This is the most physics 101 analysis I’ve ever seen. Take a random assumption and then run the math to sound smart without putting half a second of thought into the actual design you are proposing. You “randomly” pick the worst possible construction material that sounds strong and use that to argue it’s impractical? Here’s a tip: use titanium for strength to *weight*. In this case, you aren’t building this on a spaceship, so using something *heavy* isn’t a problem. A compacted soil pit lined with reinforced concrete would give a solid over pressure rating using the right materials, then you’d lay on a reinforced concrete slab and cover that with enough mass to offset the pressure. You’d have one small expensive high strength steel pressure door for loading and [a moderately powerful](https://m.globalsources.com/si/AS/IVS-Tester/6008836334568/pdtl/High-Pressure-hydraulic-pumps-up-to-500-Mpa/1026133318.htm) hydraulic pump somewhere to do the pressurization. Easy.

Any release of energy will be limited to the pressure door or the pump attachment, so just don’t point those at anything important and have people stand out of the way.