RADIOACTIVE MATERIAL PACKAGE CLOSURES WITH THE USE OF SHAPE MEMORY ALLOYS

When heated from room temperature to 165°C, some shape memory metal alloys such as titanium-nickel alloys have the ability to return to a previously defined shape or size with dimensional changes up to 7 per cent. In contrast, the thermal expansion of most metals over this temperature range is about 0.1 to 0.2 per cent. The dimension change of shape memory alloys, which occurs during a martensite to austenite phase transition, can generate stresses as high as 700 MPa (100 kpsi). These properties can be used to create a closure for radioactive materials packages that provides for easy robotic or manual operations and results in reproducible, tamper-proof seals. This paper describes some proposed closure methods with shape memory alloys for radioactive material packages. Properties of the shape memory alloys are first summarized, then some possible alternative sealing methods discussed, and, finally, results from an initial proof-ofconcept experiment described.