John R. Carroll wrote:

The AP1000 is a very good design by all accounts. China is going full bore
with these things but they bought hardware and the technology.
The emergency cooling is sort of a self licking ice cream cone.

I don't know how many reactors the Japanese are going to lose but it's at
least two so far.
Both are old but still, that's a lot of money to waste on a concrete land
mark.
I just read that they will be venting to the atmosphere for a considerable
period of time.
Possibly as long as a year - which seems a bit overstated - but people are
going to be unable to go home until the mess is buttoned up.
This is going to be an ongoing saga.

The Bank of Japan dumped more than eighty billion dollars into the Japanese
economy this morning.
That's real money.


By WILLIAM TUCKER

Even while thousands of people are reported dead or missing, whole
neighborhoods lie in ruins, and gas and oil fires rage out of control,
press coverage of the Japanese earthquake has quickly settled on the
troubles at two nuclear reactors as the center of the catastrophe.

Rep. Ed Markey (D., Mass.), a longtime opponent of nuclear power, has
warned of "another Chernobyl" and predicted "the same thing could happen
here." In response, he has called for an immediate suspension of
licensing procedures for the Westinghouse AP1000, a "Generation III"
reactor that has been laboring through design review at the Nuclear
Regulatory Commission for seven years.

Before we respond with such panic, though, it would be useful to review
exactly what is happening in Japan and what we have to fear from it.

The core of a nuclear reactor operates at about 550 degrees Fahrenheit,
well below the temperature of a coal furnace and only slightly hotter
than a kitchen oven. If anything unusual occurs, the control rods
immediately drop, shutting off the nuclear reaction. You can't have a
"runaway reactor," nor can a reactor explode like a nuclear bomb. A
commercial reactor is to a bomb what Vaseline is to napalm. Although
both are made from petroleum jelly, only one of them has potentially
explosive material.

Once the reactor has shut down, there remains "decay heat" from traces
of other radioactive isotopes. This can take more than a week to cool
down, and the rods must be continually bathed in cooling waters to keep
them from overheating.

On all Generation II reactors—the ones currently in operation—the
cooling water is circulated by electric pumps. The new Generation III
reactors such as the AP1000 have a simplified "passive" cooling system
where the water circulates by natural convection with no pumping required.

If the pumps are knocked out in a Generation II reactor—as they were at
Fukushima Daiichi by the tsunami—the water in the cooling system can
overheat and evaporate. The resulting steam increases internal pressure
that must be vented. There was a small release of radioactive steam at
Three Mile Island in 1979, and there have also been a few releases at
Fukushima Daiichi. These produce radiation at about the level of one
dental X-ray in the immediate vicinity and quickly dissipate.

If the coolant continues to evaporate, the water level can fall below
the level of the fuel rods, exposing them. This will cause a meltdown,
meaning the fuel rods melt to the bottom of the steel pressure vessel.

Early speculation was that in a case like this the fuel might continue
melting right through the steel and perhaps even through the concrete
containment structure—the so-called China syndrome, where the fuel would
melt all the way to China. But Three Mile Island proved this doesn't
happen. The melted fuel rods simply aren't hot enough to melt steel or
concrete.

The decay heat must still be absorbed, however, and as a last-ditch
effort the emergency core cooling system can be activated to flood the
entire containment structure with water. This will do considerable
damage to the reactor but will prevent any further steam releases. The
Japanese have now reportedly done this using seawater in at least two of
the troubled reactors. These reactors will never be restarted.

None of this amounts to "another Chernobyl." The Chernobyl reactor had
two crucial design flaws. First, it used graphite (carbon) instead of
water to "moderate" the neutrons, which makes possible the nuclear
reaction. The graphite caught fire in April 1986 and burned for four
days. Water does not catch fire.

Second, Chernobyl had no containment structure. When the graphite caught
fire, it spouted a plume of radioactive smoke that spread across the
globe. A containment structure would have both smothered the fire and
contained the radioactivity.

If a meltdown does occur in Japan, it will be a disaster for the Tokyo
Electric Power Company but not for the general public. Whatever steam
releases occur will have a negligible impact. Researchers have spent 30
years trying to find health effects from the steam releases at Three
Mile Island and have come up with nothing. With all the death,
devastation and disease now threatening tens of thousands in Japan, it
is trivializing and almost obscene to spend so much time worrying about
damage to a nuclear reactor.

What the Japanese earthquake has proved is that even the oldest
containment structures can withstand the impact of one of the largest
earthquakes in recorded history. The problem has been with the
electrical pumps required to operate the cooling system. It would be
tragic if the result of the Japanese accident were to prevent
development of Generation III reactors, which eliminate this design flaw.

Mr. Tucker is author of "Terrestrial Energy: How Nuclear Power Will Lead
the Green Revolution and End America's Energy Odyssey" (Bartleby Press,
2010).

--
Steve W.