25 herold 20160830 retrieval final

P. Herold – 08/2016US/D WorkshopWashington, USA, Sept. 7-9, 2016

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Impact of retrieval requirements on repository design

− Results of R&D project funded by BMWi (PTKA) −

Philipp Herold, Sabine Dörr, Eric Kuate Simo, Wilhelm Bollingerfehr, Wolfgang Filbert

DBE TECHNOLOGY GmbH

Washington, DCSeptember 7-9, 2016


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1. Final Disposal in Germany – HLW program

2. Regulatory requirements related to retrievability

3. Retrieval strategy

4. Retrievability in drift disposal concept

5. Retrievability in borehole disposal concept

6. Summary

Contents


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Final Disposal in Germany• Disposal in deep rock salt formations was the preferred

option for the last decades• Summer 2013: German parliament (Bundestag) passed

new law for restart of site selection process for HLW repository and implemented commission “Storage of HLW”

Exploration Mine Gorleben (DBE, 2016)

Final report commission “Storage of HLW”:• Recommends disposal of HLW in deep geologic

formations with the possibility of retrieving waste packages as preferred option in Germany

• Determined site selection criteria, considering salt, clay, crystalline rock as potential host rocks

• Prepared a roadmap for site selection process, which will start in 2017


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Retrievability − Regulations

Safety Requirements Governing the Final Disposal of Heat-Generating Radioactive Waste:

Mandatory for the design, further exploration, construction, emplacement operations and decommissioning of HLW/SF repository

Compliance has to be demonstrated (in a verifiable way)

Demonstration of technical feasibility before or during licensing

Stipulate retrievability as a design criterion

“Retrievability is the planned technical option for removing emplaced radioactive waste containers from the repository mine.”

“During the operating phase up until sealing of the shafts or ramps, retrieval of the waste containers must be possible.”


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Safety Requirements

“Measures taken to secure the options of recovering or retrieval must not impair the

passive safety barriers and thus the long-term

safety.”based on (NEA 2011)

Retrievability Recovery

“The number of open emplacement zones should be kept to a minimum. These should be promptly loaded, then backfilled and reliably sealed

from the mine building.”

→ Operations of emplacement, backfilling, and sealing take place in parallel during complete operational period


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Retrieval Strategy• In the framework of R&D projects (funded by German Federal Ministry for

Economic Affairs and Energy), DBE TECHNOLOGY GmbH developed a suitable strategy and technical solutions to retrieve waste packages

• Focus on underground operations• Waste package management plan after retrieval does not exist

“Re-mining”-strategy:• Emplacement of waste containers, backfilling and sealing as designed• Conceptual adaptations to facilitate retrieval and improve conditions during

potential retrieval period without impacts on long-term safety• In case of retrievability decision, excavation of new access drifts to the

emplacement areas and waste packages, exposal and removal of the waste packages

Transfer of the waste packages from the passive safety system of the repository back into human care


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Drift disposal – Emplacement concept

Emplacement Drift

Prototype Emplacement DevicePOLLUX® cask

Emplacement of POLLUX® casks in 250-m-long blind-ending drifts


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• Removal of all internals before backfilling of emplacement drifts (especially the rails)

During retrieval:• All emplacement drifts have to be

located between two crosscuts• Additional access drift allows an

increase in airflow (first cooling measure) and higher flexibility

• Re-activation of radiation protection areas during re-excavation of main drifts and cross-cuts or release from controlled area before backfilling

Drift disposal – Layout modifications


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• Removal of the remaining pillar and exposure of the POLLUX®

cask by means of road header and (remote controlled) demolition robots

• Backfilling after complete retrieval

Drift disposal − Excavation

• Stepwise excavation of two sub drifts by means of road header between two crosscuts parallel to emplaced waste

packages floor 0.6 m below POLLUX®

Final retrieval drift:Start of retrieval:

Step 2Step 1 Step 3

POLLUX®POLLUX®

600

600

former emplacement drift


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Prototype Emplacement Device

Drift disposal − Equipment modifications

• Retrieval without rebuilding of rails automotive drive necessary

• Usability of trunnions after emplacement not guaranteed alternative bearing structure necessary

• POLLUX® casks lie on a salt base/socket reduces lifting height

Feasibility Study for Modified Emplacement Device


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Drift disposal − Thermal input

40 Years after start of emplacement (corresponds with start of retrieval)

• 200°C design temperature at waste package surface, optimized to densest disposal of waste packages

• Barely manageable conditions inside the access drifts, cross cuts• Retrieval operation coincides with thermal maximum inside the emplacement

fields • Excavation inside the emplacement fields hardly manageable because of

very high technical cooling effort, necessary cooling breaks and geo-mechanics

1 year after emplacement 2 years after emplacement

11 years after emplacement6 years after emplacement

Temperature [°C]


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Drift disposal − Geo-mechanics

• High temperature accelerates salt creep and produces high geo-mechanical stress

• Rise of former drift floor• High convergence calls for drift re-

cutting• Additional wall and roof stabilization

needed

Displacement, 30 days after complete excavation

Failure criterion, at excavation of sub drifts 1, 2 and pillar


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Drift disposal − Conclusions

• Retrieval process is designed for total exposure of the POLLUX®-10 casks

• Modified emplacement device with rail-less drive and with new bearing structure

• Thermal input due to densest packaging of the POLLUX®-10 casks produces high rock temperatures and high geo-mechanical stress

• Optimization of thermal repository design would improve conditions during potential retrieval period but increase repository footprint

• Requirement of retrievability changes repository design significantly


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Borehole disposal − Emplacement concept

BSK 3

Triple pack

Borehole cellar

Test facility for borehole disposal of spent fuel canisters with one dummy canister → Unintentional demonstration of canister retrieval


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Conceptual adaptions from “Preliminary safety analysis for Gorleben site“ (based on nse GmbH):

Borehole disposal − Design impacts

canister with conical head

new backfill (quartz sand)

steel liner

Retrieval concept:• layout of retrieval drifts corresponds to emplacement drifts• two parallel drifts in the south improve operation and

ventilation• retrieval corresponds to reversal of emplacement process• steel liner remains in borehole after retrieval• removal of backfill (quartz sand) as major technical

challenge during retrieval• development of a suction device

1 m

• new canister shape (BSK-R)• steel liner designed for rock pressure• non-compactable and incompressible backfill• stepwise emplacement and backfilling


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Borehole disposal − Design impactsFeasibility study on suction device:• Remove backfill to free head of the BSK-R • Suction device with same outer dimensions as

BSK• Integrated drive, fan and storage space• Two suctions steps per BSK-R• First pilot tests for air intake design

Grip

Drive

Fan

Deflection dome

Transport pipe clamp

Storage space

Transport pipe

Borehole liner

Air intakeCanister head

Cladding


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Borehole disposal − Thermal inputThermal conditions:• Heat sources below mine level• Temperatures above 100°C just next to the boreholes• Steady increase of rock temperature during retrieval period• Moderate total heat input inside the mine openings expected• Third main drift improves ventilation conditions and allows higher flexibility • Additional cooling equipment during excavation necessary

Drifts at emplacement field East 2Drifts at emplacement field East 3

Time [a]

Tem

pera

ture

[°C

]


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Borehole disposal − Conclusions

• Retrieval process corresponds to reversal of emplacement process

• Unintentional demonstration of canister retrieval at existing test facility

• New suction device for backfill removal, demonstration of technical feasibility still open

• Steady increase of rock temperature but moderate total heat input expected

• No layout modifications necessary


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Summary

• Retrievability is required during complete operational period as licensing permission

• Thermal input of the waste will influence retrieval concept and to a certain extent repository design

• Requirement of retrievability could change repository design significantly

• Retrievability is compatible to German safety concept for high-level radioactive waste repository in salt formations

• Technical feasibility of all retrieval concepts and techniques has still to be demonstrated


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Thank youfor your attention.

25 herold 20160830 retrieval final

Technology