Long-term endurance test of PNC Type in-sodium hydrogen meter; Studies of leak detector development on LMFBR's SG (2)

Kuroha, Mitsuo; Takeda, Kunio; Iitsuka, Shoji; Sasaki, Shuichi; Okada, Toshio; Isozaki, Mikio; Daigo, Yoshimichi; Sato, Minoru

PNC type in-sodium hydrogen meters have been developed as leak detectors for LMFBR MONJU steam generators. In order to confirm the long-term reliability and the durability of the meters, the four meters were installed in three sodium loops at the O-arai Engineering Center, and they had been tested over a long time in flowing sodium. A period of the test was from oct. 1977 to Feb. 1980. They are called type II. The dynamic chamber of the vacuum system can separate from the static one, and be also connected with it using one flexible tube. Important findings from the test are; (1) The operating time of two meters exceeded 10,000 hours, and the total of all meters was about 35,000 hours. No trouble had been experienced in the sodium systems and the nickel membranes of them during the period, which had the good durability. Air leaks, however, occured three times in the two vacuum systems. (2) Any secular changes had hardly happened in the permeability of hydrogen through the nickel membrane and the relationship between ion pump current and hydrogen pressure. (3) The pumping speeds had decreased with increasing the amount of absorbed hydrogen. The decreasing rates differed among four ion pumps, and those of two pumps were considerably large at the beginning of absorbing hydrogen. (4) The calibration curves, which describe the relationship between hydrogen concentration in sodium and ion pump current, had changed with time. The largest cause was the decrement of the pumping speeds. (5) The UHV gauges were superior to the ion pumps from the point of the signal-to-noise ratio as the hydrogen sensor.