Year
1989
Abstract
As part of the Special Nuclear Material (SNM) Accountability Program at Three Mile Island Unit 2 (TMI-2), gamma measurement surveys for fuel characterization of the 'A' and 'B' once-through steam generator (OTSG) tube bundles, lower heads, and associated cold legs were performed from September 1988 to mid-January 1989. The OTSGs were characterized in two phases, which included measurements of the lower heads and cold legs in phase 1, and measurements of the tube bundles in phase 2. Fuel measurement strings were developed and fabricated to obtain gamma measurements in difficult to access areas. A measurement string consisted of polypropylene tubing containing Geiger-Muller (GM) probes connected to the data acquisition system. These measurement strings were inserted through the OTSG upper tube sheet to the tube bundle, lower head and associated cold legs. Miniature lights and videoprobes were also deployed through surrounding tubes to visually verify placement of the strings and location of debris material. No blocked tubes were encountered. During video-inspection of the lower heads and cold legs, a low density material of minimal depth was observed with a few areas varying in depth and consistency. Fuel estimates based on in situ exposure rates obtained during phase 1 of the measurement program for the 'A' and 'B' OTSG lower heads and cold legs were 1.0 kg and 6.3 kg, respectively. Data collected from the 'A' and 'B' OTSG tube bundles during phase 2 of the measurement program were also evaluated and fuel quantities estimated based on in situ exposure rates. The estimate of record of total fuel debris deposited in the 'A* and 'B' OTSG tube bundles Is 1.7 kg and 9.1 kg, respectively.