ROSATOM STATE CORPORATION COMPANY«Development of Technologies for Grasping andAnalyzing Properties of Fuel Debris (Estimationof Aging Properties of Fuel Debris)»Project Background & Objectives

Analyzeoverseas
experience

Determinefactors that
influence
aging

Determinemodelcomposition

Forecast model of changing of Fuel Debris (FD) properties
for the safety case for the design solutions for retrieval,transportation & container storage of the FD

Develop methodology
for the synthesizing &testing of the F1 FD
model samples

Develop methodology
for sample’s aging

Manufacturesamples:«Cold» samples«Hot» samples
Carry outTests

Develop
recommendations
Developprediction model
10 20 30 50 years

F1
applicability

2Project Implementation Plan

3

Project Implementation Plan

Manufacturing• H2O + t⁰Aging• ɑTests

Experimental study of such processes ofFD aging, as the change in mechanicalstrength, leaching of different
radionuclides, the change in the phasecomposition, the appearance of secondary
phases wrangling etc. needed to develop
predictive models of changes over time ofthe properties of the Fukushima samples
and to develop safety recommendations
retrieving and container storage of FD.

•••••Phase composition
Leaching rates
Microstructure
Mechanical strength
Secondary Uranil phases

Analysis of thetests results

verification

Input data for prediction model

Develop forecast modelof FD behavior for safety
justification during
extraction, packing,storage & transportation

4

Algorithm of Manufacturing & Investigating

Synthesis of a fuel composition with inclusion of oxides(carbonates) of fission product simulators

123

Study of the behavior of concrete during heating
Preparation of the metallic phase45

Preparation of the silicate phase
Accelerated degradation of samples

6

Leaching test during the aging of samples
Compression test: mechanical strength

78Analysis of the obtained sample fragments:
phase composition, microstructure

5RIAR/KRI Model Samples Composition (Metallic\oxide phase)
Component

Mass ContentRemarks

UO2

56.6%

The basis of nuclear fuel

ZrO2

13.1%

Zirconium is represented as two compounds
to simulate its partial oxidation, it is assumed

Zr

10%

that 50% zirconium is oxidized
Simulates the steel body and sub-shell

Fe

12.6%

PuO2

3,0%

devices, can be replaced by stainless steel

Multiply increased to study the effect on
SrCO3

1.6%aging of fuel debris

Multiply increased to study the effect on
Cs2CO3

2.5%

Nd2O3

0.3%

La2O3

0.3%

aging of fuel debris

6Sample’s Manufacturing

Mixer «drunk barrel»

Laboratory scales

Box with high-temperature furnace Xerion XVAC2300,
hydraulic press Retsch PP25 and weighing device

Grinding of thecomponents of theworking mixture
Mixingofthecomponents of theworking mixture
Prepared working mixture divides
into two parts: for metallic phasewith & without Cm

calculated part of thesamples dissolve in
concrete to obtain thesilicate phase,both with & without Cm

sintering tabletsin an oven

Calculated amounts ofrequired reagents weighed
on Sartorius brandanalytical balance with anaccuracy of 0.001 g.

Machine forpreparing billets

7

Preparation of the Metallic Phase

Vheat,cool=500 ⁰C/h
Tcool=20 ⁰C
T = 1800 ⁰C
3 hours• ZrO2 crucible• ZrO2 lid• Ar• Cs carbonate

Calcined zirconia crucible

PAr= + 15 mbar
26 Moist
Tablets(13+13):
M1 = 2,36 g
M2 =1,38 g

Q= 0,3-0,4 l/sec

26 Tablets(13+13):
Dmed = 9,5 mm
M1 = 2,36 gM2 =1,38 g
H1 = 7,5 mm
H2 = 4,3 mm

8Preparation of the Metallic Phase with Cm
Vheat,cool=500 ⁰C/h
Tcool=20 ⁰C
T = 1800 ⁰C
3 hours• ZrO2 crucible• ZrO2 lid• Ar• Cs carbonate

PAr= + 15 mbar
Q= 0,3-0,4 l/sec

Dmed = 7,4 mm
M1 = 2,16 g
H1 = 6,5 mm

Calculation of the amount of Curium
introduced into the metallic phase samples
Specific activity of SNF = 2,7×108 Bq/g.
To accelerate aging ~180 times (10 years in 20 days) => introduce into the sample the activity of244Cm = 4.3×1010 Bq/g or 244Cm = 16.5 mg/g (1.6% wt.).
Metallic phase (MP) contains ~60% of SNF => alpha-activity of the MP:
Silicate phase (SP) contains ~30% of SNF => alpha-activity of the SP:
The specific activity of 244Cm is 3×1012 Bq/g => MP:SP:
Mass of sample ~ 3 grams (before sintering)
Mass of Cm of MP = 0.86×3 = 0.0258 g.
Mass of Cm of SP = 0.43×3 = 0.01229 g.
The total amount of Cm(per 22 samples):
For the MP: 11 × 0.0258 = 0.2838 g.
For SP: 11 × 0.0129 = 0.1419 g.
Total Cm = 0.2838 + 0.1419 = 0.4257 g.
The total activity of Cm = 0,4257×(3×1012) = 1,28×1012 Bq = 34,52 Curie

9Preparation of the Silicate Phase
Tcool=20 ⁰C

ZrO2 crucible
T = 1500 ⁰C
ZrO2 lid
Metallic Phase + Concrete
PAr= + 15 mbar
Msample = 1,5 g
3 hours
Mconcrete = 1,7 g
placed in a furnace
V=400 ⁰C/h
heat,cooldark gray color

matte sheen
The result: Msample= 21,7 g., Mcrucible = 16,1 g.
The glass phase of silicate samples with Pu has
a dark gray color and a matte sheen due to thecomplete fragmentation of the metallic FD

Cracked Silicate Phase
Sample without Cm
Porous chip with sharp edges

Concrete:
cement - 17.62 %crushed stone from dense rocks - 49.28%
river sand - 24.69 %chemical additives - 0.21 %water - 8.20%

10Preparation of the Silicate Phase with Cm
Vheat,cool=400 ⁰C/h

ZrO2 crucible
T = 1500 ⁰C
ZrO2 lid
Metallic Phase + Concrete
3 hours
Msample = 2,16 g
PAr= + 15 mbar
Mconcrete = 2,74 g
placed in a furnaceT =20 ⁰C

Glass

cool

glassy sheen
In three crucibles, the metallic phasesamples with curium did not dissolve
completely, possibly due to thedifference in the composition of theconcrete loaded into each crucible (theamount of rubble in the concrete indifferent crucibles was not the same).

The bulk of the concrete evaporated, 0.14 g ofconcrete “entered” into the tablet. Several
grains of a light brown color are visible on thegraphite cup
The result: 11 brown tablets
Msample= 20,4 g., Mcrucible = 16,1 g. The glass
phase of silicate samples with Pu has a darkgray color and a matte sheen due to thecomplete fragmentation of the metallic FD

11

Matrix of Prepared Samples

Without Cm

With Cm

14
WithoutCm
36Samples

22With Cm

7
Metallic phase
Without Cm
7
Silicate phase
Without Cm
11
Metallic phase
With Cm
11
Silicate phase
With Cm

12

Samples & Tests: Basic Set of 24 Samples►▼●► Inspection (Uox) ▼ leaching ● Compression test ■ XRD ♦ SEM I I = internal irradiation

13

Complementary Samples. Total: 36 Samples

In addition to the samples initially specified in the Research
program, manufactured and investigated:1

Initial samples before impact of degrading factors with &without silicate phase - on compressive strength, phasecomposition and microstructure

2Samples with & without a silicate phase, with 244Cm added,
which will remain in the air environment - with XRD todetermine the evolution of the phase composition without theinfluence of chemical reactions

3

Three extra samples with & without a silicate phase forleaching

4
samples2
samples6
samples14

Accelerated Aging Mechanism
Metallic & Silicate
Phase with CmCm

aging accelerated ~180 times

1 year ≡ 2 days
10 year ≡ 20 days
50 year ≡ 100 days

Leaching
In solution imitation seawater(93% of resemblance)

Equipment for leaching withstable temperature
The technique of "accelerated aging":- accelerated dose collection fromα-decays for a shorter time interval due to additionof a powerful α-radiation source to the simulatedmaterial;- creation of more stringent conditions(in comparison with available in PCV / RPV) in
terms of concentrations of chemical elements
affecting the degradation process;- acceleration of the course of chemical reactions
under the influence of an increase in the soaking
temperature.

T= 95 ⁰С

Each 1st, 3rd & 7th day of the exposition until
the sample undergo damage equivalent to 10,
20, 30 & 50 years the concentrations of U, Pu,Cs, Sr, Zr, Fe, La, Nd, Cm measured

The change of the leaching rate shows theevolution of the surface layer and thewhole sample.

15Test Results

16Experimental Leaching Results
1)
2)

Data on leaching rates were obtained and treated in two ways:
Traditional method. Graphic images which show dependences of leaching rates to the sample area per day of theexperiment prepared in accordance with MCCI.
Dynamic method. Obtained results used to analyze summarized leaching rate of the revised nuclides excluding theinfluence of solutions uniting, as for each time replacement solution prepared. Data from dynamic method switched
into the real time (conversion rate = 180) and averaged over time range.

MetallicPhase

SilicatePhaseExpected Leaching Rates
Metallic Phase

Silicate PhaseFormation of Red Suspensions & Sludges
A mass output of a fine solid red-coloredsuspensions into a contact solution wasdetected in samples with Cm
20th daycontact solution ofsamples without Cm

contact solution ofsamples with Cm
no deposits

Silicate samples with Cm

100th dayouter surface- light bloom

inner surface- intense color

mechanism of red suspensions formation•a part of the red suspension caught
by the filter of the blue tape brand

•
•
•
•

filtered solution with particles
slipped through the blue tape filter•

irradiation of a contact solution with the formation ofperoxide ions and reactive oxygen species in the surface
layer
catalytic decomposition of peroxide near the exit to thesurface of metallic inclusions containing iron and chromium
corrosion of metallic inclusions and transition to thesolution of fine particles of iron oxides
sorption by pores of iron oxide particles of various heavy
metals and radionuclides from solution
Heavy metals hydrolyze and co-precipitating of redsuspensions with ironthe formation of films on the surfaces
19

Weakening of Metal Samples

20

Weakening of Silicate Samples

21

XRD. Microstructure of Metallic Samples

22

XRD. Microstructure of Silicate Samples

23

Mechanical strength
For the mechanical tests, samples were selected that simulate 0, 10, 20, 30 and 50years of fuel debris aging (σmax/days of experiment, MPa)
Hardening of metallic samples
without Cm
750

σmax, MPa

Weakening of metallic samples
with Cm
700

700

σmax, MPa

650

650
600

600

550

550

500

500

450

450

400

400
0204060

10020

Duration of «aging» in accelerated mode, days

Silicate samples withoutCm

400σmax, MPa

350

350

300

300

250

250

200

200

150

150

100

100

50

50

0020

4060

10060100

Silicate samples with Cm400

Duration of «aging» in accelerated mode, days

40

Duration of «aging» in accelerated mode, days

σmax, MPa

204060100

Duration of «aging» in accelerated mode, days

24

Expected compression force
Duration of «aging» in accelerated mode, days

Compression force,

Duration of «aging» in accelerated mode, days

Calculated duration of «aging» in real time mode, years

MPa

Calculated duration of «aging» in real time mode, years

Compression force, MPa

Metallic phase w/o Cm

0-20
0-10
511

20-40
10-20
560

40-60
20-30
635

60-100
30-50
639

0-100
0-50
586 (+53-75)

Metallic phase with Cm

565*

564*

610534568 +42-34)

Metallic samples• Compression force has changed little overtime, actually within 10-15% of statisticalerror• The samples demonstrated fragile
destruction, which corresponds to theirstructure• For samples without Cm certain increaseof compression force over time can beobserved , and for Cm samples, to theopposite, the decrease of strength on thelast time period can be observed* The samples of this type have been tested
for compression force without additional
crucible, that’s why all maximum values of
the chart were used for averaging.

Silicate phase w/o Cm

0-20
0-10118

20-40
10-20
(150-308)**

40-60
20-30
104

60-10030-50
780-1000-50
100 (+18-22)

Silicate phase with Cm

115

77123

61

94 (+29-33)

Silicate samples• More heterogeneous structure• Fragile destruction• Much lower values of compression force• Decrease of strength on the latest test
period can be observed (the minimum
value of compression force corresponds tocurium sample at the final stage).

** This sample has abnormal characteristicof destruction due to its heterogeneity –excluded from the averaging***The averaging was made for maximum
values of chart describing the destruction ofthe sample not taking into account the morevertical part of the chart, which refers to thestrength characteristics of the crucible.

Damage to the structure of Metallic samples

Metallic samples• High porosity, heterogeneity, developed external surface• Large amount of isolated iron-containing inclusions (similar to steel “globules” in Chernobyl lava)• Development of internal defects and corrosion of certain elements lead to the destruction of the sample
as these internal defect accumulate. The rate of destruction process depends on the state of metallic
inclusions• The resulting products of corrosion of metallic inclusions serve as additional “accelerator” of thedestruction26

Damage to the structure Silicate samples

Silicate samples• Smooth, glass-like surface, lower porosity• Large quantity of isolated iron-containing inclusions (similar to steel “globules” in Chernobyl lava
• The stability of silicate samples during the test period depends on the integrity of protective glass-likelayer, and in case of destruction of this layer (due to chemical, mechanical or any other factors) thedestruction rate may increase significantly

27Conclusions and Recommendations

28

Conclusions & Recommendations

Metallic Phase•
•
•

••
•

Cumulative radiation-chemical damage leads to greater degradation of fuel fragments,
than total radiation and chemical effectFe is corrodible
Ferrous hydroxide is a good coagulant of Pu and U and other elements, except for Cs, itwill lead to formation of larger quantities of small particles and hazardous fine dust.
Delay in removal of fuel fragments after 20-25 years after an accident can lead tocomplication of dose and radiation environment, because of increased emission ofplutonium, its further transit into colloidal forms and solid particles of submicrometer
dimension
Despite the fact that most of Cs emitted during high-temperature processes, but
approximately 10-20% of it is left in the form of cesium plutonate
In the FD mass areas of reduced sponginess can exist, in these areas speed of degradation
processes will be lower
For handling FD of “metallic” phase, the following requirements should be taken into
account:o to develop instruments, which let work with ceramics
o to estimate reduction of FD strength properties in course of timeo to estimate increase of dust formation with α-active and dose-producing components
o prolonged removal operations will lead to activation of degradation processes,
after the works are started and “covering” layers are opened
29

Conclusions & Recommendations

Silicate Phase•
•
•

•
•
•
•

Low integral strength of matrixes and local involvement into silicate matrixes
give high values of local strength.
Time delay of degradation processes start related to protection of PCV waterfrom intense alpha-irradiation from the MCCI surface.
In the course of scanning electron microscopy of silicate phase, formation of
secondary crystallization areas for U and Pu compounds, significantly distantfrom the place of fuel fragment and molten contact, in stratum of melted
concrete was revealed.
Mechanical strength of silicate samples is commensurate with strength of
vitrified HLW matrixes.
Leaching rate of controlled radionuclides of silicate samples is commensuratewith leaching rates of the same radionuclides of vitrified HLW matrixes.
Chemical stability of silicate stage in simulation water is slightly lower, thanchemical stability of borosilicate glass.
Prolonged removal operations will lead to activation of degradation processes,
after the works are started and “covering” layers are opened.
30

Definitions•Fuel debris (FD) – solidified melt of nuclear fuel containing materials formed in
PCVs during accident at 1F, usually consist of fuel, fissile materials, fission
products and structure materials (stainless steel, Zr cladding, control rod
materials, concrete etc)

31