[ RadSafe ] Fukushima Daiichi reactor explosion

Michael LaFontaine, P. Phys. LCS at golden.net
Sat Mar 12 08:23:05 CST 2011

The following report appeared on 
http://www.stratfor.com/, they also have footage of the explosion.

Red Alert: Nuclear Meltdown at Quake-Damaged Japanese Plant

March 12, 2011 | 0827 GMT
<http://www.stratfor.com/print/187582>PRINT Text Resize:
North Korean Artillery Attack on a Southern Island

Related Special Topic Page
Japanese Disaster: Full Coverage
Footage of Fukushima Daiichi nuclear power plant
      Explosion at Japanese Nuclear Plant
      Japan’s Fukushima Daiichi nuclear power plant

A March 12 explosion at the earthquake-damaged 
Fukushima Daiichi nuclear power plant in Okuma, 
Japan, appears to have caused a reactor meltdown.

The key piece of technology in a nuclear reactor 
is the control rods. Nuclear fuel generates 
neutrons; controlling the flow and production 
rate of these neutrons is what generates heat, 
and from the heat, electricity. Control rods 
absorb neutrons ­ the rods slide in and out of 
the fuel mass to regulate neutron emission, and 
with it, heat and electricity generation.

A meltdown occurs when the control rods fail to 
contain the neutron emission and the heat levels 
inside the reactor thus rise to a point that the 
fuel itself melts, generally temperatures in 
excess of 1,000 degrees Fahrenheit, causing 
uncontrolled radiation-generating reactions and 
making approaching the reactor incredibly 
hazardous. A meltdown does not necessarily mean a 
nuclear disaster. As long as the reactor core, 
which is specifically designed to contain high 
levels of heat, pressure and radiation, remains 
intact, the melted fuel can be dealt with. If the 
core breaches but the containment facility built 
around the core remains intact, the melted fuel 
can still be dealt with ­ typically entombed 
within specialized concrete ­ but the cost and 
difficulty of such containment increases exponentially.

Red Alert: Nuclear Meltdown at Quake-Damaged Japanese Plant
(click here to enlarge image)

However, the earthquake in Japan, in addition to 
damaging the ability of the control rods to 
regulate the fuel ­ and the reactor’s coolant 
system ­ appears to have damaged the containment 
facility, and the explosion almost certainly did. 
There have been reports of “white smoke,” perhaps 
burning concrete, coming from the scene of the 
explosion, indicating a containment breach and 
the almost certain escape of significant amounts of radiation.

At this point, events in Japan bear many 
similarities to the 1986 Chernobyl disaster. 
Reports indicate that up to 1.5 meters (4.9 feet) 
of the reactor fuel was exposed. The reactor fuel 
appears to have at least partially melted, and 
the subsequent explosion has shattered the walls 
and roof of the containment vessel ­ and likely 
the remaining useful parts of the control and coolant systems.

Red Alert: Nuclear Meltdown at Quake-Damaged Japanese Plant
(click here to enlarge image)

And so now the question is simple: Did the floor 
of the containment vessel crack? If not, the 
situation can still be salvaged by somehow 
re-containing the nuclear core. But if the floor 
has cracked, it is highly likely that the melting 
fuel will burn through the floor of the 
containment system and enter the ground. This has 
never happened before but has always been the 
nightmare scenario for a nuclear power event ­ in 
this scenario, containment goes from being merely 
dangerous, time consuming and expensive to nearly impossible.

Radiation exposure for the average individual is 
620 millirems per year, split about evenly 
between manmade and natural sources. The 
firefighters who served at the Chernobyl plant 
were exposed to between 80,000 and 1.6 million 
millirems. The Nuclear Regulatory Commission 
estimates that exposure to 375,000 to 500,000 
millirems would be sufficient to cause death 
within three months for half of those exposed. A 
30-kilometer-radius (19 miles) no-go zone remains 
at Chernobyl to this day. Japan’s troubled 
reactor site is about 300 kilometers from Tokyo.

The latest report from the damaged power plant 
indicated that exposure rates outside the plant 
were at about 620 millirems per hour, though it 
is not clear whether that report came before or 
after the reactor’s containment structure exploded.

Read more: 
Alert: Nuclear Meltdown at Quake-Damaged Japanese Plant | STRATFOR

Michael LaFontaine, P. Phys.  

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