Scrutiny of the Nirex Phased Geological Repository Concept

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Scrutiny of the Nirex Phased Geological
Repository Concept
Paul AbraitisNuclear Waste Assessment Team
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Outline

• Regulatory arrangements for oversight of ILW
  conditioning
• Scrutiny of Nirexs Phased Geological Repository
  Concept (PGRC)
• Why and how?
• Progress to date
• Future work

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Regulatory arrangements for oversight of ILW
conditioning (1)

• Uses HSE/NIIs existing nuclear site licensing
  provisions
• Formally, site licensees submit proposals for
  waste treatment and conditioning (including
  information on disposability - e.g. Nirex LoC
  assessment if destined for ILW repository)
• HSE/NII look to ensure suitability safe storage
  for the interim period
• EA/SEPA look to ensure suitability for ultimate
  disposal, and advise HSE/NII

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Regulatory arrangements for oversight of ILW
conditioning (2)

• Disposability
• The degree to which conditioned waste meets the
  standards and specifications for final disposal
• However, no ILW disposal facility in UK,
  therefore no Waste Acceptance Criteria (WAC)
• Nirex Letter of Compliance - process to assess
  disposability against PGRC

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Regulatory arrangements for oversight of ILW
conditioning (3)

• Main aims of regulatory approach
• Proper emphasis for safety short/long term
  environmental considerations
• Transparent regulatory decision making
• Appropriate balance between costs/benefits
• Avoid wasted effort, potential delays and costs
  from inappropriate waste management strategies
• Minimise possible conflicting regulatory
  requirements

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Scrutiny of the PGRC - Why?

• Agreements between the environment agencies (EA
  SEPA)
• establish an understanding of the development of
  the PGRC
• scrutinise its application by Nirex to ILW
  conditioning proposals and the LoC/LoA system
• establish an understanding of the development of
  the environmental safety case

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Scrutiny of the PGRC - How?

• Joint programme with SEPA
• Review of key aspects, identification and
  resolution of key issues
• Review against extant guidance and international
  best practice
• Resourcing
• NWAT SEPA staff
• External Consultants (where required)

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Scrutiny of the PGRC - Reviewed

• Inventory related
• Nirex's Derivation of the 2003 Assessment
  Inventory and Implications of the Associated
  Uncertainties.
• Criticality related
• NWAT Assessment of Nirex's Approach to the
  Setting of Fissile Limits for Waste Packages and
  Assessment of Possible Post-closure Criticality
  Events.
• Reports available electronically

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Scrutiny of the PGRC - Ongoing

• Review of LoC Process
• Report at checking stage
• Review of Nirex Context Notes and Viability
  Report
• 24 individual notes reviewed to date
• Compilation/summary report to be produced

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Scrutiny of the PGRC - Planned

• Overview of Nirex's Generic Post-Closure
  Performance Assessment
• Assessment context
• Scope of the assessment, including considerations
  of key exposure pathways (groundwater, gas, human
  intrusion and natural disruptive events)
• Overview of the modelling approach and
  methodology adopted for model parameterisation,
  including expert elicitation
• The approach to representing and reporting the
  uncertainty in the risk estimates
• Review of the proposed approach for more
  sophisticated assessment models

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Scrutiny of the PGRC - Planned

• Review of Nirex's Understanding of Waste Package
  Evolution During Extended Storage and
  Implications For Retrievability and Post-closure
  Containment
• To scrutinise the basis of Nirex's retrievability
  case
• To review Nirex understanding of the key
  environmental factors that could impact on waste
  package integrity and retrievability
• To consider the impact of reactive waste
  components and deleterious reaction processes
  that may be on-going and may impact upon
  long-term package stability
• To identify key uncertainties and knowledge gaps
  and to review Nirex's work programme to address
  these

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Scrutiny of the PGRC - Planned

• Review of Nirex's Understanding of Key Near Field
  Processes
• Performance of the chemical barrier
• Understanding of groundwater flow and other
  transport processes and the representation of
  those processes in models
• The significance of complexants and non aqueous
  phase liquids (NAPLs) in relation to radionuclide
  mobility specifically the influence of
  complexants (including co-disposed organics and
  their potential degradation products) on
  radionuclide solubility and sorption

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Scrutiny of the PGRC - Planned

• Review of Issues Relating to the "Letter of
  Compliance" Process, e.g.
• The choice of encapsulants
• Derivation of package limits for reactive waste
  materials
• Scrutiny of the containment BPM methodology
• Container corrosion

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Final comments

• Scope of work is wide ranging
• Relatively small resource (additional work also)
• Comments welcome
• paul.abraitis_at_environment-agency.gov.uk
• See EA website (search NWAT)
• http//www.environment-agency.gov.uk