Search

Solid mixture of PbS quantum dot and a directly attached emitter penetrating the ligand layer enables photon upconversion from near infrared.

To enhance resilience of next-generation nuclear structures, it is necessary to develop design methodology that mitigates impacts of failure caused by extremely high temperature conditions which might lead to a severe accident. The purpose of this study is to understand its deformation behavior under extremely high temperature conditions and to identify the areas that should be focused on to mitigate impacts of failure. For this purpose, this study has conducted a detailed structural analysis of a reactor vessel (RV) in a loop-type sodium-cooled fast reactor using a general-purpose finite element analysis code, FINAS/STAR. The RV was heated from the normal operation condition to the sodium boiling temperature in the upper sodium plenum for 20 hours, assuming depressurization. The analysis has revealed less significant stress and strain which were sufficiently lower than failure criteria. The upper body of the RV was identified as the important area in terms of mitigation of structural failure. The RV was eventually deformed downward about 16 cm, but it resulted in no failure. This effect contributes to maintaining the RV sodium level in a long term, thereby enhancing the RV resilience.

Two significant improvements were achieved in 2019 and 2021 Editions of ASME Boiler and Pressure Vessel Code, Section III, Division 5. One is an update of allowable stress values in Gr.91 steel as 9Cr-1Mo-V steel. The time for which the values of Sr, expected minimum stress-to-rupture, is defined were extended from 300,000 to 500,000 hours and the values in relatively high temperature and long-term region were reduced compared with those in the region less than 300,000 hours. The other is that the equations for monotonic stress-strain curves and creep strain curves were provided. These improvements affect the creep damage calculation in the evaluation of creep-fatigue damage. The reduction of Sr values increases creep damage and providing the equations allows calculating the creep damage more precisely. In this study, the impact of these improvements on the creep damage calculation is assessed by some sample problem calculations. The stress dividing coefficient of K′ for Gr.91 was improved from 0.9 in 2017 Edition to 1.0 in 2019 Edition. The effect of the improvement on creep damage was also assessed. The total creep damage almost tripled by using the updated Sr table, although and decreased by about 20% by using the provided equations rather than graphic calculation in a sample problem case. The change of the value of K′ halved the creep damage in the sample problem case. The creep damage calculations during the stress relaxation were based on the Division 5 procedures of HBB T-1433(a) and (b), and these results were compared to a calculated result using creep damage calculation procedure using the elastic follow-up concept adopted in the Japanese elevated temperate design code. Material test results of notched bar specimens are also used for comparison. The calculated result indicated that the procedure using the elastic follow-up concept was comparable to those by HBB T-1433(a) and (b), while calculation using the elastic follow-up concept is easier than that of HBB T-1433(a) and (b).

The current buckling design code of Class 1 vessels for fast reactors (FRs) power plant in Japan, “Design and Construction for Nuclear Power Plants, Division 2 Fast Reactors” by the Japan Society of Mechanical Engineers, focuses primarily on plastic buckling of austenitic steel vessel. For next-generation FRs, the higher-yield material, especially ASME Grade 91 steel, plans to be applied to the vessels such as steam generators in addition to austenitic steel. Seismic isolation system is also being devised in the next plant to meet the design seismic load in Japan. To accommodate these conditions, the standard buckling strength equations were proposed in the previous study, which were modified by considering elasto-plastic buckling of vessel. The modified equations consisted of elasto-plastic axial compression, bending, shear buckling, and their interactions, as well as ASME/BPVC CASE N-284, considering the reduction of buckling strength by cyclic larger vertical load with long-period lower horizontal load under the horizontal seismic isolation plant design. The applicability of the modified buckling equations to high-yield material was confirmed by a series of buckling tests to vessels of Grade 91 steel under cyclic loading considering horizontal seismic isolation, or with the circumferential wrinkle shape corresponding to elephant’s foot buckling (EFB) mode in the previous study. In this study, the applicability of the proposed modified buckling equations has been confirmed through the test of austenitic steel, which has lower yield stress than Grade 91 steel, with imperfections under the load condition corresponding to seismic isolation design. The experimental result has confirmed the conservativeness of the modified equations under the dominant axial compressive load accompanied with horizontal load, and the austenitic steel vessel which has the circumferential wrinkle shape corresponding to the EFB mode as a significant initial imperfection. The test has also been simulated by elasto-plastic buckling analyses considering stress-strain relationship and imperfections in the test vessels. The result of the test and its analysis have showed the applicability of the modified equations. Moreover, a series of verification analyses conducted for the modified equations with 3D buckling analysis models under the conditions in FRs power plant. These verification analysis results confirmed the contribution of the factors to the buckling strength such as initial imperfection and material, and showed that the modified equations are applicable to the vessels in FRs power plant.

The ASME Boiler and Pressure Vessel Code (ASME BPVC) Section III, Division 5, Subsection HB, Subpart B provided only one design fatigue curve for Grade 91 steel (Gr.91) at 540 °C (or 1000 °F) in 2019 and earlier versions. To overcome this disadvantage, The ASME Section III Working Group on Creep-Fatigue and Negligible Creep (WG-CFNC) had taken an action to incorporate the temperature-dependent design fatigue curves for Gr. 91 developed by Japan Society of Mechanical Engineers (JSME) into ASME BPVC Section III Division 5. As a result, the temperature dependent design fatigue curves are provided in the 2021 edition of the ASME BPVC. To clear the features of the best-fit fatigue curve equation developed by the JSME, 305 data stored in the database were analyzed. Details of the database and relationship between the best-fit fatigue curve equation and the data including the statistic values and the values of 95% and 99% lower confidence bound calculated by failure probability assessment were clarified through analysis. In addition to the best-fit fatigue curve equation, an equation for dynamic stress-strain response showing the behavior of Gr.91 steel under cyclic loading of is also provided based on the same database. Moreover, some additional available data of fatigue and creep-fatigue tests obtained in Japan are also provided for considering the creep-fatigue damage evaluation under elevated temperature condition.

The current buckling design standard of Class 1 vessels for fast reactors (FRs) power plant in Japan, “Design and Construction for Nuclear Power Plants, Division 2 Fast Reactors” by the Japan Society of Mechanical Engineers, focuses primarily on plastic buckling of austenitic stainless steel vessel. For next-generation FRs, the higher-yield material, especially ASME Grade 91 steel, plans to be applied to the vessels such as steam generators in addition to austenitic stainless steel. Seismic isolation system is also being devised in the next plant to meet the design seismic load in Japan. To accommodate these conditions, the standard buckling strength equations in Japan were proposed in previous study, which were modified by considering elasto–plastic buckling of vessel. The modified equations consisted of elasto–plastic axial compression, bending, shear buckling, and their interactions, as well as ASME/BPVC CASE N-284, considering the reduction of buckling strength by cyclic larger vertical load with long–period lower horizontal load under the horizontal seismic isolation plant design. The applicability of the modified buckling equations to high-yield material was confirmed by a series of buckling tests under the monotonic load to Grade 91 steel vessels with an initial imperfection mode in previous study. In this study, the applicability of the proposed modified buckling equations was confirmed through a series of buckling tests under cyclic loading considering horizontal seismic isolation, or with the circumferential wrinkle shape corresponding to elephant’s foot buckling (EFB) mode as the conservative initial imperfection shape. These tests were simulated by elasto–plastic buckling analyses considering stress–strain relationship and imperfections in the test vessels with high accuracy, and these test and analysis results showed the applicability of the modified equations. The effect of initial imperfection shape of large vessels manufactured by multiple plates welding on the buckling load was evaluated via a series of analyses. In these analyses, the superimposition of global imperfection shape due to accumulation of misalignment of plates in the buckling mode imperfection, and the local imperfection and residual stress by welding had minimal effect on the buckling load. These buckling test and analysis results confirmed the contribution of the factors to the buckling strength such as initial imperfection and loading, and showed that the modified equations are applicable to the vessels in FRs power plant.

In the design of components for service at elevated temperatures, fatigue and creep-fatigue due to cyclic loading are some of the most important failure modes, and the assessment of failure life at structural discontinuities is a key issue within the evaluation of the integrity of the components. Since several fatigue and creep-fatigue life evaluation methods have been proposed, this study compares and assesses these different methods by performing fatigue and creep-fatigue tests of perforated plate made of Mod.9Cr-1Mo steel. Multiperforated plate was subjected to mechanical cyclic loading at 550 °C, and crack initiation and propagation at the surfaces of the holes were observed. The stress distribution was varied by changing the hole arrangement and loading level. A series of finite element analyses (FEA) were carried out to predict the number of cycles to failure by the several failure life evaluation methods, and these predictions were then compared with the test results. Several types of evaluation methods that use the elastic FEA were applied, namely, the stress redistribution locus (SRL) method, simple elastic follow-up method, and the methods described in the design and construction code for fast reactors (FRs) published by the Japan Society of Mechanical Engineers (JSME FRs code). In addition to these, evaluation was also carried out using the results of inelastic FEA to compare these elastic FEA-based estimation methods. The comparisons indicate that, for all conditions tested, the SRL method provided a rational prediction of the fatigue and creep-fatigue life when κ = 1.6 was applied, where κ = 1.6 is the recommended reduction factor for this method in general use. A comparison of the SRL method and the results of the inelastic FEA indicated that the applicability of the value of factor κ in the SRL method depends on the elastic region remaining in the cross section including the evaluated point and the spread in the plastically deformed region in the specimen.

We define $r$-inferior regular partition which is a restriction of partition. Its generating function equals to that of the number of operations in the Glaisher correspondence. Using this result, we prove Mizukawa-Yamada's identity separately. Moreover we extend this identity to $m$-tuple version.

Larger-diameter cylindrical vessels for commercial fast breeder reactors (FBRs) are planned to increase the electric generation capacity with thinner vessels compared to the existing ones. The modified 9Cr-1Mo steel (ASME Grade 91 steel) has high yield stress and low tangent modulus after yielding, and plans to be applied as well as austenitic stainless steel for vessels in existing FBR power plants. Although elasto-plastic axial compression, bending and shear buckling are expected to occur in vessels, the current buckling strength evaluation from the Japan Society of Mechanical Engineers (JSME) standard “Design and Construction for Nuclear Power Plants, Division 2 Fast Reactors” mainly focuses on plastic buckling of thick cylindrical vessels. Seismic base isolation is being devised for next-generation FBR power plants by the increasing seismic design load in Japan. When a horizontal seismic base isolation design is adopted, cylindrical vessels are subject to cyclic vertical seismic load with long-period horizontal seismic wave. The deformation by cyclic vertical load reduces the buckling strength. In this paper, we modified the existing buckling strength equations focusing on elasto-plastic axial compression, bending and shear buckling under cyclic axial load (hereinafter called “modified equations”), and confirmed their applicability through a series of elasto-plastic buckling analyses. We also conducted a series of buckling tests on Grade 91 steel vessels in the load regions where axial compression, bending and shear buckling interact, and where axial compression and bending buckling are dominant due to large vertical load. The buckling behavior and the buckling load estimated by the elasto-plastic buckling analysis considering the actual material stress–strain relationship and imperfections in the test vessel suitably agreed with corresponding test results in the load regions.

We report photoluminescence-based ozone sensing using composite films composed of gold or platinum and red-emitting CdSe/ZnS core-shell quantum dots. The sensing efficiency of quantum dots is enhanced by the addition of noble metals. The composite films undergo reversible changes in photoluminescence intensity (measured at excitation/emission wavelengths of 365/652 - 659 nm) in the presence of ppm levels of ozone in air at 25°C and at atmospheric pressure. The sensitivity of the composite films does not saturate with ozone in the 0.5 - 200 ppm concentration range. When compared with a quantum dot-only film, the composite films show higher sensitivities to 0.5 ppm ozone of 27% (gold) and 43% (platinum). When compared with a quantum dot-only film, the photoluminescence of the gold- or platinum-palladium alloy-based film recovers faster after the removal of ozone in the surrounding atmosphere. Thus, platinum- or gold-conjugated quantum-dot films form sensor modules for the reversible and highly sensitive detection of ozone under the tested ambient conditions.

Ozone (O3) gas is widely used as a strong oxidizing agent for many purposes, such as the decomposition/removal of organic contaminants and photoresist, and the deodorization/disinfection of air and water. However, ozone is highly toxic to the human body when the air concentration exceeds about 1 ppm. Therefore, there is increasing demand for simple, sensitive, reliable, and cost-effective techniques for sensing ozone gas. This article describes the features, advantages, and disadvantages of the available, practical techniques for sensing ozone gas in ambient air. The advantages of optical gas sensors as next-generation sensors is specifically introduced. The features of photoluminescent, semiconductor nanoparticles (quantum dots, QDs) as bright phosphors with the potential for various applications is further explored. Lastly, recent research results demonstrating the ozone sensitivity of photoluminescent CdSe-based core-shell quantum dots are presented. These results strongly suggest that optical ozone sensing using photoluminescent quantum dots is a promising technique.

A case of testicular metastasis of colon cancer, which clinically mimicked a hydrocele of the testis, is presented. Imaging study suggested a scrotal hydrocele, but slow yet gradual enlargement of the hydrocele and the past history of colon cancer prompted an orchiectomy for the pathologic diagnosis and treatment. The pathologic diagnosis was testicular metastasis of colon cancer. Testicular metastasis presenting as a hydrocele is unusual, and imaging and macroscopic findings useful for the differential diagnoses are discussed. A brief review of pertinent literature is also included.

In the present study, a method for creep–fatigue life evaluation of Mod.9Cr–1Mo steel weld joint was proposed based on finite element analysis (FEA). Since the point of the creep–fatigue life evaluation in the weld joint is a consideration of the metallurgical discontinuities, FEA was performed using a model with three material properties, a base metal (BM), weld metal (WM) and a heat-affected zone (HAZ) formed in the base metal due to the welding heat input, to consider the mutual relationships among them. The material properties of these three materials were collected and utilized in FEA for considering such metallurgical discontinuities. The creep–fatigue life estimated using the proposed evaluation method based on the FEA results were compared with available creep–fatigue test data, and the proposed method was found to predict the number of cycles to failure within a factor of 3. Moreover, the elastic follow-up factors due to metallurgical discontinuities were calculated using the FEA results for a uniaxial creep–fatigue test. The values of the elastic follow-up factors for both plastic deformation and creep relaxation were less than those defined in the Japanese elevated temperature design code. These considerations will contribute to the codification of evaluation rules for creep–fatigue damage in Mod.9Cr–1Mo steel weld joints.

We report here a novel, sensitive detection method for gaseous amines (primary, secondary and tertiary) using thin films of CdSe-based core-shell type quantum dots (CdSe/ZnS and CdSeTe/ZnS) deposited on a glass substrate. The photoluminescence intensity of the quantum dot thin films rapidly decreased on exposure to amine gas in air, and it reversibly recovered after the atmosphere was changed back to air without amine gas. On the other hand, oxygen, nitrogen, argon, carbon dioxide, or hydrogen, all components of natural air, did not affect the photoluminescence intensity of the quantum dot thin films. Interestingly, the photoluminescence of quantum dot films showed higher sensitivity to n -alkylamines, such as hexylamine, when compared with bulky or branched molecules, such as diethylamine and triethylamine. Furthermore, thin films of green-emitting quantum dots showed higher sensitivity to amines when compared with red-emitting ones, which was attributed to the large surface-to-volume ratios of smaller quantum dots. The reversible, reproducible, and selective responses of CdSe-based core-shell type quantum dots to gaseous amines in air suggested that quantum dot thin films could be promising photoluminescence-based optical amine gas sensors.

For the required thickness estimation against buckling in the elevated temperature design, the external pressure chart for two kinds of ferritic steel, 2 1/4Cr-1Mo and Mod.9Cr-1Mo steel, was developed. On the basis of the guideline described in the ASME BPVC Section II, Part D, Mandatory Appendix 3 with mechanical and physical properties provided in the JSME fast reactor code, the external pressure charts for each material were constructed. The minimum stress-strain curve for evaluating the external pressure chart was applied the stress-strain equation with design yield strength, Sy, provided by the JSME fast reactor code. As a result, three external pressure charts with digital values were proposed for elevated temperature design. Moreover, the rationalization effect from the current alternative was evaluated by the sample problem. This proposal resolves two issues. One is alternative use of chart for lower strength material over the 150 °C. The other is the external pressure chart above 480°C for which ferritic steels are not available.

In the present study, to develop an evaluation procedure and design rules for Mod.9Cr-1Mo steel weld joints, a method for evaluating the creep-fatigue life of Mod.9Cr-1Mo steel weld joints was proposed based on finite element analysis (FEA) and a series of cyclic plate bending tests of longitudinal and horizontal seamed plates. The strain concentration and redistribution behaviors were evaluated and the failure cycles were estimated using FEA by considering the test conditions and metallurgical discontinuities in the weld joints. Inelastic FEA models consisting of the base metal, heat-affected zone and weld metal were employed to estimate the elastic follow-up behavior caused by the metallurgical discontinuities. The elastic follow-up factors determined by comparing the elastic and inelastic FEA results were determined to be less than 1.5. Based on the estimated elastic follow-up factors obtained via inelastic FEA, a simplified technique using elastic FEA was proposed for evaluating the creep-fatigue life in Mod.9Cr-1Mo steel weld joints. The creep-fatigue life obtained using the plate bending test was compared to those estimated from the results of inelastic FEA and by a simplified evaluation method.

Thin films of CdSe-based core-shell type quantum dots (CdSe/CdZnS, CdSe/ZnS and CdSeTe/ZnS) deposited on glass substrate were found to undergo a reversible change in photoluminescence (PL) on exposure to ozone in concentrations as low as 0.1 ppm in air. PL decreased rapidly on adding ozone and fully recovered after changing back to pure air. The PL of the CdSe/ZnS quantum dots (QDs) was not quenched by pure oxygen, nitrogen, argon, carbon dioxide, and air containing hydrogen. A comparison of various CdSe-based core-shell type QDs with different emission colors showed that green-emitting QDs with smaller size were more sensitive to ozone, while red-emitting QDs (of larger size) were more resistant to high concentrations of ozone. The response time of the sensor (for a 90 % signal change) was in the order of 10–20 min. The reversible, reproducible and selective response to ozone at room temperature under atmospheric pressure suggested that these QDs have a great potential in terms of fluorescent sensing of ozone.

The sensitivity, range of applications, and reaction mechanism of 2-hydrazinoquinoline as a reactive matrix for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) were examined. Using a reaction chamber (125 L) equipped with a stirring fan and a window for moving the MALDI-MS plate and volatile samples in and out, the sensitivities of 2-hydrazinoquinoline to gaseous aldehydes (formaldehyde, acetaldehyde, propionaldehyde, and n-butyraldehyde) and ketones (acetone, methyl ethyl ketone, and methyl isobutyl ketone) were determined to be at least parts per million (ppm) levels. On the other hand, carboxylic acids (formic acid, acetic acid, propionic acid, and butyric acid) and esters (ethyl acetate, pentyl acetate, isoamyl acetate, and methyl salicylate) could not be detected by 2-hydrazinoquinoline in MALDI-MS. In addition to 2,4-dinitrophenylhydrazine, a common derivatization reagent for analyzing carbonyl compounds quantitatively in gas chromatography and liquid chromatography, the dissolution of 2-hydrazinoquinoline in an acidic solution, such as trifluoroacetic acid, was essential for its function as a reactive matrix for MALDI-MS.

A Code Case in the framework of JSME Nuclear Codes and Standards is being developed to incorporate a seismic design evaluation methodology for piping by means of advanced elastic-plastic response analysis methods and strain-based fatigue criteria. The Code Case as an alternative seismic design rule over the current rule will provide a more rational seismic design evaluation than the current criteria. This paper demonstrates an application result of the JSME Seismic Code Case to an actual complex piping system. The secondary coolant piping system of Japanese Fast Breeder Reactor, Monju, was selected as a representative of the complex piping systems. The elastic-plastic time history analysis for the piping system was performed and the piping system has been evaluated according to the JSME Seismic Code Case. The evaluation by the Code Case provides a reasonable result in terms of the piping fatigue evaluation that governs seismic integrity of piping systems. Moreover, it is found that the supporting forces and the response accelerations of the piping system obtained by the elastic-plastic response analysis also become more rational results than those with the current elastic response analysis. The contradiction of two requirements in piping design, flexibility for thermal expansion and rigidity for seismic response, can be effectively relaxed by use of the Code Case being developed.

Containment vessel (CV) of nuclear power plants is an important structure to prevent a significant and sudden radioactive release, however, the safety margin of the containment vessel against the internal or external pressure are not numerically clarified. The head plate is one of the components which constitute the CV boundary. In order to develop the evaluation method of the pressure toughness of the head plate at beyond design basis events, the pressure failure tests and finite element analysis of the head plates subjected to convex side pressure were performed. In the tests, non-axisymmetric deformations with local deformation concentration were observed in post buckling behavior in the case of the thin thickness head plate. In this study, to evaluate these non-axisymmetric deformations in the test, finite element analyses using detailed 3-D solid model constructed by precise dimensions of the head plates measured by 3-D scanner were performed. Moreover, FEA using simplified model with uniform or non-uniform thickness model were performed. Through a series of FEA, it was clarified the effect of each thickness pattern on post buckling non-axisymmetric deformation.

In Japan, the basic designing works for a demonstration plant of Japan Sodium cooled Fast Reactor (JSFR) are now conducted. JSFR is an advanced loop type reactor concept. To enhance the safety and the economic competitiveness, JSFR employs modified 9% chromium–1% molybdenum (Mod.9Cr–1Mo) steel as a material for coolant pipes and components, because the steel has both excellent high temperature strength and thermal properties. The steel has been standardized as a nuclear material in Japan Society of Mechanical Engineers (JSME) code in 2012. In JSFR pipes, demonstration of Leak Before Break (LBB) aspect is strongly expected because the safety assessment may be performed on the premise of leak rate where the LBB aspect is assured. Although the authors have already performed a series of thermal fatigue crack growth tests of austenitic stainless steel cylinders ( Wakai et al., 2005 ), crack growth behavior in the structures made of Mod.9Cr–1Mo steel has not been investigated yet. Especially for the welded joints of Mod.9Cr–1Mo steel, “Type-IV” cracking may occur at heat affected zone (HAZ). Therefore, this study performed a series of thermal fatigue crack growth tests of thick wall cylinders made of Mod.9Cr–1Mo steel including welds, to obtain the crack growth data under cyclic thermal transients. The test results were compared to the analytical results obtained from JAEA's simplified methods ( Wakai et al., 2005 ).

Bellows structure is used to absorb the thermal expansion maintaining the boundary of the inside to outside, and it is applied to constitute the containment vessel (CV) boundary of the nuclear power plant. In this study, in order to develop the evaluation method of the ultimate strength of the bellows structure subject to internal pressure beyond the specified limit, the failure test and finite element analysis (FEA) of the bellows structure were performed. Several types of the bellows structure made of SUS304 were tested using pressurized water. The failure modes were demonstrated through the test of five and six specimens with six and five convolutions, respectively. Water leakage was caused by contact of the expanded convolution and the neighbor structure in the specimens with the shipping rod mounts. On the other hand, local failure as leakage in the deformation concentrated location and ductile failure as burst in the expanded convolution were observed in the specimen without shipping rod mounts. The maximum pressures in the test observed local and ductile failure were over ten times larger than the estimated values of the limited design pressure for in-plane instability by the EJMA standard. To simulate the buckling and deformation behavior during the test, the implicit and explicit FEA were performed. Because the inversion of the convolution accompanied by convolution contact observed in the test was too difficult a problem for implicit analysis, the maximum pressures in the step of solution converged were compared to the maximum pressures in the tests. On the other hand, explicit analysis enabled to simulate the complex deformation during the test, and the results were evaluated considering ductile failure to compare the test results.

In this study, in order to develop the evaluation method of the pressure toughness of bellows structures under the beyond design base event, the pressure failure tests and finite element analysis (FEA) of the bellows structures subjected to internal pressure were performed. Since the several tests and FEA results were reported previously by current authors, the additional tests were performed by the specimen simulating the real setting situation in the actual plant and for demonstrating the plain failure modes. Test specimens consist of the single and double ply bellows made of SUS304 were used. Total five specimens were tested, and one specimen was attached the guard pipe around the bellows to simulate the actual situation in the plant to confirm the effect of the neighbor structures to the ultimate toughness. The maximum pressure obtained in all tests were over 10 times larger than the estimated results of limiting design pressure based on in-plain instability by the EJMA standards; although the test specimens were pressurized exceed the pressure of buckling deformation. Because it is very difficult problem to simulate the inversion of the convolution accompanied convolutions contact for FEA with implicit method, FEA with simplified technique and explicit analysis were performed to simulating the complex deformation of the test specimen, and then these results were estimated in some procedures to compare with the test results. Three failure modes identified in the tests, however, the complex deformation behavior make it difficult to simulate by ordinary FEA procedure and to estimate the ultimate toughness of the bellows structures under the internal pressure. Therefore several kinds of idea for evaluating the ultimate toughness of the bellows structures were execute and suggested.

This paper describes the formulation of material characteristics of austenitic stainless steels at extremely high temperature which meets in some kinds of severe accidents of nuclear power plants. After the severe accident in Fukushima dai-ichi nuclear power plants, it has been supposed to be very important not only to prevent the occurrence of abnormal conditions, i.e. from the first to the third layer safety, but also to prevent the expansion of the accident conditions, i.e. the fourth layer safety[1] [2]. In order to evaluate the structural integrity under the severe accident condition, material characteristics which can be used in the numerical analyses, such as finite element analysis, were required [3] [4]. However, there were no material characteristics applicable to the structural integrity assessment at extremely high temperature. Therefore, a series of tensile and creep tests was performed for austenitic stainless at extremely high temperature which meets in some kinds of severe accidents of nuclear power plants, namely up to 1000 °C. Based on the acquired data from the tests, monotonic stress-strain equation and creep rupture equation applicable to the structural analysis at extremely high temperature, up to 1000 °C were formulated. As a result, these formulae make it possible to conduct the structural integrity assessment using numerical analysis techniques, such as finite element method.

Containment vessel is an important structure to prevent a significant and sudden radioactive release, however, the safety margin of the containment vessel against the internal or external pressure are not numerically clarified. Namely, the safety margins due to the relationship of the ultimate toughness of containment vessel structures and maximum design pressure is not clear. Indeed, to clarify the progress of events under the beyond design basis events (BDBE) and to design the BDBE countermeasure equipment, it is necessary to evaluate the pressure toughness of containment vessel adequately. The containment vessel of fast reactor is composed of the various structures. The head plate that composes the boundary between primary and secondary coolant in intermediate heat exchanger has an important role when the progress of the BDBE is considered. Therefore, in order to develop the evaluation method of the pressure toughness of the head plate under the BDBE, the pressure failure tests and finite element analysis of head plate structure subjected to convex side pressure was performed in this study. Two types of head plates were applied for pressure failure tests. ED type and AD type head plates were chosen as a representative to clarify the effect of shape. These head plates have 250mm diameter and 3mm thickness. The head plates were subjected to pressure on convex side by water in the pressure failure tests. In tests, almost completely inside-out of each head plate was caused after buckling. Then after that, leakage was observed near the rim. Two types of head plates had similar failure mode in spite of difference original shapes. The circumferential through-wall crack was observed near the rim of each head plates. According to the results of pressure failure tests, it is seemed that the circumferential crack was caused by straightening following bending associated with large deformation as inside-out. To clarify the relationship between bending radius and crack initiation, straightening following the bending deformation (bending-straightening) tests were performed. As a result, the crack was initiated in the test case of the bending radius smaller than 3 mm. 3 mm of bending radius generate 33 % strain. The bending radius at the time of leakage observed of head plates was estimated almost similar value at which crack initiated. Therefore, it can be concluded that a failure mode of a head plate subjected convex side pressure is circumferential through-wall crack caused by straightening following bending deformation near the rim.

This paper describes a thermal fatigue test on a structural model with a dissimilar welded joint. In the present design of Japan sodium cooled fast reactor (JSFR), there may be dissimilar welded joints between ferritic and austenitic steels especially in intermediate heat exchangers (IHX) and steam generators (SG). Creep-fatigue is one of the most important failure modes in JSFR components. However, the creep-fatigue damage evaluation method has not been established for dissimilar welded joint. To investigate the evaluation method, structural test will be needed for verification. Therefore, a thermal fatigue test on a thick-wall cylinder with a circumferential dissimilar welded joint between Mod.9Cr-1Mo steel and type 304 austenitic stainless steel (304SS) was performed. Since the coefficients of thermal expansion of these steels were significantly different, buttering layer of Ni base alloy was installed between them. After the completion of the test, deep cracks were observed at the heat affected zone (HAZ) in 304SS, as well as at HAZ in Mod.9Cr-1Mo steel. There were many tiny surface cracks in base metal (BM) of 304SS. According to the fatigue damage evaluation based on the finite element analysis results, the largest fatigue damage was calculated at HAZ in 304SS. Large fatigue damage was also estimated at BM of 304SS. Fatigue cracks were observed at HAZ and BM of 304SS in the test, so that analytical results are in a good agreement with the observations. However, though relatively small fatigue damage was estimated at HAZ in Mod.9Cr-1Mo steel, deep fatigue cracks were observed in the test. To identify the cause of such a discrepancy between the test and calculations, we performed a series of finite element analyses. Some metallurgical investigations were also performed.

A $q$-analogue of a partition identity is presented.

The tubesheet structure is one of the components that suffer the most severe loading in fast reactors, and it is one of the most difficult components to design because of such severe operation conditions and its complex three-dimensional structure with an arrangement of numerous penetration holes. In this study, to clarify the failure mode of a semispherical tubesheet structure originally designed for the steam generator in the Japan sodium-cooled fast reactor, a cyclic thermal loading test was performed using a tubesheet model test structure. The tubesheet model made of Mod.9Cr–1Mo steel was subjected to 1873 cycles of severe thermal transient loads using a large-scale sodium loop, in which sodium heated to 600 and 250 °C was flowed repeatedly with periods for each transient of 2 and 1 h, respectively. After the test, the test model was inspected by performing liquid penetrant testing. Then, observation using a scanning electron microscope and hardness testing were performed to characterize the failure mechanism in the structural model tested under the thermal transient loading with holds at elevated temperature. A thermal-hydraulic analysis was also performed to validate the measured temperature history during the thermal transient. Through these examinations and evaluation with thermal-hydraulic analysis, the manner of failure in the tubesheet under cyclic thermal loading is discussed.

The tubesheet structure is one of the components that suffer the most severe loading in fast reactors, and it is one of the most difficult components to design because of such severe operation conditions and its complex three-dimensional structure with an arrangement of numerous penetration holes. In this study, the strength of a tubesheet test model simulating a semispherical tubesheet structure subjected to cyclic thermal transients was evaluated using the finite element analysis (FEA). A test model made of Mod.9Cr–1Mo steel was subjected to 1873 cycles of severe thermal transient loading using a large-scale sodium loop, in which elevated-temperature sodium at 600 °C and 250 °C was flowed repeatedly and kept at the final temperature for 2 and 1 h, respectively. Heat transfer analysis and stress analysis were performed using the sodium temperature data measured during the test. The boundary conditions were adjusted to simulate the measured temperature distribution on the inner and outer surfaces of the test model in the heat transfer analysis, and the result was used for the stress analysis. Then, the elastic and inelastic stress analysis results were used to investigate the failure mechanism by creep-fatigue damage and evaluate the failure strength. The evaluation based on the results of inelastic analysis estimated the number of cycles to failure within a factor of 3 of the total number of thermal loading cycles 1873, which corresponds to the number of cycle at which the crack reached 2.59 mm.

The reagents 19 hydrazide and 14 hydrazine were examined to function as reactive matrices for matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to detect gaseous aldehydes. Among them, two hydrazide (2-hydroxybenzohydrazide and 3-hydroxy-2-naphthoic acid hydrazide) and two hydrazine reagents [2-hydrazinoquinoline and 2,4-dinitrophenylhydrazine (DNPH)] were found to react efficiently with carbonyl groups of gaseous aldehydes (formaldehyde, acetaldehyde and propionaldehyde); these are the main factors for sick building syndrome and operate as reactive matrices for MALDI-MS. Results from accurate mass measurements by JMS-S3000 Spiral-TOF suggested that protonated ion peaks corresponding to [M + H]+ from the resulting derivatives were observed in all cases with the gaseous aldehydes in an incubation, time-dependent manner. The two hydrazide and two hydrazine reagents all possessed absorbances at 337 nm (wavelength of MALDI nitrogen laser), with, significant electrical conductivity of the matrix crystal and functional groups, such as hydroxy group and amino group, being important for desorption/ionization efficiency in MALDI-MS. To our knowledge, this is the first report that gaseous molecules could be derivatized and detected directly in a single step by MALDI-MS using novel reactive matrices that were derivatizing agents with the ability to enhance desorption/ionization efficiency. Copyright © 2014 John Wiley & Sons, Ltd.

Mod.9Cr-1Mo steel is a candidate material for the primary and secondary heat transport system components of the Japan sodium-cooled fast reactor. However, there is little evidence to support the structural integrity of components made of Mod.9Cr-1Mo steel in a practical environment. To verify the failure mode and assess creep–fatigue damage, a thick cylinder test model made of Mod.9Cr-1Mo steel was subjected to 1873 cycles of accelerated thermal transient loading using a large-scale sodium loop through which liquid sodium at 600 °C and 250 °C flowed repeatedly, with the period of each transient being 2 h and 1 h, respectively. After completion of the test, the test model was inspected using liquid penetrant testing. Observations using a scanning electron microscope and hardness testing were then performed to characterize creep–fatigue damage in the structural model subjected to cyclic thermal transient loading in a sodium environment. Heat transfer analysis based on the measured temperature data and elastic and inelastic thermal stress analyses using finite element analysis were performed to evaluate the relationship between creep–fatigue damage and the observed crack conditions. Finally, the characteristics of creep–fatigue damage under cyclic thermal loading in a sodium environment and the evaluation methods were considered.

Containment vessel is an important structure to prevent a significant and sudden radioactive release, however, the safety margin of the containment vessel against the internal or external pressure are not numerically clarified. Namely, the safety margins due to the relationship of the ultimate toughness of containment vessel structures and maximum design pressure is not clear. Indeed, to clarify the progress of events under the beyond design basis events (BDBE) and to design the BDBE countermeasure equipment, it is necessary to evaluate the pressure toughness of containment vessel adequately. The containment vessel of fast reactor is composed of the various structures. The head plate that forms the boundary between primary and secondary coolant in intermediate heat exchanger has an important role when the progress of the BDBE is considered. In this study, in order to develop the evaluation method of the pressure toughness of the head plate under the BDBE, the ultimate pressure test of the head plate test specimen subjected to convex side pressure was performed, and also FEM analysis was performed for discussion.

We demonstrate an organic synthesis to fabricate hydrophobic core/shell CdSe/Cd1−x Zn x S quantum dots (QDs) with tunable photoluminescence (PL) between green and red at relatively low temperature using trioctylphosphine S reacted directly with cadmium and zinc acetate. A seeded growth strategy was used for preparing large CdSe cores. Large CdSe cores revealed a rod-like morphology while small one exhibited a spherical shape. Being coated with a Cd1−x Zn x S shell on spherical CdSe cores with an average size of 3.9 nm in diameter, core/shell QDs exhibited a cubic morphology (a length of 5 nm). In contrast, the core/shell QDs created using a small core (3.3 nm in diameter) show a spherical morphology. Namely, the anisotropic aggregation behavior of CdS monomers on CdSe cores occurs when the rod-like core is coated with a Cd1−x Zn x S shell. CdS interlayer plays an important role for such morphology evolution because all CdSe cores with a pure ZnS shell exhibited a spherical morphology. The PL properties of CdSe/Cd1−x Zn x S core/shell QDs depended strongly on the size and morphology of the cores. The QDs revealed a narrow and tunable PL spectrum. It is believed that this facile strategy can be extended to synthesize other core–shell QDs at low temperature.

The effect of ratcheting deformation on fatigue and creep–fatigue life in Mod.9Cr–1Mo steel was investigated. Uniaxial fatigue and creep–fatigue testing with superimposed strain were performed to evaluate the effect of ratcheting deformation on the failure cycle. In a series of tests, a specific amount of superimposed strain was accumulated in each cycle. The accumulated strain as ratcheting deformation, cycles to reach the accumulated strain, and test temperatures were varied in the tests. In the fatigue tests with superimposed strain at 550 °C, slight reductions of failure lives were observed. All of the numbers of cycles to failure in the fatigue tests with superimposed strain were within a factor of 1.5 of that of the fatigue test without superimposed strain at 550 °C. The apparent relationship between failure cycles and testing parameters was not observed. In fatigue tests with superimposed strain at 550 °C, maximum mean stress was insignificant and generated in early cycles because Mod.9Cr–1Mo steel exhibits cyclic softening characteristics. It was assumed that suppression of mean stress generation by cyclic softening reduces the effect of ratcheting strain. Conversely, failure lives were increased by accumulated strain in the test conducted at 450 °C because of stress–strain hysteresis loop shrinkage caused by cyclic softening induced by the accumulated strain. In the creep–fatigue tests with superimposed strain, test results indicated that the accumulated stain was negligible. It was concluded that the effect of ratcheting deformation on fatigue and creep–fatigue life is negligible as long the parameters are within strain limits of the design and construction code for fast reactors (inelastic strain at surface

Hydrophobic oleic acid-capped CdSe/Cd x Zn 1− x S core/shell quantum dots (QDs) with high photoluminescence (PL) efficiency of 62% and a PL peak wavelength of 602 nm were assembled in SiO 2 particles through a novel silanization technique. Ligand exchange (3-mercaptopropyltrimethoxysilane (MPS) instead of oleic acid) occurred via the connection of mercapto groups and QDs when MPS was added in the toluene solution of the QDs. After being silanized using MPS, partially hydrolyzed tetraethyl orthosilicate (TEOS) was attached to the surface of the silanized QDs. The hydrophobic CdSe/Cd x Zn 1− x S QDs were then transferred from toluene phase to water phase by the hydrolysis of TEOS through the addition of ethanol, ammonia, and water. Further hydrolysis and condensation of the TEOS and MPS causes them to form assemblies in the water phase. MPS is crucial for proper assembly of the QDs in SiO 2 particles and for controlling the size of resulting SiO 2 particles. The resulting SiO 2 particles exhibited tunable diameters from several tens to 100 nm. After being encapsulated in SiO 2 particles, the QDs revealed a PL efficiency of 25%. Because of the resulting SiO 2 particles encapsulating multiple hydrophobic CdSe/Cd x Zn 1− x S QDs and having a functional surface (mercapto group), they are applicable to bio-probes.

A method has been developed to incorporate multiple hydrophobic CdSe/CdxZn1−xS QDs into SiO2 beads by a two-step microemulsion process and retain the high photoluminescence (PL) efficiencies of the QDs. In step 1, the QDs were silanized by using partially hydrolyzed tetraethyl orthosilicate (TEOS) via replacing oleic acid (OA) on the surface of QDs. In step 2, these silanized QDs were transferred into aqueous phase in the reverse micelle solution by adding a small amount of water and stirring for a few hours. Then these silanized QDs assembled and subsequently encapsulated in a SiO2 shell by a reverse micelle synthesis. The initial silanization plays an important role for the QDs to be coated within a homogeneous SiO2 shell and retain a high PL efficiency in water. Single QDs were coated into silica beads by this two-step microemulsion process without water addition before ammonia and TEOS addition and pre-stirring for a certain time. The number of QDs incorporated into the silica beads can be controlled by adjusting the stirring time. More QDs can be incorporated into silica spheres by partially hydrolyzed 3-mercaptopropyl trimethoxysiliane (MPS) or 3-aminopropyltrimethoxysilane (APS) functionalization at step 1. An improvement in the PL efficiency (up to 35%) of silica spheres was obtained after APS functionalization of QDs. The silica coating shows a bit blueshift for the PL peak wavelength of the QDs. The full width at half maximum (FWHM) of PL spectra was decreased 4 nm after silica coating of the QDs.

The effect of ratcheting deformation and pre-strain on fatigue and creep-fatigue life in Mod.9Cr-1Mo steel was investigated. Uni-axial fatigue and creep-fatigue tests with pre-strain and progressive strain were performed to evaluate the effect of pre-strain and ratcheting strain on the failure cycle. In a series of tests, a specific amount of progressive strain was accumulated in each cycle. The accumulated strain as ratcheting deformation and cycles to reach the accumulated strain were varied in the tests. In the fatigue tests with pre-strain, failure lives were not declined. In the fatigue tests with progressive strain, slight reductions of failure lives were observed, however, they were within a factor of 1.5 of the failure life in normal fatigue test. The apparent relationship between failure cycles and testing parameters were not observed. Analyses of the test results indicated that the effect of ratcheting strain on the fatigue failure life is negligible as long as the parameters are within the strain limit of FR code (strains at surface less than 2%). In the creep-fatigue tests with progressive strain, the same conclusion of the fatigue tests was obtained. In both kinds of tests, maximum mean stresses during the tests were insignificant and/or generated in early cycle in the tests, and this character is considered as a reason of that the effect of ratcheting deformation on the fatigue and creep-fatigue lives are insignificant.

Highly luminescent CdSe/Cd x Zn 1 − x S core/shell quantum dots (QDs) have been fabricated by a facile environmentally friendly organic route. The spherical cores and core/shell QDs were created by using Cd(AC) 2 ·2H 2 O, Zn(AC) 2 , oleic acid, trioctylphosphine (TOP), Se, S, and trioctylamine. The preparative condition such as reaction time (2–6 min), temperature (from 290 to 310 °C), and feed rate of TOPSe (0.3–2 mL/min) creates various sizes of the cores with photoluminescence (PL) wavelengths between 570 and 618 nm. Spherical CdSe cores were coated with a Cd x Zn 1 − x S shell via a single coating step by using different growth kinetics of CdS and ZnS at 300 °C. The CdSe/Cd x Zn 1 − x S core/shell QDs exhibited a significant red shift of PL peaks (up to 646 nm) from the initial PL of CdSe cores with much improved PL efficiency above 40% when the shell growth. By changing the size of the core and the thickness of the shell, the emission colors of the obtained core/shell QDs can be tuned between green and red.