Patent Number: 044951426
Section: summary

The present invention relates to a system for monitoring the state of a nuclear reactor core and, more particularly, to a monitor system for monitoring the state or condition of a nuclear reactor core, employing a radiation monitor suitable for monitoring the state of a nuclear reactor core at the time of loss of coolant accident (referred to as LOCA, hereinafter). The boiling water reactor has a reactor containment vessel consisting of a dry well and a pressure suppression chamber. The reactor pressure vessel is placed in the dry well, while the pressure suppression chamber is filled with cooling water. In the event of a LOCA in the boiling water reactor, the cooling water of high pressure and temperature in the pressure vessel is dischaged as steam into the dry well through the fractured portion of the primary loop recirculation system. This steam is introduced into the pressure suppression chamber and is condensed by the cooling water in the latter. As disclosed in Japanese Patent Laid-open Publication No. 65295/76, a radiation meter, thermometer, pressure gauge and a condensate drain level meter are installed in the dry well of the boiling water reactor, in order to monitor the leakage of the cooling water due to LOCA. This monitoring system permits the operator to confirm occurrence of LOCA, but cannot provide accurate information concerning the state or condition of fuel rods in the reactor core after occurrence of LOCA. Therefore, with this known monitor system, it is not possible to take suitable countermeasures after the occurrence of the LOCA. SUMMARY OF THE INVENTION It is, therefore, a major object of the invention to accurately determine the state of fuel rods after occurrence of LOCA. To this end, according to the invention, there is provided a monitoring system comprising: means for measuring a level of the radioactivity of iodine in the primary containment vessel of a nuclear reactor; means for measuring a level of the radioactivity of noble gas; and means for judging or determining the state or condition of fuel rods in the reactor core in the event of occurrence of LOCA, upon receipt of the output from the means for measuring the level of the radioactivity of iodine and the output from the means for measuring the level of the radioactivity of noble gas.