near the bottom of the pool, being ducted to low-pressure-drop heat exchangers in the upper part of the pool. As the pool volume is relatively large, the fluid transit time around the circuit is long, ensuring that the reactor response to all normal transients is extremely slow. To investigate the thermal-hydraulics aspects of the reactor design, including its behaviour under extreme conditions, an electrically heated, natural-convection loop was designed and constructed. The core of the loop consists of a rod bundle that is a precise reproduction of one quarter of the core of the 2 MW SLOWPOKE Demonstration Reactor presently being tested at the Whiteshell Nuclear Research Establishment. With this loop, measurements of the distribution of pressure, temperature, velocity and subcooled void have been made in the simulated core, via a variety of intrusive and non-intrusive techniques. In addition, both the single- and two-phase behaviour of the system have been studied. This paper gives examples of the various in-core measurements made and also makes comparisons between the measured system behaviour and that predicted by the various steady-state and transient computer codes.

AECL is currently demonstrating the use of pool-type reactors of up to 10 MW output to produce hot water at about 90°C. The initial focus for the development is the provision of a source of hot water for institutional and municipal heating networks. Ongoing developments are designed to broaden the applications to electricity generation and industrial processes such as desalination and agricultural needs. The reactor concept is based on the Slowpoke-2 research reactor, eight of which are successfully operating in Canada and abroad.

The adsorption of oxygen on Ni(110) was investigated by nuclear reaction analysis (NRA), XPS, Δφ, temperature programmed reaction spectroscopy (TPRS) and LEED. At 423 K, (3 × 1), (2 ×1) and (3 ×1) phases are formed in sequence with increasing O2 exposure. The coverage in the (2 ×1) phase was determined by NRA, the coverages in the other phases being determined via this calibration by XPS, TPRS and Δφ. Contrary to previous reports, the maximum in the intensity of half-order beams from the (2 × 1) phase is associated with a coverage of (5.6 ± 0.5) × 1014 O atoms cm−2 or 0.49 ± 0.05 monolayers, and not 0.25 monolayers. The two (3 ×1) phases are associated with θ = 0.33 ± 0.03 and 0.64 ± 0.06 monolayers respectively. Oxygen adsorbed at 295 K is not at thermodynamic equilibrium. Annealing to T > 400 K causes significant decreases in Δφ and the formation of the (2 ×1) phase for θ > 0.3.

The rate of desorption of deuterium from the low temperature (α) state on Ni(110) follows nearly zero order kinetics. Simultaneous measurements of intensities and profiles of half-order diffraction beams and changes in work function during isothermal desorptionof D2, have shown that the zero order region is associated with the presence of islands of the (1 × 2) phase which act as reservoirs of deuterium. These results are discussed in terms of a recent model for zero order desorption which requires the presence of 3 deuterium surface phases in equilibrium. The activation energy for desorption of the α-state is 67 ± 6 kJ mol−1.

The interaction of O2 with Pt(100)–hex and (1×1) surfaces at 123 K was studied by thermal desorption spectroscopy, x-ray photoemission, and work function techniques. On the hex surface, oxygen is adsorbed entirely as the molecular state with a sticking coefficient of 0.13 and exhibits an activation energy for desorption ∼37 kJ mol−1. The saturation coverage is 0.24×1015 O2 molecules cm−2 and desorption does not lead to any dissociation. On the (1×1) surface, oxygen dissociates, even at 123 K. The sticking coefficient is 0.4, and the saturation coverage is 0.48×1015 O atoms cm−2. On warming to 240 K, a (2×1) LEED pattern is observed that is believed to originate from an oxygen overlayer on an unreconstructed substrate. At ∼360 K, the surface transforms irreversibly to the oxygen stabilized (3×1) reconstructed phase.

Using dynamic LEED measurements of spot intensities and profiles, together with thermal desorption data, we have investigated the oxidation of CO on Pt(100)−(1 × 1). At T = 355 K, either CO or O was preadsorbed and reacted off with the other species. Results from both titration sequences point to the following conclusions: Titration of preadsorbed oxygen with COg leads to rapid reaction, with a reaction probability of unity for each chemisorbed CO. Adsorbed CO does not accumulate on the surface until θo ⩽ 0.05, i.e. an intermediate, rather clean (1 × 1) Pt surface is obtained. Further evidence for this clean intermediate is provided by the fact that characteristics of the diffraction spots of the c(2 × 2) of CO develop identically during this reaction sequence and during adsorption of CO on a clean (1 × 1) Pt surface. In the reverse case, titration of preadsorbed CO with O2,g, the reaction rate is slower than the oxygen adsorption rate, leading to a pressure-dependent development of coexisting Oad and COad domains, which we observe directly with LEED. The stable phases coexisting are the c(2 × 2) of CO and the oxygen-related (3 × 1). Thermal desorption peak shapes, together with LEED observations, indicate that the CO in this case is held in c(2 × 2) islands by a matrix of surrounding oxygen atoms. In no case do mixed structures form, nor is an existing structure compressed by subsequent adsorption of the second species. Starting from a Langmuir-Hinshelwood mechanism, the differences between the two reaction sequences are discussed in terms of different activation barriers for reaction and different sticking coefficients of the adsorbing species. Special attention is given to the mobilities of the adsorbed reactants.

The potential usefulness of work function measurements made simultaneously with Rutherford backscattering has been illustrated through the study of the temporal oscillations observed in the catalytic oxidation of CO over Pt(100).

The kinetics and energetics of the interaction of O2 with Pt(100)-hex and (1 × 1) surfaces were studied by thermal desorption spectroscopy, work function techniques and X-ray photoemission. Three states of adsorbed oxygen are formed in roughly equal amounts at saturation (saturation coverage = 0.81 ± 0.04 × 1015O atoms cm−2). The state desorbing at the lowest temperature (β1) which exhibits a very narrow desorption peak is associated with a phase transition (complex to (3 × 1)) involving Pt atom displacements. The next state to desorb (β2), is best modeled by second order kinetics, a constant activation energy for desorption Ed0 (≈ 10−3 cm2 atom−1 s−1, Ed ≈ 160 kJ mol−1) and is associated with a further phase transition, (3 × 1) → hex. The high temperature state (β3) which populates first with an initial sticking coefficient of ≈ 4 × 10−3 at 573 K is believed to be associated with surface defects in the hex-overlayer. The rate of adsorption of the β2 state at T ≳ 573 K increases with increasing coverage at 0.1 ≲θ ≲ 0.3, probably because of nucleation and growth of (3 × 1) islands which act as traps for further adsorption. The maximum sticking coefficient into either the β1 or β2 states is ≈ 10−3. The initial sticking coefficient of O2 on Pt(100)−(1 × 1) is ≈ 0.1.

The structure and composition of a Pt(100) surface have been monitored by Rutherford backscattering (RBS), nuclear microanalysis (NMA), LEED, and work function (Δφ) techniques during temporal oscillations in the rate of CO oxidation. For a Δφ oscillation amplitude of 60 mV, a constant 0.46±0.06×1015 Pt atoms are out of registry with the bulk throughout an oscillation cycle. The maximum fraction of the surface that could be oscillating between the hex and (1×1) phases is thus 8%. The average CO and O coverages during the oscillations are 0.19±0.04 and 0.13±0.03 monolayers, respectively. These results are discussed in terms of a recent model for the temporal oscillations. No oscillations in Δφ have been detected in similar experiments on Pt(111).

A stream of water vapor was irradiated in a "crossed-beam" experiment by 1 MeV He+ ions. After traversing the He+ ion beam, the vapor was condensed on a quartz tube at 77°K. The deposit so formed was then isolated under vacuum and transferred to an electron spin resonance (e.s.r.) spectrometer. E.s.r. spectra were observed that arise from species formed as a consequence of radiolysis in the vapor phase. Species trapped in the deposit were identified as HO2 radicals and electrons. Addition of CH3I and N2O gives results which indicate that hydrogen atoms were also formed although they do not become trapped in the deposit.The physical parameters of the experiment have been measured or calculated. These include the pressure and velocity of molecules in the vapor stream, and the time between irradiation and deposition on the cold finger.