Many People seem to have the same misconception you've perpetuated here, that a reactor can be SCRAM'd just by dropping the rods into it. The fact of the matter is that a reactor has a MASSIVE latent heat of reaction (this doesn't tend to happen as much in military reactors because they are near weapons grade and thus have less radioactive by-products that need to decay). This heat MUST be dissipated or the core will melt. One way to get around this issue is to use a natural circulation reactor. Or to maintain an extra supply of coolent on a gravity feed.
Do you suffer painful hallucination? -- Don Juan, cited by Carlos Casteneda