Tuesday, October 14, 2014

"Nuclear Power Plants Are Not Designed to Withstand Pyroclastic Flows"


Reason #1 why nuclear power plants are not safe is because they have melt-downs at a global rate of approximately one every ten years (at least, that is what has been publicly acknowledged)
Severe nuclear reactor accidents likely every 10 to 20 years, European study suggests May 22, 2012 source Max-Planck-Gesellschaft http://www.sciencedaily.com/releases/2012/05/120522134942.htm

Reason #2 for not having nuclear power plants is that they are not structurally capable of withstanding a molten core, as indicated by their acknowledged incapacity to withstand "pyroclastic flows at high temperatures":
"Difficulties remain in protecting nuclear plants from volcanic eruptions (October 05, 2014) The Asahim Shimbun, http://ajw.asahi.com/article/behind_news/social_affairs/AJ201410050034
Nuclear plants are not designed to withstand pyroclastic flows at high temperatures. For that reason, if such flows should reach a facility, the consequences could be disastrous.
The Asahi is describing volcanic flows, but I believe that melted corium from a nuclear meltdown meets the general definition of a pyroclastic flow. The definition of a pyroclastic flow from Wikipedia:
Wikipedia Pyroclastic Flow:  A pyroclastic flow (also known scientifically as a pyroclastic density current[1]) is a fast-moving current of hot gas and rock (collectively known as tephra), which reaches speeds moving away from a volcano of up to 700 km/h (450 mph).[2] The gas can reach temperatures of about 1,000 °C (1,830 °F). Pyroclastic flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. http://en.wikipedia.org/wiki/Pyroclastic_flow

What is a nuclear melt-through but a pyroclastic flow of molten nuclear fuel and containment materials. Here is how Wikipedia defines corium:
Corium, also called fuel containing material (FCM) or lava-like fuel containing material (LFCM), is a lava-like molten mixture of portions of nuclear reactor core, formed during a nuclear meltdown, the most severe class of a nuclear reactor accident. It consists of nuclear fuel, fission products, control rods, structural materials from the affected parts of the reactor, products of their chemical reaction with air, water and steam, and, in case the reactor vessel is breached, molten concrete from the floor of the reactor room....

....During a meltdown, the temperature of the fuel rods increases and they can deform, in the case of Zircaloy cladding, above 700–900 °C. If the reactor pressure is low, the pressure inside the fuel rods ruptures the control rod cladding. High-pressure conditions push the cladding onto the fuel pellets, promoting formation of uranium dioxidezirconium eutectic with a melting point of 1200–1400 °C....

....A solidified mass of corium can remelt if its heat losses drop, by being covered with heat insulating debris, or if water that is cooling the corium evaporates.... http://en.wikipedia.org/wiki/Corium_%28nuclear_reactor%29

Nuclear power plants cannot withstand the radioactive pyroclastic flows produced by runaway nuclear reactions, as illustrated by this leaked diagram of melted corium in the river under the Daiichi nuclear site:


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