Feasibility of identifying leaking fuel rods using gamma tomography

Abstract

In cases of fuel failure in irradiated nuclear fuel assemblies, causing leakage of fission gasses from a fuel rod, there is a need for reliable non-destructive measurement methods that can determine which rod is failed. Methods currently in use include visual inspection, eddy current, and ultrasonic testing, but additional alternatives have been under consideration, including tomographic gamma measurements.The simulations covered in this report show that tomographic measurements could be feasible. By measuring a characteristic gamma energy from fission gasses in the gas plenum, the rod-by-rod gamma source distribution within the fuel rod plena may be reconstructed into an image or data set which could then be compared to the predicted distribution of fission gasses, e.g. from the STAV code. Rods with significantly less fission gas in the plenum may then be identified as leakers.Results for rods with low fission gas release may, however, in some cases be inconclusive since these rods will already have a weak contribution to the measured gamma-ray intensities and for such rods there is a risk that a further decrease in fission gas content due to a leak may not be detectable. In order to evaluate this and similar experimental issues, measurement campaigns are planned using a tomographic measurement system at the Halden Boiling Water Reactor.

The use of ionising radiation to image nuclear fuel: A review

“…Once a failure has been detected, the specific rod or rods need to be identified. One method of identifying a leaking rod is to compare the fission product distribution in the suspected failed rods [Dobrin et al (1997); Holcombe et al (2013)]. After a rod cladding failure, fission gases that would usually be in the gas-plenum escape from the rod.…”

“…Only the peripheral rods of the assembly can be seen due the low energy of the assayed g rays. The reconstruction was carried out using FBP[Holcombe et al (2013)]. …”