United States Nuclear Regulatory Commission - Protecting People and the Environment

Spent Fuel Pool Instrumentation

Ability to Monitor Level of Cooling Water

Spent Fuel Pool Instrumentation icon, consisting of a solid round, blue-green cirle, with a white outline of a 3 sided rectangle with short end top open in the center; inside the rectangle are 3 horizontal arrows pointing from the right to left side with the lower arrow having 6 vertical bars or lines tight together extending down to the bottom short end of the rectangleDuring the accident at Fukushima, the plant operators lost both their ability to cool the spent fuel pools and determine the amount of water in the pools. If enough water boiled away or was otherwise lost, the spent fuel rods could overheat and potentially release significant amounts of radiation. Weeks later, it was learned that the spent fuel was always covered, but the information gap diverted attention and limited resources from more important tasks during the accident. The NRC required all U.S. nuclear power plants to install water level instrumentation in their spent fuel pools.

The instrumentation currently in place reports at least three distinct water levels:

(1) normal level;
(2) low level but still enough to shield workers above the pools from radiation; and
(3) a level near the top of the spent fuel rods where more water should be added without delay.
NRC inspectors verified these capabilities.

Page Last Reviewed/Updated Friday, January 04, 2019