Evaluation of precipitates used in strainer head loss testing. Part I. Chemically generated precipitates

The purpose of the current program was to evaluate the properties of chemical precipitates proposed by industry that have been used in sump strainer head loss testing. Specific precipitates that were evaluated included aluminum oxyhydroxide (AlOOH) and sodium aluminum silicate (SAS) prepared according to the procedures in WCAP-16530-NP, along with precipitates formed from injecting chemicals into the test loop according to the procedure used by one sump strainer test vendor for U.S. pressurized water reactors. The settling rates of the surrogate precipitates are strongly dependent on their particle size and are reasonably consistent with those expected from Stokes’ Law or colloid aggregation models. Head loss tests showed that AlOOH and SAS surrogates are quite effective in increasing the head loss across a perforated pump inlet strainer that has an accumulated fibrous debris bed. The characteristics of aluminum hydroxide precipitate using sodium aluminate were dependent on whether it was formed in high-purity or ordinary tap water and whether excess silicate was present or not.     

Evaluation of precipitates used in strainer head loss testing: Part III. Long-term aluminum hydroxide precipitation tests in borated water

Long-term aluminum (Al) hydroxide precipitation tests were conducted in slightly alkaline solutions containing 2500 ppm boron. The solution temperature was cycled to obtain a temperature history more representative of emergency core cooling system temperatures after a loss-of-coolant accident. The observed Al precipitation boundary was close to predicted results for amorphous precipitates, which are higher than the solubility expected for crystalline forms. Bench-scale and loop head loss test results under various conditions were successfully combined into single map in a temperature - ‘pH + p[Al]_T’ domain, which yielded two bounding lines for Al hydroxide solubility in borated alkaline water that depend on whether or not loop head loss tests with Al alloy coupons are included. Precipitates were observed to form either as fine, cloudy suspensions, which showed very little tendency to settle, or as flocculated precipitates. The flocculation tendency of the precipitates can be qualitatively explained by a colloid stability theory or a phase diagram for protein solutions.     

Gettering of copper impurity in silicon by aluminum precipitates and cavities

Al precipitates as well as cavities (or open-volume defects) are known for their ability to getter impurities within Si. In order to compare their relative gettering strength we produced both Al precipitates and cavities at different depths within one Si wafer. This was done by H+ and Al+ implantation with different energies and subsequent annealing process, resulting in Al-Si alloy and cavities at depth of 300 nm and 800 nm, respectively. Cu was then implanted with an energy of 70 keV to a fluence of 1 X 1014 / cm". The Cu implanted samples were annealed at temperature from 700C to 1200C. It was found that Cu impurities were gettered primarily by the precipitated Al layer rather than by cavities at the temperature of 700~1000C, while gettering of Cu occured in both regions at the temperature of 1200C. The secondary ion mass spectrometry and transmission electron microscopy analyses were used to reveal the interaction between Cu impurities and defects at different trap sites.     

The corrosion of AA2037 aluminum alloy in alkaline aqueous solution studied using slow positron beam spectroscopy

Corrosion behavior of AA2037 T8 Al alloy in a1 M Na OH aqueous solution was investigated using slow positron beam, together with microscopy techniques and electrochemical tests. The alloy was homogenized at 510℃ for 2 h and 30 s, respectively, before final peak aging, so that one Sample A had more dispersoids than Sample B after homogenization. It was found that S parameter of the Doppler-broadened annihilation was significantly decreased near the surface in both samples in the alkaline solution. With increasing the dissolution time,Sample A showed a slower decrease rate than Sample B,which might imply that the preexistence of more dispersoids might hinder the corrosion process in Sample A.Scanning electron microscopy and atomic force microscopy observations found that the surfaces of both samples were uniformly thinned due to intense chemical dissolution by the attack of OH-. With increasing the dissolution time,Sample B was corroded more substantially and produced more and larger pits in a short dissolution time than Sample A. Furthermore, polarization curves showed that Sample A had a lower corrosion current and corrosion rate than Sample B, which revealed that the presence of the dispersoids was responsible for the better corrosion resistance in the alloy.     

Response of reinforced concrete structures to macrocell corrosion of reinforcements. Part II: After propagation of microcracks via a numerical approach

Investigation of response of reinforced concrete (RC) structures due to axisymmetric macrocell corrosion of rebars is of concern after propagation of microcracks within the concrete medium. The geometry, boundary and interfaces conditions of the present problem are identical to those stated in part I. As seen in the companion paper, the exact solution to the boundary value problem corresponding to the uncracked steel–rust–concrete composite was possible. After appearance of the microcracks the concrete behavior becomes nonlinear anisotropic with post-cracking softening, and the associated problem is analytically intractable. Therefore, it is proposed to employ a novel meshless method, namely gradient reproducing kernel particle (GRKPM), in the cylindrical coordinates. The analytical and numerical solutions pertinent to the uncracked concrete are in good agreement. Subsequently, the effects of the parameters associated with the mechanical behavior of concrete and properties of rust on the time of surface cracking, the maximum values of consumed rebar per unit area of anode and crack width openings at the time of surface cracking, and the maximum value of radial stress at the rust–concrete interface are scrutinized in some detail.     

Evaluation of aged Incoloy 800 alloy sensitization to intergranular corrosion by means of double loop electrochemical methods and image analysis

In this paper, the sensitization of aged Incoloy 800 alloy to intergranular corrosion has been systemically investigated by double loop electrochemical potentiokinetic reactivation (DL-EPR) technique in combination with oxalic acid etching test and microstructure observation. The DL-EPR results show that the specimens aged at 650 °C and 700 °C for 4 h were intensely sensitized with I_r:I_a value greater than 30% while there was no sensitization phenomenon for the specimens aged at 800 °C for 4 h. It was also found that the degree of sensitization increased gradually with the aging time in the range of 0-10 h at 650 °C, and I_r:I_a value reached the maximum −46% after an aging time of 10 h. However, further increasing aging time decreased the sensitization due to the healing effect incurred by the diffusion of chromium from adjacent grains to chromium-depleted zones. Comparison between two evaluating techniques (the DL-EPR and oxalic acid etching test) has also been conducted.     

Magnetohydrodynamic instability in annular linear induction pump: Part II. Suppression of instability by phase shift

In the previous work, the authors showed some detailed aspects of the magnetohydrodynamic instability arising in an annular linear induction pump: the instability is accompanied with a low frequency pressure pulsation in the range of 0–10 Hz when the magnetic Reynolds number is larger than unity; the low frequency pressure pulsation is produced by the sodium vortices that come from some azimuthal non-uniformity of the applied magnetic field or of the sodium inlet velocity. In the present work, an experiment and a numerical analysis are carried out to verify the pump winding phase shift that is expected as an effective way to suppress the instability. The experimental data shows that the phase shift suppresses the instability unless the slip value is so high, but brings about a decrease of the developed pressure. The numerical results indicate that the phase shift causes a local decrease of the electromagnetic force, which results in the suppression of the instability and the decrease of the developed pressure. In addition, it is exhibited that the intensity of the double-supply-frequency pressure pulsation is in nearly the same level in the case with and without the phase shift.     

Comprehensive investigation of the corrosion state of the heat exchanger tubes of steam generators. Part II. Chemical composition and structure of tube surfaces

In the frame of a project dealing with the comprehensive study of the corrosion state of the steam generators of the Paks Nuclear Power Plant, Hungary, surface properties (chemical and phase compositions) of the heat exchanger tubes supplied by the power plant were studied by Mössbauer spectroscopy (CEMS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) methods. The work presented in this series provides evidence that chemical decontamination of the steam generators by the AP-CITROX technology does exert a detrimental effect on the chemical composition and structure of the protective oxide film grown-on the inner surfaces of heat exchanger piping. As an undesired consequence of the decontamination technology, a ‘hybrid’ structure of the amorphous and crystalline phases is formed in the outermost surface region (within a range of 11 μm). The constituents of this ‘hybrid’ structure exhibit great mobility into the primary coolant under normal operation of the VVER type reactor.     

How to measure absolute stopping cross sections by backscattering and transmission methods: Part II. transmission

The transmission type measurements are described which are part of the cooperative program on stopping cross sections for 20–700 keV protons performed at the Hahn—Meitner Institut Berlin and at the Johannes-Kepler-Universität Linz. Experimental limitations on achievable precision are discussed for energy calibration, energy loss measurement and foil thickness calibration. Modifications for the standard application of the transmission method are pointed out. By means of these modifications the experimental errors in the resulting stopping cross sections can be reduced to 3%.     

The effective convectivity model for simulation of melt pool heat transfer in a light water reactor pressure vessel lower head. Part II: Model assessment and application

The paper reports detailed assessments and representative application of the effective convectivity model (ECM) developed and described in the companion paper (Tran and Dinh, submitted for publication). The ECM capability to accurately predict energy splitting and heat flux profiles in volumetrically heated liquid pools of different geometries over a range of conditions related to accident progression is examined and benchmarked against both experimental data and CFD results. Augmented with models for phase changes in binary mixture, the resulting PECM (phase-change ECM) is validated against a non-eutectic heat transfer experiment. The PECM tool is then applied to predict thermal loads imposed on the reactor vessel wall and Control Rod Guide Tubes (CRGTs) during core debris heatup and melting in the BWR lower plenum. The reactor-scale simulations demonstrate the PECM's high computational performance, particularly needed to analyze processes during long transients of severe accidents. The analysis provides additional arguments to support an outstanding potential of using the CRGT cooling as a severe accident management measure to delay the vessel failure and increase the likelihood of in-vessel core melt retention in the BWR.     

CFD analysis of the ITER first wall 06 panel. Part II: Thermal-hydraulics

The computational fluid dynamics (CFD) analysis of the FW06 panel of the ITER shielding blanket is presented in two companion papers. In this Part II we concentrate on the thermal-hydraulics of the water coolant, driven by the nuclear volumetric and plasma surface heat loads discussed in Part I. Both the detailed steady state analysis of a single cooling channel and the coarse transient analysis of the whole panel are considered. The compatibility of the hot spots with the maximum recommended temperatures for the different materials is confirmed. The heat transfer coefficient between coolant and walls is obtained post-processing the results of the simulation and compared with the results of available correlations, which may be used for simpler analyses: in the fully developed flow regions of the cooling pipes, it turns out to be well approximated by the Sieder–Tate correlation. The operation margin with respect to the critical heat flux is also computed and turns out to be sufficiently large compared with the design limit.     

Reduction of light elements loss in polymer foils during MeV-proton irradiation by application of an aluminum coating

Backscattering and forward-scattering spectrometry with 2.2 MeV-protons have been applied to detect light elements including H, C, N and O in polymer foils of aromatic polyimide (PI), polyethylene telephthalate (PET) and polyethylene naphthalate (PEN). In the case of PI, no significant loss of H, C, N and O was observed during proton irradiation. In the case of PET and PEN, on the other hand, all the light elements gradually decreased as irradiation fluence increased and the contents of 15%-H, 14%-C, 47%-O in PET and 7%-H, 5%-C 31%-O in PEN were eventually released up to a fluence of 2.1 × 10¹⁶ protons/cm². An aluminum thin film (thickness ∼0.1 μm) was sputter-deposited on the upper surface of 4 μm thick PET and PEN foils to prevent the release of light elements. In Al coated PEN foil, for example, the losses of H, C and O were 2%, 0.5% and 22% of the starting contents, respectively, considerably smaller than those found for uncoated PEN. Thus the Al coating was found to be an effective method to suppress the loss of constituent elements.     

Irradiation induced growth of CoSi2 precipitates in Si at 650°C: An in situ study

Crystalline Si samples were implanted at 350°C with 50 keV Co⁺ ions to a fluence of 10¹⁵ Co cm⁻². Small CoSi₂ precipitates were formed. We studied the precipitate growth, via in situ transmission electron microscopy, under irradiation with 100 keV Si ions at 650°C. We deduce the precipitate growth processes involved. Irradiation-induced (or enhanced) Ostwald ripening is the main growth mechanism. We also find an instability of the B-type precipitates, which leads to their transformation into A-type precipitates above a critical size. These preliminary results show that direct comparisons with kinetic Monte Carlo modelling of the precipitate growth is at hand.     

Eurofer corrosion by the flow of the eutectic alloy Pb-Li in the presence of a strong magnetic field

A new investigation of the Eurofer 97 corrosion by the MHD flow of the liquid eutectic alloy Pb-17Li is presented. The experimental data previously obtained in Riga are confirmed and an attempt to model this phenomenon is presented. The model is based on a thermodynamic analysis of the dissolution and electro-dissolution mechanisms, leading to a relevant boundary condition at the liquid-solid interface. Then, analyzing the MHD flow, guiding ideas and scaling laws are derived for the dissolution rate of the Hartmann wall. The results obtained in the regime, where the solid wall is assumed to remain planar, allow determining a plausible value for an important non-dimensional number, the dissolution number Di. A linear analysis leads to predictions on the mechanism responsible for the formation of streaks imbedded within the Hartmann layer and associated with the wall shape disturbance, as well as for the selection of the unstable mode. It is found that this mechanism is related to an additional contribution due to the electric current, based on an electro-dissolution number Ed.     

Liquid metal corrosion/erosion investigations of structure materials in lead cooled systems: Part 1

In future lead cooled nuclear power systems the heavy liquid-metal pump will be placed in the hot temperature region of the reactor. This combines corrosion problematic at elevated temperatures with erosion at the impeller of the pump. Several steels designed for conventional mechanical high loaded pumps and the SiSiC have been tested in oxygen containing stagnant lead (10⁻⁶ and 10⁻⁸ wt%) at 550 and 600 °C for 2000 and 4000 h in the COSTA-facilities. Only SiSiC shows no influence by the liquid metal. No dissolution attack occurs at cast iron steels but inner oxidation takes place. NORILOY shows no dissolution attack. All other steels are attacked by liquid lead at one of the conditions. To evaluate the erosion-corrosion attack a new test facility allowing velocities of the lead of up to 20 m/s was designed and constructed. With a CFD-code the behaviour and flow velocity of the lead are simulated.     

The effect of Nb additive on Te-induced stress corrosion cracking in Ni alloy: a first-principles calculation

Nb can improve the resistance of Ni-based Hastelloy N alloy to Te-induced intergranular embrittlement. First-principles calculations are performed to research this mechanism by simulating the Ni（111） surface and the ∑ 5（012） grain boundary. The calculated adsorption energy suggests that Te atoms prefer diffusing along the grain boundary to forming the surface-reaction layer with Nb on surface of the Ni alloy. First-principles ten- sile tests show that the Nb segregation can enhance the cohesion of grain boundary. The strong Nb-Ni bonding can prevent the Te migration into the inside of the alloy. According to the Rice-Wang model, the strengthen- ing/embrittling energies of Nb and Te are calculated, along with their mechanical and chemical components. The chemical bonds and electronic structures are analyzed to uncover the physical origin of the different effects of Te and Nb. Our work sheds lights on the effect of Nb additive on the Te-induced intergranular embrittlement in Hastelloy N alloy on the atomic and electronic level.     

Mass spectrometric studies of alloys proposed for high temperature reactor systems: II. Inconel alloy 617 and nimonic alloy PE 13

The vaporization of the alloys inconel 617 and nimonic PE 13 was studied by high-temperature mass spcctromctry. This is of particular interest for the use of these alloys in advanced gas-cooled high temperature reactors and thermonuclear fusion devices. Therefore, the partial pressures of nickel, chromium (1355–1527 K) and cobalt (1214–1517 K) over inconel 617 as well as of nickel, chromium, iron (1349 to 1493 K) and cobalt (1279 to 1500 K) over nimonic PE 13 were determined in the given temperature ranges. Chemical activities, partial free energies of mixing and excess partial free energies of the alloy components were computed from the partial pressures. The thermodynamic functions obtained are discussed.     

A novel concept of QUADRISO particles. Part II: Utilization for excess reactivity control

In high temperature reactors, burnable absorbers are utilized to manage the excess reactivity at the early stage of the fuel cycle. In this paper QUADRISO particles are proposed to manage the initial excess reactivity of high temperature reactors. The QUADRISO concept synergistically couples the decrease of the burnable poison with the decrease of the fissile materials at the fuel particle level. This mechanism is set up by introducing a burnable poison layer around the fuel kernel in ordinary TRISO particles or by mixing the burnable poison with any of the TRISO coated layers. At the beginning of life, the initial excess reactivity is small because some neutrons are absorbed in the burnable poison and they are prevented from entering the fuel kernel. At the end of life, when the absorber is almost depleted, more neutrons stream into the fuel kernel of QUADRISO particles causing fission reactions. The mechanism has been applied to a prismatic high temperature reactor with europium or erbium burnable absorbers, showing a significant reduction in the initial excess reactivity of the core.     

Mechanical behavior of δ-phase Pu-Ga alloys. Part II: Model verification and application

We validated the mechanical threshold strength (MTS) model, developed in Part I, with approximately 50 different experimental results from the literature for both yield strength and ultimate tensile strength on Pu-Ga alloys. One standard deviation of the differences between the model’s yield-strength predictions and the experiments was 7.5% of the measured yield strength. The model also worked well predicting the ultimate tensile strength (UTS) of the alloys with gallium concentrations of 1 wt% or greater, although the accuracy of the UTS predictions was not as good as for yield strength. After validating the model, we studied the effects of gallium concentration, grain size, iron and nickel content, and carbon concentration on the yield strength of Pu-Ga alloys. The gallium concentration affected the yield strength more than any other microstructural variable. The yield strength increased 50% between 1 at.% Ga and 5.4 at.% Ga alloying addition. The grain size also produced a measurable strengthening effect, typical of other face-centered cubic metals. The yield strength increased 15% with a reduction in grain size from 50 μm to 10 μm. Finally, we found that there were no observable yield-strength effects resulting from different amounts of iron, nickel, or carbon impurities.     

Vibrations of probe used for the defect detection of helical heating tubes in a fast breeder reactor: Part 1. Experimental results by using mock-up

This paper deals with the vibration and the sensor signal noise of the eddy current testing (ECT) probe used for a defect detection of helical heating tubes in the fast breeder reactor “Monju”, developed in Japan. ECT probes are used for the detection of defects in a heating tube. The heating tube is composed of a helical tube and a straight tube because of their advantages of thermal efficiency and saving space. No vibrations of the ECT probe have been generated in usual straight heating tubes. However, vibrations of the ECT probe in the helical tube cause some noise and decrease the sensitivity of the ECT probe. The experiment was performed using a mock-up, and the noise characteristics of an ECT sensor mounted in an ECT probe were examined. The experimental results showed that the sensor signal noise during the insertion process of the ECT probe was higher than that of the return process, and vibrations of the insertion process had a certain emerging frequency. Attaching the long and flexible guide probe to the top of the ECT probe was an effective countermeasure against sensor signal noise.