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http://ansnuclearcafe.org/
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* The International Nuclear and Radiological Event Scale
The International Nuclear and Radiological Event Scale (INES) was developed by the IAEA and the OECD in 1990 to better communicate and standardise the reporting of nuclear incidents or accidents to the public.
INES explains the significance of events from a range of activities, including industrial and medical use of radiation sources, operations at nuclear facilities and transport of radioactive material.
Events are classified on the scale at seven levels: Levels 1–3 are called “incidents” and Levels 4–7 “accidents”. The scale is designed so that the severity of an event is about 10 times greater for each increase in level on the scale.
Events without safety significance are called “deviations”
and are classified Below Scale / Level 0.
Chernobyl rated as 7 (Major Accident) on the scale and Three Mile Island rated 5 (Accident with Wider Consequences).
7 Major Accident
6 Serious Accident
5 Accident With Wider Consequences
4 Accident with Local Consequences
3 Serious Incident
2 Incident
1 Anomaly
0 Below Scale/No Safety Significance
The Japanese nuclear safety agency rated the damage at a nuclear power plant at Fukushima at a four on a scale of one to seven, which is not quite as bad as the Three Mile Island accident in the United States in 1979, which registered a five.
The Chernobyl explosion in the Ukraine in 1986, the worst nuclear power accident ever, was rated a seven. That was the only event classified as a major accident in nuclear power history, exploded due to an uncontrolled power surge that damaged the reactor core, releasing a radioactive cloud that blanketed Europe.
The Three Mile Island accident in Pennsylvania was a partial core meltdown in which the metal cladding surrounding the fuel rods started to melt. That metal surrounds the ceramic uranium fuel pellets, which hold most of the radiation and power the reactor.
Nuclear reactors operate at between 550 and 600 degrees F (between 288 and 316 degrees C). The metal on the fuel rods will not melt until temperatures are well above 1000 degrees F. The ceramic uranium pellets themselves won’t melt until about 2000 degrees.
About half the reactor core at Three Mile Island melted before operators restored enough cooling water to stop the meltdown. The core holds the uranium fuel rods, which must be cooled by water to prevent overheating.
En
The explosion at a nuclear plant in Fukushima, Japan destroyed a building that houses a reactor Saturday, triggering a radiation leak and fears of a nuclear meltdown.
But a representative of the global nuclear power industry asserts the possibility of a meltdown is “diminishing by the hour,” making a meltdown “most unlikely.”
Ian Hore-Lacy, director of communications of the World Nuclear Association, told “Early Show on Saturday Morning” co-anchor Russ Mitchell the situation is “less dangerous than it was yesterday. The challenge remains to keep the fuel cool in the reactor, particular they that number one unit of the Fukushima Dai-ichi plant.
* * *
Hore-Lacy said they should just “sit tight and watch. It’s really — I mean that hydrogen explosion … was a surprise. But hydrogen is always a factor in any nuclear reactor, but I think that the focus here has been on keeping the things cool, and obviously there was a hydrogen buildup somewhere and (it led to the explosion). … But that was a bit of a diversion. I don’t think it’s increased the risk of radiation release at all. There is a slight risk of radiation release, but not, I think, of any magnitude. And there is a possibility that some fuel may be damaged. But I think that a meltdown, particularly at this stage, some 30 hours after shutdown, is most unlikely.”
He observed that Japanese nuclear plants are constructed with earthquakes in mind, saying, “They’re all built in the secure knowledge that they’ll almost certainly have to endure serious earthquakes during their lifetime. And the reactors themselves are built in a very robust way, on solid rock. And I think, with all the earthquakes that have been in Japan, I don’t think any of the basic reactor structures have ever been damaged. Although, of course, all the services around are liable to be damaged.”
At 20:30 local time Japan Sat 3/12/11 Chief Cabinet Secretary Edano announced at the press conference as follows:
1. Hydrogen explosion occurred at 15:36 between containment and reactor building of Fukushima Daiichi unit 1. Walls of reactor building were blown out or damaged.
2. It was confirmed that unit 1 containment integrity was maintained. Explosion was not inside the containment as it is inert.
3. Radiation level at the Fukushima Daiichi site border once increased when containment vent was conducted and reached 1,015 micro Sv per hour around the time when explosion occurred; however, the radiation level turned to decrease after the explosion down to 860 at 15:40 and 70.5 micro Sv per hour at 18:58.
4. Government has agreed to TEPCO decision to fill the entire containment up with sea water. The filling sea water will contain boron. TEPCO started the work for filling up at 20:20.
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