Various definitions of the term Ultimate Heatsink

NRC definition:
“Loss of ultimate heat sink. In addition to disabling the emer-
gency diesel generators, the tsunami disabled Fukushima’s
“ultimate heat sink”—the systems, such as seawater pumps
and motors, used to remove heat from the reactor coolant
system and to cool emergency systems throughout the plant
following an accident”
Source: Union of Concerned Scientists, pp 12 “U.S. Nuclear Power Safety One Year after Fukushima” David Lochbaum | Edwin Lyman

The existence of the following device is allowed in the NRC definition of “Ultimate Heatsink”. The Torus acts the Heatsink for the injected coolant in this particular part of the Emergency Coolant. In addition, other steam turbine powered pumps introduce and propel coolant through other backup loops. Condensers located in the reactor buildings for one such additional emergency coolant loop.


HPCI pump used for high pressure emergency coolant injection to the reactor, this pump is turbine driven by steam
Source: BWR Plant Photos – inside and outside

The NRC explanation of the multiple cooling systems and multiple heatsinks as an “ultimate heatsink” does not help public understanding of the reasons for the sequential failure of the 3 reactors. To understand that multiple cooling systems and multiple heatsinks do exist, an authority must describe the systems. Unexplained technical terms in public documents fog the issue.

If one does not know of the multiple cooling systems, one has little hope of learning the fact from the NRC definition of Ultimate Heatsink. The questions relating to the sequential failure of system after system has everything to do with system considerations and design.

So, given the fact of multiple systems and heatsinks, what went wrong? An assumption at design staged regarding the time it would take to repair the grid connection. Eight hours. It took more than 70 hours. What system needs to change?

If the reactor powers the grid, grid failure must not equal reactor failure, for the reactor can power every emergency system from decay heat. As it does the emergency pumps.

The existence of these multiple pumps in each reactor is a real impediment to non technical explanations of what went wrong, and what system is inadequate.

It is the low voltage DC supply system. Not for the pumps but for the valves. The Ultimate Switches. There are lots of them.

The backup pump

2 Responses to “Various definitions of the term Ultimate Heatsink”

  1. CaptD Says:

    I love this wording: “There is no god heatsink.”

    If that was a typo then it was inspired!

  2. nuclearhistory Says:

    Yea, it was deliberate. I edited it out though. That’s the way I feel about the idea that denies the multiple systems that DO exist. Everyone makes mistakes. But I have no ideological opposition to pumps in the buildings. Just solenoids that don’t work.

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