91 92. june 9 overview febex-dp-and_ufd r&d activities related to febex-dp_zheng

Used Fuel Disposition Campaign

FEBEX-DP Collaboration

Liange Zheng, Hao Xu, Jonny Rutqvist, Jens Birkholzer Lawrence Berkeley National Laboratory June 9, 2016

Used Fuel Disposition

Part 1: Overview of FEBEX-DP

FEBEX: Full-scale Engineering Barriers EXperiment Experiment were based on Spanish HLW

emplacement concept for a granitic host rock It was initiated by ENRESA in 1994 under the

auspices of EU It is composed of laboratory experiments, Mock-up

and in situ tests, and THC/THM modeling.

Mock-up test February 1997– now

Galleries


FEBEX Jan 1996 – Jun 1999

FEBEX II Aug 2000 – Dec 2004

NF-PRO (WP3.3) Jan 2005 – Dec 2007

FEBEX-e

Planning and design Set-up 1st Operational Phase 2nd Operational Phase Excavation

94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15

FEBEX-DP

16

Partial dismantling Final dismantling

FEBEX in situ Test

Zürich

Grimsel


FEBEX: in situ Test Partial Dismantling of heater 1 (2002)

Dismantled section


FEBEX–DP: Dismantling of heater 2

Objectives Bentonite characterization

– Density, water content and spatial distribution – Chemical changes

Characterization of corrosion and microbial processes

– On instruments/sensors and coupons – Bacterial growth – All under evolving redox-conditions

Mineralogical interactions at material interfaces

– Concrete - bentonite, heater/liner – bentonite, rock - bentonite

– Impact on pore water composition

Integration of the monitoring results and modelling

– THM/THMC modelling – Pre- and post dismantling

5


S49



Hot sections

Cold sections

Hot sections

Cold sections



Part 2: UFD R&D Activities Related to FEBEX-DP

Coupled THMC modeling The hydration of bentonite:

Non-Darcy flow – the presence of a threshold gradient Decrease of intrinsic permeability of the buffer due to swelling Action of thermal osmosis to counteract flow towards the heater

The chemical evolution in the bentonite Changes of more soluble minerals (gypsum, calcite and pyrite) and aqueous concentration, evolution of pH and Eh, alteration of smectite

Experimental work Synchrotron X-ray Microtomography Measurements to characterize the micro-

cracks of the bentonite(LBNL). Characterization of the microstructure of Bentonite and interface areas using

SEM – EDS – BSEI and X-ray CT Scan (SNL) Hydrothermal Experiments (LANL)


THMC Modeling: Key Model Features

1D Model For hot sections Chemical reactions includes aqueous complexes, cation exchange, mineral dissolution-precipitation Two mechanical models were tested

Linear Swelling: dSlKd sws βσ 3=

Porosity change:

Permeability change: ( )Kekk

0

0

σσ −

=

BExM


0

5

10

15

20

25

30

35

0.4 0.6 0.8 1 1.2

Wat

er co

nten

t (%

)

Radial distance (m)

Data 5.2 yrs Data 18.3 yrs

THMC-LS, 5.2 yrs THMC-LS, 18.3 yrs

THMC-BExM 5.2 years THMC-BExM 18.3 yrs

Model Results: T, RH and WC

Observations: As expected, THMC model outperform TH model in matching the RH data near the heater. THMC model reasonably match the water content and porosity data at 5.2 years (dismantling of heater 1) and at 18.3 years (dismantling of heater 2). The cooling period after heaters were switched off leads to significant redistribution of moisture.

0

10

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0 1000 2000 3000 4000 5000 6000 7000

Rela

tive

hum

idity

(%)

Time (day)

R = 0.52 mWCSE2-03WCSE2-04WCSE1-03WCSE1-04THMC-LSTH modelTHMC-BExM

Temperature

Relative humidity

Water content


Model Results: Stress

E2 F2

Observations: Reasonable match between model results and stress data.

-1

0

1

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9

0 1000 2000 3000 4000 5000 6000 7000

Nor

mal

Str

ess (

MPa

)

Time (day)

E2 data, r=1.1 mF2 data, r=1.1mTHMC-LS Radial THMC-LS circumferential THMC-BExM radialTHMC-BExM circumferential -1

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0 1000 2000 3000 4000 5000 6000 7000

Nor

mal

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ess (

MPa

)

Time (day)

E2 data, r=0.5 mTHMC-LS circumferential THMC-LS Radial THMC-BExM circumferentialTHMC-BExM radial


Model Results: Cl-

Observations: Porosity increase and permeability reduction in THMC model does not significantly improve the fit to measured Cl data; However, after 18 years, the model results for the THC and THMC model are similar. Increase in permeability near the granite improves the fit to Cl data

0.E+00

5.E-02

1.E-01

2.E-01

2.E-01

3.E-01

3.E-01

4.E-01

0.4 0.6 0.8 1 1.2 1.4

Conc

entr

atio

n (m

ol/L

)

Radial distance (m)

Cl- data S29, 1930 days

data S19, 1930 days

data S28, 1930 days

THC model, 5.2 yrs

THC model, 18.3 yrs

THMC-LS 5.2 yrs

THMC-LS, 18.3 yrs

THMC-BExM, 5.2 yrs

0.E+00

5.E-02

1.E-01

2.E-01

2.E-01

3.E-01

3.E-01

4.E-01

4.E-01

0.4 0.6 0.8 1 1.2 1.4

Conc

entr

atio

n (m

ol/L

)

Radial distance (m)

Cl-

data S29, 1930 days

data S19, 1930 days

data S28, 1930 days

THMC-LS base

THMC-LS sensitivity

( )0

0φφA

ekk =A Sensitivity case


Checking the Microscopic Structure

Synchrotron X-ray Microtomography Measurements - Characterization of the microstructure of the material. - Description of the crack network in a quantitative fashion. - Study the mechanisms involved in the propagation of cracks. - Provide data for models.

Scanned with the 3.22 μm resolution setup

S59


Sample as is (cropped), FOV ~6mm, 3.22 μm vx size Virtual cut to show the inside of the sample Cut sample with the medial axis of the crack network labeled with the aperture value All the (aperture color labeled) medial axes of the cracks in the sample Connected component labeling of the fractures larger than 1000 vx in volume



B-D

-59-

15

B-D

-59-

8

B-D

-59-

3

Sample rendering Aperture-labeled medial axes Overlapped data

1 mm



Bentonite – Concrete Interface Characterization (SEM – EDS – BSEI) (SNL)

16

Back-Scattered Electron Image (BSEI) of Bentonite – Cement Interface

X-ray Map Line Scan: Ca

Portlandite Grain? Approx. Interface Location

So far – no indication of strong elemental gradients beyond the interface region

Cracks (desiccation?) tend to be abundant at the interface

Portlandite mineralization at the interface?

More elemental line-scans needed to resolve compositional gradients

Work in Progress!!!


Ongoing and Future Work

Coupled THMC modeling Considering thermal osmosis and dual continuum for transport to improve the fit to conservative species. Refining chemical models to match reactive species

Synchrotron X-ray Microtomography Measurements

Taking more measurements for samples for section 59 and 49

Developing a tool to characterize the fracture network in a quantitative fashion

Used Fuel Disposition Sample from B-D-59-8

Thin horizontal slice from the whole measured volume, highlighting the microstructure and the fracture network (in yellow, on the right).

1 mm

Used Fuel Disposition Sample from B-D-59-15

Thin horizontal slice from the whole measured volume, highlighting the microstructure and the fracture network (in yellow, on the right).

An aggregate particle in this sample displays negative crystals (dissolution?)

1 mm


Displaying a thin slice of the sample reveals some more details about the method: B-D-59-3 B-D-59-8 B-D-59-15

To quantify the fracture network characteristics of the different samples we use a simple procedure (optimization of the process is ongoing): - Segment the voids from the dataset - Calculate the medial axis of the resulting binary dataset - Calculate the local thickness of the binary dataset - Label the medial axes with the local thickness value in the same position A statistical analysis of the aperture values becomes now possible and can be used to characterize and compare different sample in a quantitative fashion.

.5 mm


Example of the results from a 3.22mm x 3.22mm x 1.61mm volume for each sample (3.22 μm voxel size, theoretical resolution)

0

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150000

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5 15 25 35 45

BD 59-3

BD 59-8

BD 59-15

Bin [μm] Bin [μm]

Aperture analysis of the medial axes: Absolute values %

Larger amount of small voids due to a very (micro-) porous aggregate particle in BD 59-15

BD 59-3 has larger fractures

The negative crystals of BD 59-15 contribute to the larger aperture values amount

Used Fuel Disposition Some comments/conclusions

- Synchrotron X-ray microCT can be used effectively to characterize the microstructure of the sample, with special focus on fracture networks.

- Measurements at different resolutions found that a 3.22 μm vx size and ~6 mm field of view is the best compromise, in the context of the resolution vs. FOV problem.

- Still, given the high heterogeneity of the samples, the volumes investigated are hardly representative of the whole material. Plus sampling issues can be present as well.

- Encouraging results have been obtained in the perspective of developing an experimental strategy to monitor the development of cracks during the sample drying, to obtain further information about the fracturing mechanisms present.

- Quantitative characterization of the voids/fractures in the sample can be successfully carried out to compare different volumes and/or samples.

Science

91 92. june 9 overview febex-dp-and_ufd r&d activities related to febex-dp_zheng