Corium (reactor technology)

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As corium - an artificial word form from English core , for "(reactor) core", and for chemical elements characteristic word ending -ium - the molten material is referred to, which in a nuclear reactor at a core melt is formed. It is a lava-like mixture of nuclear fuel , control rods and the materials of the affected parts of the reactor, their chemical reaction products with air and water, and, if the reactor vessel is breached, molten concrete from the floor of the reactor hall.

Corium formed in the reactor accident at the Three Mile Island nuclear power plant , the Chernobyl disaster and the Fukushima nuclear disaster .

Some reactor types have a core catcher to catch the corium.

Composition and origin

The heat that leads to the melting of the reactor can come from the nuclear chain reaction , but the main heat source is usually the decay heat of the fission products in the fuel rods. The heat generated by decay first falls off quickly and then more and more slowly, since the short-lived isotopes have the largest share of the activity. Another heat source is the chemical reaction of hot metals with atmospheric oxygen or water vapor.

The chain reaction and the associated increased heat production can continue in parts of the corium if a critical mass is reached locally . This can be determined by the fact that long after the core meltdown, short-lived fission products are still present in too large quantities to be able to originate from the controlled chain reaction before the core meltdown. Since the chain reaction generates large amounts of heat and fresh radioactive fission products, this process is very critical with regard to the potential danger.

The temperature of the corium depends firstly on the dynamics of its internal heat generation - the amount of isotopes that generate decay heat and their dilution by other molten materials - and secondly on its heat losses - the physical arrangement and heat dissipation to the environment. A compact mass will lose less heat than a thinly spread layer. Corium at a sufficiently high temperature can melt concrete. A solidified corium mass can melt again on its own if its heat losses decrease, for example because it is covered with heat-insulating debris or if the water that cooled it has evaporated.

Crusts that have a heat-insulating effect can form on the corium mass. The heat distribution in the corium mass is influenced by the different thermal conductivity of molten oxides and metals. Convection in the liquid phase increases the heat transport significantly.

The melted reactor core releases volatile compounds. These can remain gaseous, such as molecular iodine or noble gases , or condense into aerosol particles when they leave the high temperature region. A high proportion of the aerosol particles come from the material of the control rods. The gaseous compounds can be adsorbed by the surface of the aerosol particles.

Composition and reactions of the corium

The composition of the corium depends on the type of reactor, especially the materials used for the control rods and as a coolant. There are differences between the corium formed in pressurized water reactors and boiling water reactors .

On contact with water, the boron carbide from the control rods of the boiling water reactor first forms boron oxide and methane, then boric acid . Boron can also be added to these reactions from the boric acid in an emergency refrigerant.

Zirconium from zircaloy , along with several other metals, reacts with water and generates zirconium (IV) oxide and hydrogen . The production of hydrogen is a major source of danger in reactor accidents.

The relationship between oxidizing and reducing atmospheres and the relationship between water and hydrogen influence the formation of chemical compounds. Differences in the volatility of the reactor core materials affect the rate of elements released. For example, the silver-indium-cadmium alloy of the control rods releases almost only cadmium in an inert atmosphere. In the presence of water, on the other hand, the indium forms volatile indium (I) oxide and indium (I) hydroxide , which evaporates and forms an aerosol of indium (III) oxide . In a hydrogen-rich atmosphere, the oxidation of the indium is prevented, which means that less indium is released.

Cesium and iodine from the decomposition products react to form volatile cesium iodide , which condenses as an aerosol.

During a core melt, the temperature of the fuel rods rises and the rods begin to deform, in the case of the zircalloy above 700-900 ° C. When the pressure in the reactor is low, the pressure inside the fuel rods ruptures their fuel rod cladding . If the pressure in the reactor is high, it presses the fuel rod cladding onto the fuel pellets and thereby causes the formation of uranium dioxide - zirconium - eutectic , which has a melting temperature of 1200 to 1400 ° C. An exothermic reaction takes place between steam and zirconium , which can generate so much heat that it is self-sustaining even without the contribution of the heat of decay. Hydrogen is released (at normal temperature and normal pressure) in a ratio of about 0.5 m³ per kg of zircalloy. Hydrogen embrittlement can occur in the reactor materials . Volatile fission products are released from the damaged fuel rods. Between 1300 and 1500 ° C the silver-cadmium-indium alloy of the control rods melts together with their coating and volatile metals evaporate. At 1800 ° C, the cladding oxides begin to melt and flow. At 2700–2800 ° C, the uranium oxide itself melts and the geometry of the reactor core collapses. This can occur at lower temperatures when a eutectic uranium oxide-zirconium compound is formed. Now the corium is as good as free of volatile components that are not chemically bound, which reduces heat production by around 25%, since the volatile isotopes are now elsewhere.

The temperature of Corium can be 2400 ° C in the first few hours after the core meltdown and exceed 2800 ° C. A large amount of heat can arise from the reaction of the metals in the corium (especially zirconium) with water. If the corium mass is flooded with water or if molten corium mass falls into a water container, this can lead to a further rise in temperature and the production of large quantities of hydrogen, which in turn increases the pressure in the reactor container. The steam explosion caused by such sudden contact between corium and water can cause the materials to explode, creating projectiles which, upon impact, damage the container. Further pressure fluctuations can result from the combustion of the released hydrogen. The risk of detonation can be reduced by using catalytic recombiners .

Breaking through the reactor pressure vessel

Without sufficient cooling, the inside of the reactor overheats, it deforms as a result of the thermal expansion of the components, and it collapses as soon as the temperature reaches the melting point of the materials. The melt now collects at the bottom of the reactor pressure vessel . If it is cooled sufficiently, it can freeze and the spread of the damage remains limited to the reactor. However, the corium can also melt through the reactor pressure vessel and flow out, or it can be expelled as a molten stream by the pressure inside the reactor. The failure of the reactor can be caused by the overheating of its bottom by the corium melt, which leads first to creep rupture and then to rupture of the container. A high level of cooling water above the corium layer can enable a thermal equilibrium to be established below the creep temperature of the metal without the reactor pressure vessel breaking.

If the container is cooled sufficiently, a crust can form between the melt and the reactor wall. The layer of molten steel on top of the oxide creates a zone of increased heat conduction to the reactor wall. This condition, known as the “heat knife”, increases the likelihood that local softening will take place on the side wall of the reactor pressure vessel and that corium will then escape.

If the pressure in the reactor pressure vessel is high, the corium mass can be pushed out when the vessel bottom is broken through. In the first phase only the melt itself is expelled. A hollow is then formed in the center of the opening and gas is expelled along with the melt, causing the pressure in the reactor to decrease rapidly. The high temperature of the melt also causes rapid erosion and enlargement of the opening. If there is a hole in the bottom of the container, almost any corium can be expelled. A hole in the side wall of the container can result in only part of the corium escaping and part of it remaining inside the reactor. Melting through the reactor vessel can take anywhere from a few minutes to several hours.

After the reactor pressure vessel has been breached, the conditions in the reactor space below the core determine what gases are generated. When water is present, steam and hydrogen are generated. Dry concrete creates carbon dioxide and small amounts of steam.

Interactions between Corium and Concrete

The thermal decomposition of concrete results in u. a. Water vapor and carbon dioxide . These can further react with the metals in the melt by oxidizing them and reducing them to hydrogen and carbon monoxide . The decomposition of concrete and the volatilization of its alkaline components are endothermic processes, i.e. they absorb heat. The aerosols released during this phase are mainly based on silicon compounds that come from the concrete. Other volatile elements such as B. Cesium can be bound in non-volatile insoluble silicates .

Several reactions can take place between the concrete and the corium melt. Free and chemically bound water is released from the concrete as steam. Calcium carbonate decomposes, producing carbon dioxide and calcium oxide . Water and carbon dioxide penetrate the corium mass, oxidizing exothermically the non- oxidized metals contained therein and generating hydrogen gas and carbon monoxide. Large amounts of hydrogen can be produced. Calcium oxide, silicon dioxide and silicates melt and are mixed with the corium.

The oxide phase, in which the non-volatile fission products are concentrated, can remain stable for a considerable time at temperatures from 1300 to 1500 ° C. A possibly existing layer of denser molten metal, which contains fewer radioisotopes - Ru , Tc , Pd  ..., initially of molten zirconium alloy, iron, chromium, nickel, manganese, silver and other construction materials and metallic fission products, and tellurium , which is bound as zirconium telluride is - as the oxide layer - in which Sr , Ba , La , Sb , Sn , Nb , Mo and other substances are concentrated, and which initially consists mainly of zirconium dioxide and uranium dioxide, possibly with iron oxide and boron oxides - can between the oxides and form a separating layer on the underlying concrete, which slows down the penetration of the corium and solidifies over the course of a few hours. While the heat in the oxide layer is mainly generated by decay heat, in the metal layer it is mainly generated by the exothermic reaction with the water that comes out of the concrete. The decomposition of the concrete and the volatilization of the alkali metal compounds consume significant amounts of heat.

The erosion of the concrete base plate proceeds rapidly for about an hour and continues to a depth of about one meter. Then it slows down to a few centimeters per hour and comes to a complete standstill as soon as the melt cools below the decomposition temperature of the concrete (around 1100 ° C). Complete melting can take place within a few days even through several meters of concrete. The corium then penetrates several meters into the ground below, cools down and solidifies. While corium and concrete interact with one another, very high temperatures can be reached. Less volatile aerosols of Ba, Ce , La, Sr and other fission products are formed during this phase and into the containment introduced, while most of the aerosols previously incurred have already put down. As the zirconium telluride decomposes, tellurium is released. Gas bubbles moving through the melt increase aerosol formation.

The thermal hydraulics of the Corium-concrete interactions (CCI or MCCI, molten core-concrete interactions ) is well understood. However, the dynamics of the movement of the corium inside and outside the reactor vessel is highly complex and the possible scenarios are numerous. Slow dripping of the melt into an underlying water bath can lead to complete cooling, while rapid contact of a large mass of corium with water can lead to a destructive steam explosion. The reactor vessel can hold back the corium completely, but the bottom of the reactor or some of the instrument bores located in it can also be melted through.

The thermal load that the corium represents for the floor under the reactor vessel can be monitored by a grid of fiber optic sensors embedded in the concrete . Pure quartz glass fibers are required for this because they can withstand higher levels of radiation.

In some constructions of reactor buildings, e.g. B. EPR , core catchers are provided, separate areas for the expansion of the corium, where the melt can settle without coming into contact with water and without reacting to a large extent with concrete. Only when a crust has formed on the melt can limited amounts of water be added to cool the mass.

Materials based on titanium (IV) oxide and neodymium (III) oxide seem to be more resistant to corium than concrete.

The deposition of corium on the inner surface of the containment , e.g. B. by escaping from the reactor pressure vessel under high pressure, can lead to failure of the containment by heating ( direct containment heating , DCH).

Individual incidents

The Three Mile Island accident

The core meltdown at the Three Mile Island nuclear power plant resulted in a slow partial meltdown of the reactor core. About 19,000 kg of material melted and shifted within two minutes, about 224 minutes after the emergency shutdown . A puddle of corium formed at the bottom of the reactor vessel, but it was not breached. The layer of solidified corium was between 5 and 45 cm thick.

Samples were taken from the reactor. Two corium masses were found, one inside the fuel rod assembly and one in the bottom vault of the reactor vessel. The samples were mainly dull gray, with yellow in some places.

The mass turned out to be homogeneous and consisted mainly of molten nuclear fuel and fuel element casings. The elements contained in mass fractions were about 70% uranium , 13.75% zirconium and 13% oxygen . The remainder consisted of stainless steel and inconel built into the melt. The loose debris showed a slightly lower uranium content (about 65% by mass) and a higher content of metallic construction materials. The heat of decay of the corium 224 minutes after the emergency shutdown was estimated to be 0.13 W / g and 600 minutes after the emergency shutdown it fell to 0.096 W / g. Noble gases, cesium and iodine were not present. This indicates that they had evaporated from the hot material. The samples were fully oxidized, indicating that there was enough steam to oxidize all of the available zirconium.

Some samples contained a small amount (less than 0.5%) of metallic melt consisting of silver and indium (from the control rods ). A secondary phase of chromium (III) oxide was found in one of the samples. Some metallic inclusions contained silver but no indium, suggesting temperatures high enough to volatilize both cadmium and indium. Almost all metallic components, with the exception of the silver, were completely oxidized, but the silver was also oxidized in some places. The inclusions, rich in iron and chromium, are believed to have originated from a molten nozzle that did not have enough time to disperse in the melt.

The density of the samples varied between 7.45 and 9.4 g / cm³ (the density values ​​of the UO 2 and ZrO 2 are 10.4 and 5.6 g / cm³). The porosity of the samples varied between 5.7 and 32%, the average was 18 ± 11%.

Strips of interconnected pores were found in some samples, suggesting that the corium had melted long enough to allow bubbles of steam or molten build material to form and migrate through the melt. Well- mixed solid solution of (U, Zr) O 2 indicates that the temperature of the melt reached 2600 to 2850 ° C.

The structure of the solidified material shows two phases: (U, Zr) O 2 and (Zr, U) O 2 . The zirconium-rich phase was found around the pores and at the grain boundaries and contains some iron and chromium in oxide form. This phase separation suggests slow gradual cooling rather than rapid quenching. Judging from the type of phase separation it took about 3 to 72 hours.

The Chernobyl accident

Large amounts of corium were formed during the Chernobyl disaster . It should be added that the core meltdown there was covered with sand, lead and boron for several days from above by helicopters to mitigate the effects after about 24 hours and liquid nitrogen was also pumped from the outside under the corium, which further erosion after clearly slowed down below.

The molten mass of the reactor core dripped under the reactor vessel and has solidified there in the form of stalactites , stalagmites and lava flows. The best-known formation is the "elephant's foot", which is located under the reactor floor in a steam distribution corridor.

The corium was formed in three phases:

  • In the first phase, which lasted only a few seconds, the local temperatures were more than 2600 ° C. A zirconium-uranium oxide melt formed from a maximum of 30% of the reactor core. The investigation of a highly radioactive particle ( hot particle ) showed that Zr-UO and UO x -Zr phases had formed. The 0.9 mm thick fuel rod cladding made of niobium-zircalloy formed successive layers of UO x , UO x + Zr, Zr-UO, metallic Zr (O), and zirconium (IV) oxide . These phases were found individually or together in the hot particles that had been scattered from the reactor core.
  • The second phase, which lasted six days, was characterized by an interaction of the melt with the silicate-containing building materials: sand , concrete and serpentinite . The molten mixture is rich in silica and silicates .
  • The third stage followed when the fuel formed layers and the melt broke through to the lower floors and solidified there.

The Chernobyl corium consists of uranium dioxide, the reactor fuel, its shell of zircalloy, molten concrete and decomposed and molten serpentinite, in which the reactor was wrapped for thermal insulation . The analysis indicated that the corium was heated up to 2255 ° C and remained above 1660 ° C for at least four days.

The molten corium settled on the bottom of the reactor shaft, with a layer of graphite debris forming on its surface. Eight days after the meltdown penetrated the melt, the lower biological shield ( biological shield ) of the reactor space spread out on the ground, and relied radionuclides free. Further radioactivity was released when the melt came into contact with water.

Three different types of lava can be found in the foundation of the reactor building: black and brown lava and a porous ceramic . They are silicate glasses with inclusions from other materials. The porous lava is brown lava that fell into water and therefore cooled quickly.

During the radiolysis of the water in the basin of the pressure relief system below the reactor, hydrogen peroxide was formed . The hypothesis that the water in the basin was partially converted to H 2 O 2 is confirmed by the fact that the white crystalline minerals studtite and metastudtite were formed in the lavas , the only minerals that contain hydrogen peroxide.

The corium masses consist of a highly heterogeneous silicate glass matrix with inclusions. The following phases can be distinguished:

  • Uranium oxides from the fuel pellets
  • Uranium oxides with zirconium (UO x + Zr)
  • Zr-UO
  • Zirconium (IV) oxide with uranium
  • Zirconium silicate with up to 10% uranium as mixed crystal (Zr, U) SiO 4 , ( "Chernobylite" ).
  • Uranium-containing glass forms the material of the glass matrix itself; mainly a calcium aluminum silicate with small amounts of magnesium oxide, sodium oxide and zirconium (IV) oxide.
  • Metal in the form of solidified layers and spherical inclusions of Fe-Ni-Cr alloy in the glass phase.

Five types of material can be identified in the Chernobyl corium:

  • Black ceramic , a vitreous carbon black material, the surface of which is pitted with many cavities and pores. Usually near where the corium was formed. Its two versions contain about 4-5 and 7-8 percent by weight of uranium, respectively.
  • Brown ceramic , a glassy brown material, mostly shiny, but also matt. Usually on a layer of solidified molten metal. Contains very small metal balls. Contains 8–10 percent by weight uranium. Multi-colored ceramics contain 6-7% fuel.
  • Slag-like granular corium , slag-like irregular gray-magenta to dark brown glassy grains with a crust. Formed by prolonged contact of the brown ceramic with water. In large piles on both levels of the depressurization system.
  • Pumice , crumbly pumice-like gray-brown porous formations formed from molten brown corium that was foamed by steam when it came in contact with water. In large piles in the pressure relief system basin near the drain holes. There they were carried by the current of the water as they were light enough to swim.
  • Metal , melted and solidified. Most of it in the steam distribution corridor. Also as small spherical inclusions in all of the above-mentioned oxide-based materials. Contains no actual fuel, but some metallic fission products , e.g. B. Ruthenium -106.

The melted reactor core collected in space 305/2 until it reached the edges of the steam release valves; then he moved further down to the steam distribution corridor. He broke or burned through into room 304/3. Three streams of corium emanated from the reactor. Stream 1 consisted of brown lava and molten steel; the steel formed a layer on the floor of the steam distribution corridor, on the +6 level, with brown corium on top. From this area, brown corium flowed through the vapor distribution channels into the depressurization basins at Levels +3 and 0, where it formed porous and slag-like formations. Stream 2 was black lava and entered the steam distribution corridor on the other side. Stream 3, which also consisted of black lava, flowed to other areas below the reactor. The structure known as the “elephant's foot” is located in room 217/2 and consists of black lava that formed a multilayered structure similar to tree bark. It is said that it melted two meters into the concrete. The mass of the elephant's foot is given as 0.4 to two tons, depending on the source. Because the material was dangerously radioactive and hard and solid, and because remote-controlled systems could not be used because of the high levels of radiation that affected the electronics, an AK-47 was fired at to cut off pieces for analysis.

The Chernobyl melt was a silicate melt with inclusions of Zr / U phases, molten steel and zirconium silicate with a high uranium content ("Chernobylite", a black and yellow artificial mineral). The lava flow consists of more than one type of material - a brown lava and a porous ceramic material have been found. The ratio between uranium and zirconium is very different in the different parts of the solid mass. A uranium-rich phase was found in the brown lava, which has a U: Zr ratio of 19: 3 to 38:10. The uranium-poor phase in the brown lava has a U: Zr ratio of about 1:10. The thermal history of the mixture can be determined from the examination of the Zr / U phases. It can be shown that the temperature before the explosion was higher than 2000 ° C in parts of the core, while in other areas it was higher than 2400-2600 ° C.

The composition of some of the corium samples is as follows (in percent):

Corium type SiO 2 U 3 O 8 MgO Al 2 O 3 PbO Fe 2 O 3
pumice 61 11 12 07th 00 04th
Glass 70 08th 13 12 00.6 05
slag 60 13 09 12 00 07th

Decay of the lava

The corium is subject to a decay process. The elephant's foot, which was hard and firm after its formation, is now so criss-crossed that a pad with glue could easily peel off one to two centimeters of the upper layer. The shape of the structure itself changes as the material slides down and settles. The temperature of the corium now deviates only a little from that of the surroundings. The material is therefore exposed to the temperature cycle of day and night as well as weathering by water. The heterogeneous nature of the corium and the different expansion coefficients of the components cause the material to age when it passes through temperature cycles . During the solidification, strong internal stresses were built up due to the unregulated cooling rate . The water that seeps into pores and microcracks and freezes there accelerates the bursting. The process is similar to that of creating potholes in roads.

Like strongly irradiated uranium fuel, Corium tends to spontaneously generate dust (spontaneous self- atomization of the surface, see sputtering ). The alpha radiation from the isotopes inside the glass-like structure causes Coulomb explosions that destroy the material and release sub-micron particles from its surface. However, with 2 × 10 16 α decays per gram and 2 to 5 × 10 5 Gy β or γ radiation, the radioactivity is not strong enough to significantly change the properties of the glass. This would  require 10 18 α decays per gram and 10 8 to 10 9 Gy β or γ radiation. The solubility of the lava in water is also very low (10 −7 g · cm −2 day −1 ), which makes it unlikely that it will dissolve in water.

How long the ceramic form of the material can delay the release of radioactivity is unclear. Between 1997 and 2002 a number of papers were published that suggested that the entire 1200 tons of lava would turn into submicrometer-fine mobile powder within a few weeks as a result of its own radiation. However, another work says that this decay is likely not to happen quickly and suddenly, but rather slowly and gradually. The same paper also says that only 10 kg of uranium escapes from the damaged reactor per year. This low rate of uranium leaching indicates that the lava can withstand its surroundings. The paper goes on to say that by improving the building, leaching can be reduced.

On some of the surfaces of the lava flows, new uranium minerals, such as UO 3 · 2H 2 O ( eliantinite ), (UO 2 ) O 2 · 4H 2 O ( studtite ), uranyl carbonate ( rutherfordin ), and two unnamed compounds Na 4 have started to form (UO 2 ) (CO 3 ) 3 and Na 3 U (CO 3 ) 2 · 2H 2 O. They are water-soluble and thus enable the mobilization and transport of uranium. They appear to be whitish-yellow spots on the surface of the solid corium. In comparison with the lava itself, these secondary minerals show a concentration of plutonium several hundred times lower and a concentration of uranium several times higher.

Strength of the activity of various isotopes in the Chernobyl corium, April 1986

The Fukushima accident

As of March 11, 2011, the entire power supply and cooling of five nuclear reactors at the Fukushima Daiichi nuclear power plant gradually failed . Power was restored in time for two of the reactors, while core meltdowns occurred in the other three.

Individual measured values ​​for radioactivity and temperature in the destroyed reactors remained high in the following weeks and months and changed surprisingly (see list in the article System status during the Fukushima nuclear disaster ). The power plant operator TEPCO assumed on the basis of the measured temperatures that residues of the molten fuel elements had collected as corium on the bottom of the respective reactor pressure vessel and damaged it, presumably perforating it. The Nuclear Regulatory Commission assumed early on, at least in one of the blocks, that the melt had penetrated into the containment. The estimates of the extent of the destruction of the individual reactor cores or the pressure vessels continue to fluctuate; the areas are still not accessible.

Web links

Individual evidence

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  33. ↑ UK_CH_370 INSP photo: pumice-like corium formations in the lower level of the Pressure Suppression Pool . Insp.pnl.gov. Retrieved January 30, 2011.
  34. ↑ UK_CH_371 INSP photo: pumice-like corium formations in the lower level of the Pressure Suppression Pool . Insp.pnl.gov. Retrieved January 30, 2011.
  35. ↑ UK_CH_372 INSP photo: pumice-like corium formations in the upper level of the Pressure Suppression Pool . Insp.pnl.gov. Retrieved January 30, 2011.
  36. ↑ AA Borovoi, A. Yu. Gagarinskii : Emission of Radionuclides from the Destroyed Unit of the Chernobyl Nuclear Power Plant . In: Atomic Energy . Volume 90, number 2, pp. 153-161, doi: 10.1023 / A: 1011357209419 .
  37. ^ A b Richard F. Mold: Chernobyl Record: The Definitive History of the Chernobyl Catastrophe . CRC Press, 2000, ISBN 978-1-4200-3462-2 , pp. 128 ( limited preview in Google Book search).
  38. ↑ UK_CH_368 INSP photo: “Elephant's foot” in Corridor 217/2 . Insp.pnl.gov. Retrieved January 30, 2011.
  39. ↑ UK_CH_524 INSP photo: "Elephant's foot", color . Insp.pnl.gov. Retrieved January 30, 2011.
  40. ↑ UK_CH_522 INSP photo: "Elephant's foot", color . Insp.pnl.gov. Retrieved January 30, 2011.
  41. ↑ USSR report: Chemistry . Foreign Broadcast Information Service, 1991.
  42. ↑ SV Ushakov, BE Burakov, SI Shabalev and EB Anderson: Interaction of UO 2 and Zircaloy During the Chernobyl Accident . In: MRS Online Proceedings Library Archive . tape 465 , January 1996, p. 1313-1318 , doi : 10.1557 / PROC-465-1313 .
  43. ↑ V. Zhydkov: Coulomb explosion and steadiness of high-radioactive silicate glasses (PDF; 314 KB). In: Condensed Matter Physics, 2004, vol. 7, No. 4 (40), p. 845-858 doi: 10.5488 / CMP.7.4.845
  44. ↑ a b A. A. Borovoi: Nuclear fuel in the shelter . In: Atomic Energy . 100, No. 4, 2006, pp. 249-256. doi : 10.1007 / s10512-006-0079-3 .
  45. ↑ V. Baryakhtar , V. Gonchar, A. Zhidkov, V. Zhidkov: Radiation Damages and Self-sputtering of High-radioactive Dielectrics: Spontaneous Emission of Submicronic Dust Particles . In: Condensed Matter Physics . tape 5 , no. 3 , January 2002, p. 449-471 , doi : 10.5488 / CMP.5.3.449 .
  46. ↑ Environmental characterization of particulate-associated radioactivity deposited close to the Sellafield works (PDF; 5.5 MB) Retrieved on February 25, 2010.
  47. ↑ UK_CH_528 INSP photo: patches of secondary minerals on the surface of corium . Insp.pnl.gov. Retrieved January 30, 2011.
  48. ↑ Core of Stricken Reactor Probably Leaked, US Says ( April 21, 2011 memento on WebCite ). New York Times, April 6, 2011, archived from the original on April 21, 2011, retrieved on April 21, 2011.