Radioactive contamination monitoring device and monitoring method

#The present invention relates to a radioactive contamination monitoring device and a monitoring method, and in particular, relates to a radioactive contamination monitoring device and a monitoring method of monitoring for radioactive contamination of an object to be monitored whose surrounding space is narrow.

#As a main turbine in a nuclear power plant deteriorates due to secular changes, a turbine rotor or nozzle diaphragm is replaced by a new one to improve operation efficiency and enable longer utilization. During the replacement, radioactive substances adhering to an outer surface of the replaced old part such as a turbine rotor and nozzle diaphragm are decontaminated by blasting or the like and it is necessary to check the effect of decontamination by a radioactive contamination monitoring device so that the replaced part can be transported out of a radiation controlled area as domestic waste. On the other hand, surface metals removed by decontamination, sand containing radioactive substances, and parts from which radioactive substances cannot be removed due to a device structure or the like are packed in a drum and temporarily stored on a premise as low level radioactive waste before being transported to a low level radioactive waste burying center where the low level radioactive waste is buried in a concrete pit.

#Because the space between nozzle wings to be monitored is very narrow, it has been very difficult to monitor for residual radiation of nozzle wings and the like after decontamination by blasting or the like using a commercial radioactive contamination monitoring device, prolonging a removal work period. For example, the space α between nozzle wings of a turbine rotor is about 3.9 mm to 24 mm and very narrow. Also, through-holes and non-through-holes formed on a horizontal joint surface of a turbine nozzle diaphragm have very small inside diameters.

#FIG. 1 is a schematic diagram of a radiation detection unit according to an embodiment of the present invention.

#FIG. 2 is a schematic diagram of the radiation detection unit according to another embodiment of the present invention.

#FIG. 3 is a schematic diagram of the radiation detection unit according to still another embodiment of the present invention.

#Embodiments according to the present invention will be described below with reference to drawings when appropriate. A detailed description of a common structure of a radioactive contamination monitoring device, for example, a radiation detection unit using scintillators, a photoelectric conversion unit that makes a photoelectric conversion of a detected signal by an electron multiplier tube, and a signal processing unit that is also described in Patent Literature 1 described above is omitted and instead, features of the present application will be described.

#FIG. 1 shows a radiation detection unit according to an embodiment of the present invention. A light guide bar 11 of a radiation detection unit 10 shown in FIG. 1 has a rod shape and is a regular quadrangular prism having a square cross-section. A scintillator 12 is arranged on two adjacent side faces of the light guide bar 11. As described later, the radiation detection unit 10 is suitable for monitoring for radioactive contamination of an inner surface of a through-hole such as a tapped hole.

#FIG. 2 shows the radiation detection unit according to another embodiment of the present invention. In a radiation detection unit 13 shown in FIG. 2, a scintillator 14 is also arranged at the tip of the light guide bar 11, in addition to the two adjacent side faces where the scintillator 12 is arranged in the radiation detection unit 10 shown in FIG. 1. The radiation detection unit 13 is suitable for monitoring for radioactive contamination of an inner surface of a non-through-hole such as a tapped hole with a bottom.