Measurement and analysis of in-vessel component activation and gamma dose rate distribution in Joyo, 2

Yamamoto, Takahiro; Ito, Chikara; Maeda, Shigetaka; Ito, Hideaki; Sekine, Takashi

JAEA-Technology 2017-036, 41 Pages, 2018/02

JAEA-Technology-2017-036.pdf:7.86MB

In the experimental fast reactor Joyo, the damaged upper core structure (UCS) was retrieved into the cask in May 2014 The dose rate on UCS surface was quite high due to the activation for over 30 years operation. In order to attain the optimum safety design, manufacture and operation of equipment for UCS replacement, the method to evaluate UCS surface dose rate was developed on the basis of C/E obtained by the in-vessel dose rate measurement in Joyo. In order to verify the evaluation method, the axial gamma-ray distribution measurement on the surface of the cask, which contained UCS, was conducted using a plastic scintillating optical fiber (PSF) detector. This paper describes the comparison results between calculation and measurement as follows. (1) The measured axial gamma-ray distribution on the cask surface had a peak on proper location with considering the cask shielding structure and agree well with the calculated distribution. (2) The C/E of axial gamma-ray distribution on the cask surface was ranged from 1.1 to 1.7. It was confirmed that the calculation for UCS replacement equipment design had a margin conservatively. Then, the results showed that the developed evaluation method for UCS replacement equipment design was sufficiently reliable.

Inspection and repair techniques in reactor vessel of sodium cooled fast reactor, 9-7; ray dose rate evaluation of upper core structure

Yamamoto, Takahiro; Ito, Keisuke; Ito, Chikara; Maeda, Shigetaka; Ito, Hideaki; Sekine, Takashi; Masui, Tomohiko*

no journal, , 

no abstracts in English

Evaluation of -ray dose rates on the upper core structure of the experimental fast reactor Joyo

Ito, Chikara; Yamamoto, Takahiro; Maeda, Shigetaka; Ito, Hideaki; Sekine, Takashi

no journal, , 

In the experimental fast reactor Joyo, the upper core structure (UCS) was replaced. We have evaluated -ray dose rates on UCS in order to conduct radiation shielding design of the UCS cask and radiation exposure control in the UCS removal work. The -ray dose rates was calculated using the QAD-CGGP2R and corrected by the measured in-vessel axial distributions of -ray dose rate. In order to verify the -ray dose rate evaluation procedure, we measured spatial distribution of -ray on the surface of the cask, which contained UCS using plastic scintillating optical fiber (PSF) during the UCS removal work. The calculated PSF output values were approximately twice as large as measured through the UCS. Correcting the calculated -ray dose rates on the surface of the cask by results of the comparison has shown appropriate -ray dose rates distribution.

Measurement and analysis of in-vessel component activation and dose rate distribution in Joyo

Yamamoto, Takahiro; Maeda, Shigetaka; Ito, Chikara

no journal, , 

In the experimental fast reactor Joyo, the damaged upper core structure (UCS) was retrieved into the cask in May 2014 for its replacement as a part of the restoration work of the incident concerning with the irradiation test sub-assembly named MARICO-2. The dose rate on UCS surface was quite high due to the activation for over 30 years operation. In order to attain the optimum safety design, manufacture and operation of equipment for UCS replacement, the method to evaluate UCS surface dose rate was developed on the basis of C/E obtained by the in-vessel dose rate measurement in Joyo. In order to verify the evaluation method, the axial -ray distribution measurement on the surface of the cask, which contained UCS, was conducted using a plastic scintillating optical fiber (PSF) detector. As a result, the measured axial -ray distribution on the cask surface had a peak on proper location with considering the cask shielding structure and agree well with the calculated distribution and the C/E of axial -ray distribution on the cask surface was ranged from 1.1 to 1.7. It was confirmed that the calculation for UCS replacement equipment design had a margin of conservatively. Then, the results showed that the applied evaluation method for UCS replacement equipment design was sufficiently reliable. In the in-vessel repair work for sodium cooled fast reactors (SFRs), the design and work condition estimation are important. The accumulated experience provides valuable insights into further improvements for in-vessel repair techniques in SFRs.