In situ measurement of molecular hydrogen for nuclear reactor safety studies

Pulsed-UV laser Raman spectroscopy is a sensitive diagnostic technique for detecting gas-phase molecules as low as 1 ppm. The authors used this technique to measure the generation rate of molecular hydrogen in experiments which simulate severe nuclear reactor accident conditions. These experiments were carried out at the Sandia Laboratories Annular Core Research Reactor (ACRR). The results reported here mark the first application of laser spectroscopy to the real-time detection and quantitative measurement of any species in a nuclear reactor environment. For this experiment an in-pile test section with UV-transmitting optics was used to measure the real-time generation rate of hydrogen from the reaction of steam with a zircaloy cladding on nuclear fuel rods. A schematic diagram of the experimental apparatus is shown. A krypton-fluoride excimer laser operating at a wavelength of 248.5 nm and a pulse repetition rate of 10 Hz was used as the Raman excitation source. Raman signals backscattered from steam and hydrogen were collected by an 18-cm diam quartz telescope used to image the signals onto the entrance slit of a 0.33 -m monochromator. Butyl acetate and N,N-dimethylformamide liquid filters were used to suppress backscattered laser light from the in-pile test section