That's ^ what I was thinking. Sounds like all your problems are solved if you verify the pressure at the wrench. That has to be easier and cheaper than all the other solutions.

Well, even when you know the torque of a bolt the amount of tension is still in doubt, and the tension is what is creating the seal integrity.

Measuring the pressure at the wrench gets us close, but doesn't address the degradation of the wrench itself. We might try this just for the fun of it, though. We actually have numerous wrenches (for a variety of torquing needs). Some of them are pneumatic, some are electric and some are open-end "maxi-break" wrenches. This is just one issue.

The wrenches currently cost us about $7000 + the cost of the remote handling modifications. I'm not sure whether or not some type of solid film lube would help (or last). I've talked to the wrench vendor and they "allow" the wrenches to be used without lubrication (mostly in nuclear applications), but strongly caution about the degradation.

Significant testing was done early on to determine the torque required to ensure proper sealing. We installed a target a couple of years ago that failed its seal test right away. We went back and tightened the bolts a little bit more (who knows how much?) and the test passed, so we incorporated that torquing info into our procedure. Ever since then, the seal performance has been fine until this current target.

Bottom line, hearing all of this discussion (which I really appreciate) and thinking about ways to integrate some of these new ideas brings me back to simply ensuring that the torque we are applying is reasonably accurate. This can be by measuring the torque output of the wrenches in the cell (some sort of torque tester) or by utilizing a wrench that doesn't rely on air pressure (electric wrench). The techs seem to think the electric wrench is do-able, but we would need to modify it to enable the torque adjustment remotely.

These kinds of problems are what I deal with every day. I just got back from a demo of a video scope. The ones we have been using cost > $50k each and last about 1 hour in the radiation environment. Of course, the targets cost >$1 million each, so learning about their failure modes is important. We are going to hang one of these targets vertically from a crane and drill holes in the nose tomorrow. That is always interesting...

I'd go with strain-gaged washers. Here's a link to Transducer Techniques, but there are others out there as well - LWO Series Load Cell @ Transducer Techniques

It will cost you 8 x $725 per container, but you can verify at any time the tension in each bolt, even long after it's left your facility. That may offer you some compliance benefit, or at the very least give you a competitive advantage. You could probably negotiate quantity discounts, and any loadcell manufacturer is more than happy to engineer a custom solution from custom materials, Inconel 718 for instance.

Interesting idea, but it would be very difficult for us and would cost a fortune. We would not have an easy way to connect the transducers to any sort of unit to read the loads. We'd have to:

1. Route wiring from the base unit outside the cell through a penetration and into the cell (through 40" of high-density concrete with air dams and fire stop material)
2. Install a new target into the cell with the transducers in place
3. Install target, install bolts and then connect transducers to penetration cabling
4. Torque bolts (this part would work great)
5. Cut the cables to the transducers and abandon them in place

then...during target removal, we'd have to throw what's left of the transducers away (any non-metallic material like wire insulation is going to be a brittle, crumbly mess) and start over by installing new transducers with next target.

the bolts are there to hold the lid on... what??

the box in photo #1 does not seem to be a waste cask

does the thing ever have to be opened back up?

i.e. why use bolts at all....

This is not a waste cask - we are bolting a "target module" onto a carriage so that it can be inserted into a core vessel for proton irradiation/neutron production. That bolted interface contains the bulk flow mercury seal.

Once the target module is "spent" due to radiation-induced material degradation (or from a unique phenomenon where we've seen damage due to mercury cavitation), we have to replace the module. Replacement takes about 100 hours. We ship spent target modules for disposal, but that's easy.