EFDA-JET-CP(01)09/04

Operation, Maintenance and Decontamination of the JET Torus Access Facilities

ABSTRACT Since the introduction of 20 grams of tritium in the JET machine in 1997 the Torus Access Facilities have been used extensively for the removal of highly tritiated components from the torus during engineering shutdown periods. Such components are also neutron activated and beryllium contaminated. Operations within these facilities are mostly of a hybrid nature encompassing both robotic and manual activities in air feed full-pressurised suits. Access to such facilities is through airlocks that provide containment or double lidded door systems that maintain the containment boundary. Remote and manned access depend on achieving a delicate balance in the ventilation system such that a sufficient depression is held in-vessel whilst a number of access points are open. In addition both the breached Torus and the Torus Access Facilities require an increase in ventilation of one order of magnitude when compared to that provided by the Active Gas Handling Plant. This is provided by the Controller/Dresser Unit (CDU) Ventilation system that discharges through a monitored stack. Low doses to operators and very small environmental discharges demonstrate that the ventilation systems achieve tritium containment Airborne tritium levels of up to 150MBq/m3 and surface levels exceeding 2MBq/cm2 have been experienced during the Remote Tile Exchange and the Inboard Pellet Injector shutdowns. The use of sacrificial layers, vacuum cleaning, strippable and tie-down coatings within the Access Facilities are successfully used to control both tritium and beryllium contamination. Strict work and posting procedures have lead to shorter clean up times and to a reduction in Respiratory Protective Equipment (RPE) or declassification of some areas. The practicalities of tritium absorption affecting the radiological status of equipment and the implications this holds for future tritium operations are described in addition to the design and experiences gained in the operation of such facilities.
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EFDC010904 5.43 Mb