TFTR Health Physics Tritium Measurements Following D-D Operations

Abstract

Measurements within the Tokamak Fusion Test Reactor (TFTR) vacuum vessel atmosphere in 1985 indicated low levels of tritium oxide (HTO). From January to July 1987 approximately 3 × 1018 D-D fusion neutrons were produced in TFTR operations. These reactions would be expected to produce a triton for each reaction or 5.4 GBq (145 milliCuries) of tritium. An HTO measurement made of the vessel on 7/10/87, five days after the last pulsing of the machine, but before the machine was let up to air, indicated an HTO level of 1 MBq m−3 (28 µCi m−3) or approximately six times the DOE concentration guide value of 185 kBq m−3 (5 µCi m−3). The ICRP 30 Derived Air Concentration (DAC) limit of 800 kBq m−3 (22 µCi m−3) will become the limit when Draft DOE Order 5480.11 is implemented. A venting program for the vessel was set up with the objective of limiting the internal dose equivalent to personnel working inside the vacuum vessel. An HTO/HT measurement indicated a 57:1 ratio.HTO was detected in Neutral Beam Injectors (NBI). Tritium concentrations were also detected in a roughing pump in oil/water mixtures within the pump reservoirs. The water to oil tritium concentration ratio was 660:1.The graphite indicated an outgassing effect during the activities within the vessel. In addition, the loose powdered graphite with its tritium absorption presented the first known contamination problem for a tokamak operation. Smearable contamination levels up to 600 Bq/100 cm2 (36,000 dpm/100 cm2) were detected inside the vacuum vessel. This paper discusses the measurements, contamination problems, and results of dealing with the first operational health physics tritium-related activity in a fusion energy research tokamak.