Monticello Nuclear Plant Failure & Water Loss Incident

The Monticello nuclear plant that sits about 40 miles from downtown Minneapolis had another failure Tuesday. While the reactor was operating workers attempted to do maintenance work on an electrical system. This caused the reactor to lose the power to the reactor cooling water pumps. The water level began to drop. The NRC cites that the water did not drop low enough to turn on the HPCI and RCIC emergency cooling systems. Both of these have set points above the top of the fuel core.

The NRC cites water levels in both positive numbers and negative numbers. Most of the data out of Japan related to the Fukushima Daiichi disaster document the “0” water level to be the top of the fuel core. Some diagrams such as the emergency set point diagram below use “0” as a level above the core. The NRC citation that the HPCI and RCIC did not activate indicates the core likely did not uncover but the report caused confusion about what “0” level is being used.

The rapid water loss at Monticello highlights how fast things can go from routine to an emergency situation by simply losing an electrical bus.  Monticello also shut down on August 16th due to a gasket leak on a pipe inside the containment structure.

Other reactor diagrams show “0” as this one below does, our reactor water level diagrams from TEPCO also use the fuel tops as “0”

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