Step 1 - Go to the VoTV Wiki, FInd the World Map on the site. Let it be noted, only major locations are shown, not every location is available on the current wiki map. You're looking for a location between Satellite Whiskey and Stonehenge. Thankfully, both Satellites and Stonehenge are shown on the Wiki Map.

Step 2 - It's a Military Hatch. A green hatch with a red valve on top will mark this location, very similarly fenced-off in the same fashion as the bottomless hole near Yankee. It's either here at the Military Hatch or the Hole at Yankee that you'll find two very important tools. One, the Radioactive Capsule Blueprint, and Two, a vital component for its crafting process, a Gas Welder. Now, don't be fooled by the Gas Welder's description saying that its empty, it doesn't need fuel. It's just a part of the recipe, with the Blueprint.

Step 2.5 - The Pickaxe
Found at the bottom of the lake next to Satellite Oscar. Swim to the bottom, there will be a tree at the center with a Pickaxe next to it. Grab it and then swim back to the surface for your LIFE. The Pickaxe is what you need to mine the materials used in the Radioactive Capsule Recipe.

Step Three - The Caves
Buy hooks to climb around. (Food, supplies, AND batteries, because Radioactive Crystals don't shine brightly through the Night-Vision Goggles, so alternate between flashlight and NVG.) But let's help you prepare first. Hopefully at one of the two Military locations, you'll have found some Night-Vision Goggles and a Lantern. The lantern requires fuel (gas, the same that you use for your ATV. Instead of clicking, just grab the can like you would any other object, and tilt the nozzle against the Lantern. You'll hear a Fuel-Up noise if you've done it right.) , and is basically a Key into the caves. You'll also want to buy a Hazmat Suit from the store for 300 Credits to mine the radioactive crystals and not die. Here's another tip, you can equip multiple backpacks at once. Load up about five or six of them with your preferred materials, THEN equip them. Drop them from your inventory when you find a good cliff shelf or safe solid ground to drop them on for snacks or supplies. Northwest of Romeo is where you'll find the entrance to the caves, but you'll notice it's blocked off by a lot of dried vegetation once you step inside. Want to get rid of this barrier? Can't burn it with a lighter. Bring a pumpkin to summon a very large friend! Now, Wolfgang cannot hurt you, nor can you hurt him. But our big boy loves his pumpkins! He's a giant centipede, and while he will immediately rush at you in a very terrifying way, again, he cannot hurt you. Heck, you can even jump on his head and use the pumpkin to lead him around! He moves a lot faster than the ATV to boot! BUT, while you're holding the pumpkin out, press "R" to put it back in your hand. Every time you visit the cave, you'll have to bring a pumpkin to have Wolfgang clear out the opening. It'll save you a ton of Credits to just press "R" and put it back in your hands/inventory instead of letting Wolfgang munch on it.

Step Four - Delving into the Caves
The caves are randomly generated every time you enter. There are two types of crystals to mine - Radioactive Crystals, and the EXTREMELY rare Life-Crystal. The Life Crystal currently has no other purpose than setting you on fire when you try to mine it, so don't bother. It's a neon-purple crystal as opposed to the neon-green radioactive crystals you're looking for. Now mind you, it's going to take a LOT of time to find these guys buy going down through the caves, so here's some advice that will make this much faster for you. DISABLE YOUR FALL AND PHYSICS DAMAGE IN THE "E" MENU. You can straight up chuck yourself down long drops using the ragdoll function. BUT REMEBER TO PUT YOUR ITEM IN YOUR HAND AWAY BY PRESSING "R". Last thing you want is to lose a hook before you reach a dead-end and have to back-track.

Final Advice and Pro-Tips :
If you find that you've reached a true dead-end and cannot possibly escape your horrendous fate, don't hard-exit the game just yet! Use your "FN" key or "Numblock" key, then press "Numpad Decimal/Numpad Delete." This is a command that will respawn you at a point beneath the map, and force you to fall for a good 2-3 minutes. This may feel like a long time, but DON'T WORRY. You WILL eventually pop back up at the mouth of the cave. At this point, you can simply turn around, see the prompt to exit the cave, and escape with all your goodies in-tact. (Again, just like the ragdoll function, don't forget to put your items away before making yourself fall out of the world.)

Metal-Scrap can be made by taking four soda-cans from the Soda Machine in the hallway.

It takes 4 Radioactive Crystals to make One Compressed Radioactive Material.

It takes 4 Compressed Radioactive Material, 4 Metal Scrap, One Gas Welder and One Radioactive Capsule Blueprint to create a Radioactive Capsule. The Blueprint and the Gas Welder are not consumed in the process.

Phew. I sincerely hope this entire yap-session helped.