[ RadSafe ] what happens when the rods melt

Anagnostopoulos, Harry H.Anagnostopoulos at nv.doe.gov
Thu Mar 17 12:07:31 CDT 2011

If the rods melt, will the fuel go critical again?

In addition to the previous excellent answers regarding geometry,
poisons also play a role.

1. The control rods will also melt, mixing in with the fuel
2. Once the plant operators realized that they had a potential core
damage condition, they would have activated the Standby Liquid Control
system. This uses pressure accumulators to inject boric acid directly
into the reactor vessel.
3. Seawater is being injected into the primary containment and, where
possible, into the reactor vessels. The operators included boric acid
with the seawater, further poisoning the reactor and providing an
inventory in the primary containment in the event that fuel breeches the
reactor vessel.

Also, the reactor pedestal (supporting the reactor vessel bottom) is
very thick concrete and contains a chamber of sand and other materials.
This is designed to mix with the fuel, which dilutes it and helps to
spread it out, making for even poorer geometry.

Harry Anagnostopoulos, CHP

"In preparing for battle I have always found that plans are useless, but
planning is indispensable."
-    President Dwight D. Eisenhower

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