Plant Dynamics Evaluation of a MONJU Ex-vessel Fuel Storage System during a Station Blackout

The prototype fast breeder reactor ＂MONJU＂ has an EVSS （ex-vessel fuel storage system） which consists mainly of an EVST （ex-vessel fuel storage tank） and an EVST sodium cooling system. EVST sodium cooling system consists of three independent loops. During the normal operation, the primary sodium in the EVST is circulated by natural convection and the secondary circulation in the EVST sodium cooling system is powered by electromagnetic pumps. When an SBO （station blackout） occurs, all the pumps and blowers are tripped. Therefore, it was necessary to evaluate the cooling ability by the natural circulation of sodium in the EVST sodium cooling system and air through the air cooler during the SBO. In this study, an analysis and evaluation of the plant dynamics for the spent fuel and the EVSS structural integrity during an SBO were performed. When the number of cooling loops was not changed and natural circulation occurred in only two loops, the sodium temperature in the EVST increased to approximately 450 ~C. However, the structural integrity of the EVSS was maintained. The analytical results, therefore, help clarify the number of necessary cooling loops for efficient decay heat removal and sodium temperature behavior in an SBO.     

Influence of fetal calf serum on differentiation of mesenchymal stem cells to chondrocytes during expansion

Mesenchymal stem cells (MSCs) should be expanded in vitro while maintaining their multilineage potential before differentiation to one mesenchymal lineage for application to regeneration therapy. The effect of fetal calf serum (FCS) on undesirable differentiation during subcultivations for the expansion was investigated. The expression level of the aggrecan gene, which is a marker of chondrogenic differentiation, gradually and markedly increased during the subcultivations of MSCs with the addition of 10% FCS and without additional cytokines. The percentage of cells positive for CD90 and CD166, which are markers of MSCs, decreased, and the percentage of large polygonal cells and the average cell adhesion area increased during the expansion. There was a marked difference in the increase in the aggrecan expression level between the two expansion cultures employing different FCS lots, although their proliferation rates were almost the same. The decrease in FCS concentration resulted in a higher percentage of CD90(+)CD166(+) cells, a lower percentage of large polygonal cells, and a lower level of aggrecan expression. Consequently, FCS components could stimulate MSC differentiation to chondrocytes and a lower concentration could decrease this differentiation.     

Changes of infrared absorption by light soaking and thermal quenching in a-Si : H

The light- and thermal-induced changes of Si---H bonds in undoped a-Si : H have been studied on the infrared absorption of Si---H stretching mode, using the infrared photothermal deflection spectroscopy and the photothermal bending spectroscopy. The results show that the IR absorption of Si---H bonds increases by light soaking of the high power 500 mW/cm². The change of IR absorption of Si---H bonds reoccurs by thermal annealing at 200°C. This change is related to the increase of the dangling bonds under light soaking. Furthermore, we observe the change of the elasticity modulus by light soaking, using the photothermal bending spectroscopy. The structural change in a-Si : H is discussed based on these results.     

Development of a new pH-swing CO2 mineralization process with a recyclable reaction solution

A new CO₂ mineral sequestration process using the pH swing of a weak base–strong acid solution was proposed. In this process, an alkaline-earth metal was extracted selectively from silicate waste material, such as steelmaking slag or waste concrete, in an acidic condition using a weak base–strong acid solution. The reacted solution containing alkaline-earth metal ions and a weak-base, behaves as a CO₂ absorbent. The acidic extraction solution was regenerated from the basic absorbent solution by precipitating the alkaline-earth metal with CO₂ as the carbonate. The thermodynamic analysis of this process shows that a series of reactions proceeds spontaneously and the overall reaction is exothermic. The feasibility of the proposed process was confirmed using steelmaking slag as a silicate material and ammonium chloride solution as a weak base–strong acid solution. It was confirmed that this series of reaction proceeds successfully under mild conditions. Calcium ions were extracted selectively from steelmaking slag using an ammonium chloride solution, and the reacted solution absorbed CO₂ followed by the precipitation of CaCO₃ at 80 °C. On the basis of these experimental analyses, the energy consumption of the proposed process was roughly estimated as 300 kWh/ton-CO₂.     

High-accuracy roundness measurement by a new error separation method

This paper presents a new error separation method for accurate roundness measurement called the orthogonal mixed method. This method uses the information of one displacement probe and one angle probe to separate roundness error from spindle error. This method was developed from the mixed method, which uses the information of two displacement probes and one angle probe to carry out the error separation. In the present paper, the relationship between the characteristics of the mixed method and the probe arrangement is analyzed. Well-balanced harmonic response of the mixed method is verified to be obtainable for the case where the angular distance between the displacement probe and the angle probe is set at 90°. This orthogonal mixed method also had the simplest probe arrangement, because it requires only one displacement probe and one angle probe to realize the error separation. Optical probes were used to construct an experimental measurement system that employs the orthogonal mixed method. The displacement probe and the angle probe both use the principle of the critical angle method of total reflection, and they have stabilities of 1 nm and 0.01 in., respectively. The measurement results show that roundness measurement can be performed with a repeatability on the order of several nanometers.     

Statistical evaluation of fatigue crack propagation properties including threshold stress intensity factor

The relationship between fatigue crack propagation rate, da/dn, and range of stress intensity factor, ΔK, including threshold stress intensity factor, ΔK_th, is analyzed statistically. A non-linear equation, da/dn = C{(ΔK)^m-(ΔK_th)^m}, is fitted to the data by regression method to evaluate the 99% confidence intervals. Several experimental results on fatigue crack propagation properties of welded joints are compared by using these confidence intervals.     

Safety analysis of a supercritical-pressure water-cooled fast reactor under supercritical pressure

The supercritical-pressure water-cooled fast reactor (SWFR) is a fast spectrum supercritical water-cooled reactor (SCWR) studied by the University of Tokyo. The SWFR is designed as a two-pass core with an outlet temperature 500 °C. The SWFR has fuel channels cooled by downward flow, higher power density, and smaller coolant density reactivity feedback compared with Super LWR. This paper describes the safety analyses of abnormal events for the SWFR. SPRAT-F code is used for the safety analysis at supercritical pressure considering the downward flow cooled seed fuel channel. This code is based on a 1-D node junction model with point kinetics and decay heat calculations. Flow redistribution among parallel paths is calculated by pressure-loss balance and momentum conservation. The initiating events are selected from those of LWRs. For the safety analysis, nine abnormal transients and four accidents are selected with considering types of abnormality. By the numerical analyses, it was found that the loss of flow events can be mitigated by the “water source” effect of the downward flow blanket channels in the abnormal transients and accidents. All the abnormal events satisfy the criteria with margin.     

Study on time resolution of single event TOF-RBS measurement

Flight paths and times of secondary electrons, induced by a focused ion beam, from a sample to a secondary electron detector (SED), were simulated with various shield shapes of a SED for improving the time resolution of time-of-flight Rutherford backscattering spectrometry (TOF-RBS) using the secondary electron signal as a start signal, the results of which were compared with experimental time resolutions of the TOF-RBS measurement. The fluctuation in the flight path and, hence, flight time of the secondary electron deteriorates the time resolution of TOF-RBS. The simulated flight time differences for SEDs with or without a shield were 4.4–41 ns with a shield and 1.0 ns without a shield, respectively, indicating that the SED without the shield would improve the time resolution of the single event TOF-RBS. The time resolutions of TOF-RBS using 150 keV Be⁺ for Au/Si sample with SEDs with and without a shield were 5.6–9.2 and 4.4 ns, respectively. The improved time resolution for SEDs without the shield was confirmed experimentally.     

First 3-D calculation of core disruptive accident in a large-scale sodium-cooled fast reactor

The SIMMER-IV computer code is a three-dimensional fluid-dynamics code coupled with a fuel-pin model and a space- and energy-dependent neutron transport kinetics model. The present study has attempted the first application of SIMMER-IV to a core disruptive accident in a large-scale sodium-cooled fast reactor. A principal point of this study was to investigate reactivity effects with fuel relocation under three-dimensional core representation including control rods. The calculation has indicated that the fuel discharge from the core was disturbed by a significant flow resistance at the entrance nozzle in the current design. Additional static neutronic calculations have been performed to compare basic neutronic characteristics between different scale cores. The static neutronic calculations have clarified that the outward fuel compaction within the inner core increased the reactivity in the large-scale core unlike the small-scale core.     

Status of engineering design of liquid lithium target in IFMIF-EVEDA

In International Fusion Materials Irradiation Facility (IFMIF), intense neutron flux (4.5 × 10¹⁷ n/m² s) with a peak energy of 14 MeV are produced by means of two deuteron beams with a total current of 250 mA and maximum energy of 40 MeV that strike a liquid Li target circulating in a Li loop. Major design requirement is to provide a stable Li jet at a speed of 10–20 m/s with a surface wave amplitude on the Li flow less than 1 mm for handling of an averaged heat flux of 1 GW/m² under a continuous 10 MW deuterium beam deposition. The target system consists of a target assembly, a replaceable back-plate, a Li main loop and a Li purification loop. In July 2007, Engineering Validation and Engineering Design Activities (EVEDA) started under Broader Approach. In this paper, status of the engineering design of the IFMIF Li target system performed in 2007/2008 is described. The future EVEDA tasks to develop the target system are also summarized.