Introduction Near surface trench is one of

the most common methods for

disposal of LILW.

Trench design besides waste

characteristics, site

characteristics, type of barriers

and characteristics of cover

layers are influencing on

overall safety of disposal.

Introduction LILW wastes have different

physical and chemical

properties because of their

different sources.

In long term, degradation

of waste packages due to

corrosion and also

settlement of backfill

layers and cover can

reduce safety of disposal

trench. So evaluation of

different aspects of trench

in design stage is an

important step toward

ensuring operational as

well as long term safety

disposal.

Finite Element

Simulation

Numerical methods have

been used in engineering

project, extensively.

Stability analysis of near

surface trenches in

Anarak Repository has

been evaluated by finite

element method to predict

deformations and

settlements. In primary

stage of trenches design

dimension of trenches has

been selected based on

design criteria. 2-

dimensional profile of

trench with wastes and

backfill layers has been

considered for convenient

meshing and further

analysis.

Iran Radioactive Waste Management Co. (IRWA)/ Atomic Energy Organization of IRAN/ Tehran/Iran

Material Assignment

For assignment of material

properties, elasticity properties

of host rock, backfill layers and

waste packages should be

considered. Mohr-Colomb

criterion was selected for

material properties

assignment. This area consist

of two parts include of

alluvium layers and host rock.

Conclusion

Weights of cover layers, waste

packages and backfill layers

which are considered as

external loads can influences

on trench's performance. Solid

wastes and solidified waste

after corrosion will have very

low strength and they can't

tolerate external loads and

finally settlement may occur.

Finite element simulation for

trench's geotechnical model

(as one of simulation method)

was performed to analyze the

trench deformations under

different conditions.

Displacement, plastic strain

and stress concentration in the

trenches evaluated in different

situation.

Results 1. Stability analysis of

trenches with high stiffness

and cover loads

The model was analyzed with

high stiffness for

consideration wastes in

primary conditions.

maximum stress and

deformation are 0.64 MPa

and 1.96 cm.

2. Stability analysis of

trenches with low stiffness

and cover loads

Waste packages in trenches

will corrode and baring

capacity of them will be

decreased.

These deformations can be

followed by settlements and

decrease of performance of

covers.

deformations increased to

28 cm

Study Area

The Anarak site has been

selected as disposal facility for

LILW in Iran. This site is located

in Isfahan province, about 24

km west of Anarak city and 90

km northeast of Naein. This

site has been located in a

syncline structure which

consists of clay, marl and

sandstone layer that create

good condition for controlling

of radionuclides migration.

Abstract. At this paper, simulation and stability analysis of near surface disposal trenches in Anarak Repository has been evaluated by

finite element method. Emplacing of waste packages in the trenches impose extra load to bottom and sides of trenches and it may

increase deformations in the trench walls and cover. Also corrosion of waste packages in long term may increase deformations and

settlements and finally failure of trenches may be occur. 2D model of trench containing waste packages with elasto-plastic behavior of

materials in finite element software has been designed and analyzed. Amount of deformations were measured and considered in design

of trenches.

Material Young Modulus (E)

GPa

Poisson ratio

)ν(

Friction Angle (φ)

Cohesion (C(

MPa

Host rock (clay and

marl stone)

1.96 0.23 40 6

Backfill and Soil layers 25*10-3 0.25 34 0.05

Waste Packages 204 0.29 - -

Deformation and stresses of model for wastes with low stiffness

Location of boreholes for site

characterization

MATERIAL PROPERTIES OF WASTE

PACKAGES, SOIL AND ROCKS

Conceptual Design for Near Surface

Disposal