IAEA International Atomic Energy Agency Presenter Name School of Drafting Regulations for Borehole Disposal of DSRS 2016 Vienna, Austria Borehole drilling and completion, repository design

IAEA Outline/ Contents Main components of the BDC design and their safety functions Adapting the generic design to a specific site Drilling and completing a disposal borehole 2

IAEA Main references 3 TECDOC 1644 Requirements for disposal Guidance for borehole disposal Technology of the BDC

IAEA Main components of the BDC and their safety functions 4

IAEA Borehole Design 1 102

IAEA 1 m Ground surface Closure zone, minimum 30 metres Anti-intrusion plate Casing removed over top two metres Backfill with native soil Disposal zone Concrete closure seal GEOSPHERE

IAEA Components disused sources capsule Container backfill Container Repository backfill Casing Centraliser Borehole grout Geosphere Container to container spacing of 1m Anti-intrusion plate immediately above the waste A closure zone with a minimum length of 30 metres concrete closure seal Casing removal (top 2m) 7

IAEA Components and safety functions 1 8 COMPONENT SAFETY FUNCTION/ DESIGN RATIONALE Disused sealed sourcesNone – is assumed that the radionuclides in the sealed sources are free to migrate Capsule Container Capsule and container are made from corrosion- resistant stainless steel which provide absolute physical containment for a time that is dependent on the rate of corrosion The capsule and container are designed to be easily handlable Container backfill Repository backfill Borehole grout All these materials are cementitious. This produces high pH conditions that reduce the rate of container and capsule corrosion. The cement also provides surfaces on which radionuclides can sorb.

IAEA Components and safety functions 2 9 COMPONENT SAFETY FUNCTION/ DESIGN RATIONALE CasingFacilitates operation by supporting the borehole wall, excluding groundwater, providing a smooth surface to prevent snagging when emplacing waste packages It has no long-term safety function Casing centraliserFacilitates operation by ensuring that the borehole is close to vertical Container to container spacing Provides adequate concrete to provide pH buffering; provides dilution by spreading out any contaminant plume Anti-intrusion platePrevents inadvertent drilling into the disposal zone Closure zone minimum 30mProvides isolation of the waste by placing it out of reach of normal deep excavation activities eg roads, foundations of buildings

IAEA Components and safety functions 3 10 COMPONENT SAFETY FUNCTION/ DESIGN RATIONALE Concrete closure sealSeals the borehole and provides isolation of the wastes through its physical presence and containment of radionuclides by protecting the waste packages from damage and corrosion Casing removal (top 2m) A security measure that prevents unauthorized access to the waste by hiding the borehole location from sight. The precise location will be known to the authorities who, in any event, would have equipment that was capable of finding it GeosphereProvides isolation of the wastes from the human environment and containment of radionuclides by protecting the waste packages from damage and corrosion. In the event of radionuclide migration from the facility, it will also provide retardation allowing more time for radionuclides to decay

IAEA Influences on the site-specific design 11

IAEA Influences on facility design 12 Inventory Regulation/ legislation Site properties Fixed parameters (Waste package design, MHC etc) Economic/ practical issues Facility Design Safety assessment

IAEA Economic and Practical issues Choice of site Remoteness of the site/ access to transport and utility infrastructure Availability of suitably qualified contractors with appropriate equipment Availability of construction and emplacement materials eg casing, cement, sand, water Site properties (groundwater, weathered zone, complexity, topography…) Stakeholder and Regulatory interactions 13

IAEA Regulation/ legislation Determines the safety standards to be met May also prescribe other issues eg Format of the safety case or safety assessment Who is permitted to design the facility The need (or not) for retrievability Use of the Model Regulations will anticipate many of the questions to be answered Licensee will need to have a very good understanding of how regulations will impact on what is planned 14

IAEA Inventory Compared to (say) disposal of NPP wastes, inventory characterization of disused sealed sources is straightforward Key parameters to be determined for each source: Identification of radionuclide/ nuclear reaction/ emissions Activity at specified date Physical size of source to be disposed Current storage and handling arrangements / means of retrieval from store / weight Means of removal of bare source from operating shield Need for shielding during conditioning/ containerization HENCE relevant to design: Number of waste packages -> number of boreholes Need (or not) for MHC and remote handling, lifting equipment etc 15

IAEA Inventory and decay 16

IAEA Important Site properties Depth to water table Existence of near-surface weathered rocks Separation of near-surface and deep water bodies Rate of surface erosion/ geomorphology Properties of potential host geology Structural Geomechanical Geochemical Etc –see previous lecture 17

IAEA Adapting the generic design to a specific site 18

IAEA Important design issues to be determined 19 ISSUEHOW DECIDED Which site?Governmental or community decision Where on the site?Avoid large faults, nearby surface facilities How many boreholes, what depth?Design optimization based on the inventory and the site properties – see later New borehole or modify existing characterization borehole? Largely an economic and practical issue

IAEA Borehole design optimization 1 20 First decide the length of the disposal zone(s) from: 1. Number of packages – dependent on number and type of sources 2. Package to package spacing – reference design has 1m spacing but could be half this Package to package spacing

IAEA Cro ssla nd Con sulti ng -30m Required length of disposal zone Water table Dry season Wet season Total b/h depth determined by disposal zone length plus 30m or max depth of water table (whichever is greater) Borehole design optimization 2

IAEA 22 Aquiclude Aquifer Min. depth of disposal 30m Aquifer depth 70m Required b/h depth 100m Near-surface weathered rocks Groundwater 20m Phreatic surface Borehole Design Optimization 3

IAEA Drilling and completing a disposal borehole 23

IAEA 24 Drilling BDC designed to use techniques that are widely available Borehole diameter 0.26m minimum – is typical of boreholes used for groundwater abstraction Would normally used rotary air percussion drill Not necessary to core the disposal borehole but retain samples of chippings for every metre of borehole

IAEA Construction - Drilling 25

IAEA 26 Construction 1 Borehole to be cased (lined) to full depth

IAEA 27 Construction 2 Borehole to be cased (lined) to full depth Insertion of mild steel or HDPE casing with centralizers

IAEA 28 Construction 3 Borehole to be cased (lined) to full depth Mild steel or HDPE tubing Concrete plug at the base (placed using tremmie pipe)

IAEA Casing insertion and grouting 29

IAEA 30 Construction 4 Borehole to be cased (lined) to full depth Mild steel or HDPE tubing Concrete plug at the base (placed using tremmie pipe) Grouting of annulus (ditto) Checks and hold point to confirm borehole is correctly built and ready for operation

IAEA Summary Main components of the BDC design and their safety functions Containers and capsule, backfill, casing etc Influences on the site-specific design Practical/ regulatory/ inventory/ site properties Adapting (optimizing) the generic design for a specific site Two examples given – one leads to one borehole, the other, two Steps in the construction of a disposal borehole 31

IAEA 32 Thank you!