The Windscale reactors were built in a hurry in 1950 to produce nuclear weapons after Russia managed to test it's first atom bomb in 1949 and are not really representative of modern power generating technology.
Obviously Windscale wasn't modern and SL-1 certainly wasn't either. My point was that simple designs are poor designs, that modern designs are complex for good reason. The added system complexity of automation is well worth it when it comes to nuclear power.
One of the aggravating factors at Windscale was their inability to perform maintenance tasks behind the reactor. They had canisters of radioactive material smashing open behind the reactor and it took them ages to even notice. That was a very simple reactor design; basically a nuclear pile. It was also an awful design that was irradiating England even before it caught fire.