Vanadium alloys, including the highly purified V-4Cr-4Ti alloy called NIFS-Heat2, in the form of sodium-enclosed irradiation capsules, were irradiated up to a damage level of 5dpa in the Joyo reactor at temperatures from 395 to 601°C. An increase of the ductile–brittle transition temperature (DBTT) by neutron irradiation and irradiation hardening were observed. No significant loss of ductility was observed even for irradiation at 395 and 450°C. The addition of titanium to V-Cr alloys was effective for irradiation hardening at high temperature. Hydrogen uptake in the cleaning process during dismantling of the irradiation capsules caused ductility loss of the highly purified V-4Cr-4Ti alloys; the alloys recovered their ductility when they were annealed at 400°C in vacuum. The uniform formation of Ti(OCN) precipitate was suppressed in highly purified V-4Cr-4Ti alloys irradiated in Joyo in a liquid-sodium environment

This paper investigates the polarization‐maintaining optical fibers with one circular hollow pit (SCF) and two circular hollow pits (DCF) outside a circular core. The modal birefringence of the following fibers are investigated: with homogeneous core, with radially inhomogeneous core. The relation between the modal birefringence (ΔB) and the polarization dispersion (Δτ) is also investigated. The homogeneous core fibers are analyzed by the improved point‐matching method. To analyze the inhomogeneous core fibers, the core is divided into several homogeneous layers and the improved point‐matching method is then applied. The main conclusions drawn in this paper are as follows: (1) the maximum modal birefringence for DCF can be attained 3.5 times larger than that for SCF; (2) the modal birefringence for inhomogeneous core fiber cannot be greater than that for homogeneous core fiber, even if the core index is chosen equal to the maximum index value of inhomogeneous core; (3) zero polarization mode dispersion can be attained near the wavelength where the modal birefringence takes the maximum value; however, it is not zero at that very wavelength. The relative error of propagation constant computed by our method is less than 10−9 so that the relative errors of the modal birefringence and polarization mode dispersion are less than 10−4.

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