Originally Posted by
pasta
It's not as simple as drilling a shaft and backfilling on top of the device, either; if you do that, it turns out that the explosion just shoots all your backfill back up the shaft. You need to excavate sideways from the bottom of the shaft too; there's quite a good writeup of the last US test, with a drawing of the shot cavity here:
https://en.wikipedia.org/wiki/Cannikin
That Cannikin engineering drawing is fascinating.
If you look carefully at that schematic it shows the bottom lateral to be a tunnel rather than a drilled hole. Note that the scale is sufficient for it to be named on the drawing as a "crawlway" for a human ! There are various scaled items in the drawing from which one can estimate the crawlway tunnel to be approxximately 24" tall and 36" wide. I'd guess the spherical cavity at the base of the milled and under-reamed casing to be approximately 6' diameter which figures as humans have to do some interesting contortions at that point, including ultimately with a device between their legs !. The casing itself looks to be approximately 30" or so, maybe 40" max at that point. I appreciate that was for a 5-megaton device, so the device itself was quite large. Manually excavating those shafts, then getting the test equipment into position, then getting the nuclear device into place itself - all by hand - must have been quite a job.
if you go to these links
https://web.archive.org/web/20131029...19401a_121.pdf (see p11 etc)
https://nuke.fas.org/guide/usa/nuclear/testing.htm
https://en.wikipedia.org/wiki/Underg...eapons_testing (see esp Pumbob Rainier)
Note that the offset nature of the Plumbob Rainier tunnelled test is what they are seeking to recreate in the subsequent drilled+lateral offset test configurations, so that the explosion collapes the wellbore before any surface ejection occurs. But this time using a vertical 30-48" bottom hole conductor and lateral shaft, rather than a horizontal tunnel and terminating spiral.
You can also infer from
https://en.wikipedia.org/wiki/Operat..._(nuclear_test)
that the horizontal tunnel was of sufficient dimensions to be a human crawlway.
Whether one can achieve equivalent geometries without using manual mining at the bottom of 30-48" shafts for modern (smaller) devices is an interesting issue. Modern (directional) drilling techniques, coil tubing, and all the jewelry that go into making multilateral completions might conceivably allow for a human-less shot hole construction. That would be ironic as it was the experimentation with civilian use of nuclear explosives that then indirectly begat the fracced shale oil & gas technologies that in turn would be used to create a modern nuclear test shot hole. Those might be (say) 7" bottom holes which a modern MIRV physics package ought to fit into.
Interesting technical challenge. One can see why the Chinese might want to get all their ducks lined up in a row to be sure everything works and they have the capabilities in sufficient volume well in advance. I read somewhere that the USA crammed over 100 tests into the final year or so as the CBT came into force. The Chinese might want to get quite a rapid salvo of tests done before suspending and yanking the curtain down again before other countries are able to squeeze in the validation tests they might want to get in.
Will the Nevada site soon sprout some more test shotholes, empty but waiting, ready for the US/UK (and I think, now France as well) test programme to run some quickies if the window opens briefly ?