AssessmentoftheBiodegradabilityof Containers forLow ... · samplesfrom reinforced concrete. ... Biomineralization and corrosion rateof mild steel under ... Carrying out the study

Assessment of the Biodegradability ofContainers for Low- and Intermediate-Level Nuclear Waste

Borys ZlobenkoV. M. Kadoshnikov , R. Belevtzev: Institute of Environmental Geochemistry of

National Academy of Sciences of UkraineM. Fomina: Zabolotny Institute of Microbiology and Virology of National

Academy of Sciences of UkraineBucharest, November 23-28, 2008

INSTITUTE OF ENVIRONMENTAL GEOCHEMISTRY

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Second Research Coordination Meeting of IAEA CRP:Behaviour of Cementitious Materials in Long Term Storage and Disposal of Radioactive Waste

IAEA Research Agreement No. 14729

Report for the first Year

� Introduction� Isolation and characterization of microorganisms (fungi and thiobacilli sp.);�Choice of working conditions, test methods, analytical investigations;� Investigating the action of microscopic fungi on concrete

7,26Е+14462513,19Е+162735701,99Е+12620,31,22Е+1650688113Total

4,45E+13137013,14E+14826252,29Е+089,89,98E+1216082482Kharkov

1,70E+13109163,03E+16141551,10Е+11137,55,10E+14400310Odessa2,69E+1469261,41E+14273170,00E+0001,00E+136401512Lvov 2,34E+1457958,54E+14689141,85Е+124135,59E+1519872709Kiev 1,61E+1489132,60E+14805593,40E+10606,10E+154331100Dnipropetrovs’k

Activity, Bq

Numbers, pieces

Activity, Bq

Numbers,

pieces.Activity, Bq

Volume, m3

Activity, Bq

Volume, m3

Mass, t

Spent ionizing sources without containers

Spent ionizing sources in bioshielding

Spent ionizing sources Low and

intermediate liquid waste

Low and intermediate solid waste

State RADON enterprise

Kiev State “RADON” Enterprise

General view of the Chornobyl Exclusion Zone

General view of the Vector site

General view of Liquid Radioactive Wastes Treatment Plant (LRWTP)

Liquid Radioactive Wastes Treatment Plant (LRWTP)

� LRWTP is intended for Liquid Radioactive Wastes treatment, accumulated during operation and generated during ChNPP decommissioning and operational Shelter object’s LRW� LRWTP is intended for LRW treatment during the 10-years period of operation. Its minimal designed capacity is 2500 m3 of non-treated LRW per year.� LRWTP consist of:• installation on Liquid Radioactive Waste retrieval from existing storages;• transportation installation – for LRW transportation to treatment installation;• treatment installation – LRW cementation with the purpose of immobilization.

Basic technical characteristics of Lot 3 Complex VECTOR

Two type of waste packages � – concrete containers

KTZ-3.0 with solid waste� - metallic drums KT-0.2 with solidified liquid radwaste in cement matrix

Type of disposal facility- near-surface, of mound-type, with multi-barrier system of RW localization:

- The waste form matrix, concrete containers, monolith reinforcedconcrete structures and the near field geological environment are the main barriers.

- The buffer material filling the compartments after placement ofwaste packages, upper sealing layer, drainage system are additional barriers.

Introduction�Concrete and reinforced concrete are widely used as engineered barriers in nuclear disposal facilities in view to their isolating ability, mechanical stability and low cost.

Concrete containers KTZ-3.0Repository Lot 3 Waste disposal facility . General view

� Several types of containers (KTZ-3.0, ZNKP-2,1) protective reinforced concrete containers for low and intermediate level waste, were designed in Ukraine for different stages of radioactive waste management.� As part of the program studying the long term

behaviour of materials used for nuclear waste disposal (low and intermediate level waste), the biodegradability of concrete and reinforced concrete must be determined according to Ukrainian requirements (NP306. 608-96).

Introduction reviews

� Cracking affects the appearance of concrete. In reinforced concrete cracking allows easier access to air and moisture which can cause steel to rust and eventually weaken the concrete. � Although most laboratory and field microbiallyinduced corrosion studies have concentrated on bacterial involvement, other microorganisms, especially fungi, can also influence corrosion processes

Introduction reviews� In some environments, e.g., the soil, fungi may

dominate the microbiota and be a significant cause of corrosion. Evaluation of the cement degradation induced by the metabolic products of two fungal strains has been reviewed-Perfettini, 1990.� Fungi can be very radiation-resistant and can survive

and colonize concrete barriers under severe radioactive contamination. In 1997-1998, extensive fungal growth was observed on the walls and other building structures in the inner part of the "Shelter" built over the fourth Unit of the Chernobyl nuclear power plant (Zhdanova et al. 2000).

Concrete corrosion associated with Thiobacillus sp.

� Sulfur-Oxidizing bacteria (genus Thiobacillus) are the microorganisms most often associated with the biological degradation of concrete structures� Literature data suggest that, regardless of the initial

populations of the various species of thiobacili in soils, once the process of sulfur oxidation begins, T.thiooxidans or T. ferrooxidans will eventually become the dominate organisms-Rogers, 1993.� According to modern point of view in biofilm the

transformation of monosulfides to disulfides takes place that increase the corrosion rate.

Characterization of microorganisms (fungi and thiobacilli sp.)

� Fungal cultures selected for this study were strains isolated from radionuclide-polluted soils in Ukraine.� In our investigation we used specimens of genus Aspergillus - Aspergillus niger and of genus Cladosporium - Cladosporium clаdosporioіdes. These species of fungi have been commonly reported as potentially causing deterioration of building materials. � Institute of Microbiology and Virology of NAS of Ukraine provided the cultures of these fungi: (Aspergillus niger van Tieghem strain 42 and Cladosporium cladosporioides Fresenius de Vriesstrain 4). � Fungi of genuses Aspergillus and Cladosporium are able to grow in a wide range of pH values: from 2.0 to 10.0.

Concrete corrosion associated with Thiobacillus sp.

� The presence of Thiobacillus sp, is investigated in samples from reinforced concrete. Standart methods were used to isolate microbes. � The investigation objective is the study of biogenic sulfides distribution and qualitative composition in the biofilm formed by sulfate-reducing bacteria (SRB) on the mild steel surface. � Biomineralization and corrosion rate of mild steel under the influence of Desulfovibrio sp. Kyiv-10 strain have been studied in dynamic: 10, 40, 50, 60 and 250 days.

Test methods, analytical investigations

� In consequence of complex study on micro-organisms interaction with reinforce concrete samples has been investigated.�Fungal strains were maintained at 25°C on modified Czapek-Dox agar medium comprising: NaNO3(3.0 g/l), K2HP04 (1.0 g/l), MgS04·7H20 (0.5 g/l), KCl (0.5 g/l), sucrose (30 g/l) and agar No. 2 (20 g/l): 14-day-old cultures were used as fungal inoculum

Test methods, analytical investigations (cont.)

�The concrete samples consisted of chips of concrete containers KTZ-3.0, barrier concrete manufactured for the disposal of low and intermediate level radioactive waste. �Concrete chips were sterilized by autoclaving 3 times (120°°°°С, 60 min) and were then oven-dried at 100°°°°C at least overnight.

Test methods� A concrete chip was inserted into a hole of corresponding size that had been cut out from the centre of the Czapek-Dox agar in the Petri dish, leaving a 2 mm gap between the concrete and the agar. Four 10 mm diameter disks of fungal inoculum cut from the edge of fungal colonies were placed around the concrete chip, also leaving a 2 mm gap. � In the centre of each dish a socket was cut out by a micro-spatula, and a sample, which had been previously autoclaved at 0.5 atm. and desiccated at 75-800С, was put into it. Micromicetes were inoculated at 1-2 mm distance around the sample at the surface of agarised medium.

Test methods (cont).

Then the Petri dishes were sealed by “Parafilm” to prevent drying of the medium and incubated for one month at 25°°°°C and then over one year at ambient temperature

Analytical investigations� Petrographic and mineralogical observations of concrete surfaces were carried out using a Polmi-A microscope (Carl Zeiss, Germany).� Following light microscopic observations of fungal colonization and deterioration of concrete samples in microcosms, scanning electron microscopy (Philips XL30) was used to analyze concrete transformations by fungi. � Mineralogical and elemental analyses of concrete transformations were carried out using X-ray powder diffraction (XRD) and energy dispersive X-ray analysis (EDXA) coupled with ESEM.� Biofilm exudates sampled from microcosms after 5 months of growth were also analyzed for metal content using an atomic absorption spectrophotometer AAS-8500 F (Japan) with reference to appropriate standard solutions.

Oecizing № Cultures of mycromicetes Agarised

medium Concrete

Morphologic characteristics of concrete

1. Aspergillus flavipes – 38 *** ***** Heavy sporification, drops of yellow exudation

2. Aspergillus niger – 42 ***** ***** Mycelium with heavy sporification, small drops of yellow exudation

3. Cladosporium cladosporioides – 3

** *** Heavy sporification

4. Cladosporium cladosporioides – 4

** *** Heavy sporification �When investigating the action of microscopic fungi of genera Aspergillus and Cladosporium on concrete specimens in the model system, it was shown that the fungi can colonize successfully the concrete surface during 1 year and cause its destructive changes.

Investigating the action of microscopic fungi on concrete in model experiment

� However the fungi did not colonize those sections of concrete surface which were filled with granite. The fungi leached chemical elements of concrete into nutrition medium, accumulated them in their biomass and caused their transformation into newly-formed crystals of calcium oxalates on the surface of concrete.

Fungi produced drops of exudate on the surface of colonized concrete which were retained for at least 6 months of exposure

�After 1 year of exposure of the concrete chips to the fungi, deterioration symptoms such as expansion and discolouration of the cement matrix, discolouration of clinker grains, crystallization and formation of cracks were observed by light and petrographic microscopy

� Among the fungal cultures tested, A. nigerdemonstrated the highest capacity for concrete deterioration (Table 1). � Electron microscopic studies of concrete exposed to

A. niger over one year showed spalling layers covered with a mycelial net, cracking, and the formation of abundant crystals on the concrete surface and encrusting fungal hyphae crystals formed by A. nigershowed the presence of calcium. � XRD analysis identified crystalline precipitates within the biomass and on the concrete surface as calcium oxalate dihydrate (weddellite) and calcium oxalate monohydrate (whewellite)

Leaching of calcium, silicon, aluminum and ironfrom micromycetes grown in submerged culture

in the presence of ground concrete

The leaching of chemical elements from concrete by microfungi of genera Aspergillusand Cladosporium during fungal growth on the medium containing ground barrier concrete under submerged conditions has been studied. It was shown that the leaching of chemical elements depended on the process of growth and metabolites excretion, on fungi species and on concrete concentration on the medium. Specificity of metals mobilization by different fungi was found.

Evaluation of the reinforce concrete containers degradation

� Fungal degradation of aluminosilicates and silicates is believed to occur as a result of the production of organic acids, inorganic acids, alkalis and complexingagents � We study of the cement degradation induced by the metabolic products of fungal strains which produces gluconic and oxalic acids. � These acids induce (after one year of contact) a dissolution of portlandite (with a low leaching of calcium), an increase in the cement porosity, a loss of the bending strength� In this study, oxalic acid produced by A. niger reacted with calcium from the cement matrix of the concrete to form the secondary mycogenic mineral phases, whewellite and weddellite.

Evaluation of the reinforce concrete containers degradation

�The second strain, a Cladosporiumclаdosporioіdes produces gluconic and malicacids, responsible (during the same period) for a very important dissolution of portlandice(with a leaching of calcium: 4.2% of the initial content and increase the porosity.

EDXA spectra of Au/Pd coated samples showing that crystals associated with hyphaecontained calcium

Scanning electron microscopy of the deteriorated concrete samples revealed spalling layers and deep cracks explored by the fungal mycelium, and precipitation of abundant crystals of calcium oxalate, often associated with and encrusting fungal hyphae.Calcium-containing crystals can be seen encrusting the fungal hyphae.

Conclusion � Fungal biogeochemical activity over a long-term scale may have negative environmental consequences for the management of barrier materials used in nuclear waste disposal. � Fungi successfully colonized barrier concrete, generally avoiding granite aggregates, and biochemically (by excretion of protons and ligands) and biomechanically deteriorated the concrete. � Fungi dissolved the cement matrix leaching structural elements and accumulating them within the fungal biofilm and associated microenvironment. Oxalate-excreting Aspergillus niger formed abundant calcium oxalate crystals on the concrete and encrusting fungal hyphae

The programme of work shall beYear 2:

� Carrying out the study of resistance of concretesimulators of products of a metabolism ofmicroorganisms;� Determination of main analytical relationships

between the state and properties of reinforcedconcrete; � Studying parameters of destructive changes as a

result of action of microorganism metabolism product;

We thank Prof. I. Kozlova for help with microorganisms identification (Zabolotny Institute of Microbiology and Virology, Kyiv, Ukraine). This research has been supported by Ministry of Ukraine of Emergencies and Affairs of Population Protection from the Consequences of ChornobylCatastrophe.

Acknowledgements

Thank you for your attention