Evaluation of radiation shielding, nuclear heating and dose rate for JT-60 superconducting modification

The radiation shielding, nuclear heating and dose rate have been evaluated for JT-60 superconducting modification. The double-walled structure of a vacuum vessel was adopted so that the maximum nuclear heating at the inboard side of the superconducting TF coil could be suppressed to be lower than 2.5 mW/cm3. The 316 stainless steel (SS316L) boards outside the vacuum vessel are installed for effective gamma-ray shielding. The dose rate with a reduced activation ferritic steel pedestal for the first wall in the vacuum vessel was estimated. This pedestal reduced the in-vessel dose rate by 40% compared to SS316L pedestal. The dose rate outside the boron carbide doped concrete cryostat was estimated at shutdown after 10 years operation.