A Calorimeter for the Nondestructive Assay of Tritium-Contaminated Samples

Tritium is handled routinely at laboratories in the United States, Canada, Japan, and Europe. There are several applications for nondestructive assay of solid tritium-contaminated samples including environmental clean-up, routine assay of tritium handling equipment, assay of fuel elements used by fusion reactors including the proposed ITER reactor, and routine monitoring of fission reactor core materials. Present technologies for the assay of medium-level tritium-contaminated solid samples either require substantial sample preparation or rely on surface contamination alone. Preparation of solid tritium-contaminated samples poses the problem of further contamination and thus should be avoided if possible. The only method that offers high sensitivity, accuracy and safety is calorimetry. Since the average energy of tritium decay is well known (+/- 0.3%), the level of contamination can be directly inferred from the nuclear heating of the contaminated material. The sensitivity of the technique improves tremendously at low temperatures (8 degrees K). Fortunately, these temperatures can be reached using mechanical refrigeration rather than liquid cryogens, reducing the complexity and cost of the final system. The device envisioned would be fully automated with a sensitivity of 1.5mCi (0.6GBq), an accuracy of 0.3% and a production cost of less than $40,000. In addition to the assay of tritium, this device could be used to assay other low-energy radioactive contamination.