H. Kodaka

Neutron irradiation effects on critical temperatures of A15-type superconducting composites

Abstract For several Nb3Sn and V3Ga superconducting composites, T c was measured by the inductance method after reactor irradiation and post-irradiation annealing. The neutron irradiated specimens showed marked degradation of T c , for example to 29.1% of T c0 in in-situ Nb3Sn at a neutron fluence of 4 × 10 19 neutrons/cm 2 (E > 0.1 MeV ) . After isochronal annealing to 1073 K the T c degradations recovered 84, 89 and 98% for bronze, tape and in-situ Nb3Sn, respectively. The recovery stages appeared at about 723 and 1023 K, which correspond to the movement of radiation-induced and equilibrium vacancies, respectively. The recovery in V3Ga tape was 97% at 1023 K, of which main stage occur about 773 K. The shape changes of the inductance-temperature curves after neutron irradiation and isochronal annealing suggest effects of cascade damage on the T c degradation.

Effects of neutron irradiation on the critical current of bronze processed multifilamentary Nb3Sn superconducting composites

The influence of fast neutron irradiation on critical current Ic and its strain dependence in a bronze processed fine multifilamentary Nb3Sn superconducting composite has been investigated. The neutron irradiation has been performed in a fission reactor at the reactor ambient temperature (≂355 K) up to the neutron fluence φt=3.6×1019 n/cm2 (E>0.1 MeV). The effects of annealing after irradiation have also been investigated. From the measurement of Ic at various magnetic fields, the scaling law for the change in dose has been found to be held in a certain range of neutron dose. The strain sensitivity of Ic under common ratio of applied magnetic field to bulk upper critical field B*c2 is affected slightly by irradiation up to φt=1.5×1019 n/cm2 but remarkably by annealing after irradiation to 3.6×1019 n/cm2. The strain scaling law has been found to be the specimen irradiated to 1.5×1019 n/cm2 and also to the one annealed (723 K, 2 h) after 3.6×1019 n/cm2 irradiation. The exponent value for B*c2 in pinning for...

strain effects in irradiated “in situ” Nb3Sn superconductors

Abstract The critical currents have been measured as a function of tensile strain for neutron irradiated Nb3Sn conductors. The samples are “in situ” and powder metallurgically formed conductors. Neutron irradiations have been carried out up to a fluence of 4 × 10 19 n/cm 2 (E > 0.1 MeV ) at the reactor ambient temperature of about 60°C. The neutron fluence dependence of the critical currents are affected by the fabrication procedure. Strain sensitivity of the critical current is slightly enhanced by neutron irradiation, that is, a synergism between the effects of the irradiation and strain on the critical current has been found.

Superconducting properties of neutron irradiated Nb3Al multifilamentary wires fabricated by the Nb-tube process

Abstract The superconducting critical temperature and the critical current of Nb-tube processed Nb 3 Al multifilamentary wires irradiated at reactor ambient temperature have been measured as a function of neutron (n) fluence up to 1.2 × 10 19 n cm −2 ( E > 0.1 MeV). The critical temperature decreases monotonically with neutron fluence. The neutron fluence dependence of the critical temperature for these Nb 3 Al wires is found to be basically similar to that for Nb 3 Al bulk samples. On the other hand, the critical current in magnetic fields of 6 T and 8 T remains almost unchanged up to a fluence of 1.4 × 10 18 n cm −2 and then rapidly decreases with increasing fluence. This peculiar dependence on neutron fluence of the critical current may be attributed to off-stoichiometric composition and the extremely small size of Nb 3 Al filaments. The critical currents decrease monotonically with applied tensile strain for both unirradiated and irradiated samples. The rate of decrease in the critical current with strain for irradiated samples tends to be smaller than that for unirradiated samples.

Depression of the superconducting transition temperature in neutron irradiated La2CuO4+δ

Abstract The influence of neutron irradiation to the superconductivity of the oxygen loaded La 2 CuO 4+ δ , which were prepared from one single crystal of La 2 CuO 4 , was investigated. The neutron irradiation were performed at 10 K. The superconducting transition temperature ( T c ) dropped monotonously with increasing the neutron fluence. The depression rate of T c was −1.3 K/10 17 n/cm 2 . A rise of T c could not be observed by the neutron irradiation.

Irradiation effects on mechanical properties of low activation Mn-Si-Cr steels

Abstract Alloying with silicon and manganese instead of nickel was calculated to be effective for the reduction of radioactivity after exposure to 14 MeV neutrons. Two compositions, Fe-17%Mn-4.5%Si-6.5%Cr and Fe-22%Mn-4.5%Si-6.5%Cr-0.2%N, were chosen for new low activation steels. Tensile tests were performed using miniature specimens at temperatures ranging between 4.2 and 473 K. Both steels showed high strength and ductility. After neutron irradiation to 1.6 × 10 25 n/m 2 at K , both steels retained good ductility at temperatures higher than 170 K.

Effect of Neutron Irradiation on Nb3Sn Superconducting Composites

The influence of neutron irradiation at ambient temperature on critical current and its strain dependence in bronze processed (Nb,Ti)3Sn superconducting composites has been investigated up to the fluence of 3.0×1019 n/cm2 ( E > 0.1MeV ). The critical current Ic at 4 T increased with fluence up to ~3×1018 n/cm2 and then decreased to almost zero at 3.0×1019 n/cm2. Addition of Ti reduced the fluence at which degradation of Ic took place. The characteristic strain values in Ic vs. strain relation are altered with fluence. These results are discussed through the changes in the upper critical magnetic field and the mechanical properties induced by neutron irradiation.

Strain and irradiation effects in practical superconducting wires for fusion application

Abstract Strain dependence of the critical current Ic has been investigated on several practical superconducting wires for high field application. The wires examined are Nb3Sn, Nb3Al and PbMo6S8 composites which are in the course of development. The effect of wire constitution coupled with fabrication process is also included. Improvement of the strain characteristics in these conductors through proper choice of parameters is briefly discussed. Effects of neutron irradiation on Ic are also presented. Changes in the mechanical properties of the constituents induced by irradiation alter the strain characteristics of Ic. Roles of the third additive elements and filament size are discussed.

Instrumented Charpy Impact Tests at Low Temperatures for Several Steels

Instrumented Charpy testing is recently of interest to study the impact property and fracture toughness of materials, and the standardization of the test procedures is currently discussed for the pressure vessels of power reactors.1 The instrumented impact testing system consists of an instrumented tup with strain gages to sense to compression loading, a dynamic transducer amplifier and a signal recording and display device. Such a system enables us to get load-time curves associated with fracture behavior of the test specimens.

LOW TEMPERATURE IRRADIATION FACILITY AT KYOTO UNIVERSITY REACTOR

The low Temperature irradiation facility constructed in a horizontal exposure hole at the Kyoto University Reactor (KUR) has been enabled us to study extensively in the fields of radiation damage and so on. The new refrigeration system is very profitable for long run operation of irradiation at ≃18 K during the reactor power of 5 MW. Impile and out-loop measurements of physical properties have been performed for many kinds of metals, alloys, ionic crystals, superconductors and organic materials.