Electron impact-dissociated ion detection-type hydrogen meter

The present invention provides a hydrogen meter for detecting hydrogen generated by sodium-water reaction used for safety management for an FBR type reactor. Namely, a partition membrane is disposed so as to partition a space into a sodium side in which liquid sodium is present and a vacuum side in which vacuum atmosphere is maintained, and hydrogen atoms permeate. An electron generating device irradiates electrons from the vacuum side toward the partition membrane. A shield electrode accelerates hydrogen ions dissociated from the surface of the partition by irradiation of electrons, and inhibits electrons from flowing to a collector electrode. The collector electrode collects hydrogen ions accelerated by the shield electrode. A current detection means detects electric current flowing to the collector electrode, to detect hydrogen. In this case, it is preferred that the partition membrane and the collector electrode are set at an identical electric potential. In addition, the partition membrane is preferably a noble metal system such as made of platinum or palladium. The method of the present invention has good response relative to generation of hydrogen, so that hydrogen can be detected at a high S/N ratio. Further, no special and large scaled ion pumps are not necessary. (I.S.)