Calorimetry: An NDA Method for Tritium Measurement and Accountancy

The measurement and characterization of tritium, for its monitoring in processes or its accounting in radioactive wastes, can be addressed with nonintrusive and nondestructive methods such as the standardized (American Society for Testing and Materials C1458-16) large-volume calorimetry (LVC) technique. This type of calorimeter is isothermal and measures the heat flow generated by tritiated objects. The heat flow is detected with Peltier sensors. They are strategically located around the tritiated object to measure thermal fluxes in all directions. This method is matrix independent, the typical relative uncertainty is less than 1%, and the duration depends on the thermal conductivity and the volume of the measured object. The tritium quantity is calculated thanks to the tritium-specific power (324 mW/g) assuming that 100% of the measured heat flux comes from tritium.

This technique was applied for measuring tritiated drums or objects with volumes ranging from 1 to 250 L, more particularly, for the so-called LVC1380, which has been codeveloped and copatented by the CEA and KEP Technologies in France for drums bigger than 200 L. The new technology is based on the measurement of a differential heat flux on a measurement cell and a reference concentric cell without using a symmetrical reference cell. This device enables the quantification of tritium inventories in the waste drum, whatever the physical and chemical forms of tritium. The CEA has performed qualification tests of this calorimeter with ghost drums. The CEA now operates the LVC1380, and the first results in a tritium nuclear environment have been obtained with adsorbed tritiated water on zeolite inside molecular sieve traps (MST). This paper presents the measurement capabilities of this new LVC calorimeter and some illustrating results obtained with MST drums.