Oxide Measurement of a fuel element.

[M98Ranger]

Everyone,


I am a Mechanical Engineer working on a design modification (or existing product recommendation) for an Idaho National Laboratory project.

What follows is the situation description. At the end is the question. You can skip down to the bottom of the post (which details the bottom-line of my thread if you don't have time);

This is just background information. An existing tool [at INL] has an eddy current probe at the end, which is lowered into the (Advanced Test Reactor (ATR) Canal water approximately six feet and placed in six different locatioins along the curved surface of a fuel element. This tool is designed to measure oxide layer thickness around the fuel element (fuel elements are of course extracted from the reactor). In addition to being extremely time consuming, the readings from the tool are inconsistent. This inconsistency is due to what has been surmised, (by various technicians and other professionals involved in the process) to be a combination of the curvature of the fuel element surface, water chemistry, operator error, etc.

The question I have is whether or not supersonic sound wave analysis, in order to obtain the oxide thickness would work in lew of the eddy current probe method. Why is it that the eddy current probe methods seems to be the industry standard when it seems that supersonic sound analysis would do the same job with less error?

When I say less error, I am referring to the fact that the INL eddy current probe design is such that (purportedly...and if my understanding of the situation is correct) the operator has a hard time lining it up the same way each time. Also, if for some reason the normally de-ionized water (is that the correct term...its getting too late for me) becomes ionized, then using the eddy current method in combination with operator error would cause even greater data inconsistency.

So, the bottom line is, DO ANY OF YOU KNOW if there is a significant reason/reasons to not use supersonic sound wave analysis to detect corrosion layers on the surface of fuel elements?

 

[Astronuc]

Eddy-current liftoff method for oxide thickness measurement is standard in the industry, either a sapphire-tipped stylus probe or pancake coils. Normally one calibrates the probe on standards that are representative of the metal substrate and oxide (and crud) being measured. Modern probes and systems must now compensate for the effects of Zn-bearing cruds.

There is no supersonic technique, but I think one is referring to ultrasonic, which is high frequency (MHz range) pulsed acoustical waves. UT can be measure for wall thinkness of tubes using pitch-catch, time of flight methodology. I'm not sure that it is practical for oxide thickness which are on the order of microns (10-100 μm) on older, moderate to high exposure Zr-alloys.

One problem for UT would be porosity in the oxide, and the relatively thickness of the monoclinic or tetragonal phases in the oxide layer.

 

[Noxi]

One concern regarding UT is the integrity of the fuel pellets since there is no proof that they won´t be affected by the sonic waves, another thing is the CRUD-buildup (BWR) and possibility of interference.