Radioactive gas measurement apparatus and failed fuel detection system

Abstract

To provide a radioactive gas measurement apparatus that is simply constructed and can efficiently measure Xe- 133 in a radioactive gas on-line under the condition that the radioactive gas is mixed with interference N-13, an apparatus is provided for measuring a radiation emitted from Xe- 133, including an anticoincidence counter circuit 13 that conducts counting if it receives an output of a main detector 1 when it does not receive outputs of scintillation detectors 2 and 9 , and a gate circuit 14 , a plate-shaped semiconductor detector is used as the main detector 1 , and a material not emitting a characteristic X ray in the range from 70 to 90 keV is used for a shielding structure. In particular, the thickness of the semiconductor detector 1 is set to fall within a range from 2 mm to 7 mm, thereby improving the analysis precision.

What is claimed is:  
     
         1 . A radioactive gas measurement apparatus, comprising: 
 a radiation detection system having a main detector and a sub-detector that are arranged at positions diametrically opposed to each other with respect to a sampling chamber, into or out of which a radioactive gas flows, and a shield for shielding a background radiation surrounding the detectors; and    an anticoincidence counter circuit in a measuring circuit, in which a particular radiation emitted from the radioactive gas is measured with an anticoincidence count processing using signals of both the detectors,    wherein the main detector is a plate-shaped semiconductor detector having a thickness less than a diameter of a surface thereof orthogonal to the thickness direction.    
     
     
         2 . A radioactive gas measurement apparatus, comprising: 
 a main detector and a first sub-detector having the shape of a well and surrounding the main detector that are arranged at one of two positions diametrically opposed to each other with respect to a sampling chamber, into or out of which a radioactive gas flows;    a second sub-detector arranged at the other of the two positions; and    an anticoincidence counter circuit as a measuring circuit, in which a particular radiation emitted from the radioactive gas is measured with an anticoincidence count processing using signals of the main detector and two sub-detectors,    wherein the main detector is a detector made from a plate-shaped semiconductor having a thickness less than a diameter of a surface thereof orthogonal to the thickness direction.    
     
     
         3 . The radioactive gas measurement apparatus according to  claim 1  or  2 , wherein the thickness of said plate-shaped semiconductor detector is between 2 mm and 7 mm.  
     
     
         4 . The radioactive gas measurement apparatus according to  claim 1  or  2 , wherein said shield for shielding the background radiation is made of a material that does not emit a characteristic X ray within a range of energy from 70 to 90 keV inclusive.  
     
     
         5 . A failed fuel detection system, wherein radiation intensity emitted from Xe- 133  contained in an off-gas in a reactor condensate system is measured by the radioactive gas measurement apparatus according to one of  claims 1  to  4 , the measurement values are collected on the time series, and the resulting time-series data is analyzed to detect a fuel failure in a reactor.