Something Odd Is Happening at Reactor Number 4

George Washington's picture

NHK reports:

The
operator of the troubled Fukushima Daiichi nuclear power plant is
carefully monitoring the situation at the Number 4 spent fuel pool,
where the water temperature is rising despite increased injections of
cooling water.

Tokyo Electric Power Company, or TEPCO, says it
will inject 210 tons of water into the pool on Monday, after finding on
Sunday evening that the temperature in the pool had risen to 81
degrees Celsius.

***

On Friday, TEPCO found that the
pool's temperature had reached 91 degrees, so it began injecting 2 to 3
times the amount of water.

***

The Number 4 spent fuel pool stores 1,535 fuel rods, the most at the nuclear complex.

(Bear in mind that the amount of radioactive fuel at Fukushima dwarfs Chernobyl.)

As I noted on April 2nd:

Nuclear engineer Arnie Gundersen notes that the spent fuel rods in reactor number 4 have no water, and the rods are exposed:

In addition, the official Japanese atomic energy website shows 4,250 sieverts/hour of radiation inside the containment vessel at reactor 4 ("S/C" stands for suppression chamber):

These are very high levels of radiation. As I noted on April 10:

Radiation levels were apparently about 300 sieverts per hour ... right after Chernobyl exploded.

To
be clear, the Chernobyl figure is radiation released into the
environment, while the reactor 4 figure is radiation within the
containment vessel. I have seen no evidence to date that reactor 4 is
leaking.

This is especially odd given that reactor 4 was supposedly shut down prior to the earthquake
for maintenance. In other words, reactor 4 was - according to
official reports - shut down, and shouldn't have very much radiation at
all. Something doesn't add up.

In contrast, the radiation inside the cores of the other reactors are much lower:

  • Reactor 1: 0
  • Reactor 5: 0
  • Reactor 6: 0

Indeed, the Japanese nuclear agency prominently displays the radiation data for all of the reactors except number 4 on it's main page. Number 4 is conspicuously absent, and you have to type in the url for the correct web page to find it.

The building housing reactor 4 doesn't seem to be quite as badly damaged as those housing other reactors:

However, a Fukushima engineer says he helped cover up a cracked containment vessel at reactor number 4 for decades.

On
the other hand, the fact that no radiation is being reported in the
drywell of reactor 4 (noted by "D/W" in the nuclear agency's tables) -
while there it is for several of the other reactors - might imply that
the containment vessel has maintained its stability.

At
this point, I don't have enough information to determine why the
radiation levels inside reactor 4 are so high compared to the other
reactors, let alone what it means. It might mean that reactor 4 is in
trouble. On the other hand, it could mean that reactor number 4 is the
only reactor which still has core integrity. In other words, maybe the
other reactor cores have much lower radioactive levels because most of
the radiation has already leaked out.