From the Fox News write up:
"We all went out on the tennis court, and they had an exact duplicate of the reactor on the tennis court. We would run out there with our wrenches and we'd check off so many bolts and nuts and they'd put them back on," he wrote. "And finally when we went down into the reactor itself, which was extremely radioactive, then we would dash in there as quickly as we could and take off as many bolts as we could, the same bolts we had just been practicing on. Each time our men managed to remove a bolt or fitting from the core, the equivalent piece was removed on the mock-up."
...
"They let us get probably a thousand times more radiation than they would now."