Application of IAEA BDC Scoping  Tool and AMBER Modelling in Safety Assessment of Malaysian Borehole Disposal Facility

Description of disposal system Borehole height is 140.25 m. Disposal in saturated zone. Groundwater is assumed to be discharged to a river located 1300 m from the disposal borehole or water abstraction wells. Abstracted groundwater is used by farmer for drinking and agricultural purposes.

Schematic representation of the Malaysian BDC

Radionuclide inventory

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Calculation toolsIAEA BDC Screening Tool – assess the potential suitability of the borehole site based on hydrogeological and geochemical characteristics.

AMBER Modelling – a dynamic compartmental model representing migration of radionuclide contaminants from the borehole to the geosphere and finally the biosphere via groundwater.

Radionuclide Activity (Bq)Co-60 5.82 E+10Kr-85 4.79 E+11Sr-90 6.08 E+10

Cs-137 5.10 E+11Ra-226 1.19 E+11Am-241 4.22 E+11Ni-63 6.47 E+9

Number of capsules 60

AMBER Model

Scenarios (calculational cases)

ResultsIAEA BDC Scoping Tool

The IAEA BDC Screening Tool also derived data on failure time for source capsule, disposal container, backfill cement and containment barrier cement that were further utilized in the AMBER calculation.

AMBER ModellingSimulation result

Scenario Description Design Represents the evolution of the disposal

system when the borehole is implemented as designed and functioned as expected.

Defect Represents the evolution of the disposal system when the capsule and/or disposal container does not perform as envisaged in the Design Scenario.

Well Represents the evolution of the disposal system when the geosphere-biosphere interface considered is a water abstraction well, instead of a river (in Design Scenario), located at certain distance from the disposal borehole.

Erosion Represents the evolution of the disposal system when the disposal zone is uncovered after a certain period of time and radionuclide is released to the biosphere.

Scenario Calculated peak dose rate, Sv y-1

Time of calculated peak

dose rate, y Design 3.6E-12 4.2E+5

Defect

1 defective disposal container containing an intact capsule 3.6E-12 4.2E+5

1 defective capsule in an intact disposal container 3.6E-12 4.2E+5

1 defective waste package 3.6E-12 4.2E+5 30 defective waste packages 3.6E-12 4.1E+5 60 defective waste packages 3.6E-12 4.1E+5

Well

10m from disposal borehole 3.2E-4 1.3E+4 20m from disposal borehole 9.6E-5 1.4E+4 30m from disposal borehole 4.1E-5 1.5E+4 40m from disposal borehole 2.0E-5 1.6E+4 50m from disposal borehole 1.1E-5 1.6E+4

100m from disposal borehole 1.3E-6 1.8E+4 500m from disposal borehole 2.7E-8 1.7E+5

Erosion Erosion rate = 0.001 m y-1 2.5E-6 7.0E+4 Erosion rate = 0.01 m y-1 2.3E-3 7.0E+3

ConclusionThe IAEA BDC Scoping Tool indicates that the physical containment provided by the capsule and disposal container is not sufficient to ensure safety of the disposal system for the specified hydrogeological and geochemical conditions and radionuclide inventory. More detailed modelling using the AMBER software tool indicates that the BDF is effective in providing safe solution for the disposal of both long-lived and short-lived radionuclides in most of the scenarios considered. In the scenarios where the dose limit 3E-4 Sv y-1 is exceeded, the likelihood of the occurrence of such scenarios is very low. There are two scenarios which exceed the dose criterion; well at 10 m and erosion of 0.01 m/y.

E. Phillip1, R. Little2, N. Zakaria1, M.A.W. Yusof1

1Nuclear Malaysia, Malaysia2Quintessa Limited, United Kingdom

Red ZoneIt is unlikely that the containment provide by the capsule and disposalcontainer alone will be sufficient to ensure safety of the disposal systemfor the specified groundwater cosnditions and inventory; furtherassessment is required.

Warning: Water at this site is not potable, well pathway may not be relevantPeak Total Dose from Well Pathway = 2.5e0 [Sv/y] at 12051 [y]Peak Total Dose from Gas Pathway = 8e-1 [Sv/y] at 12051 [y]

3e-7[Sv/y] 3e-4[Sv/y]

Max Peak Total Dose = 2.5e0[Sv/y]

IntroductionBorehole disposal concept (BDC): Disposal of radioactive waste particularly disused sealed radioactive sources (DSRSs) in specially engineered and purpose drilled borehole. In the BDC, waste packages are emplaced in narrow diameter borehole and operated directly from the surface.

Cost-effective for safe management of DSRSs for non-nuclear power country with limited amount of DSRSs.

BackgroundBDC is a viable disposal option for managing DSRSs in Malaysia due to limited quantities of DSRSs available.

Prior to the implementation of the BDC, a post-closure radiological safety assessment is carried out to evaluate the reliability and safety of the concept to a point of licensability using the generic safety assessment developed by the IAEA as a starting point. As part of the assessment, IAEA BDC Scoping Tool and AMBER Modelling are used.

Borehole Geosphere Biosphere

Disturbance TcGeo

Di�_DtZ_SR

Adv_DtZ_SR

Di�_SR_Dtz

GWater_WellScenario

OtherWater

GW_Imigation

GWater_ToWaterCourse

Schematic presentation of BDF

The borehole disposal facility (BDF) development project in Malaysia has started since 2011.

In situ con�guration of a waste package in borehole

Closure zone (70m)

Plugging (0.25)

Disposal zone (60m)

Exlusion zone (10m)