Neutron Irradiation Effects on Superconducting Nb-Ti Wires for Fusion Reactor

A systematic study has been carried out on Nb-Ti wire of two different kinds of metallurgical structure, to examine the effects of neutron irradiation on the critical density J_c. The samples used were Nb-47.6 a/0 Ti (sample #A) and Nb-59.8a/0 Ti (sample #B), which were aged at 380°C for 0~10⁴min and irradiated to 1.3×10¹⁸n/cm² (E _n0.1 MeV). The sample temperature during the irradiation is believed to have been below 70°C. The values of J_c of both #A and #B aged up to 50 min were found to increase with irradiation. But when aged beyond 100 min, #B had its value of J_c lowered by the irradiation. The presence of Ti enriched precipitates such as α and ω phases in the samples was surmised from the behavior shown by the critical temperature T_c. The T_c of f #A and #B changed little by irradiation when aged not longer than 100 min, but with aging beyond 500 min, #B showed a decrease in its value of T_c. This decrease indicates that the Ti concentration in the matrix may have increased through radiation-induced breakup of the above-mentioned precipitates, which, in turn, would have brought about the reduction observed in J_c upon irradiation. It is concluded that superconducting Nb-Ti wire with J_c endanced by precipitation does not appear very resistant to neutron irradiation. This underlines the importance of the choice of superconducting materials to be used in fusion reactor magnets.     

热中子辐照提高掺硼YBaCuO超导体Jc的研究

掺杂天然硼的熔融织构生长（Ｍｅｌｔ－ｔｅｘｔｕｒｅｄＧｒｏｗｔｈ）的ＹＢｘＢａ２Ｃｕ３Ｏｙ（ｘ＝０．０１５,０．０３５）超导体经注量为５＊１０＾１７ｃｍ＾－２的热中子辐照后,磁临界电流密度Ｊｃ增至３．８倍。＾１０Ｂ（ｎ,α）＾Ｌｉ、＾７Ｌｉ＊（Ｑ＝＋２．７９ＭｅＶ）核反应出射的高能粒子能在超导体中产生均分布的,可以作为磁通钉扎中心的辐照伤,以便提高Ｊｃ。掺硼超导体热中子辐照后射性副产物的半衰期较短     

Improved Graphite Damage Model for Predicting Property Changes of HTGR Graphites under Isothermal and Nonisothermal Irradiations

Graphite components of a High Temperature Gas-Cooled Reactor (HTGR) core will be subjected to fast neutron irradiation-induced damages causing changes in engineering properties which are dependent significantly on irradiation temperature and neutron fluence. A Graphite Damage Model (GDM) elaborated to interpret observed isothermal irradiation behavior of various polycrystalline graphites has been improved in order to apply it to nonisothermal irradiations. The paper outlines the physical and mathematical formulations of the improved GDM together with some comparisons between predictions and measurements. On the basis of nonlinear fittings of the model functions to measured data, a total of 28 global modeling parameters have been determined successfully. Furthermore, a recurrence formula has been devised to permit a nonisothermal irradiation behavior to be predicted in terms of the new GDM. This has been proved by comparison of the predicted changes in linear dimension and thermal conductivity with the measured ones of some graphite materials irradiated at constant and changing temperatures.     

Particle Release from Vanadium Metal Surface by Neutrons

Sputtering yields from vanadium metal surface due to neutron irradiation were studied. A carefully prepared Pyrex glass tube, containing a vanadium foil as target and a polyethylene film pasted on a nickel plate as catcher, was sealed after evacuation, irradiated in a reactor, disassembled to take up the film, and the ⁵²V activity on it was counted for estimating the thermal neutron sputtering yield due to the recoil by(n, γ) reaction. The reactivation of the film gave the fast neutron sputtering yield. These values were found to be 2.3×10^?9 and 2.1×10^?1 respectively.     

Effect of Fast-Neutron Irradiation on Twinning Deformation of Zirconium

Unirradiated zirconium specimens and specimens irradiated to a fluence of 4.1 ×10¹⁹ n/cm² were subjected to tensile deformation at room temperature. During the straining, the specimens were removed at intervals from the testing machine for microphotographie inspection, to determine the progress of slip line density Ns, the twin volume fraction Vt and the twin density Ni, as function of strain. The effect of neutron irradiation on these values were studied in detail. The resulting data indicated that the neutron irradiation inhibited the growth of twins in the early stage of deformation, up to a plastic strain ?_p of about 11%, beyond which level the irradiation tended instead to inhibit nucleation. Between growth of twins and nucleation, it was the latter phenomenon that was found more effective in promoting slip deformation. The break in the slope of plots relating the reciprocal work hardening de/da to the true plastic stress σ_p gave the twin stress σ_t, which proved to represent a good approximation of the stress of twin nucleation.     

Neutron Irradiation Effects on Thermally Activated Process of Tensile Properties of Titanium

This paper deals with the relationship between mechanical properties and irradiation, effects for titanium irradiated to fast neutron fluxes. The neutron fluences applied are 6.9×10¹⁸, 8.6 × 10¹⁸ and 3.0 × 10¹⁹ n/cm². Tensile deformation is carried out over the temperature range of 77–about 600°K retaining the strain rate constant on one hand and changing the strain rate by a factor of about 5 and 10 on the other.

The fluence (φ) dependence of the yield stress at room temperature for an athermal component of the stress, σμ is greater than that for a thermal component σ* which does not change remarkably after irradiation. Their increments Δσ, Δμ and Δ σ* are proportional toσ ^1/3, σ^1/2σ^1/4 and, respectively.

The relationship between activation volume V* and effective shear stress τ* is investigated for both the unirradiated and irradiated specimens. In terms of the τ*/τ*₀ analysis (τ*_o is the value of τ* at T = 0°K), V* shows a tendency to decrease with increase in neutron fluence.

Irradiation defects observable by electron microscopy seem to be related to the athermal activation stress (σ_u) and those too small to be observed by electron microscopy to the thermal activation stress. The yield stress in the thermal activation can be given by Conrad's formula. The activation energy H₀ shows a constant value of about 1.8 eV irrespective of the neutron fluence applied. This value is 0.3–0.4eV higher than that for unirradiated specimens.     

Temperature and Dose Dependence of Swelling in 10% and 20% Cold-Worked Type 316 Stainless Steels

Void swelling in 10% cold-worked (10% CW) and 20% cold-worked (20% CW) type 316 stainless steels was investigated by 200 keV C⁺ ion irradiation and transmission electron microscope observation. Both 10% CW and 20% CW 316 steels show the swelling maximum at 923 K. Swelling in 10% CW 316 is much higher than that in 20% CW 316. The voids in the former material are larger and fewer than those in the latter material. The bilinear equation is applicable to describe swelling dose relation for both materials, except 10% CW 3 16 at higher doses than 50 dpa, where sharp swelling increase is observed. Heat to heat variability seems to exist in incubation dose, though it is not large. With regard to swelling rate, all three heats examined show good coincidence for both 10% CW and 20% CW 316 steels. Comparison of 20% CW 316 swelling rate for various irradiation projectiles indicates that the swelling rate is described as a simple function of the projectile mass, and there may exist a scaling law between the different projectile data.     

Microstructural study of an irradiated high-nickel alloy by X-ray line profile analysis and TEM observations

The microstructure was investigated in previously deformed specimens of a high-nickel alloy with four levels of initial dislocation density, both before and after irradiation in BOR-60 reactor at 370–400°C and three displacement rates. The network dislocation density, dislocation loop radius and loop number density were determined by both X-ray line profile analysis and TEM observations. The dependence of dislocation structure parameters on irradiation conditions and initial network density was obtained.     

Behavior of Helium Bubbles in Cold Worked Aluminium-Lithium Alloys

Abstract

Various kinds of cold worked Al-Li alloys were irradiated in JRR-2 and the change in microstructure with post-irradiation annealing was examined in an electron microscope. In 30% cold worked specimen, bubbles are preferentially distributed on sub-boundaries. The grain interior contains only a small amount of bubbles. On the contrary, in 2% cold worked specimen, in which distinct sub-boundaries are rarely formed, most of bubbles are distributed within the grains. Bubbles aligned on a dislocation are frequently observed.

These experimental results are explained as follows. In heavily cold worked specimen, moving dislocations collect most of He atoms or their clusters in the course of sub-boundary formation after irradiation. In slightly cold worked specimen, dislocation density is insufficient to perform this process and He atoms or their clusters precipitate either upon dislocations or within the grains.     

Radiation Blistering of Vanadium Irradiated with 40keV 4He Ions

The vapor pressure of strontium in the temperature range of 494~660°K has been determined by the mass spectrometric Knudsen effusion method. The temperature dependence of the vapor pressure in Pa is given by the equation: log 10.750 ± 0.122 - (8,427±69)/T. From the values of vapor pressure, heats of vaporization of strontium were obtained to be ΔH° _u298= 163.8 ±1.6 kJ/mol by the second law treatment and ΔH°_u298 = 161.9 ±0.5 kJ/mol by the third law treatment.     

Impact of Material Configuration Behind First Wall on Helium Formation in In-Vessel Components of Fusion Reactor

The results of neutron transport calculations of the He formation based on the JENDL gas-production cross section file are discussed for some metals and alloys, namely ²⁷A1, Ti, ⁵¹V, Cr, ⁵⁵Mn, Fe, Ni, Zr, Mo, austenitic stainless steel (Ti modified 316 SS: PCA), Ni-base alloy (Inconel 625), ferritic steel (Fe-11Cr-1Mo: HT-9), Ti-base alloy (Ti-6A1-4V) and V-base alloy (V-5Cr-5Ti). Impacts of the two shields having the steel-rich and the H₂O-rich compositions and the two blankets having the Li₂O/Be-base and the liquid Li/Be-base compositions on the He formation rate in the above-mentioned metals and alloys are discussed. The relation between the He formation rate and the fast neutron flux (14.1 MeV>E>0.1 MeV) is investigated. The decrease of He formation at any distance Δ from the first wall more than Δ_as, the distance where the shape of neutron spectrum reaches its asymptotic form, is modelled by the simple formula based on the exponential dependence, as those reported so far for the fast neutron flux and the displacement damage rate.     

Pyrolytic Graphite Irradiated with 4 keV Hydrogen Ions Using Reflection High-Energy Electron Diffraction

Separation of barium isotopes with a selective two-step photoionization process was accomplished using a continuous wave dye laser and ultra-high pressure mercury lamp. Narrow line-width laser light was tuned to the 6s^{2 1}S₀--6s6p ¹P₁ resonance line (553.6 nm), and only a single isotopic component in an atomic beam was excited through the isotope shift. The excited atoms were successively ionized by uv radiation and deflected by a static electric field.

The spectrum of the ion current separated isotopically agreed well with spectroscopic data within the system resolution of 65 MHz. The isotopic enrichment of ¹³⁸Ba was 97%, which corresponded to the selectivity of 1.36. The ionization rate defined as what portion of the incident atoms was ionized was approximately 4x10^?5%. The photoionization cross section was estimated from the experimental results by using the least squares method. The resultant value was (4±1)x10^?23m².