a comparison of the hlw underground repository cost for the vertical and horizontal emplacement...

www.elsevier.com/locate/pnuceneProgress in Nuclear Energy 49 (2007) 79e92

A comparison of the HLW underground repository cost for thevertical and horizontal emplacement options in Korea

S.K. Kim a,*, Y. Lee a, J.W. Choi a, P.S. Hahn a, Tai-Wan Kwak b

a Korea Atomic Energy Research Institute, Radwaste Disposal System Development, 150 Dukjin-dong, Yuseung-gu,

Daejon 305-353, Republic of Koreab Chungnam National University, 220 Geung-dong, Yuseong-gu, Daejon 305-764, Republic of Korea

Abstract

This study presents the results of an economic analysis for a comparison of the vertical and horizontal emplacement alternativeswith respect to an HLW repository. According to the cost analysis undertaken in the Korean case, the horizontal emplacementoption was more economical than the vertical one. In order to estimate such an emplacement alternative, a conceptual frameworkshould be designed first to the cost objects, and then cost drivers and economic indicators are taken into consideration. The majordifference between a vertical emplacement and a horizontal one was that the long horizontal disposal drifts of the horizontalemplacement replace the disposal holes and disposal tunnels of the vertical emplacement with vertical holes. Therefore, in thecase of a horizontal emplacement, several canisters are installed in the long horizontal disposal drifts instead of one canister perone disposal hole of the vertical emplacement option.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Cost estimation; Spent fuel; Repository; Construction cost; Cost driver

1. Background

The repository cost is classified as aboveground facilities and underground facilities. In this paper, only the costs ofthe underground facilities were considered in order to compare the cost between the vertical emplacement and hor-izontal one.

An underground facility cost is required to disposal of the spent fuel, generated from a nuclear power plant, ina deep place underground in order to safely isolate the spent fuel from the ecosystem for a long period of time.The repository cost with respect to the disposal of spent fuel largely consists of the construction cost, operatingcost and closure cost (Kukkola et al., 2003).

* Corresponding author. Tel.: þ42 868 8892; fax: þ42 868 8198.

E-mail address: [email protected] (S.K. Kim).

0149-1970/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.pnucene.2006.09.004

mailto:[email protected]

http://www.elsevier.com/locate/pnucene

80 S.K. Kim et al. / Progress in Nuclear Energy 49 (2007) 79e92

In addition, in estimating the disposal cost, the disposal process and various cost estimation methods should be takeninto account. Since no spent fuel repository has been built in Korea to date, it is difficult to accurately predict the cashoutflows with respect to the repository construction cost. For this reason, the data from a reference repository are used.

The disposal area contains the central tunnel, panel tunnels, deposition tunnels and the deposition holes. Thedimensions of the total disposal area are about 2� 2 km (exactly 1.8� 2.2 km).

Fig. 1 and Table 1 show the concept of the underground facilities (Saanio et al., 2004). The authors referred to a con-ceptual drawing of the underground structure of the repository in order to estimate the costs of the undergroundfacilities. Fig. 1 shows the layout of the tunnel. As shown in Fig. 1, the underground repository has shafts dug outon both sides, which are connected to the access tunnel. This access tunnel is connected to the disposal tunnel andthe panel tunnel in order that the disposal canister can be transported. The concept of this design is that the disposalhole is vertically dug out downwards from the disposal tunnel floor, and therefore the PWR spent fuel and CANDUspent fuel may be placed in two different sectors separately. Depth of the underground facilities is assumed to be500 m.

2. Conceptual design of the emplacement options

2.1. Vertical emplacement

Figs. 2 and 3 show the conceptual design of vertical emplacement option. Disposal holes are closed immediatelyafter a canister deposition. Holes are closed with bentonite blocks, as shown in Fig. 3. Blocks are compacted witha high pressure to the shape of pineapple rings and disks. Pineapple ring shaped blocks are used by the side of thecanisters and disk shaped blocks on the bottom and top of the canisters.

Table 2 shows the technical variables of the vertical emplacement option.

2.2. Horizontal emplacement

It is crucial to have a number of underground tunnels in order to transfer and place the disposal canister into thedisposal hole in the rock. The access tunnel is employed to move the disposal canister to the repository, whereas thedisposal tunnel was designed to place the disposal canister into the disposal drifts.

Fig. 4 shows the layout of the disposal drifts in the horizontal emplacement option.

Fig. 1. Disposal area of the underground facilities. Green panel is for CANDU canisters.

81S.K. Kim et al. / Progress in Nuclear Energy 49 (2007) 79e92

Canisters can be emplaced horizontally. In the case of the horizontal emplacement alternative, canisters are placedinto perforated steel containers which are surrounded by buffer bentonite, as shown in Fig. 5. Lengths of the disposaldrifts are assumed to be 301 m.

In the vertical emplacement alternative, canisters are disposed in vertical holes, one canister per one hole, whereasseveral canisters are installed in the long horizontal disposal drifts in the case of a horizontal emplacement.

But, in the case of the horizontal emplacement alternative, additional research and development is required. Instal-lation machines of the canister and bentonite blocks are complicated. A horizontal emplacement has not beendesigned in as much detail as a vertical emplacement.

Fig. 6 shows the dimensions of the container in the horizontal emplacement option.

Table 1

Dimensions of the underground facilities

Item Value

Technical variables

Disposal area 1.8 km � 2.2 km

Depth 500 m

Canister shaft Diameter 6 m

Personnel shaft Diameter 4.5 m

Ventilation shaft Diameter 4 m

Deposition tunnels Length 95 758 m

Number of tunnels 377

Length 251 m per tunnel:

width 5.00 m, height 6.15 m

Panel tunnels Length 14 900 m

Width 6.00 m

Height 7.60 m

Central tunnels Length 2650 m

Width 7.00 m

Height 8.40 m

Access tunnel Width 8.00 m

Height 7.95 m

Fig. 2. Overview of the vertical emplacement.


3. Cost estimation methodologies

Given the condition that price change rates are taken into account and the cost is accrued at the rate of C1, C2,C3, ., Cn, the repository construction costs can be expressed by the following Eq. (1) (Choi et al., 2004):

FV¼Xn

i¼1

Cið1þ rÞðn�iÞð1þ f Þðn�iÞ ð1Þ

where r is the interest rate, f the inflation, i the elapsed year, and n is the completion year.

Fig. 3. Dimension of disposal hole and disposal tunnel in the vertical emplacement.

Table 2

Technical variables

Item Value

Deposition holes Number 2835 (CANDU)

Number 11 375 (PWR)

Diameter 2240 mm

Depth 7830 mm

Distance between holes PWR 6 m (centre points)

CANDU 4 m (centre points)

Deposition tunnels Length 95 758 m

Number of tunnels 377

Length 251 m per tunnel: width 5.00 m, height 6.15 m


In the case of a cost analysis of an HLW repository, the following categorization of the methods or tools can beconsidered

- volume based cost accounting- activity based cost accounting (Horngren et al., 1994).

In the case of a cost estimation for HLW underground facilities, the author chose the volume based cost calculationmethod because of the easiness of the calculation.

Table 3 shows the comparison of the methodologies for the cost analysis.When estimating the construction cost, it is necessary to estimate it in the order of the objects whose cost is likely to

be high, and break down the cost objects selected to estimate the cost using the top-down estimation method (Park et al.,2005). At this time, the cost driver whose cost is considered to be the most crucial should be estimated first. And thus thecost driver whose cost is relatively higher should be estimated more accurately than the rest of the cost drivers.

Since Korea has no experience in building a repository with respect to the disposal of spent fuel, a foreign casestudy was used as a reference case with respect to the number of cost units except for the cost of the buffer. Forexample, the cost of bentonite is 150 V/ton, and the labor cost for compacting the buffer is 200 V/ton.

The disposal cost can be expressed as follows, in the form of the unit cost of uranium which is a raw material ofspent fuel (SKB, 2003).

Unit cost of U¼ Total disposal costs

Weight of the disposed Uð2Þ

Since an uncertainty about the cost might arise as a consequence of our unfamiliarity with or lack of experience inrelated areas, a contingency cost should be taken into account in order to cope with such a problem. In addition, an

Access Tunnel

PanelTunnel

PWR(41 canisters/drift)CANDU

(52 canisters/drift)

OperationChamber

DisposalDrift

OperationChamber Disposal

Drift

5.5 m 5.5 m 7 m 7 m15 m 15 m

40m

301 m 301 m

40 m

Fig. 4. Layout of the disposal drifts in horizontal emplacement.

Copper canister

Bentonite rings

Bentonite block

Steel container

Steel lid

Disposal container

Fig. 5. Container for a canister in the horizontal emplacement alternative.


owners cost is included in the construction cost. This cost includes such expenses as development, designing, projectand permission related cost. In Finland, such costs were estimated to be approximately 15% of the construction cost(Choi et al., 1998).

The investment cost relates to two subgroups e the construction cost and the machinery and equipment cost. Withrespect to the estimation of the excavation capacity for the tunnels, the area of a cross section was estimated in a con-servative manner by multiplying the width by the height. The investment cost includes the machinery cost required forthe mixing and emplacement of the backfilling materials.

A major part of the disposal cost is the operation cost. The operation and maintenance cost includes all expensesrequired to operate the repository. These expenses include all the direct and indirect labor costs, taxes, equipment,outside support services, insurance against accidents and so on.

The wages required for the backfilling work were included in the labor cost, but the machinery and system costswere included in the investment cost. On the whole, the operating cost is subdivided into fixed and variable costs. Thetotal variable cost is correlated with the changes in the cost drivers.

The costs accrued during the closing steps are required to undertake such finishing works as a backfilling of thedisposal tunnel and a closure of the shaft which is a pathway connecting the aboveground facilities and the under-ground facilities.

The disposal tunnel is filled with crushed rock floors. The shaft is filled with these materials as well. The total costfor a plugging within the repository is estimated by using the unit cost necessary to undertake a plugging with concreteat the access of the shaft.

4. Cost estimation terms

POSIVA (Finland) in co-operation with KAERI (Korea Atomic Energy Research Institute) undertook a research inorder to estimate the cost necessary to construct underground facilities with a disposal capacity of up to 36 000 ton of

4.83 m

1.020.52 0.525.83 m

0.5

Buffer

Canister Canister

0.5

2.06 mBuffer

Fig. 6. Dimensions of container in the horizontal emplacement.

Table 3

Comparison of the cost estimating methods

Category Cost analysis Capital budgeting analysis

(Nagano, 2003)

Volume based

cost accounting

Activity based cost

accounting (Amos, 2004)

Project financing assessment

Object Project/HLW repository Project/HLW repository Project/HLW repository

Purpose Comparison of the techniques Cost management by

means of cost drivers

To decide whether to

invest in the project or not

Index Amount of spent

fuel to be disposed

Amount of activity for

disposing of the spent fuel

IRR, NPV, pay-back

period, profitability etc.

for investment appraisal

Drawback Adjustment needed when

allocating the overhead costs

Not easy to categorize the cost

pool by the activity

and to convert it to a unit

cost per kg U generated

All the specifications of the

project to be assessed

should be fixed prior

to the calculation

The authors did not estimate the social cost because of an uncertainty.


spent fuel, which was presented by KAERI as an example. The repository and the disposal tunnel were estimated to be3.3 million m3 in size and 105 km long, respectively (Choi et al., 1998).

4.1. Disposal capacity

It was assumed that the disposal capacity was up to 36 000 ton of spent fuel for the cost estimation. This is the totalamount of spent fuel expected to be generated from the nuclear power plants which will be built and operated by 2015,according to the long-term power plan published by the former Ministry of Commerce and Trade (the Ministry ofCommerce, Industry and Energy). 20 000 ton of PWR spent fuel and 16 000 ton of CANDU spent fuel are coveredby such a disposal capacity (Choi et al., 1999).

In this paper, in order to dispose of such fuel, given the assumption that the situation requires 11 375 PWR disposalcanisters and 2926 CANDU disposal canisters, the cost necessary to dispose of the fuel into the deep rock in a mannerensuring safety against a radiation and a cost effectiveness was estimated. It was assumed that four assemblies are putinto the PWR disposal canister, while there were 33 assemblies in a basket within the CANDU disposal canister, inorder to fill the disposal canisters which consisted of nine layers accommodating 297 CANDU assemblies. The size ofthe disposal canister was assumed to be 40 ton in weight, 1.22 m in diameter and 4.83 m long.

4.2. Repository construction period

Fig. 7 shows a total of eight construction stages. The URL stage lasts for 10 years, encompassing the URL design-ing and construction period. The first stage also lasts for 10 years. During this period two CANDU panels and onePWR panel are built. In addition, during the first stage, the URL is operated and a trial operation of the repository

Fig. 7. Implementation time schedule.

0

100

200

300

400

500

600

700

2007 2014 2037 2044 2051 2059 2066 2077[Year]

[MEU

R]

Fig. 8. Cash flow for the underground facilities of a repository.


is undertaken. During the second stage, the CANDU disposal canisters are disposed of for 20 years and at the end ofthe stage a minimum of three PWR panels are built at the other side of the access tunnel.

The periods of stages 3, 4, 5, and 6 require 7.5 years each (total 30 years). During these stages, PWR spent fuel isdisposed of and eight panels (two each) are built during each stage. Lastly, the closure stage requires 10 years, whenworks such as backfilling of the panel tunnels, access tunnels and shaft are undertaken. Therefore, it is assumed thatthe disposal program would require a total of 80 years (Saanio et al., 2004).

4.3. Cash flow

In this case of a cost estimation, a cash flow should be considered for long periods because the construction of therepository was assumed to be 80 years. Fig. 8 shows the cash flow for the underground facilities of an HLW repository.

Fig. 9 shows the sensitivity of an escalation at the point of completion of the repository. In this case of a costestimation for an HLW repository, the authors used a price change of 2.3%, a discount rate and an interest rate of4.36%. These measures were fixed by Article 50 of the Korean Electricity Enterprise Act.

0 2000 4000 6000 8000 10000 12000

2.3

3

4

Esca

latio

n[%

]

Unit cost/kgU [EUR]

Fig. 9. Sensitivity of an escalation.

Table 4

Thermal properties

Medium Property Value

Spent fuel Density (kg/m3) 2000

Thermal conductivity (W/m�C) 0.135

Specific heat (J/kg�C) 2640

Cast iron Density (kg/m3) 7200

Thermal conductivity (W/m�C) 52


Copper shell Density (kg/m3) 8900



Compacted bentonite Density (kg/m3) 1970



Backfill material Density (kg/m3) 2270



Rock Density (kg/m3) 2650




Fig. 10. Temperature distribution of the vertical emplacement.

Fig. 11. Temperature distribution of the horizontal emplacement (spacing; tunnel (30 m), canister (8 m)).


5. The results of cost estimation

The total costs accrued in each stage required for the construction of the underground facilities had been estimated,based on the overnight cost estimated method used by POSIVA (Finland) and KAERI with respect to the investmentcost and operating cost. Backfilling of the disposal tunnels and panel tunnels is the major cost item of the operatingcosts.

Total cost of the Korean case study is 2636 MV. Investment costs are 986 MV (37.4%), operating costs are 1469MV (55.8%) and closure costs are 181 MV (6.8%).

First of all, in order to compare the costs of each emplacement alternative, it is important to understand theconceptual design of each alternative.

Compared to the vertical emplacement, the horizontal emplacement alternative has the following qualitative char-acteristics (Saanio et al., 2004):

� The disposal tunnels are not needed at all. Long horizontal disposal drifts replace both the disposal holes and thedisposal tunnels of the repository with vertical holes.� Is more sensitive to the geology. Larger fracture zone in a long disposal drift can, for example, destroy the whole

hole. Collapsed muck in the drift may quite easily disturb on installation. Also a grouting of the disposal driftmay be difficult.� Needs more research and development. Installation machines of the canister and bentonite blocks are

complicated.� May have advantages in a backfilling. If long horizontal disposal drifts are to be backfilled successfully, it is

easier when disposal tunnels do not exist.

Fig. 12. Temperature distribution of the horizontal emplacement (spacing; tunnel (40 m), canister (7 m)).


5.1. Thermal analysis

Checking the thermal analysis should be preceded before a comparison of the cost for each emplacement optionbecause the design requirement should be satisfied, in terms of the thermal criteria, which should be below 100 �Cbetween the canister and the buffer (Choi et al., 1998).

The thermal properties for a thermal analysis have been presented in Table 4 and the authors have used the NISAcode for the heat transfer analyses.

Figs. 10e12 show the temperature distribution of the vertical emplacement (spacing; tunnel (40 m), canister(6 m)), horizontal emplacement (spacing; tunnel (30 m), canister (8 m)), and the horizontal emplacement (spacing;tunnel (40 m), canister (7 m)), respectively. These analyses were carried out for estimating the temperature distribu-tion of each emplacement option.

0 10 20 30 40 50Time (year)

40

50

60

70

80

90

100

Tem

pera

ture

(ºC

)

Vertical. 40m-6mHorizontal. 30m-8mHorizontal. 40m-7m

Buffer

Rock

Fig. 13. Temperature variation of each emplacement option.

Investment costs

0 200 400 600 800 1000

Vertical emplacement

Horizontalemplacement(spacing:

tunnel(40m),canister(7m))


tunnel(30m),canister(8m))

Unit : MEUR

Fig. 14. Investment costs.


These results were calculated for an understanding of the temperature distribution of the peak temperature. Asshown in Fig. 13, the peak temperatures were 98.6 �C (16 years) in the vertical emplacement, 95.6 �C (20 years)in the horizontal emplacement with a tunnel space of 30 m, and 95.2 �C (12 years) in the horizontal emplacementwith a tunnel space of 40 m, which satisfied the thermal criteria of the design requirement where the temperaturemust be below 100 �C between the canister and the buffer. Therefore, the proposed vertical and horizontal alternativescould be accepted for a cost comparison in terms of each emplacement option.

5.2. Cost analysis

Figs. 14e16 show the cost difference depending on the emplacement methods for the investment costs, operatingcosts, and closure costs, respectively.

Operating costs


Horizontal emplacement(spacing:tunnel(40m), canister(7m))

Horizontal emplacement(spacing:tunnel(30m), canister(8m))

0 200 400 600 800 1000Unit : MEUR

Fig. 15. Operating costs.

Closure costs

128 130 132 134 136



tunnel(40m), canister(7m))



Unit : MEUR

Fig. 16. Closure costs.


Fig. 17 shows the dominant cost difference for the vertical and the horizontal emplacement options in Korea. It wasfound that the horizontal emplacement option was the most economical alternative because of the excavation volumeof the disposal holes and the backfilling cost. In the case of the horizontal emplacement, the disposal holes are notneeded at all.

The dominant cost difference, as shown in Fig. 17, was calculated from a summation of the investment costs, op-erating costs, and closure costs.

6. Conclusions

From the comparison of the vertical and the horizontal emplacements, it was found that the horizontal emplace-ment option was the most economical alternative because of the disposal holes’ excavations and the backfillingcost. Because, in the case of a horizontal emplacement, the long horizontal disposal drifts replace both the disposalholes and the disposal tunnels of the vertical emplacement alternative with vertical holes.

As for the difference of such underground facilities, in the case of a horizontal emplacement, the excavation costsand the backfilling costs of the disposal drifts may be critical factors for decreasing the total costs.

In the case of a cost estimation for the Korean case study, only the technical dominant cost drivers have beenconsidered.

Therefore, it is essential to take all cost drivers into consideration for assessing which option is the best one for theKorean geological environment.

Acknowledgement

This work is supported financially by Ministry of Science and Technology under the Mid- and Long-Term NuclearR&D Project. Authors would like to express gratitude for its support.

References

Amos, Scott, 2004. Skills & Knowledge of Cost Engineering. AACE Press, West Virginia, USA, pp. 84e86.

Choi, J.W., et al., 1998. Safety and technical criteria for a reference concept development of the HLW geological repository system. KAERI/TR-

1161, Korea Atomic Energy Research Institute, pp. 46e48.

Choi, J.W., et al., 1999. Technology assessments of disposal alternatives to determine a reference geological repository system for HLW, KAERI/

TR-1361. Korea Atomic Energy Research Institute, pp. 4e7.

Choi, S.B., et al., 2004. Financial Management. Daekeung Press, Seoul, pp. 124e126.

Horngren, Charles T., et al., 1994. Cost Accounting: a Managerial Emphasis. Version 8.0. Prentice-Hall Press, USA, pp. 31e35.

Kukkola, Tapani, et al., 2003. KAERI’s Spent Fuel Repository Design Evaluation and Cost Estimation. Posiva Oy, Olkiluoto, Finland, pp. 71e75.

Dominant Cost Difference

0 400 800 1200 1600 2000






Unit : MEUR

Fig. 17. A comparison of the cost for the vertical and the horizontal emplacement options.


Nagano, Koji, 2003. System analysis of spent fuel management in Japan, (II) methodologies for economic analysis of spent fuel storage. Journal of

Nuclear Science and Technology 40 (4), 182e191.

Park, J.D., et al., 2005. Cost Management Accounting. Heungsul Press, Seoul, pp. 182e186.

SKB, 2003. Costs for management of the radioactive waste products from nuclear power production, TR-03-11. SKB, Sweden, pp. 15e17.

Saanio, Timo, et al., 2004. KRS-1 Pre-conceptual Design of Korean Reference HLW Disposal System, vol. 1. Posiva Oy, Olkiluoto, Finland.

pp. 74e84.

a comparison of the hlw underground repository cost for the vertical and horizontal emplacement...

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