Haruyuki Namba

Concentration profiles of tritium penetrated into concrete

Abstract Concentration profiles of tritium in cement paste, mortar and concrete were measured after exposure to tritiated water vapor for a given time. Tritium penetrated a distance of about 5 cm from the exposed surface during an exposure of 6 months. The model of tritium behavior in concrete materials reported by the present authors was developed in this study with the consideration of the effects of sand and aggregate on both the diffusion coefficient of tritiated water vapor and the isotope exchange capacity. Predictive calculations based on the tritium transport model were also carried out in some situations of tritium leakage. The results of the calculations show that a large amount of tritium will be trapped in the concrete walls, and the trapped tritium will be gradually released back to the tritium handling room over the time of months to years even after the decontamination of the room is completed.

Application of Adaptive Structure Concepts to Construction of Space Systems in Orbit: Concepts and Formulation

Application of adaptive structures concept to construction of large space structure systems in orbit is studied. Adaptive structure elements for space construction are introduced, and they provide necessary shape change functions for parts of a total structure. The formulation for dynamics of structures including these elements by using a modular multibody analysis is introduced.

Self-Deployable Antenna Using Centrifugal Force

We have previously proposed a concept for an antenna that can self-deploy in zero gravity using centrifugal force. Before deployment, the antenna has the shape of a polygonal column with a diameter of 0.5 meters and a height of 1 meter. When it deploys completely, it becomes a polygonal disk with a diameter of 2 meters and a thickness of 30 millimeters. We have performed alternative deployment tests in zero gravity in water by forces closely simulating centrifugal force. The tests verify that the antenna can deploy completely. However, the tests cannot simulate zero gravity and the centrifugal force completely. In this paper, the reliability of the deployment in zero gravity using centrifugal force is verified by structural analysis.

Self Deployable Mechanism for Large Disk Antenna Using Centrifugal Force

In this paper, a self deployable large disk antenna is proposed for power transmission between locations in space. Its mechanism of self deployment is examined through a geometrical study. This antenna is discussed for use in a power transmitting test using an S-520 sounding rocket in a few years time.

Dynamics of large space-structure elements in orbit through adaptive deployment construction

By using a modular maltibody dynamics code, dynamical behavior of space structure elements is investigated to get an effective construction scenario for large space systems in orbit. Deployment construction of a triangular key structure for a solar power satellite in low earth orbit is treated, and the dynamical responses through the deployment in orbit plane, orbit normal or parallel plane are simulated. Illustrative examples clearly show the large variety of resulting dynamical behavior during and after deployment construction.

Passive and active systems of adaptive joints for truss structures in space

New two methods for vibration suppression of flexible structures in space are proposed based on non-linear simulation analyses. One is a flexible truss joint with intentionally introduced free-play dead band, which changes i ts dynamic characteristics passively corresponding t o the intensity of externallinternal excitation. Another one is an active joint, which changes mechanically its on/off status of free-play capability corresponding t o the stress/strain level a t the joint or corresponding t o the operational requirements of the structure. These two concepts are based on a common idea which is intentionally introduced free-play dead band. The efficiency of these concepts is discussed based on simulation analyses.

Development of Decontamination Method for the Concrete Contaminated With C-14 Nuclide in Fugen

Planning and preparation on decommissioning of the Fugen Nuclear Power Plant have been carried out, and it is one of the most important issues to reduce amount of the radioactive waste for decreasing the disposal cost of them in the dismantling process. In Fugen, the concrete of the reactor building is contaminated with C-14 that was generated due to the activation of CO2 gas during the plant operation. In this study, concrete samples were taken from the reactor building to survey how C-14 is penetrated into the concrete. Concentration of C-14 and C-14 existing rate in each element of the sample specimens were measured in order to investigate C-14 existing feature in the concrete. Besides, depth of the neutralization was measured in order to study on potential relationship with penetration of C-14. Then the following results were obtained: (1) C-14 is penetrated deep beneath of the surface, the depth is approximately as deep as 250mm. (2) C-14 exists only in cement portion of the concrete. It does not exist in aggregates. (3) Analytical study showed that CO2 gas containing C-14 could be penetrated into deeper position in hot and dried air condition during reactor operation, which is coming from that CO2 gas penetrating into concrete tend to move faster in void portion of the porous concrete than in liquid portion of that. Possible methods for removal of C-14 from the concrete are studied based on the above findings. This study showed that C-14 is localized in confined cement portion in 250mm depth of concrete. It is also cleared that CO2 gas containing C-14 in concrete could be removed by heating at a particular temperature. Therefore, it is expected that almost C-14 could be removed from concrete using the combination of both separating of cement portion and heating of it. In the next step of this study, planning the practical procedure for dismantling the reactor building and the removal and disposal method of C-14 will be carried out on the basis of the results of this study. The widely measurement with sampling more specimens is also planned in order to investigate C-14 contaminated distribution of the whole reactor building.© 2008 ASME