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Study of mineral grains extracted from the Chernobyl “lava”

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  • A.N. Frumkin Institute of Physical chemistry and Electrochemistry
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Results of a spectroscopic and microstructural investigation of mineral grains extracted from lava-like fuel-containing materials – Chernobyl “lava” – are presented. Raman, photoluminescence and infrared spectra reveal the presence of abundant U4+, traces of Sm3+ and Cr3+ in grains of U-containing zircon and ZrO2. No oxidation of UO2 particles is observed. The ZrO2 grains consist predominantly of the monoclinic polymorph and are often twinned. Raman spectra indicate the presence of the tetragonal polymorph, which is likely stabilized by the presence of U. It is suggested that spontaneous transformation of partially stabilized tetragonal (Zr,U)O2 to the monoclinic phase, and a corresponding volume expansion, are important factors affecting the rate of mechanical degradation of the “lava”. Transmission electron microscopy of U-rich zircon suggests the absence of precipitation of any independent U-containing phases, implying that U is fully incorporated within the zircon lattice as an impurity. Grains of rutile, corundum, quartz and natural zircon originating from construction materials of the reactor are described. Results obtained here are important for the validation of computer codes describing severe nuclear accidents.
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ORIGINAL PAPER
Study of mineral grains extracted from the Chernobyl lava
Andrey A. Shiryaev
1,2,3
&Boris E. Burakov
4,5
&Irina E. Vlasova
2
&Maximilian S. Nickolsky
1,3
&Alexei A. Averin
1
&
Alexei V. Pakhnevich
6,7
Received: 14 March 2020 /Accepted: 20 July 2020
#Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract
Results of a spectroscopic and microstructural investigation ofmineral grains extracted from lava-like fuel-containing materials
Chernobyl lava”–are presented. Raman, photoluminescence and infrared spectra reveal the presence of abundant U
4+
,tracesof
Sm
3+
and Cr
3+
in grains of U-containing zircon and ZrO
2
. No oxidation of UO
2
particles is observed. The ZrO
2
grains consist
predominantly of the monoclinic polymorph and are often twinned. Raman spectra indicate the presence of the tetragonal
polymorph, which is likely stabilized by the presence of U. It is suggested that spontaneous transformation of partially stabilized
tetragonal (Zr,U)O
2
to the monoclinic phase, and a corresponding volume expansion, are important factors affecting the rate of
mechanical degradation of the lava. Transmission electron microscopy of U-rich zircon suggests the absence of precipitation of
any independent U-containing phases, implying that U is fully incorporated within the zircon lattice as an impurity. Grains of
rutile, corundum, quartz and natural zircon originating from construction materials of the reactor are described. Results obtained
here are important for the validation of computer codes describing severe nuclear accidents.
Keywords Chernobyl accident .Zircon .Zirconium oxide .Uranium oxide .Spectroscopy
Introduction
During severe accidents involving the reactor core of a
Nuclear Power Plant (NPP) complex interactions between
nuclear fuel (usually UO
2
-based), zirconium-based cladding,
steel and construction materials occur (Hofmann et al. 1989).
An important feature of these processes is characteristically
high temperatures, which may well exceed 2300 °C for sev-
eral hours during initial stages of the accident, and remain as
high as 1500 °C for several days. Interaction of molten corium
a U-Zr-O melt with admixture of Fe and other elements
with construction materials may occur in certain cases (MCCI;
molten coriumconcrete interaction). Resulting materials pos-
sess a wide range of physical-chemical properties, and their
characterisation is far from complete. In particular, experi-
mental MCCI studies are necessarily limited in terms of
interacting compounds and, most importantly, in terms of du-
ration of high-temperature condition, which rarely exceeds
minutes (Journeau 2006).
During the accident at the fourth unit of the Chernobyl NPP
(ChNPP) in 1986, explosive destruction of the reactor core
occurred. Subsequent interaction of damaged and partially
molten fuel rods with silicate-based construction materials
such as serpentinite and concrete led to the formation of the
so-called Chernobyl lava-like fuel-containing material
(LFCM) or simply lava(Anderson et al. 1993;
Arutyunyan et al. 2010; Burakov et al. 1991; Burakov 2019;
Shiryaev et al. 2016, and references therein). Formation of a
lavapool in rooms beneath the former reactor shaft took
Editorial handling: L. Nasdala
*Andrey A. Shiryaev
shiryaev@phyche.ac.ru; a_shiryaev@mail.ru
1
A.N. Frumkin Institute of Physical Chemistry and Electrochemistry,
Russian Academy of Sciences, Leninsky pr. 31, korp. 4,
119071 Moscow, Russia
2
Department of Chemistry, Lomonosov Moscow State University,
Leninskie Gory 1, bld. 3, 119991 Moscow, Russia
3
Institute of Ore Geology, Petrography, Mineralogy and
Geochemistry (IGEM), Russian Academy of Sciences,
Staromonetny per, 35, 119017 Moscow, Russia
4
V.G. Khlopin Radium Institute, 2nd Murinsky av. 28, 194021 St.
Petersburg, Russia
5
A.F. Ioffe Institute, Politekhnicheskaya str. 26, St Petersburg 194021,
Russia
6
Paleontological Institute RAS, Profsoyuznaya str. 123,
117997 Moscow, Russia
7
Frank Laboratory of Neutron Physics, Joint Institute for Nuclear
Research, 141980 Dubna, Russia
https://doi.org/10.1007/s00710-020-00718-8
/ Published online: 29 July 2020
Mineralogy and Petrology (2020) 114:489–499
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... ЖИГАНЮК, 2021 тельность и предложили сценарий образования ЛТСМ. Принято считать, что ЛТСМ являются результатом взаимодействия оксида урана таблеток ядерного топлива (содержащих также продукты деления и активации) с циркониевым сплавом оболочки твэлов и силикатами, входящими в состав конструкционных материалов реактора (серпентинитовой засыпки, песка, бетона и т.д.) [1][2][3][4][5][6][7][8][9][10][11]. ...
... Часть специалистов считает, что в первый день аварии циркониевый сплав оболочки твэлов расплавился изнутри и начал растворять в себе оксид урана топливных таблеток с образованием циркониевой-уран-кислородного расплава [1][2][3][4][5][7][8][9][10]. Это произошло из-за интенсивного тепловыделения и малого теплосъема в твэлах при вводе положительной реактивности. ...
... Аварийная ситуация, сложившаяся на 4-м блоке Чернобыльской АЭС 26 апреля 1986 года, привела к интенсивному тепловыделению и малому теплосъему в твэлах [1][2][3][4][5][6][7][8][9][10][11]. Это вызвало значительное повышение температуры до 2500-2600 ∘ C оксида урана UO 2 топливных таблеток и в зонах контакта оксида урана со сплавом циркония Zr + 1 % мас. ...
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Модель эволюции микроструктуры лавообразных топливосодержащих материалов (ЛТСМ) 4-го блока Чернобыльской АЭС обновлена на примере коричневой керамики. Подтверждено, что поведение ЛТСМ определяется не одним или несколькими физическими и химическими процессами, а их взаимосвязью и взаимовлиянием. Физические и химические процессы, протекающие в ЛТСМ, дополнены еще двумя новыми. Уточнено влияние на поведение ЛТСМ еще одного процесса известного ранее. Добавлены новые стадии эволюции микроструктуры. Уточнены продолжительности известных и определены продолжительности новых стадий. Дан прогноз состояния и поведения ЛТСМ. В ближайшей перспективе разрушения ЛТСМ не будет, в отдаленной-они полностью разрушаться. Оценены сроки разрушения ЛТСМ, размеры частиц, на которые может разрушиться стеклофаза. Все включения оксидов урана попадут за пределы ЛТСМ. Зерна оксида урана разрушаться до нескольких микрон, а часть из них, возможно, и до субмикронного уровня. До 50 т микронных порошков оксидов урана неизбежно будут участвовать в формировании аэрозолей, которые и будут представлять основную опасность для человека. Предложены некоторые методические и технологические подходы к созданию методов твердофазного кондиционирования ЛТСМ.
... The LFCM were formed in the course of the nuclear reactor accident, when the nuclear reactor got out of control. During the first decade after the accident, experts determined and analyzed actor structural materials (the serpentinite backfill, sand, concrete, and others) [1][2][3][4][5][6][7][8][9][10][11]. ...
... Some experts consider that the zirconium alloy in the fuel rod shells had melted from the inside on the first day of the accident and began to dissolve uranium oxide fuel tablets, which resulted in the formation of the zirconium-uranium-oxygen melt [1][2][3][4][5][7][8][9][10]. It happened due to the intensive heat generation and the low heat removal in the fuel rods after the introduction of a positive reactivity. ...
... The emergency situation at Unit 4 of Chornobyl NPP on April 26, 1986, led to intensive heat generation and low heat removal in the fuel rods [1][2][3][4][5][6][7][8][9][10][11]. This circumstance stimulated a substantial increase of the temperature (to 2500-2600 ∘ C) of uranium oxide UO 2 in fuel tablets and in the contact areas between uranium oxide and zirconium alloy Zr + 1 wt%.Nb. ...
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The model of microstructure evolution of lava-like fuel-containing materials (LFCM) in Unit 4 of the Chornobyl NPP has been updated by an example of brown ceramics. It was confirmed that the behavior of the LFCM is not only governed by a single or a few physical and chemical processes, but also by their interrelation and mutual influence. The list of physical and chemical processes taking place in the LFCM was supplemented with two new ones. The influence of another, previously known process on the LFCM behavior was clarified, and new stages of microstructure evolution are added. The durations of the known evolution stages are refined and those of new stages were determined. The state and behavior of the LFCM were forecast. In particular, there will be no destruction of the LFCM shortly soon, but in the long run, they will be destroyed. The time required for the destruction of the LFCM and the size of particles obtained after the glass phase will have destroyed are evaluated. All inclusions of uranium oxides will escape beyond the LFCM. The uranium oxide grains will be broken down to a size of several microns, and some of them, possibly, to the submicron level. Up to 50 metric tons of micro-sized particles of uranium oxide powders will inevitably participate in the formation of aerosols. The latter will pose the main hazard to humans. Some methodological and technological approaches to the development of new methods for solid-phase conditioning of the LFCM are proposed. K e y w o r d s: lava-like fuel-containing materials, evolution model, microstructure, physical and chemical processes, forecast, methodological and technological approaches, New Safe Confinement , oxidation, radiation-stimulated phase formation, crystallization.
... ЖИГАНЮК, 2021 тельность и предложили сценарий образования ЛТСМ. Принято считать, что ЛТСМ являются результатом взаимодействия оксида урана таблеток ядерного топлива (содержащих также продукты деления и активации) с циркониевым сплавом оболочки твэлов и силикатами, входящими в состав конструкционных материалов реактора (серпентинитовой засыпки, песка, бетона и т.д.) [1][2][3][4][5][6][7][8][9][10][11]. ...
... Часть специалистов считает, что в первый день аварии циркониевый сплав оболочки твэлов расплавился изнутри и начал растворять в себе оксид урана топливных таблеток с образованием циркониевой-уран-кислородного расплава [1][2][3][4][5][7][8][9][10]. Это произошло из-за интенсивного тепловыделения и малого теплосъема в твэлах при вводе положительной реактивности. ...
... Аварийная ситуация, сложившаяся на 4-м блоке Чернобыльской АЭС 26 апреля 1986 года, привела к интенсивному тепловыделению и малому теплосъему в твэлах [1][2][3][4][5][6][7][8][9][10][11]. Это вызвало значительное повышение температуры до 2500-2600 ∘ C оксида урана UO 2 топливных таблеток и в зонах контакта оксида урана со сплавом циркония Zr + 1 % мас. ...
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The model of microstructure evolution of lava-like fuel-containing materials (LFCM) in Unit 4 of the Chornobyl NPP has been updated by an example of brown ceramics. It was confirmed that the behavior of the LFCM is not only governed by a single or a few physical and chemical processes, but also by their interrelation and mutual influence. The list of physical and chemical processes taking place in the LFCM was supplemented with two new ones. The influence of another, previously known process on the LFCM behavior was clarified, and new stages of microstructure evolution are added. The durations of the known evolution stages are refined and those of new stages were determined. The state and behavior of the LFCM were forecast. In particular, there will be no destruction of the LFCM shortly soon, but in the long run, they will be destroyed. The time required for the destruction of the LFCM and the size of particles obtained after the glass phase will have destroyed are evaluated. All inclusions of uranium oxides will escape beyond the LFCM. The uranium oxide grains will be broken down to a size of several microns, and some of them, possibly, to the submicron level. Up to 50 metric tons of micro-sized particles of uranium oxide powders will inevitably participate in the formation of aerosols. The latter will pose the main hazard to humans. Some methodological and technological approaches to the development of new methods for solid-phase conditioning of the LFCM are proposed.
... Chemical alteration of the initially-formed material can drastically affect its mechanical behaviour. A series of studies, discussing the dissolution mechanisms and the formation of new phases during Chernobyl "lavas" aging [4][5][6] , can indicate the Fukushima MCCI composition, hence its degradation behaviour, is also time-dependent. ...
... Potential cracks formation, induced by this internal volume expansion, can drastically affect the integrity and, consequently, the mechanical strength. In addition, mechanically unstable ZrO 2 , which is highly probable to be present within the MCCI volume, could also act as a source for crack generation since potential transformation from tetragonal to monoclinic phase is associated with volume expansion 6 . The effect of cracks presence in the embedded MCCI on the material stiffness and strength, need to be highly evaluated prior to decommissioning. ...
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... In the present study we also find tentative evidence for Ce substitution into the zircon structure (see Supplementary Fig. 6). Sm 3+ incorporation has been reported in zircon-formed Chernobyl LFCMs 39 and it has been shown that a small amount of Pu 3+ may be incorporated into the zircon structure. For example, computational modelling of the Pu-zircon system suggested that a defect cluster consisting of two near-neighbour Pu 3+ centres (located on the Zr site) with a closely associated oxygen vacancy charge-ensuring charge neutrality can occur 40 . ...
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The Fukushima Daiichi accident generated degraded nuclear fuel material, mixed with other reactor components, known as molten core-concrete interaction (MCCI) material. Simulant MCCI material was synthesised, excluding highly radioactive fission products, containing depleted U, and incorporating Ce as a surrogate for Pu. Multi-modal µ-focus X-ray analysis revealed the presence of the expected suite of U-Zr-O containing minerals, in addition to crystalline silicate phases CaSiO3, SiO2-cristobalite and Ce-bearing percleveite, (Ce,Nd)2Si2O7. The formation of perclevite resulted from reaction between the U-Zr-O-depleted Ce-Nd-O melt and the silicate (SiO2) melt. It was determined that the majority of U was present as U4+, whereas Ce was observed to be present as Ce3+, consistent with the highly reducing synthesis conditions. A range of Fe-containing phases characterised by different average oxidation states were identified, and it is hypothesised that their formation induced heterogeneity in the local oxygen potential, influencing the oxidation state of Ce.
... 3 Investigation of a limited number of samples of these materials has been conducted but analysis was restricted by their high radioactivity, complicating the handling and characterisation process. [6][7][8][9][10][11] To gain deeper insight into the properties of materials arising from nuclear reactor accidents, in a safe and efficient manner, a suite of simulant brown and black LFCM samples with much lower radioactivity, i.e. excluding ssion products, were synthesised and characterised. [12][13][14] Detailed bulk analysis of these simulant materials was reported and the morphology and mineralogy were found to closely approximate those of real LFCMs. ...
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Detailed chemical analysis of the solidified molten fuel still residing in the stricken Chernobyl reactor unit 4 are inferred using multi-modal micro-focus x-ray analysis of a low-radioactivity proxy. A fascinating mixture of molten UO2, nuclear fuel cladding, concrete, stainless steel and other nuclear reactor components, these materials behaved like lava, solidifying to form a complex, highly radioactive glass-ceramic. Using element-specific chemical probes (micro-x-ray fluorescence and x-ray absorption spectroscopy), coupled with micro-diffraction analysis, the crystalline phase assemblage of these heterogeneous materials was established, which included “chernobylite” and a range of compositions in the (U1-xZrx)O2 solid solution. Novel insight to nuclear accident fuel chemistry was obtained by establishing the oxidation state and local coordination of uranium not only in these crystalline phases, but uniquely in the amorphous fraction of the material, which varied depending on the history of the nuclear lava as it flowed through the reactor. This study demonstrates that micro-focus X-ray analysis of very small fractions of material can yield rich chemical information, which can be applied to nuclear-melt down materials to aid decommissioning and nuclear fuel management at nuclear accident sites.
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The results of experimental studies of the spectra of photoluminescence, excitation and EPR at 4.2-300 K natural and some synthetic samples of zircon are presented. A model of the center, which determines the known yellow photoluminescence of zircon, is proposed. This complex center consists of a metal complex of a transition group with a closed electron shell [(MeOn) m-] and a charge compensator. The chemical nature of the metal and the compensator is not exactly established, but the complex (VO4) 3- is closest in terms of luminescence spectroscopy. For the first time in the minerals, the lines of reabsorption of luminescence by isomorphic U4 + ions were discovered and interpreted, and luminescence in the IR region of the spectrum was also detected, where Nd3 + and Yb3 + centers were detected.
Book
Theoretical Background.- Experimental Techniques.- Luminescent Minerals.- Interpretation of Luminescence Centers.- Applications of Laser-Induced Time-Resolved Spectroscopic Techniques.- Minerals Prospecting.- Minerals Radiometric Sorting.- Identification of Minerals.- Waste Storage Geomaterials.- Luminescent Bio-Minerals.- Conclusion.
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The paper commemorates the 30th anniversary of the severe nuclear accident at the Fourth Unit of the Chernobyl Nuclear Power Plant. Results of the investigation of radioactive glassy lava-like materials formed as a result of the accident are presented. Leaching of Pu, Am and Cs in distilled water and sodium carbonate solution at 25°C from matrices of black and brown Chernobyl “lava” is comparable, however, leaching of Cs from black “lava” in seawater at 25 and 90°C is almost 2 times higher than that for brown “lava”. Chemical alteration of black and brown “lava” in seawater is much more intensive that in distilled water and sodium carbonate solution. Comparison of leaching behavior of Chernobyl “lava” and aged samples of nuclear glass is not clear so far because of the lack of data. Further study of Chernobyl “lava” as analogues of vitrified high level waste (HLW) and possibly, Fukushima’s corium is needed.
Article
The paper commemorates 30 th anniversary of severe nuclear accident at the 4 th Unit of Chernobyl NPP. Results of the investigation of radioactive glassy lava-like materials formed as a result of the accident at their current state are presented. Complementary analytical methods: vibrational spectroscopy, XAFS, SEM, EBSD, X-ray tomography, provide new information about structure of the Chernobyl lava matrix and inclusions. Most of these techniques are applied to the lava samples for the first time and allow to derive consistent model of the lava and to resolve some of existing controversies. The glassy matrix of the lava is an anhydrous depolimerised metaluminous glass with signs of devitrification. Principal inclusions are (U,Zr)O 2-x and (Zr,U)O 2-x solid solutions with tetragonal and monoclinic structures, UO 2 and U-rich zircon. Cracking around large inclusions are observed; some of them could be caused by volume expansion during tetragonal to monoclinic transition in zirconia. The lava accumulations are characterized by different stability against spontaneous destruction, with the pumice-like lava being the least stable, generating radioactive aerosols and particles with sizes up to 250 µm.