Study of Chernobyl “lava”, corium and hot particles:
experience of V.G. Khlopin Radium Institute (KRI)

Boris Burakov
DSc, Head of Laboratory
V.G. Khlopin Radium Institute (KRI)
St. Petersburg, Russia
e-mail: burakov@peterlink.ru
1990

1990

160 employees of V.G. Khlopin Radium Institute have been working in Chernobyl since 1986 till 1992

V.G. Khlopin Radium Institute (KRI)
study of radioactive materials since 1922
at present time KRI is a research institute of Russian State Corporation for Atomic Energy (ROSATOM)

•
•
•
•
•
•
•
•
•
•

First European cyclotron built in 1937
First sample of Soviet Pu, obtained in 1945
Industrial Soviet technology of Pu extraction 1945-1949
Chernobyl investigation 1986-1992 (and present time)
Unique collection of Chernobyl “lava”, corium and hot particles
available for international research and training
Hot-cell facility for research using any kind of spent nuclear fuel andliquid HLWStudy of actinide-doped ceramics and HLW glasses
Production of isotopes
Radio-ecological monitoring
Applied training of international young scientists in the field of
nuclear waste management
2

V.G. Khlopin Radium Institute (KRI)First European cyclotron (1937)

Crystals of NpO2

Solution of PuCl3
Radiation damage effects inzircon crystal doped with Pu-238

Hot-cell facility

Borosilicate glass
doped with Pu-238

Backgroundbasic papers

1.
2.
3.

4.

5.

6.

7.
8.

9.
10.

11.
12.

Chernobyl: The Soviet Report. Nuclear News, Vol.29, #13, Oct. 1986.
Боровой А.А. Внутри и вне «Саркофага». Препринт КЭ ИАЭ, Чернобыль 1990. – Borovoy A.A. Inside and outside“Sarcophagus”. Issue of CE IAE, Chernobyl 1990 (in Russian).
Borovoy A.A. , Galkin B.Ya., Krinitsyn A.P., Markushev V.M., Pazukhin E.M., Kheruvimov A.N., Checherov K.P. New products
formed by reaction of fuel with construction materials in the 4th block of the Chernobyl NPP. Soviet Radiochemistry, 32(6)(1990) 659-667.
Лебедев И.А., Мясоедов Б.Ф., Павлоцкая Ф.И., Френкель В.Я. Содержание плутония в почвах европейской части страны
после аварии на Чернобыльской АЭС. Атомная Энергия, т.72, вып.6, июнь 1992, с. 593-598. – Lebedev I.A., Myasoedov B.F.,
Pavlotskaya F.I., Frenkel V.Ya. Plutonium contents in the soils of European part of USSR after accident at Chernobyl NPP.
Atomic Energy, Vol.72, #6, June 1992, pp. 593-598 (in Russian).
Киселев А.Н., Ненаглядов А.Ю., Сурин А.И., Чечеров К.П. Экспериментальные исследования лавообразных
топливосодержащих масс (ТСМ) на 4-м блоке ЧАЭС (по результатам исследований 1986-1991 годах). Препринт ИАЭ,Москва 1992 – Kiselev A.N., Nenaglyadov A.Yu., Surin A.I., Checherov K.P. Experimental study of lava-like fuel containing
masses (FCM) at 4th Unit of ChNPP (based on results obtained in 1986-1991). Issue of IAE, Moscow 1992 (in Russian).
Trotabas M., Blanc J-Y., Burakov B., Anderson E., Duco J. Examination of Chernobyl samples. Impact on the accident scenario
understanding. Report DMT/92/309, SETIC/LECR-92/36, Report IPSN/93/02, Report RI-1-63/92, March 1993.
Pazukhin E.M., Fuel-containing lavas of the Chernobyl NPP 4th block – topography, physicalchemical properties, formation scenario.
Radiochemistry 36(2) (1994) 109-154.
Burakov B.E., Anderson E.B., Shabalev S.I., Strykanova E.E., Ushakov S.V., Trotabas M., Blanc J-Y., Winter P., Duco J. The
Behaviour of Nuclear Fuel in First Days of the Chernobyl Accident. Mat. Res. Soc. Symp. Proc. Scientific Basis for Nuclear Waste
Management XX, Vol.465, 1997,1297-1308.
Burakov B.E., Anderson E.B., Strykanova E.E. Secondary Uranium Minerals on the Surface of Chernobyl “Lava”. Mat. Res. Soc.
Symp. Proceedings Scientific Basis for Nuclear Waste Management XX, Vol.465, 1997, 1309-1311.
Burakov B.E., Shabalev S.I., Anderson E.B. Principal Features of Chernobyl Hot Particles: Phase, Chemical and Radionuclide
Compositions. In S. Barany, Ed. Role of Interfaces in Environmental Protection, Kluwer Academic Publishers, 145-151, NATO
Science Series, Earth and Environmental Sciences, Vol. 24. 2003.
Боровой А.А., Велихов Е.П. Опыт Чернобыля, Часть 1, Москва, 2012 – Borovoy A.A., Velihov E.P. Experience of Chernobyl,
Part 1, Moscow, 2012 (in Russian).
Nasirow R., Poeml P. Gamma-ray spectrometry of Chernobyl ceramic samples. Internal Report of JRC Institute of Transuranium Elements.
Karlsruhe, 2013.

4

After explosion – first days [11]5Cross-section of Chernobyl “Shelter” [11]4Backgroundgeneral information• About 3.5 wt.% spent fuel was ejected from the core [1,2]• About 50 kg Pu was spread in European part of USSR [4](it means 6 wt.% of total Pu of Chernobyl NPP’s 4th Unit)• More than 90 wt.% fuel is inside “Shelter” or “Sarcophagus” [2], but
this information is controversial• At least 11-15 wt.% fuel (inside “Shelter”) is related to Chernobyl“lava” [5], but this information is controversial

7

Backgroundbasic glossary• Chernobyl “lava” – it is a result of high-temperatureinteraction between destroyed fuel, Zr-cladding andsilicate materials (concrete, sand, serpentinite) – can becalled silicate-rich corium• Chernobyl corium – melted fuel-containing material,
which does not have silicate matrix• Chernobyl “hot” particles – are highly radioactive solid
particles from less than 1 µm to hundreds µm in size
Note: Chernobyl hot particles usually contain U but not always!

8Natural volcanic lava

Chernobyl “lava”-stream called “Elephant foot”, 1990 [2]gamma-doze on the surface of “Elephant foot” in 1990 exceeded 10 Sv/h,and gamma-radiation field in the room was 6-7 Sv/h

10

Chernobyl “lava” in steam discharge corridor, 1990 [2]11

Backgroundgeneral information• Initial mechanical durability of Chernobyl “lava” was veryhigh. Shooting by machine-gun AK-47 was applied to break“Elephant foot” matrix and collect first samples in 1987 [2]• Essential decrease of mechanical durability and even selfdestruction of “lava” matrices was observed in 1990 [2]• Chemical alteration of “lava” matrices was observed in1990 – formation of “yellow stains” consisted of secondary
uranium minerals (uranyl-phases) [9]12New-formed yellow minerals at the surface ofChernobyl “lava”, 1991

13

Samples of Chernobyl “lava”
collection of V.G. Khlopin Radium Institute• Most samples of “lava” were collected at different
locations in 1990 using hands and hammer only. All
people involved into sampling were overirradiated• Some pieces of “lava” (dozens cubic cm each) werepartially dissolved in HF in order to extract inclusions ofdifferent uranium-bearing phases

14

Before going inside “Shelter”, 1990

Boris Burakov 1990
15

Inside “Shelter”:
packing “lava” sample for shipment to Leningrad, 1990
photo by Boris Burakov, 1990

16

Map of KRI sampling inside “Shelter” [8]17Current study of highly radioactive Chernobyl
samples – what for?
• Transfer of experience to young scientists• Tutorials on material science of highly radioactive solids• Modeling of severe nuclear accidents and corium
behavior• Modeling of properties of Fukushima’s corium• Chernobyl “lava” as analogue of HLW glass• New-formed artificial unstable radioactive phases as aresult of corium and “lava” chemical alteration• New-formed very stable crystalline radioactive phases(inclusions in the “lava” matrices) as perspective durable
host-phases of radionuclides
18Samples of black “lava” – “Elephant foot”
collection of V.G. Khlopin Radium Institutesamples were collected in 1990 and stored at KRI under laboratory conditions
partial self-destruction was observed for some pieces in 2011 (picture 4).
photo by V. Zirlin and B. Burakov

19

Samples of brown “lava” – from steam discharge corridor
collection of V.G. Khlopin Radium Institutesamples were collected in 1990 and stored at KRI under laboratory conditions
pictures were taken in 2011 by V. Zirlin and B. Burakov

20

Samples of brown “lava” – from room #305
collection of V.G. Khlopin Radium Institutesample was collected in 1990 and stored at KRI under laboratory conditions
pictures were taken in 2011 by V. Zirlin and B. Burakov
formation of secondary uranium minerals under laboratory conditions ?

21

Some Chernobyl samples from KRI collection
have not been studied yet

19Sample of corium (fuel-steel melt) – from room #305
collection of V.G. Khlopin Radium Institutesample was collected in 1990 and stored at KRI under laboratory conditions
picture was taken in 2011 by V. Zirlin and B. Burakov

23

Sample of corium (fuel melt on the surface of steel pipe)
room #305
collection of V.G. Khlopin Radium Institutesample was collected in 1990 and stored at KRI under laboratory conditions
picture was taken in 2011 by V. Zirlin and B. Burakov

24

Sample of corium (fuel-steel melt) – near “Elephant foot”
collection of V.G. Khlopin Radium Institutesample was collected in 1990 and stored at KRI under laboratory conditions
picture was taken in 2011 by V. Zirlin and B. Burakov

25

Samples of Chernobyl “hot” particles
collection of V.G. Khlopin Radium Institute• Some particles were separated from soil
samples collected near 4th Unit in 1986
• Most particles were separated from soil samples
collected at Western Plume (0.5-12 km from 4thUnit) in 1990-1991• Some fuel fragments and particles werecollected inside “Sarcophagus” in 1990

26

“Red forest” – pine-tree forest died as a result ofChernobyl fallout, June 1986
photo – courtesy of Dr. R.V. Arutyunyan (IBRAE, Russia)

Collecting hot particles, 1990

Boris Burakov, 1990
28

Separation of hot particles from soil sample [7]at V.G. Khlopin Radium Institute – using collimated beta-gamma-detector

29

Methods of analyses
at V.G. Khlopin Radium Institute

•
•
•
•

Optical microscopy
SEM (BSE imaging)
Quantitative and qualitative EMPA
Bulk powder XRD (secondary uranium minerals, mineralinclusions separated from “lava” matrices)• Precise XRD of single hot particles and mineralinclusions separated from “lava” matrices• Gamma-spectrometry of bulk samples and single hotparticles30Chernobyl “lava”
brief summary or the results obtainedat V.G. Khlopin Radium Institute31

Images of polished “lava” samples
1,2 – in reflected light in optical microscope; 3,4 – SEM-BSE
1,3 – brown “lava” from steam discharge corridor; 2 – black “lava” from “Elephant foot; 4 – black “lava”
from steam discharge corridor

32

Chernobyl “lava” consist ofsilicate glass matrix + inclusions

33

Radionuclide composition of Chernobyl “lava”
on June 2013 [12](recalculated for 26.04.1986) [3,7]Type of“lava”

137Cs

2∙107
Black

144Ce

(2∙109)Radionuclides, Bq/g
154Eu
244Cm
241Am
5∙105
5∙104
1.2∙106

239,240 Pu

238Pu

8.2∙105

4.3∙107(2.3∙107)(1.3∙106) (1.2∙107) (3.5∙107) (7.3∙107) (3.8∙107)
Brown 4.1∙107 (2.1∙109) 1.2∙106 1.1∙105 2.8∙106 1.8∙106
9.2∙105

34

Simplified bulk chemical composition (matrix + inclusions)of Chernobyl “lava” [6,7]Type of“lava”
Black
Brown

U
4-5
8-7

Zr
2-6
5-6

Element content, wt. %
Na
Fe
Mg
Ca
2 - 100.3 - 6 1 - 5
3 - 13
4
1-2
4
5

Si
19 - 36
31 - 33

Al
3-8
4

Results of electron-probe microanalysesof glass-like silicate matrix of Chernobyl “lava”
avoiding inclusions of crystalline phases [6,8]Element content, wt. %
U
Zr
K
Na
Fe
Mg
Ca
Black 2.7-4.0 3.1-3.7 1.4-2.7 0.4 0.3-6.7 1.2-3.2 5.1-7.2
Brown 2.0-2.4 2.4-2.9 1.2-2.3 0.6 0.2-0.4 3.5-4.4 4.5-8.2
Porous 2.9
4.0
2.3
0.5
0.2
4.5
7.5

Type of“lava”

Si
28-37
37
35

Al
2.7-4.4
2.8-4.0
3.8
35

Inclusions in matrices of Chernobyl “lava” are ofvery different phase and chemical compositions!

36Inclusions in brown “lava” matrix(from steam discharge corridor)
1,2 – in reflected light in optical microscope; 3,4 – SEM-BSE
photo by Boris Burakov, 1990-1991

Zr-U-O37

Inclusions in black and brown “lava” matrices
SEM-BSE
1,2 – black “lava” from steam discharge corridor; 3 – brown “lava” from steam discharge corridor;
4 – black “lava” from “Elephant footphoto by Boris Burakov, 1990

38

Inclusions in black and brown “lava” matrices(from steam discharge corridor)
SEM-BSE
1,2 – brown “lava”; 3,4 – black “lava”
photo by Boris Burakov, 1990

39

Crystals of high-uranium zircon, (Zr,U)SiO4,
are typical for all types of Chernobyl “lava”
Up to 10 wt. % uranium was incorporated into the crystalline structure of
zircon in the form of solid solution !

40

High-uranium zircon, (Zr,U)SiO4, from Chernobyl “lava”
crystals were extracted after partial dissolution of “lava” matrix in HF
photo by Boris Burakov, 1990

41

New-formed yellow minerals at the surface of Chernobyl“lava”, 1991

42

SEM-BSE image of new-formed minerals at the surface ofChernobyl “lava” [9]photo by Boris Burakov, 1990

43

Phase composition of new-formed minerals at the surfaceof Chernobyl “lava” (from powder XRD analysis [6])• Na3H(CO3)22H2O• UO32H2O• Na4(UO2)(CO3)3• Na2CO32H2O• UO44H2O• UO2CO344

Chernobyl “hot” particles
brief summary or the results obtainedat V.G. Khlopin Radium Institute45

SEM-BSE images of fuel fragment (A) and hot particles(B,C,D) of fuel composition (UOx) [10]possible mechanical self-destruction along grain boundaries

46

Multi-grain fuel (UOx) hot particles (collected in 1990)
photo by Boris Burakov, 1990

non-alteredaltered ???
dissolution along grainboundaries ?

47

Fuel hot particles (UOx) with molten morphology (?)
photo by Boris Burakov, 199048

We also found Zr-bearing hot particles with phases:
Zr-U-O and UOx with Zr etc.
up to 40 % of all particles in some places of Western Plume !

49

Multi-phase hot particles [10]polished cross-sections, SEM-BSE

50

Multi-phase hot particle [10]SEM-BSE image51

No interaction between fuel (UOx) and zircaloy (almost
pure metallic Zr) is possible in air. Fast oxidation of
metallic Zr blocks this process
No conditions for Zr-U-O melt formation after explosionof reactor core !

52Formation of Zr-U-O melt
1) In corium of Chernobyl reactor (before explosion) – it is matrix of real hot particle2) Laboratory experiment (melting at 2600ºC in vacuum) of Zr + UO2 – it is synthetic sample
photo by Boris Burakov, 1990

48

Crystalline U-bearing phases identified in Chernobyl“lava” and hot particles•

Cubic UOx – similar to stoichiometric UO2 (a = 5.462-5.473 Å)•

Cubic UOx with Zr (0,5 to 20 wt.% Zr) (a decreases from 5.468 to 5.318 Å). Chemicalcomposition – (U0.985Zr0.015)O2-(U0.895Zr0.105)O2. In some hot particles Zr content ishigher – up to (U0.56Zr0.44)O2•

Tetragonal phase Zr-U-O with varied chemical composition from (Zr0.86U0.14)O2 to(Zr0.89U0.11)O2•

Monoclinic zirconia with U (up to 6 wt.% U) with varied chemical composition from
(Zr0.995U0.005)O2 to (Zr0.967U0.033)O2•

Solid solutions with non-identified structures: (Zr0.56U0.44)O2; (Zr0.68-0.71U0.32-0.29)O2;(Zr0.75-0.77U0.25-0.23)O2 – only in hot particles•

High-uranium zircon, (Zr0.95U0.05)SiO4-(Zr0.90U0.10)SiO4(for bulk concentrate: а = 6.617; с = 5.990 Å).

54Conclusions•

High-temperature (at least 2600°C) interaction between nuclear fuel andzircaloy cladding took place in local part of Chernobyl reactor core before
the explosion•

Solid highly radioactive materials were formed and partially dispersed as aresult of Chernobyl accident. They have different phase and chemicalcomposition. It means their different behavior in environment•

Active chemical alteration of Chernobyl corium is going on•

Results of Chernobyl material study can be used for modeling severe
nuclear accident at different types of nuclear reactors (not only RBMK)•Results of Chernobyl material study can be used for development ofceramic waste forms and other durable advanced materials

55

KRI collaboration on study of Chernobyl“lava” and “hot” particles

KRI collaboration with French colleagues on study ofChernobyl “lava”, 1991-1993

KRI collaboration with German colleagues on study ofChernobyl “lava” and hot particles since 2004 till now
•

•

•

•

Geisler T., Burakov B. E., Zirlin V., Nikolaeva L., and Poml P. A Raman
spectroscopic study of high-uranium zircon from the Chernobyl “lava”. Eur. J.
Mineral., (2005),17, pp. 883-894.
P. Pöml, B. Burakov, T. Geisler, C.T. Walker, M.L. Grange, A.A. Nemchin, J. Berndt,
R.O.C. Fonseca, P.D.W. Bottomley, R. Hasnaoui, Micro-analytical uranium isotope
and chemical investigations of zircon crystals from the Chernobyl „„lava‟‟ andtheir nuclear fuel inclusions. J. Nucl. Mater., (2013) Vol. 439, pp. 51-56.
P. Pöml. P., Burakov B., Study of a “hot” particle with a matrix of U-bearing
metallic Zr: Clue to supercriticality during the Chernobyl nuclear accident. J.
Nucl. Mater. (2017), Vol. 488, pp. 314-318.
Two fragments of black and brown Chernobyl “lava” are under investigation at ITU
now in the framework of ITU-KRI Agreement.

KRI collaboration with Russian colleagues (from Moscow) on
study of Chernobyl “lava” and hot particles since 2012 till now
•

•

•

•

Batuk O.N., Conradson S.D., Aleksandrova O.N., Boukhalfa H., Burakov B.E., Clark D.L.,
Czerwinski K.R, Felmy A.R., Lezama-Pacheco J.S., Stepan N. Kalmykov S.N., Moore
D.A., Myasoedov B.F., Reed D.T., Reilly D.D., Roback R.C., Vlasova I.E., Webb
S.M.,Wilkerson M.P. Multiscale Speciation of U and Pu at Chernobyl, Hanford, Los
Alamos, McGuire AFB, Mayak, and Rocky Flats. J. Environmental Science andTechnology, (2015) pp. 6474-6484.
Vlasova I., Shiryaev A., Ogorodnikov B., Burakov B., Dolgopolova E., Senin R., Averin A.,
Zubavichus Y., Kalmykov S. Radioactivity distribution in fuel-containing materials(Chernobyl “lava”) and aerosols from the Chernobyl “Shelter”. Radiation
Measurements, 83 (2015) 20-25.
Shiryaev A.A., Vlasova I.E., Burakov B.E., Ogorodnikov B.I., Yapaskurt V.O., Averin A.A.,
Pakhnevich A.V., Zubavichus Y.V., Physico-chemical properties of Chernobyl lava
and their destruction products. Progress in Nuclear Energy, 92 (2016) 104-118.
Some polished micro-samples of Chernobyl “lava” and hot particles are under joint
analysis at Radiochemical Department of Moscow State University now in the frameworkof collaboration between KRI, MSU and A.N. Frumkin Institute of Physical Chemistry andElectrochemistry.

Testing of neutron detector (developed by “PDC UGR” JSC)
using samples of Chernobyl “lava”, February 2017
Collaboration between KRI and Russian Pilot and Demonstration Center for
Decommissioning of Uranium-Graphite Nuclear Reactors” JSC (“PDC UGR” JSC)KRI proposals on cooperation with Japanese colleagues• Consulting on fuel-debris and corium investigation, removal,
treatment and final disposal• KRI participation in material study of Fukushima’s corium in Japan• Training of Japanese colleagues at KRI using real highly radioactive
Chernobyl samples (“lava”, corium, hot particles)• Joint search, extraction and study of Fukushima’s hot particles

Acknowledgements•Colleagues from KRI: Mr. Zirlin V.A., Mrs. Nikolaeva L.D.,
Dr. Krinitsyn A.P., Dr. Pazukhin E.M., Mr. Shabalev S.I.,
Dr. Pleskachevskiy L.A., Dr. Pakhomov S.A.

• Dr. Britvin S.N (St. Petersburg State University)• Colleagues from Radiochemical Department of Moscow State
University: Prof. Kalmykov S.N., Dr. Vlasova I.E. and Dr. Petrov V.G.
• Colleagues from Germany: Dr. Philipp Poml (ITU, Karlsruhe) andProf. Thorsten Geisler (University of Bonn)• Dr. Shiryaev A.A. (A.N. Frumkin Institute of Physical Chemistry andElectrocjhemistry of the Russian Academy of Sciences, Moscow)
Special thanks to Mr. Tadahiro Washiya (CLADS, JAEA) andMr. Masaki Nakagawa (NDF) for invitation to attend this meeting!

62

Thank you!

52