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Cherry Tweeds part

Cherry Tweed s part

QuestionAnswer
Key Principles of Geological disposal ISOLATE radioactivity from the surface CONTAIN until most of the hazard has decayed PASSIVE safety, not requiring human action
3 things that geological disposal needs Needs suitable geology, a willing community and wastes packaged in suitable form
Multi barrier system cementitious wasteform/stainless steel container/cement backfill/rock Solid gas wasteform/durable metal container/clay backfill/rock
sources of radioactive waste for geological dispoasal Enrichment and fuel fabiration/medical/defence/new nuclear/reprocessing/power stations
derived Inventory Uncertainty comes from Most recent was 2013 reprocessing assumptions lifetimes of existing reactors uncertainty in waste inventory management of Pu Industry plans Policy management of LLW/ILW boundary
What is Geological Disposal? Emplacement of packaged radioactive waste in an engineered underground geological disposal facility or repository, where the geology provides a barrier against the escape of radioactivity and there is no intention to retrieve the waste.
aims of geological disposal ISOLATE radioactivity from people MAINTAIN a stable geological cacoon PREVENT any releases reachinng people and the environment in harmful concentrations CONTAIN until 99.9% decayed
three types of host rock Hard crystalline; granite and metamorphic Sediments; clays and volcanic sediments Evaporites; salt domes But the total environment of the rocks is more important
things we need... processes to be slow low groundwater flowrate (low hydaulic gradient, absense of flow drivers, fast flow pathway away, low groundwater supply) stable hydrochemistry stable stresss non susceptable to tectonics wel buffered against changing climate
ILW characteristics Activity content, which is beyond the limits for disposal at LLWR butdoes not generate heat Diverse inc. large components. The main sources of these wastes are the operation and decommissioning of nuclear facilities.
Spent fuel - higher strength rock GDR In tunnel vertical borehole High integrity waste container Clay buffer Chemically condition groundwater to reduce corrosion of waste container Control movement of groundwater to and around waste container Less dependence on host rock
Spent fuel - lower strength sedimentary rock GDR In tunnel axial emplacement of waste containers Waste container to provide containment for heat generating time period Clay buffer to attenuate release of radioactivity after failure of waste container Host rock retards release of radioactivity
Spent fuel - evaporite rock GDR In tunnel axial emplacement of waste containers Waste containers isolate and contain waste during emplacement ops only Relies principally on dry impermeable salt of host rock
ILW/LLW - higher strength rock GDR Waste packages emplaced in vaults Backfilled with cementitious grout High pH environment Reduces radionuclide solubility
ILW/LLW lower strength sedimentary rock GDR Waste packages emplaced in vaults but ths time Concrete lined tunnels Cementitious grout backfill this time Low pH cements may be used to avoid cement / host rock interactions
ILW/LLW evaporite rock GDR Waste packages stacked in vaults (emplacement rooms) Emplaced waste encapsulated by creep closure of host rock forming low permeable barrier around the waste Host rock dry impermeable salt
alternatives to GDR Long term surface storage; active management/repackaging Partitioning and transmutation not yet proven at industrial scale Deep borehole disposal for small volumes of waste but more R&D
Deep borehole details 43cm bottom-hole diameter disposal at depth between 3000-5000m minimum 50m spacing bottom-hole temperature 150oC borehole sealing will be cement and bentonite outer diameter reduces with depth and different borehole lining
Safety Case a collection of arguments and evidence in support of the safety of a facility or activity. include the findings of a safety assessment and a statement of confidence in these findings inc. guide to R&D Basis for decisions Tool for communication
Safety assessment the evaluation of long-term performance, of compliance with acceptance guidelines and of confidence in the safety indicated by the assessment results
Information timeline site selection; initial site evaluation surface investigation; prelim environmental safety evaluation Underground ops; initial environmental SC Underground ops 2; pre-ops envrionmental SC operations; post-ops ESC Closure; final ESC
Pathways for radionuclides to leave GDF: aka How can the rock be ‘short circuited’? Via groundwater pathway Via gas pathway Human intrusion
How does rock delay movement Groundwater flow Rock matric diffusion sorption diffusion and dispoersion
assessments of timeframes 1; containment; backfill resaturates 2; the package corrodes 3;the backfill; low solubilty reduces mobility 4; geological barrier, radionuclides sorb to rocks and are less mobile 5; continuing safety
stages in performance assesment FEP analysis, FEP diagram (features, events and processes) Scenario and conceptual model mathematical model softwar development
Created by: emmaperry
 

 



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