A powder processing technique is developed for the fabrication of tetragonal zirconia-nickel functionally gradient materials. The powder volume fraction, the linear shrinkage during drying, and the pore radius of monolithic zirconia-nickel green compacts with vari ous zirconia/nickel volume ratios were measured. A multilayer zirconia-nickel green compact with a step wise compositional gradient was formed by slip cast ing and then pressureless-sintered. The key to success ful fabrication is to avoid the fracture of green com pact during drying process in an ambient atmosphere. In conclusion, it is desirable to minimize differences in permeability and pore radius between neighboring lay ers in a multilayer green compact.
The corrosion rate of carbon steel in compacted bentonite was evaluated with regard to the test period length, temperature, chemicals of solution and bulk density of compacted bentonite.The average corrosion rate decreased gradually with increasing test period up to 180 days in immersion tests. The corrosion rate of carbon steel in compacted bentonite at a dry density of 1.32g/c was estimated to be about 0.01 mm/y which was one order of magnitude lower than that in bentonite slurry. No significant influence of temperature on corrosion rates was observed in compacted bentonite in the range of 50-180 *C . Variation of kinds and concentration of anion(chloride, floride, sulfate, and carbonate)in aqueous solution did not have much influence on the corrosion rate of carbon steel.Immersion tests of carbon steel in compacted bentonite at a dry density of 0.69 -1.32 g/cm 3 , which was mixed with an aqueous solution(synthetic sea water and distilled water), were carried out. The corrosion rate in compacted bentonite decreased from 0.04 to O.O05mm/y as the density of bentonite increased.This result suggests that the corrosion rate of carbon steel in compacted bentonite is governed by the diffusivity of corrosive materials. In general, oxygen is the dominate factor affecting corrosion rate, therefore prediction of the average corrosion rate of carbon steel was carried out on the basis of the diffusion behavior of dissolved oxygen in compacted bentonite.The prediction agreed with experimental results. INTRODUCTIONThe Japanese concept for high-level radioactive waste management is based on immobilization with borosilicate glass, folllowed by 30 to 50 years of storage for cooling, and ultimate disposal in underground formations deeper than several hundred meters (I ) . Candidate sites have not been selected yet, and site characteristics such as composition of groundwater have not been determined.According to the current engineered barrier system concept, waste glass packed in the waste container(overpack) is emplaced in a borehole. Buffer materials are emplaced between the overpack and host rock. These engineered barrier systems act as a primary barrier to the release of radionuclies from the radioactive waste to host rock.The primary role of the overpack is to confine the radionuclides for more than several hundred years. The life of the overpack will be mainly limited by corrosion Two types of materials were sellected as candidate overpack materials for achieving this long life. One is corrosion allowance type material and the other is high corrosion resistance type material. Carbon steel is the primary candidate of corrosion allowance type metal.Immersion tests in test solution have been conducted in order to estimate the influence of individual environmental factors on the corrosion behavior of carbon steel. Immersion tests in bentonite slurry have also been carried out to estimate
The in vivo host range of human T-cell leukemia virus type 1 (HTLV-1) has not been definitively established. To determine if hematopoietic stem cells from patients with adult T-cell leukemia-lymphoma (ATL) are infected with HTLV-1, we used a clonogenic progenitor assay followed by the polymerase chain reaction for the detection of HTLV-1 DNA. In vitro growth characteristics of myeloid (CFU-GM) and erythroid (BFU-E) progenitor cells among nonadherent T-cell-depleted bone marrow (BM) mononuclear cells (NA-T-MNCs) from 10 patients with ATL was not significantly different from those of HTLV-1-seronegative controls (P = .20); numbers of colonies per 1 x 10(5) NA-T-MNCs were 34.9 +/- 7.6 for CFU-GM and 39.0 +/- 12.5 for BFU-E in patients with ATL, whereas those were 32.1 +/- 9.5 for CFU-GM and 41.4 +/- 12.7 for BFU-E in normal controls. HTLV-1 DNA was not detected in individual colonies formed by CD34+ cells from any of the patients. Similarly HTLV-1 DNA was not detected in 1 x 10(3) CD34+ cells sorted on a fluorescence-activated cell sorter (FACS) from six patients with ATL studied. In contrast, HTLV-1 DNA was detected in BM mononuclear cells from all patients. These observations clearly indicate that hematopoietic progenitor cells from patients with ATL are normal in their colony-forming capacity and that CD34+ cells from patients with ATL are not infected with HTLV-1 in vivo.
The conceptual design and fabrication test of a full-scale ceramic overpack were performed from the viewpoint of structural barriers as a part of program to evaluate their potential use as overpack under conditions of deep geological disposal.Materials investigated were porcelain (used for insulators) and A1 2 0 3 with high purity of 99.7 %. The selected design consisted of a cylindrical body with hemispherical heads at each end. The design thickness of overpack is the sum of the structural thickness and corrosion allowance. The thickness required to resist the lithostatic pressure was estimated by the basic cylinder buckling formulas and finite element stress analyses in both case of uniform and non-unifom external pressure conditions. These analyses showed that structural thickness of 119 mm was necessary for overpack of porcelain and 40 -for A1 2 03 under the predicted maximum uniform pressure. In addition, fracture probability of delayed failure, one of significant degradation mode, was estimated for overpack of porcelain.A full-scale overpack of porcelain, of dimensions 800 mm outer diameter x 2200 mm length x 150mm wall thickness, was fabricated under the ordinary level of fabrication technology.
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