In this article and videos, we will explore what the definition of corium is, what it is composed of, how it forms, plus how it reacts with other things such as concrete and reactor vessels. Then we will explore the history of corium formation and behaviour in regards to Three Mile Island, Chernobyl and Fukushima. Finally, we will conclude with some corium analysis at Fukushima and Chernobyl, explaining the differences between them, plus the dangers that they pose to humanity.
According to Wikipedia, “Corium, also called fuel containing material (FCM) orlava-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. (A picture of TMI corium below)
Corium 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.
Composition and formation
The heat causing the melting of a reactor may originate from the nuclear chain reaction, but more commonly decay heat of the fission products contained in the fuel rods is the primary heat-source. The heat production from radioactive decay-heat drops quickly, as the short half-life isotopes provide most of the heat and radioactive decay, with the actual curve of decay-heat being a sum of the decay-curves of numerous isotopes of elements decaying at different exponential half-life rates. A significant additional heat source is the chemical reactions of hot metals with oxygen or steam.
Radioactive chain-reaction and corresponding increased heat-production may progress in parts of the corium if a critical mass occurs locally. This condition can be detected by presence of short-life fission products long after the meltdown, in amounts that are too high to be from the controlled reaction inside the pre-meltdown reactor. Because nuclear chain-reactions generate high amounts of heat and highly-radioactive fission products, this condition is highly undesirable from a reactor vessel structure and biological safety perspective.
The temperature of corium depends on its internal heat-generation dynamics: the amount of decay-heat-producing isotopes, dilution by other molten materials, heat losses modified by the corium physical configuration, and heat losses to the environment. A compact corium mass will lose less heat than a thinly spread layer. Corium of sufficient temperature can melt concrete. 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.
Crust can form on the corium mass, acting as a thermal insulator and hindering thermal losses. Heat distribution throughout the corium mass is influenced by different thermal conductivity between the molten oxides and metals. Convection in the liquid-phase significantly increases heat transfer.
The molten reactor core releases volatile elements and compounds. These may be gas phase, such as molecular iodine or noble gases, or condensed aerosol particles after leaving the high-temperature region. A high proportion of aerosol particles originate from the reactor control rod materials. The gaseous compounds may be adsorbed on the surface of the aerosol particles.
Corium composition and reactions
The composition of corium depends on the design-type of the reactor, and specifically on the materials used in the control rods, coolant and reactor vessel structural materials. There are differences between pressurized water reactor (PWR) and boiling water reactor (BWR) coriums.
Zirconium from zircaloy, together with other metals, reacts with water and produces zirconium dioxide and hydrogen. The production of hydrogen is a major danger in reactor accidents. The balance between oxidizing and reducing chemical environments and the proportion of water and hydrogen influences the formation of chemical compounds.
Variations in the volatility of core materials influence the ratio of released elements to unreleased elements. For instance, in an inert atmosphere, the silver-indium-cadmium alloy of control rods releases almost only cadmium. In the presence of water, the indium forms volatile indium(I) oxide and indium(I) hydroxide, which can evaporate and form an aerosol of indium(III) oxide. The indium oxidation is inhibited by a hydrogen-rich atmosphere, resulting in lower indium releases. Caesium and iodine from the fission products that can react to produce volatile caesium iodide, which condenses as an aerosol.
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 dioxide–zirconium eutectic with a melting point of 1200–1400 °C.
An exothermic reaction occurs between steam and zirconium, which may produce enough heat to be self-sustaining without the contribution of decay heat from radioactivity. Hydrogen is released in an amount of about 0.5 m3 of hydrogen (at normal temperature/pressure) per kilogram of zircaloy oxidized.
Hydrogen embrittlement may also occur in the reactor materials and volatile fission products can be released from damaged fuel rods. Between 1300 and 1500 °C, the silver-cadmium-indium alloy of control rods melts, together with the evaporation of control rod cladding. At 1800 °C, the cladding oxides melt and begin to flow. At 2700–2800 °C the uranium oxide fuel rods melt and the reactor core structure and geometry collapses. This can occur at lower temperatures if a eutectic uranium oxide-zirconium composition is formed. At that point, the corium is virtually free of volatile constituents that are not chemically bound, resulting in correspondingly lower heat production (by about 25%) as the volatile isotopes relocate.
The temperature of corium can be as high as 2400 °C in the first hours after the meltdown, potentially reaching over 2800 °C. A high amount of heat can be released by reaction of metals (particularly zirconium) in corium with water.
Flooding of the corium mass with water, or the drop of molten corium mass into a water pool, may result in a temperature spike and production of large amounts of hydrogen, which can result in a pressure spike in the containment vessel.
The steam explosion resulting from such sudden corium-water contact can disperse the materials and form projectiles that may damage the containment vessel by impact. Subsequent pressure spikes can be caused by combustion of the released hydrogen. Detonation risks can be reduced by the use of catalytic hydrogen recombiners.
Reactor vessel breaching
In the absence of adequate cooling, the materials inside of the reactor vessel overheat and deform as they undergo thermal expansion, and the reactor structure fails once the temperature reaches the melting point of its structural materials. The corium melt then accumulates at the bottom of the reactor vessel.
In case of adequate cooling of the corium melt, the melt can solidify and the spread of damage is limited to the reactor itself. However, corium may melt through the reactor vessel and flow out or be ejected as a molten stream by the pressure inside the reactor vessel. The reactor vessel failure may be caused by heating of its vessel-bottom by the corium melt, resulting first in creep failure and then in breach of the vessel. Cooling water from above the corium layer, in sufficient quantity, may obtain a thermal equilibrium below the metal-creep temperature, without reactor vessel failure.
If the vessel is sufficiently cooled, a crust between the melt and the reactor wall can form. The layer of molten steel at the top of the oxide may create a zone of increased heat transfer to the reactor wall; this condition, known as “heat knife”, exacerbates the probability of formation of a localized weakening of the side of the reactor vessel and subsequent corium leak.
In case of high pressure inside the reactor vessel, breaching of its bottom may result in high-pressure blowout of the corium mass. In the first phase, only the melt itself is ejected; later a depression may form in the center of the hole and gas is discharged together with the melt with a rapid decrease of pressure inside the reactor vessel; the high temperature of the melt also causes rapid erosion and enlargement of the vessel breach.
If the hole is in the center of the bottom, nearly all corium can be ejected. A hole in the side of the vessel may lead to only partial ejection of corium, with a retained portion left inside the reactor vessel. Melt-through of the reactor vessel may take from a few tens of minutes to several hours.
After breaching the reactor vessel, the conditions in the reactor cavity below the core govern the subsequent production of gases. If water is present, steam and hydrogen are generated; dry concrete results in production of carbon dioxide and smaller amount of steam.
Thermal decomposition of concrete produces water vapor and carbon dioxide, which may further react with the metals in the melt, oxidizing the metals, and reducing the gases to hydrogen and carbon monoxide. The decomposition of the concrete and volatilization of its alkali components is an endothermic process. Aerosols released during this phase are primarily based on concrete-originating silicon compounds; otherwise volatile elements, for example, caesium, can be bound in nonvolatile insoluble silicates.
Several reactions occur between the concrete and the corium melt. Free and chemically-bound water is released from the concrete as steam. Calcium carbonate is decomposed, producing carbon dioxide and calcium oxide. Water and carbon dioxide penetrate the corium mass, exothermically oxidizing the non-oxidized metals present in the corium and producing gaseous hydrogen and carbon monoxide; large amounts of hydrogen can be produced. The calcium oxide, silica, and silicates melt and are mixed into the corium.
The oxide phase, in which the nonvolatile fission products are concentrated, can stabilize at temperatures of 1300–1500 °C for a considerable period of time. An eventually-present layer of more dense molten metal, containing fewer radioisotopes (Ru, Tc, Pd, etc., initially composed of molten zircaloy, iron, chromium, nickel, manganese, silver, and other construction materials and metallic fission products and tellurium bound as zirconium telluride) than the oxide layer (which concentrates Sr, Ba, La, Sb, Sn, Nb, Mo, etc. and is initially composed primarily of zirconium dioxide and uranium dioxide, possibly with iron oxide and boron oxides), can form an interface between the oxides and the concrete farther below, slowing down the corium penetration and solidifying within a few hours. The oxide layer produces heat primarily by decay heat, while the principal heat source in the metal layer is exothermic reaction with the water released from the concrete. Decomposition of concrete and volatilization of the alkali metal compounds consumes a substantial amount of heat.
The fast erosion phase of the concrete basemat lasts for about an hour and progresses into about one meter depth, then slows to several centimeters per hour, and stops completely when the melt cools below the decomposition temperature of concrete (about 1100 °C). Complete melt-through can occur in several days even through several meters of concrete; the corium then penetrates several meters into the underlying soil, spreads around, cools and solidifies.
During the interaction between corium and concrete, very high temperatures can be achieved. Less volatile aerosols of Ba, Ce, La, Sr, and other fission products are formed during this phase and introduced into the containment building at time when most of early aerosols are already deposited. Tellurium is released with the progress of zirconium telluride decomposition. Bubbles of gas flowing through the melt promote aerosol formation.
The thermal hydraulics of corium-concrete interactions (CCI, or also MCCI, “molten core-concrete interactions”) is sufficiently understood. However the dynamics of the movement of corium in and outside of the reactor vessel is highly complex, and the number of possible scenarios is wide; slow drip of melt into an underlying water pool can result in complete quenching, while a fast contact of large mass of corium with water may result in a destructive steam explosion. Corium may be completely retained by the reactor vessel, or the reactor floor or some of the instrument penetration holes can be melted through.
The thermal load of corium on the floor below the reactor vessel can be assessed by a grid of fiber optic sensors embedded in the concrete. Pure silica fibers are needed as they are more resistant to high radiation levels.
Some reactor building designs, for example, the EPR, incorporate dedicated corium spread areas (Core Catchers), where the melt can deposit without coming in contact with water and without excessive reaction with concrete. Only later, when a crust is formed on the melt, limited amounts of water can be introduced to cool the mass.
Materials based on titanium dioxide and neodymium(III) oxide seem to be more resistant to corium than concrete. Deposition of corium on the containment vessel inner surface, e.g. by high-pressure ejection from the reactor pressure vessel, can cause containment failure by direct containment heating (DCH).
Three Mile Island accident
During the Three Mile Island accident, slow partial meltdown of the reactor core occurred. About 19,000 kg of material melted and relocated in about 2 minutes, approximately 224 minutes after the reactor scram. A pool of corium formed at the bottom of the reactor vessel, but the reactor vessel was not breached. The layer of solidified corium ranged in thickness from 5 to 45 cm.
Samples were obtained from the reactor. Two masses of corium were found, one within the fuel assembly, one on the lower head of the reactor vessel. The samples were generally dull grey, with some yellow areas.
The mass was found to be homogenous, primarily composed of molten fuel and cladding. The elemental constitution was about 70 wt.% uranium, 13.75 wt.% zirconium, 13 wt.% oxygen, with the balance being stainless steel and Inconel incorporated into the melt; the loose debris shown somewhat lower content of uranium (about 65 wt.%) and higher content of structural metals.
The decay heat of corium at 224 minutes after scram was estimated to be 0.13 W/g, falling to 0.096 W/g at scram+600 minutes. Noble gases, caesium and iodine were absent, signifying their volatilization from the hot material. The samples were fully oxidized, signifying presence of sufficient amount of steam to oxidize all available zirconium.
Some samples contained a small amount of metallic melt (less than 0.5%), composed of silverand indium (from the control rods). A secondary phase composed of chromium(III) oxide was found in one of the samples. Some metallic inclusions contained silver but not indium, suggesting high enough temperature of volatilization of both cadmium and indium. Almost all metallic components, with exception of silver, were fully oxidized; however even silver was oxidized in some regions. The inclusion of iron and chromium rich regions probably originate from a molten nozzle that did not have enough time to be distributed through the melt.
The bulk density of the samples varied between 7.45 and 9.4 g/cm3 (the densities of UO2 and ZrO2 are 10.4 and 5.6 g/cm3). The porosity of samples varied between 5.7% and 32%, averaging at 18±11%. Striated interconnected porosity was found in some samples, suggesting the corium was liquid for sufficient time for formation of bubbles of steam or vaporized structural materials and their transport through the melt. A well-mixed (U,Zr)O2solid solution indicates peak temperature of the melt between 2600 and 2850 °C.
The microstructure of the solidified material shows two phases: (U,Zr)O2 and (Zr,U)O2. The zirconium-rich phase was found around the pores and on the grain boundaries and contains some iron and chromium in the form of oxides. This phase segregation suggests slow gradual cooling instead of fast quenching, estimated by the phase separation type to be between 3–72 hours.
(For more information about the TMI nuclear accident, click on the following link.)
Three Mile Island (TMI) Coverup; via A Green Road
Chernobyl corium lava flows formed by fuel-containing mass in the basement of the plant Large amounts of corium were formed during the Chernobyl disaster. The molten mass of reactor core dripped under the reactor vessel and now is solidified in forms of stalactites, stalagmites, and lava flows; the best known formation is the “Elephant’s Foot”, located under the bottom of the reactor in a Steam Distribution Corridor.
The corium was formed in three phases.
The first phase lasted only several seconds, with temperatures locally exceeding 2600 °C, when a zirconium-uranium-oxide melt formed from no more than 30% of the core. Examination of a hot particle shown a formation of Zr-U-O and UOx-Zr phases; the 0.9 mm thick niobium zircaloy cladding formed successive layers of UOx, UOx+Zr, Zr-U-O, metallic Zr(O), and zirconium dioxide. These phases were found individually or together in the hot particles dispersed from the core.
The second stage, lasting for six days, was characterized by interaction of the melt with silicate structural materials – sand, concrete, serpentinite. The molten mixture is enriched with silica and silicates.
The third stage followed, when lamination of the fuel occurred and the melt broke through into the floors below and solidified there.
The Chernobyl corium is composed from the reactor uranium dioxide fuel, its zircaloy cladding, molten concrete, and decomposed and molten serpentinite packed around the reactor as its thermal insulation. Analysis has shown that the corium was heated to at most 2255 °C, and remained above 1660 °C for at least 4 days.
The molten corium settled in the bottom of the reactor shaft, forming a layer of graphite debris on its top. Eight days after the meltdown the melt penetrated the lower biological shield and spread on the reactor room floor, releasing radionuclides. Further radioactivity was released when the melt came in contact with water.
Three different lavas are present in the basement of the reactor building: black, brown and a porous ceramic. They are silicate glasses with inclusions of other materials present within them. The porous lava is brown lava which had dropped into water thus being cooled rapidly.
During radiolysis of the Pressure Suppression Pool water below the Chernobyl reactor, hydrogen peroxide was formed. Hypothesis that the pool water was partially converted to H2O2 is confirmed by the identification of the white crystalline minerals studtite andmetastudtite in the Chernobyl lavas, the only minerals that contain peroxide.
The coriums consist of a highly heterogeneous silicate glass matrix with inclusions. Distinct phases are present:
uranium oxides with zirconium (UOx+Zr)
metal, present as solidified layers and as spherical inclusions of Fe-Ni-Cr alloy in the glass phase
Five types of material can be identified in Chernobyl corium:
Black ceramics, a glass-like coal-black material with surface pitted with many cavities and pores. Usually located near the places where corium formed. Its two versions contain about 4–5 wt.% and about 7–8 wt.% of uranium.
Brown ceramics, a glass-like brown material usually glossy but also dull. Usually located on a layer of a solidified molten metal. Contains many very small metal spheres. Contains 8–10 wt.% of uranium. Multicolored ceramics contain 6–7% of fuel.
Slag-like granulated corium, slag-like irregular gray-magenta to dark-brown glassy granules with crust. Formed by prolonged contact of brown ceramics with water, located in large heaps in both levels of the Pressure Suppression Pool.
Pumice, friable pumice-like gray-brown porous formations formed from molten brown corium foamed with steam when immersed in water. Located in Pressure Suppression Pool in large heaps near the sink openings, where they were carried by water flow as they were light enough to float.
Metal, molten and solidified.
Mostly located in the Steam Distribution Corridor. Also present as small spherical inclusions in all the oxide-based materials above. Does not contain fuel per se, but contains some metallic fission products, e.g. ruthenium-106.
The molten reactor core accumulated in the room 305/2, until it reached the edges of the steam relief valves; then it migrated downward to the Steam Distribution Corridor. It also broke or burned through into the room 304/3. The corium flowed from the reactor in three streams.
Stream 1 was composed of brown lava and molten steel; steel formed a layer on the floor of the Steam Distribution Corridor, on the Level +6, with brown corium on its top. From this area, brown corium flowed through the Steam Distribution Channels into the Pressure Suppression Pools on the Level +3 and Level 0, forming porous and slag-like formations there.
Stream 2 was composed of black lava, and entered the other side of the Steam Distribution Corridor. Stream 3, also composed of black lavas, flown to other areas under the reactor. The well-known “Elephant’s Foot” structure is composed of two metric tons of black lava, forming a multilayered structure similar to tree bark. It is said to be melted 2 meters deep into the concrete. As the material was dangerously radioactive and hard and strong, and using remote controlled systems was not possible due to high radiation interfering with electronics, shooting at it from an AK-47 was used to split off chunks for analysis.
The lava flow consists of more than one type of material—a brown lava and a porous ceramic material have been found. The uranium to zirconium for different parts of the solid differs a lot, in the brown lava a uranium rich phase with a U:Zr ratio of 19:3 to about 38:10 is found.
The uranium poor phase in the brown lava has a U:Zr ratio of about 1:10. It is possible from the examination of the Zr/U phases to know the thermal history of the mixture, it can be shown that before the explosion that in part of the core the temperature was higher than 2000 °C, while in some areas the temperature was over 2400–2600 °C.
The composition of some of the corium samples is as follows:
Degradation of the lava
The corium undergoes degradation. The Elephant’s Foot, hard and strong shortly after its formation, is now cracked enough that a glue-treated wad easily separated its top 1–2 centimeter layer. The structure’s shape itself is changed as the material slides down and settles. The corium temperature is now just slightly different from ambient, the material is therefore subject to both day-night temperature cycling and weathering by water.
The heterogeneous nature of corium and different thermal expansion coefficients of the components causes material deterioration with thermal cycling. Large amounts of residual stresses were introduced during solidification due to the uncontrolled cooling rate. The water, seeping into pores and microcracks and freezing there, the same process that creates potholes on roads, accelerates cracking.
Corium (and also highly irradiated uranium fuel) has an interesting property: spontaneous dust generation, or spontaneous self-sputtering of the surface. The alpha decay of isotopes inside the glassy structure causes Coulomb explosions, degrading the material and releasing submicron particles from its surface.
However the level of radioactivity is such that during one hundred years the self irradiation of the lava (2 × 1016 α decays per gram and 2 to5 × 105 Gy of β or γ) will fall short of the level of self irradiation which is required to greatly change the properties of glass (1018 α decays per gram and 108 to 109 Gy of β or γ). Also the rate of dissolution of the lava in water is very low (10−7 g·cm−2 day−1) suggesting that the lava is unlikely to dissolve in water.
It is unclear how long the ceramic form will retard the release of radioactivity. From 1997 to 2002 a series of papers were published which suggested that the self irradiation of the lava would convert all 1,200 tons into a submicrometre and mobile powder within a few weeks.But it has been reported that it is likely that the degradation of the lava is to be a slow and gradual process rather than a sudden rapid process.
The same paper states that the loss of uranium from the wrecked reactor is only 10 kg (22 lb) per year. This low rate of uranium leaching suggests that the lava is resisting its environment. The paper also states that when the shelter is improved, the leaching rate of the lava will decrease.
Some of the surfaces of the lava flows have started to show new uranium minerals such as UO3·2H2O (eliantinite), (UO2)O2·4H2O (studtite), uranyl carbonate (rutherfordine), and two unnamed compounds Na4(UO2)(CO3)3 and Na3U(CO3)2·2H2O. These are soluble in water, allowing mobilization and transport of uranium. They look like whitish yellow patches on the surface of the solidified corium. These secondary minerals show several hundred times lower concentration of plutonium and several times higher concentration of uranium than the lava itself.
It is possible to see in the photo shown below that the corium (molten core) will cool and change to a solid with time. It is thought that the solid is weathering with time.
The solid can be described as Fuel Containing Mass, it is a mixture of sand, zirconium and uranium dioxide which had been heated at a very high temperature until it has melted. The chemical nature of this FCM has been the subject of some research. The amount of fuel left in this form within the plant has been considered. A silicone polymer has been used to fix the contamination.
Unit 2 retained RCIC functions slightly longer and corium is not believed to have started to pool on the reactor floor until around 18:00 on March 14 
The reactor core isolation cooling system (RCIC) was successfully activated for Unit 3, however the Unit 3 RCIC subsequently failed and at about 08:00 on March 13 the nuclear fuel had melted into corium.”
The question of multiple melt throughs has been answered by the official testimony by NRC nuclear experts, in the video above. The only question left is to determine how much of Unit 1, 2 and 3 corium left containment, and where the melted coriums are now. The official TEPCO position is that none of the coriums left containment, from any of the reactors. Other experts believe that ALL of these 3 coriums left the buildings and are burrowing underground.
The TEPCO “analysis” about what happened does NOT mention the fact that the reactor vessels are NOT holding water and have not done so since March 2011. They also do NOT mention that the containment vessels are not holding water or pressure either.
How can three steel reactor vessel/containment tanks each hold 60-90 tons or more liquid molten corium that is at a temperature of 3,000 degrees F. for more than 18 months without a “melt-through”?
The only question left is to figure out what happened to the corium after it left Fukushima containment. For that, we can possibly learn something from Chernobyl, and it’s melt through plus explosion. The above video shows how Chernobyl corium went down through several floors into the basement of the plant. The corium MAINLY used pipes and openings to move downwards, rather than melting through several meters of concrete.
The difference between Fukushima coriums and Chernobyl corium is that the 1 Chernobyl corium was mixed with a huge amount of sand that surrounded the reactor. The Chernobyl corium was also mixed with graphite that was moderating (slowing down) the reaction inside the reactor. Graphite slows the nuclear reaction down. Both the sand and graphite combined with melted fuel as it headed downwards, diluting it, and slowing it down.
The Soviets tried valiently to put out the melted corium fire by dumping sand, lead and boron on top of what was left of the blown up reactor vessel, in order to put out the out of control nuclear corium fire. The goal that the Soviets had was to keep the melted corium from reaching groundwater. Worst case, corium reaching groundwater could have caused an even worse explosion with more radiation than the initial meltdown and explosion.
The reason why the Soviets forced 1 million people into the effort to clean up, decontaminate and prevent the corium from reaching groundwater, is that it was feared that if the corium did reach groundwater and exploded, that the whole continent would become uninhabitable, rather than just hundreds or thousands of square miles from the initial explosion and nuclear fire.
The Chernobyl disaster involved approximately 50-180 tons of nuclear fuel that went up into the air either with the nuclear fire or with the initial explosion. By comparison, Fukushima involves up to 1,240 tons of highly radioactive fuel and even more spent fuel in spent fuel pools.
How much radioactive material is at the Fukushima plant?
Chernobyl – 180 tons of fuel exploded into the atmosphere
There was an ‘estimated’ 50 tons of reactor fuel and 800 tons of graphite
left in the reactor at Chernobyl after the meltdown and subsequent nuclear explosion there. The reactor contents melted down and combined with tons of sand, lead and boron dumped on top of the melted corium, with all of the above mixed in with it.
It is not known how much fuel was ejected in the multiple fires and/or explosions at Fukushima. The reactors at Fukushima contain much more fuel in their cores and spent fuel pools by far, compared to Chernobyl. Anyone stating that the Fukushima disaster is only a small percentage of Chernobyl is either ignoring basic facts, is totally ignorant about what happens after a meltdown, or is trying to keep the nuclear industry alive by covering up the worst nuclear disaster in history. So how did this disaster happen?
Inside of nuclear reactors, fuel rods are made up of long, hollow zirconium metal tubes, filled with stacked pellets of uranium oxide fuel that look like miniature hockey pucks. The zirconium tubes are the first thing to go when cooling water is lost. They melt at around 2,000 degrees Fahrenheit (1,200 degrees Celsius). Once the zirconium tubes melt or degrade and split open from heat, the uranium/plutonium pellets inside of that tube fall out and gather together at the bottom of the reactor or spent fuel pool.
The uranium/plutonium pellets that drop to the bottom have a melting temperature of around 5,000 degrees F (2,800 degrees C). Once the fuel pellets gather together, they heat up and melt down spontaneously, and this creates a molten lava-like mass known as “corium.” This corium lava mass then ‘melts’ it’s way down through concrete, or follows paths of least resistance, such as through tubes, pipes and instrumentation channels, much like what happened at Chernobyl. Fukushima had control rod and instrumentation holes at the bottom of the reactor, making an easy path for the molten radioactive lava to exit the reactor vessel.
Now the radioactive lava hits the concrete below the reactor vessel.
According to Wikipedia; “concrete can be damaged by many processes, such as the expansion of corrosion products of the steel reinforcement bars, freezing of trapped water, fire or radiant heat, aggregate expansion, sea water effects, bacterial corrosion, leaching, erosion by fast-flowing water, physical damage and chemical damage (from carbonatation, chlorides, sulfates and distillate water). http://en.wikipedia.org/wiki/Concrete#Fire
(Fukushima used seawater after the plant lost power to try and cool the reactors and spent fuel pools down.)
Concrete exposed to seawater is susceptible to its corrosive effects. In the submerged zone, magnesium and hydrogen carbonate ions precipitate a layer of brucite, about 30 micrometers thick, on which a slower deposition of calcium carbonate as aragonite occurs. These layers somewhat protect the concrete from other processes, which include attack by magnesium, chloride and sulfate ions and carbonation.
Sea water corrosion contains elements of both chloride and sulfate corrosion. Up to about 300 °C, the concrete undergoes normal thermal expansion. Above that temperature, shrinkage occurs due to water loss; however, the aggregate continues expanding, which causes internal stresses.
Up to about 500 °C, the major structural changes are carbonation and coarsening of pores. At 573 °C, quartz
undergoes rapid expansion due to phase transition
, and at 900 °C calcite
starts shrinking due to decomposition. At 450-550 °C the cement hydrate decomposes, yielding calcium oxide. Calcium carbonate
decomposes at about 600 °C. Rehydration of the calcium oxide on cooling of the structure causes expansion, which can cause damage to material which withstood fire without falling apart. Concrete in buildings that experienced a fire and were left standing for several years shows extensive degree of carbonation from carbon dioxide which is reabsorbed.
The parts of a concrete structure that is exposed to temperatures above approximately 300 °C (dependent of water/cement ratio) will most likely get a pink color. Over approximately 1000 °C it turns yellow-brown.
One rule of thumb is to consider all pink colored concrete as damaged that should be removed. (Corium destroys concrete and keeps eating through it, as long as the temperature of the corium is above 1,000 degrees F., at a rate of approximately 5 cm. per hour.)
Fire will expose the concrete to gases and liquids that can be harmful to the concrete, among other salts and acids that occur when gases produced by a fire come into contact with water.
If concrete is exposed to very high temperatures very rapidly, explosive spalling of the concrete can result. In a very hot, very quick fire the water inside the concrete will boil before it evaporates. The steam inside the concrete exerts expansive pressure and can initiate and forcibly expel a spall.
and optical centers
are easily formed, but very high fluxes are necessary to displace a sufficiently high number of atoms in the crystal lattice of minerals present in concrete before significant mechanical damages are observed.”
“Thermal decomposition of concrete produces water vapor and carbon dioxide
, which may further react with the metals in the melt, oxidizing the metals, and reducing the gases to hydrogen and carbon monoxide
. The decomposition of the concrete and volatilization of its alkali components is an endothermic process. Aerosols released during this phase are primarily based on concrete-originating silicon compounds; otherwise volatile elements, for example, caesium, can be bound in nonvolatile insoluble silicates
Several reactions occur between the concrete
and the corium melt. Free and chemically-bound water is released from the concrete as steam. Calcium carbonate
is decomposed, producing carbon dioxide and calcium oxide
. Water and carbon dioxide penetrate the corium mass, exothermically oxidizing the non-oxidized metals present in the corium and producing gaseous hydrogen and carbon monoxide; large amounts of hydrogen can be produced. The calcium oxide, silica
, and silicates
melt and are mixed into the corium. The oxide phase, in which the nonvolatile fission products are concentrated, can stabilize at temperatures of 1300–1500 °C for a considerable period of time.
An eventually-present layer of more dense molten metal, containing fewer radioisotopes (Ru
, etc., initially composed of molten zircaloy, iron, chromium, nickel, manganese, silver, and other construction materials and metallic fission products and tellurium bound as zirconium telluride) than the oxide layer (which concentrates Sr
, etc. and is initially composed primarily of zirconium dioxide and uranium dioxide, possibly with iron oxide and boron oxides), can form an interface between the oxides and the concrete farther below, slowing down the corium penetration and solidifying within a few hours.
The oxide layer produces heat primarily by decay heat, while the principal heat source in the metal layer is exothermic reaction with the water released from the concrete. Decomposition of concrete and volatilization of the alkali metal compounds consumes a substantial amount of heat.
The fast erosion phase of the concrete basemat lasts for about an hour and progresses into about one meter depth, then slows to several centimeters per hour, and stops completely when the melt cools below the decomposition temperature of concrete (about 1100 °C). Complete melt-through can occur in several days even through several meters of concrete; the corium then penetrates several meters into the underlying soil, spreads around, cools and solidifies.
During the interaction between corium and concrete, very high temperatures can be achieved. Less volatile aerosols of Ba
, and other fission products are formed during this phase and introduced into the containment building at time when most of early aerosols are already deposited. Tellurium is released with the progress of zirconium telluride decomposition. Bubbles of gas flowing through the melt promote aerosol formation.
The thermal hydraulics
of corium-concrete interactions (CCI, or also MCCI, “molten core-concrete interactions”) is sufficiently understood.
However the dynamics of the movement of corium in and outside of the reactor vessel is highly complex, and the number of possible scenarios is wide; slow drip of melt into an underlying water pool can result in complete quenching, while a fast contact of large mass of corium with water may result in a destructive steam explosion. Corium may be completely retained by the reactor vessel, or the reactor floor or some of the instrument penetration holes can be melted through.
The thermal load of corium on the floor below the reactor vessel can be assessed by a grid of fiber optic sensors
embedded in the concrete. Pure silica
fibers are needed as they are more resistant to high radiation levels.
Some reactor building designs, for example, the EPR
, incorporate dedicated corium spread areas (Core Catchers
), where the melt can deposit without coming in contact with water and without excessive reaction with concrete.
Only later, when a crust is formed on the melt, limited amounts of water can be introduced to cool the mass.
Materials based on titanium dioxide
and neodymium(III) oxide
seem to be more resistant to corium than concrete.
Deposition of corium on the containment vessel inner surface, e.g. by high-pressure ejection from the reactor pressure vessel, can cause containment failure by direct containment heating (DCH).”
At Fukushima, some authorities and nuclear experts admit that multiple out of control, 60-90 ton blobs of 3,000 -5,000 degree F highly radioactive coriums were produced as the fuel rods melted down in reactors 1, 2, and 3 as well as in their spent fuel pools. Coriums left the reactor vessels in reactors 1, 2 and 3, dropping down onto the concrete pad beneath the reactor core. This much has been agreed to by the NRC, as outlined in their testimony video in this article.
What happened after the meltdown occured in all three Fukushima reactors and multiple spent fuel pools is subject to debate. The answers will not be known for sure until a rigorous analysis is done by independent experts, which are VERY hard to find. TEPCO and other nuclear industry ‘experts’ almost always seem to draw conclusions that minimize, deny or completely cover up what actually happened.
What is fact, is that extreme high heat, (such as from corium) combines with salt water and this creates conditions for both spalling and melting concrete. According to Wikipedia, it would only take several days for the corium to exit the reactor buildings, either horizontally or downwards through the concrete base. So let’s examine specifically how and where the coriums could have left the Fukushima reactor buildings, and then examine some actual evidence of this happening.
“Below is a rough drawing to show the concrete thicknesses, potential corium flow paths and structures at Fukushima. The illustrated volume of corium in the drawing is not intended to be a visual estimate of volume, but is to aid seeing the potential areas corium could flow. One structure of note is the small sand pit below the torus pipe where it meets the containment bulb.
This sand pit creates a small dip in the floor of containment at the edge where the pipe connects and shows a thin spot in containment to the pipe. There is an estimated 10.3 meters of concrete directly below the reactor. The reactor itself is housed in a tube of concrete, the control rod mechanisms are inside so many penetration holes are likely. The concrete at the bottom of the suppression chamber is about 2.7 meters and the side wall of the suppression chamber is about 1.5 meters thick. The sump hole in the bottom of the suppression chamber leaves even less concrete below it.”
The Japanese government, nuclear regulators, and TEPCO supposedly have no idea where the coriums are in any (or outside of) any of the reactors. Almost two years after the accident happened, they are still trying to figure out how to even find the ‘missing’ coriums. So far, all pro nuclear apologists and industry regulators are VERY sure that NONE of the coriums have left containment.
In all of their press releases, they keep harping on that ‘fact’, and they keep on claiming that Fukushima is only 10% of Chernobyl in severity, despite having no evidence to support this premise, other than computer models and theories. There is however, evidence to support that all coriums have left the buildings. Pro nuclear apologists also deny that any explosions at Fukushima actually caused nuclear fuel to exit either spent fuel pools or reactor vessels, despite plenty of evidence that this indeed happened.
Fukushima 5 Minute Summary Of Events 2011 to 2012; via A Green Roadhttp://agreenroad.blogspot.com/2012/06/fukushima-5-minute-summary-of-events.html
Total Fukushima Radiation Released Into Ocean, Air, Groundwater, Storage Tanks; via A Green Roadhttp://agreenroad.blogspot.com/2012/02/total-fukushima-radiation-released-into.html
Fukushima Spewing Equivalent of 112 Hiroshima Nuclear Bombs Worth of Radiation Every Hour; via A Green Road
Dr. Paolo Scampa Reports That Fukushima Released 3,000 Billion Lethal Doses Of Radiation; via A Green Road
Comparing Contaminated Zones Around Chernobyl And Fukushima Ocean Radiation Released; via A Green Road
What really happened at Fukushima? via A Green Road
The official position of TEPCO is that the three 60-90 ton 3,000 degree F coriums never melted more than cavity the size of a cylinder 2.75m in diameter by 1.85m thick below any of the reactor vessels. TEPCO contends that all three coriums stopped before exiting the reactor vessels, in all three reactors and that no fuel left any of the spent fuel pools, through any explosion.
Their best attempts to find out where the coriums went to, is to drill a hole in #2, and look around. Despite zero pressure and no water inside, plus high radiation levels, they concluded nothing unusual was happening and that all of the reactor fuel was still sitting inside. One year after the accident, and the nuclear experts are still almost completely stumped about the basic facts around what happened, how much radiation was released, the extent of damage to reactors, spent fuel pools, etc.
An easy way to find out if the coriums left the reactors and/or buildings is to figure out if the reactor vessels still hold pressure. No holes in the reactor vessels means water levels would be high and pressures would hold. According to TEPCO provided measurements, none of the three reactors are holding pressure and water levels are low. All by itself, this lack of pressure and ability to hold water indicates holes and corium exiting the buildings. But to admit that would be to admit failure, and they cannot do that. The nuclear apologists version of reality is that Fukushima is in cold shutdown, and that they are ‘decommissioning’ the whole complex, but is it really in cold shutdown?
How can one ‘decommission’ multiple out of control nuclear fires going down into ground? How can anyone decommission melted down reactors as well as multiple spent fuel pools that melted down and then caught fire and/or exploded?
Is Fukushima really in cold shutdown? via A Green Road http://agreenroad.blogspot.com/2012/03/fukushima-is-it-really-in-cold-shutdown.html
Ex Fukushima Engineer Confesses; No Cold Shutdown, Warned of Tsunami 20 Yrs Ago; via A Green Road http://agreenroad.blogspot.com/2012/04/ex-fukushima-engineer-confesses-no-cold.html
If TEPCO and the nuclear industry as a whole were to decide to face reality and admit to the true horror of what happened, the next step would be to figure out where the coriums went. One way to do this would be to dig slant wells into the ground below all three reactor units at Fukushima. Until this is done, the coverup and denial of the worst nuclear accident in history will continue. The radiation emissions from these spent fuel pools, open reactors and multiple out of control nuclear fires showering the whole planet with radiation will also continue, without any end.
Click on the following link to watch a video of a corium fire…
Radioactive Smoke/Steam Coming Out Of Ground At Fukushima 2.28.2012; via A Green Roadhttp://agreenroad.blogspot.com/2012/02/tokyo-alert-severe-radioactive-smoke.html
Neither TEPCO nor the Japanese government will admit that they were using MOX fuel and that this fuel blew up on them, spreading plutonium in nano sized particles all around the world.
However, in 2005, Kyushu Electric Power Co proposed and received permission by residents for adding plutonium ‘Kyushu Electric Power Co. obtains consent from local residents to utilize plutonium in LWR’.
Again, TEPCO and the nuclear apologists will avoid mentioning the term ‘plutonium’ in reference to Fukushima, because that means something extremely horrible happened, thousands or millions of times worse than a uranium fuel meltdown and explosion. Just how bad is this Fukushima plutonium fuel and the subsequent disastrous release of hundreds of pounds of plutonium into the upper atmosphere?
How Dangerous Is 400-600 Pounds Of Plutonium Nano Particle Dust Liberated By Fukushima? Via A Green Road
Hot Particles (Fuel Fleas) From Fukushima Continue To Circulate Globally; via A Green Road
Fukushima Nano Bucky Balls Weaponized With Uranium, Plutonium, And Cesium; via A Green Road
There are many questions that come out of the above analysis. One question left is; how far did the multiple coriums go down into the soil beneath the Fukushima plant? Another question is; what effect on global human and animal health will this nano sized plutonium, cesium, and strontium have?
According to Wikipedia, experts theorize that the coriums can only go down a few feet, at most 25′ to 75′ deep. Other experts believe that the coriums are traveling deep into the ground, eating through soft sandstone at a rapid rate until they reach the liquid core of the earth, and this is called the ‘China Syndrome’. No matter how shallow or deep these coriums went, having 200 tons of out of control radioactive lava fire in the form of multiple coriums below ground means that humanity is facing a huge crisis, which is just beginning….
The ongoing Fukushima nuclear crisis is just beginning. The proof of this crisis is that radiation levels all around the globe are slowly rising, which would indicate a constant source of a large amount of unprotected, unfiltered radiation coming from somewhere. More proof is in the fact that TEPCO has stopped measuring groundwater and ocean radiation levels. The movement of contaminated groundwater into the ocean, although they do have ‘plans’ on building an underground barrier of some kind.
Fukushima; Pacific Ocean Catastrophe Confirmed; via A Green Road http://agreenroad.blogspot.com/2012/04/fukushima-pacific-ocean-catastrophe.html
Fukushima Leaking Radioactive Water Into Ocean Plume; via A Green Road http://agreenroad.blogspot.com/2012/04/fukushima-leaking-radioactive-water.html
Fukushima Daichi is subject to almost daily earthquakes, which are further destabilizing and causing problems at the destroyed Fukushima nuclear plant. Yet, the TEPCO ‘authorities’ ignore this and are proceeding at a leisurely pace, when a disaster is awaiting both Japan and the whole world, if they do not take care of the threat of Fukushima Reactor Spent Fuel Pool #4 collapsing and spilling all of it’s highly radioactive contents on the ground.
Fukushima Reactor 4; Global Life Extinction Event If It Collapses; via A Green Road
To prove that Fukushima is located on earthquake and subsidence risk type of soil, we can look at a basic geology lesson; “the Fukushima Daiichi Power Station is located on the east coast of Honshu island, in northeastern Japan, on a Cenozoic sedimentary ground, i.e. belonging to the current geological era (from 65.5 million years ago to the present). It is separated from the Abukuma granite plateau by the Futuba fault.”
The 1,300 meters under Fukushima Daichi consist of the following layers of mudstone and sandstone:
– T3: muddy and sandy rock (Tomioka layer, Neogene)
– T2: sandstone with some inclusion of tuff (Tomioka layer, Neogene)
– T1: sandstone with heavy inclusion of tuff (Tomioka layer, Neogene)
– TI: clayey sandstone (Taga layer, Paleogene – Neogene)
– Yu: alternating muddy and sandy rocks (Yunagawa layer, Early Miocene)
– Sr: hard sandstone and muddy rocks (Shiramizu layer, intermediate between the Oligocene and Miocene)
Further on in this material, it states that “in several of these cross-sections, an ancient fault, predating the later Miocene, is clearly visible under the nuclear site. Whereas the geological survey conducted prior to the construction of the plant does not reveal this fault (drilling did not go down more than 200 meters), it is clear from the documents dated 2009 and 2010 that Tepco and the NSC have known about it for several years….
The good news is that the radioactive water leaking from the plant will not be able to spread towards the Japanese inland and the Abukuma plateau due to the downward slope of the geological layers. The bad news is that there exists a fault which appears to be active right under the Fukushima Daiichi plant itself: this allows, and will continue to allow, radioactive pollution of aquifers over a depth of several hundreds of meters, as it runs through the different “waterproof” strata. This also means that the radionuclides will naturally be carried towards the sea by this underground water stream flowing through the permeable layers of sandstone…..Sandstone is indeed the ideal rock for aquifers, as it is both permeable and fractured, providing easy movement of water. And finally, there is the problem of the type of rock on which the plant was built being rather “soft”, meaning that an earthquake can only destabilize the buildings.As early as March 31, 2011, Tepco announced that the groundwater was contaminated with radioactive iodine, according to an analysis of a sample taken at a depth of 15 meters under the first reactor (link). Today, if one or more coriums have sunk into the ground, this pollution has very likely been increasing.
But Tepco no longer shares any information about the pollution of groundwater. Their only concern is to present a beautiful reassuring façade, which will never solve this disastrous pollution of soil and groundwater: underground contamination is irreparable, because there is no access to it.“
Another unknown factor in all of this is to find out how long these coriums will keep on fissioning and sputtering radiation from underground into both fresh drinking water, the ocean and the air, which then goes around the world.
Less than 800 milligrams of uranium created the ‘Fat Man Bomb’ dropped on Hiroshima, which wiped out an entire city. What will hundreds of hundreds of TONS of nano sized uranium and plutonium particles do, released into the upper atmosphere?
Fukushima Spewing Equivalent of 112 Hiroshima Nuclear Bombs Worth of Radiation Every Hour; via A Green Road
Having 200 TONS of mixed uranium, plutonium and other deadly dangerous heavy metals and other items mixed together into 3 out of control underground fires does not bode well for humanity. These corium blobs may continue to fission and have transient criticalities, for hundreds of years, or much longer. Since this has never happened before, no one really knows what will happen.
Certainly, it is easy to predict that NOTHING GOOD will happen if these blobs are allowed to keep radiating the whole world for hundreds of years. Meanwhile, TEPCO is hiring ‘experts’ to try and find their ‘non-missing coriums’ with cosmic ray radiography.
“We now have a concept by which the Japanese can gather crucial data about what is going on inside their damaged reactor cores,” Konstantin Borozdin of Los Alamos’ Subatomic Physics Group said.
What we do know is that; “used nuclear fuel is a redox-sensitive semiconductor consisting of uranium dioxide containing a few percent of fission products and up to about one percent transuranium elements, mainly plutonium. The rapid increase in temperature in the cores of the Fukushima reactors was caused by the loss of coolant in the aftermath of the damage from the tsunami. Temperatures probably well above 2000 °C caused melting of not only the UO2 in the fuel but also the zircaloy cladding and steel, forming a quenched melt, termed corium. Substantial amounts of volatile fission products, such as Cesiums and Iodines, were released during melting, but the less volatile fission products and the actinides (probably 99.9%) were incorporated into the corium as it cooled.
Bottom line; this is the worst nuclear disaster ever, and is multiple times worse than Chernobyl. This unimaginable nuclear disaster is JUST BEGINNING. The worst of this disaster is yet to be experienced by humankind, due to the plutonium released, and due to the ongoing releases of radiation and other poisons from the Pandoras Box consisting of multiple coriums that left the reactor vessels, that are now down in the soil.
The financial cost has yet to be experienced, as that part of this experience is just now starting to hit home both in Japan and around the world. This disaster will cost TRILLIONS, in Japan alone, but that figure is only the tip of the iceberg in terms of global financial impact. The amount of money that this disaster is going to cost all humanity boggles the mind when one considers the global impact.
Fukushima Crisis Total Cost Up To $10 TRILLION Dollars; via A Green Road http://agreenroad.blogspot.com/2012/06/fukushima-crisis-total-cost-up-to-10.html
Despite the sunshine and roses mass media outlet reports, who are in turn owned global corporations (such as GE) who are all friendly to each other, deadly radiation is STILL going into groundwater, up into the air and into the ocean and will continue doing so for hundreds of years or longer, unless something more is done.
Total Fukushima Radiation Released Into Ocean, Air, Groundwater, Storage Tanks; via A Green Road http://agreenroad.blogspot.com/2012/02/total-fukushima-radiation-released-into.html
On 3/11; 15-28 Nuclear Reactors/SFP’s In Japan Were Damaged, Not 3 or 4 ; via A Green Road http://agreenroad.blogspot.com/2012/03/14-nuclear-reactors-at-4-japan-sites.html
TEPCO Loses ALL Insurance Coverage; Japanese Nuclear Plants; Via A Green Roadhttp://agreenroad.blogspot.com/2012/03/tepco-loses-insurance-coverage-for-all.html
Fukushima; Today’s Titantic and Costa Concordia; via A Green Road http://agreenroad.blogspot.com/2012/04/fukushima-todays-titantic-and-costa.html
Multiple Nuclear Reactors Bombed; All Nuclear Reactors ARE Bombs; via A Green Roadhttp://agreenroad.blogspot.com/2012/04/multiple-nuclear-reactors-bombed-all.html
Here are some very recent radiation measurements from Hawaii, as of January 2013, showing radiation ‘spikes’ or surges going over 200 CPM. Anything over 100 CPM is dangerous, and means it is time to leave that area. Hawaii is directly downwind of Fukushima.
According to Dr. Helen Caldicott MD, a nuclear expert; The Fukushima corium story hasn’t finished and will never finish — I think it means the end of Japan financially. (VIDEO)