korea hydro & nuclear power co., ltd. (khnp) nuclear engineering & technology institute...

24-28 Nov., 2008The 2nd RCM, IAEA CRP

KHNP-NETEC

Korea Hydro & Nuclear Power Co., Ltd. (KHNP)Nuclear Engineering & Technology Institute (NETEC)

Joo Wan Park and Chang Lak Kim

The 2nd Research Co-ordination Meeting on Behaviour of Cementitious Materials in Long Term Storage The 2nd Research Co-ordination Meeting on Behaviour of Cementitious Materials in Long Term Storage and Disposal of Radioactive Waste Bucharest, Romaniaand Disposal of Radioactive Waste Bucharest, Romania

Long-term Behavior of Cementitious Materials in the Korean Long-term Behavior of Cementitious Materials in the Korean

Repository EnvironmentRepository Environment

(Research Agreement No. 14246)(Research Agreement No. 14246)


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Today……

Background

- Briefs on LILW Management & National Disposal Project

Objectives & Scope

Overall Implementation Plan

Research Work Done & Results

2


Nuclear Energy in Korea

Under constructionIn operation ( CANDU

Seoul

Daejeon

Gori

Uljin

Wolsong &Sinwolsong

Yonggwang

Planned

(As of November 2008) Commercial operation of Gori Unit #1 began in 1978

Currently total 20 NPPs (16 PWRs and 4 CANDUs) in commercial operation

6 under construction 2 currently in planning Nuclear share of

electricity 38.6 %WolsongLILW Disposal Center

3


LILW Management

Arising of LILW from: Application of RI and Operation of NPP Amount of radioactive waste storage (As of Dec.

2007):LocationLocation

Number ofReactors

Number ofReactors

KoriKori 44

YonggwangYonggwang 66

UlchinUlchin 66

WolsongWolsong 44

StorageCapacity(drums)

StorageCapacity(drums)

50,20050,200

23,30023,300

17,40017,400

9,0009,000

TOTALTOTAL 99,90099,900

Cumulativeamount(drums)

Cumulativeamount(drums)

35,56035,560

16,45416,454

12,87712,877

6,0356,035

70,92670,926

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Status of National LILW Disposal Project

Name: Wolsong LILW Disposal Center Site Location: Gyeongju (South Eastern Part of Korean Peninsula) Area: 2,096,491 m2 (2.1 Mm2) Capacity: 100, 000 drums (Phase I), 800,000 drums (Final) Disposal Type: Silo type disposal (Phase I) Project Duration: ’06. 1 ~ ’10. 6 License: Approved for Construction & Operation by MEST

(Regulatory Authority) on July 2008 Construction: Started on August 2008

5


A Bird’s Eye View of Wolsong Site

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Concept of Surface Facility and Disposal Silos

6 Silos for phase 1

Vertical shaft

Entrance portal of C/O tunnels

Surface facilities

C/T

O/T

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Operational Tunnel

Construction Tunnel

Vertical Shaft

Disposal Silos

Concept of Surface Facility and Disposal Silos

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Concept of Facility Closure

Crushed Rock

Crushed Rock

Concrete Overpack

Concrete Plug

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Objectives To investigate the closure concepts and cementitious backfill materials for the facility closure. To gain practical experiences in major issues considered in closure concept of the Korean LILW repository.

Scope Characterization of concrete container and cementitious backfill materials in the Korean LILW repository Development of repository closure concept and evaluation of long-

term behavior of cementitious materials Radionuclide transport modeling considering concrete degradation in repository conditions

Objectives and Scope

10


Year 1

Characterization of concrete container and cementitious backfill materials in the Korean LILW repository

Packaging consideration for disposal in silo type repository Investigation of backfill materials for repository closure Performance test for physico-chemical properties of backfill materials

Year 2(On-going)

Development of repository closure concept and evaluation of long-term behavior of cementitious materials

Establishment of closure concept for unit silo and disposal facility Evaluation of gas generation and migration in disposal silo Degradation modeling of concrete structure and/or backfill materials


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Year 3

Radionuclide transport modeling considering concrete degradation in repository conditions

Development of conceptual models for intact and degraded conditions

Implementation of input parameter database and quality assurance for safety/performance assessment

Safety/performance assessment of disposal facility using a proprietary computer tool


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Research Work Done & Results

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■ Laboratory Test of Cementitious Backfill Materials

■ Gas Generation & Migration Studies

■ Degradation Modeling of Concrete Structure

■ Comparison of Silo Closure Option in the Site-specific

Condition

13


Lab. test of cementitious backfill materials

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Case Material Composition

I cement:fly ash:water:sand1:0.25:0.56:2.585

(used in domestic nuclear facility)

II cement: water: sand1:1.13:4

(used in Sweden SFR)

III cement: water: sand1:0.5:0.5

(porous cement mortar)

■ Composition of cement mortars

Test Item Unit Test Method

Specific gravity g/ ㎤ ASTM C 642

porosity % ASTM D 4284

Compressive strength N/ ㎟ KS L 5105

Hydraulic conductivity m/s ASTM D 5084

Gas permeability ㎡ Torrent method

Critical pressure Pa Torrent method

Bulk density g/ ㎤ KS F 2308

■ Test methods

AP

Qlmk

A

Q

PP

hPK

22

21

22

where K : gas conductivity (m/s), P1 : inlet pressure(kg/ ㎡ ),

P2 : atmospheric pressure(kg/ ㎡ ),

h: thickness of specimen (m), Q : gas flow rate( ㎥ /s), A : Area( ㎡ ), γ : gas unit mass /volume(kg/ ㎥ ).

where K : gas conductivity (m/s), P1 : inlet pressure(kg/ ㎡ ),

P2 : atmospheric pressure(kg/ ㎡ ),

h: thickness of specimen (m), Q : gas flow rate( ㎥ /s), A : Area( ㎡ ), γ : gas unit mass /volume(kg/ ㎥ ).

where k : hydraulic conductivity (m/s), Q : flux per unit time( ㎥ /s), A:cross-sectional area of specimen( ㎡ ), P : water pressure(kg/ ㎡ ), l : thickness of specimen (m), m : unit mass of water ( ㎏ / ㎥ ).

where k : hydraulic conductivity (m/s), Q : flux per unit time( ㎥ /s), A:cross-sectional area of specimen( ㎡ ), P : water pressure(kg/ ㎡ ), l : thickness of specimen (m), m : unit mass of water ( ㎏ / ㎥ ).

Hydraulic conductivity

Gas permeability

14


mixing condition

of domestic NPP mixing condition

of swedish

disposal facility

bubbled cement

mortar

1.E- 12

1.E- 11

1.E- 10

1.E- 09

1.E- 08

hyd

raulic c

onductivi

ty[m

/s]

■ Test results

CaseDry density

(g/ ㎤ )Porosity(-) )×10-2

Compressive strength(N/ ㎟ )

Hydraulic conductivity( ㎝ /s)×10-9

Gas permeability( ㎡ )×10-16

I 1.871 6.89 83.4 0.6763 1.421

II 1.923 27.54 8.9 2.6987 7.068

III 0.802 24.66 7.7 269.82 180.256

Hydraulic conductivity of various mixing conditions of cement mortar Hydraulic conductivity of various mixing conditions of cement mortar

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Gas Generation in a Silo Metal corrosion, Microbial degradation : GAMMON (UKAEA) Radiolysis : MAXH2 (KHNP) DAW, 200 L Steel Drum, 16700 Drums in a Silo

Most of gas generation comes from metal corrosion in the form of H2.

After 1,000 yrs, H2 gas generation is about 9.0×104 m3 .

Gas generation is rapidly increased immediately after closure.

Gas generation due to microbial degradationGas generation rate due to metal corrosion

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Spatial distribution of gas pressure in the model domain after 1000 years of hydrogen gas generation from the radioactive waste

Vertical cross section and mesh of the model domain and seven monitoring points used in the numerical simulations

TOUGH-II simulation Sensitivity analysis - gas gen. rate, material(concrete, host rock) properties

Temporal change of mass fraction of gas dissolved in groundwater at the seven monitoring points in the model domain

Gas Migration Study (On-going)

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Gas Migration Study (On-going) Sensitivity Analysis Results

Spatial distribution of mass fraction of gas dissolved in groundwater in the model domain after 1000 years of hydrogen gas generation: (a) Case 1: gas gen. rate x 2 (b) Case 2: hyd. cond. of concrete x 0.1, (c) Case 3: hyd. cond. of host rock x 2, (d) Case 4 : case1 + case.

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■ Concrete degradation factors considered

Sulfate and Mg Attack => Expansive Force, Crack and Spalling

Ca(OH)2 Leaching => reduce the pH, promote the corrosion of reinforcing steel

Alkali-Aggregate Reaction => Crack formation in concrete

Chloride Attack & Carbonation => Oxidation due to Cl ion penetration, Neutralization (pH 12 8), Enhancement of Ca(OH)2 leaching in low pH condition

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Degradation Modeling of Concrete Structure

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4th step

3rd step

2nd step

1st step

Concrete Neutralization

Corrosion

Cracking of Concrete

Depassivation

Carbonation

Chloride attack

Volume increase

Porosity and hydraulic

permeability increase

Above threshold

level

Phase 1Initiation period

Phase 2Propagation period

Corrosion of Reinforcing Steel

20


Service Life Models

Diffusion Model => Migration of chemical species only by diffusion in concrete

Empirical Model => Empirical mathematical models (US DOE)

Reactive-Transport Model => Migration of chemical species by advection and dispersion

=> Complex chemical reaction models and thermodynamic data

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Diffusion model and empirical model are considered in this stage.

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0

0.2

0.4

0.6

0.8

1

0 500 1000 1500 2000 2500 3000

Time (yr)

Ct/C

o

α=0.3

α=0.45

α=0.6

tD

xerfCtxC s

21),( Analytical solution of diffusion

equation

oo t

tDtD )(

Power function Phase I

■ Effect of α value on chloride diffusion in diffusion model

Evaluation of Concrete Degradation

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■ Corrosion Rate of Reinforcing Steel in diffusion model


xd

tCDsremaining gwi

2

4.941100%

Corrosion rate of reinforcing

steel Phase II

99.99988

99.99992

99.99996

100.00000

100.00004

0 200 400 600 800 1000 1200 1400

Time (yr)

Reb

ar r

emai

ning

(%)

DO Conc.: 0.24 mg/L,

DO diffusion coeff.: 2×10-8 cm2/yr

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■ Effect of w/c ratio in empirical model

0

2000

4000

6000

8000

10000

0 5 10 15 20 25 30 35 40 45

Concrete Thickness (cm)

Tim

e t

o O

nse

t o

f C

orr

osio

n (

yr)

w/c=0.5 w/c=0.45

w/c=0.3 w/c=0.15

42.0

22.1

])[/(54.2

129)(

Clcw

x

yrt

c

c

Corrosion onset time (Phase I)

10-5 m/yrCorrosion time (Phase II)

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Comparison of Silo Closure Option

■ 5 Option for a Silo Closure

■ Groundwater Flow Analysis – Regional & Local Models

■ Radionuclide Transport Assessment

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Silo Closure Option

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Crushed Rock

Cement MortarCrushed Rock

Bentonite

Crushed Rock Crushed Rock

Host Rock Host Rock

Host Rock Host Rock

Crushed Rock

Radioactive waste +

Crushed rock

Radioactive waste +

Crushed rock

Radioactive waste +

Crushed rock

Crushed Rock

Radioactive waste +

Crushed rock

CASE1-M1 CASE1-M2

CASE2-M1 CASE2-M3

Concrete Concrete

ConcreteConcrete

Bentonite(10%)+Sand(90%)

Host Rock

Crushed Rock

Radioactive waste +

Crushed rock

CASE2-M2

Concrete


Groundwater Flow Modeling - Regional

A A’

A A’

0.7

km

SILO

River boundary

General head Boundary

1.6

2k

m

2.18km

41.0m

48.2m

32.5m

25.5m41.5m

36.5m

19.3m

25.6m

Visual Modflow 3D

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Visual Modflow 3DVisual Modflow 3D

Concrete (width : 0.6~1.2m)

Inner (width: 0.2m)

Outer (width: 1.2m)

Radioactive waste + Crushed Rock (24mx24mx35m)

Crushed Rock (24mx24mx15m)

A A’

200m

200m

A A’

155m

Groundwater Flow Modeling - Local

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CASE1- M12.45E- 01

CASE1- M21.91E- 01

CASE2- M12.34E- 01

CASE2- M21.33E- 01

CASE2- M31.22E- 02

0.00E+00

5.00E- 02

1.00E- 01

1.50E- 01

2.00E- 01

2.50E- 01

3.00E- 01

CASE

Dar

cy V

elo

city

(m/y

ear)

CASE1- M11.06E- 03

CASE1- M28.18E- 04

CASE2- M11.61E- 04

CASE2- M21.10E- 03

CASE2- M34.95E- 05

0.00E+00

2.00E- 04

4.00E- 04

6.00E- 04

8.00E- 04

1.00E- 03

1.20E- 03

1.40E- 03

CASE

Dar

cy V

elo

city

(m/y

ear)

Intact ConcreteIntact Concrete After Fully DegradedAfter Fully Degraded

Option Intact Concrete After Fully Degraded

Case1_M1 1 1

Case1_M2 7.72E-01 7.81E-01

Case2_M1 1.50E-01 9.56E-01

Case2_M2 1.04E+00 5.41E-01

Case2_M3 4.33E-02 4.96E-02

Groundwater Infiltration into a Silo

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Radionuclide Transport Assessment

■ Reference Scenario

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■ Conceptual Model

■ Mathematical Modeling : Compartment model

■ Assessment Tool : MOSAIC developed by KHNP &

MSCI

The connection symbol “” denotes advective mass transfer, while the symbol “↔” denotes diffusive/dispersive mass transfer from one compartment to another compartment, respectively

Radionuclide Transport Assessment

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Comparison of NF Release Rate

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Thank you for your attention !

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