How was a reactor repaired while irradiated fuel remained inside?

Details

After nearly two years of nuclear operation, personnel entered the pressure vessel of the Heavy Water Components Test Reactor (HWC TR) to repair and modify a gas baffle near the core while irradiated fuel remained in the reactor. The work involved removing virtually all the reactor internal components down to the reactor core and was completed in about three weeks. Appropriate shielding and special clothing kept personnel radiation exposure within allowable Savannah River Plant guides.