Abstract: A method for measuring longitudinal variation in chromatic dispersion in an optical fiber, comprising: (i) launching into a first end and a second end of optical fiber an optical signal at a wavelength ?1 to collect backscatter power P(z) for different positions z within said optical fiber and providing measured OTDR backscatter traces; (ii) deriving from the measured OTDR backscatter traces at the single OTDR wavelength ?1 either (a) the longitudinal MFD(z) data or (b) the relative MFD data; and (iii) calculating estimated longitudinal dispersion D(z) from the longitudinal MFD(z) data or the relative MFD data, without utilizing any other wavelength data.

Abstract: The spacer envelope measurement system includes a generally U-shaped fixture having support plates extensible into positions overlying the spacer for supporting the fixture from the spacer. Extensible heads are carried by the fixture for engaging the spacer, followed by the heads of measurement gauges whereby, upon extending the heads into clamping engagement with the spacer along opposite sides thereof, the measurement gauges accurately determine the lateral dimensions of the irradiated spacer. A spacer bar clamp member is pivotal between positions opening the fixture opposite the base leg of the U-shaped fixture, enabling the bundle to reside within the U-shaped opening and a second position closing the opening for aligning the fixture and the bundle. The measurements are taken under water in a nuclear fuel service pool.