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Preparing Posiva’s Post-Closure Safety

Case Towards the Operational Phase

Annika Hagros1, Heini Reijonen1,2, Barbara Pastina3, Nuria Marcos1,

Pirjo Hellä1

1) Saanio & Riekkola Oy, 2) Geological Survey of Finland, GTK, 3) Posiva Oy

International Conference on the Safety of Radioactive Waste Management, IAEA, Vienna, 21–25 November 2016.

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• Posiva’s safety case for the construction license

• Regulatory feedback and other input

• Overall safety case methodology

• Management of changes

• Conclusions

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Source: Posiva Oy

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• Posiva’s spent nuclear fuel repository at Olkiluoto is based

on the KBS-3V design. A repository for low and intermediate

level waste from the encapsulation plant will be located in the

same disposal facility at a shallower depth.

• In 2012, Posiva submitted a construction licence application

(CLA). The licence was granted in 2015.

• The application was supported by a safety case, TURVA-

2012*.

• Posiva aims to submit an operating licence application (OLA)

in 2020.

* POSIVA OY, Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto – Synthesis 2012, POSIVA 2012-12, Eurajoki

(2012).

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• Lessons learned from the previous safety case, TURVA-

2012

• Feedback received from the Radiation and Nuclear Safety

Authority (STUK) on the CLA, including 34 specific

requirements for the next safety case*

• The latest updates in the regulations (e.g. updated of STUK’s

YVL Guide D.5, new YVL Guide D.7)

• New challenges related to the implementation of repository

construction and operation.

* RADIATION AND NUCLEAR SAFETY AUTHORITY, Safety Case for the Disposal of Spent Nuclear Fuel in Olkiluoto:

Decision, Presentation Memorandum, 1/H42252/2015, Helsinki (2015).

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• A safety case is the synthesis of evidence, analyses and arguments that

quantify and substantiate the claim that the repository will be safe after

closure and beyond the time when active control of the facility can no

longer be assumed.

• Posiva’s safety case will consist of a portfolio of main reports and a

number of supporting reports.

• Uncertainties in the initial state are handled through a systematic

screening of possible deviations using a modified failure mode and effect

analysis (FMEA).

• Uncertainties during the long-term evolution of the disposal system are

handled through a systematic analysis of how the various FEPs might act

on the components of the disposal system during its evolution, followed

by the formulation and analysis of scenarios.

*

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Synthesis

Description of the overall methodology of analysis, bringing together all the lines of argument for safety, and the statement of confidence and the evaluation of compliance with long-term safety constraints

Design Basis (DB)

Safety functions, performance targets and design requirements, their bases and the links between them

Initial State (IS)

Initial state of the repository system and the present conditions of the surface environment

LILW Repository Assessment (LILW-RA)

Assessment of the long-term performance of the repository for LILW from the encapsulation plant and identification of interactions with the SNF repository

Performance Assessment and Formulation of Scenarios (PAFOS)

Assessment of fulfilment of performance targets taking into account the expected and alternative climate and surface environment evolutions. Scenarios formulation based on uncertainties/deviations identified in the assessment

Models and Data (M&D)

Models and data used in the performance assessment and in the transport, release and dose calculations for the disposal system

Analysis of Releases (AOR)

Overview of the main results from the radionuclide release and transport modelling from the repository system to the surface environment and evaluation of radiological consequences

Complementary Considerations (CC)

Supporting evidence for safety including natural and anthropogenic analogues

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Selection of process to be analysed

•Production of repository components (e.g. canister)

Setting up analysis objectives

•e.g. defining potential deviations from the intial state

Desciprion of process steps

•e.g. manufacturing

Analysing failure modes (workshop)

•What can go wrong?

Analysing effects and their (workshop)

- Severity

- Occurrence

- Detection

Screening of failure modes of interest and input to

scenario formulation

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• Requirements freeze, design freeze, data freeze: Introduced in the early

phase of the safety case work to provide consistency. Note that not all

data are frozen at the same time, as the output of certain models will

serve as input to other models.

• Design developments during the safety case process: Important

developments take as the design reaches full maturity and is optimized

for industrialization and operation.

• A change management process is needed to manage traceability and

reliability of the safety case and to facilitate the assessment of impact of

changes on the safety case results.

• For this purpose, the whole modelling chain used in the safety case is

documented and linked to the approved input data through a database.

*

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Figure 2-4 of POSIVA 2012-09

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• Requirements, design and stepwise data freezes need to be performed in a

safety case that is developed in parallel with design optimization and operational

readiness activities.

• The design is currently being optimized for industrialization and operation and

large-scale demonstrations will also take place. The handling of changes and

new information arising from these activities is a major challenge in the safety

case process.

• A change management process is essential to incorporate changes in a

controlled way, so that their long-term safety impacts are properly assessed. The

proposed changes need to be considered holistically, including the impact not

only on long-term safety but also on the overall management of

uncertainties.

• As deviations (“planned” vs. “as built”) cannot be excluded completely, an

analysis of their potential impact on long-term safety is needed.

Thank you for your attention!

More information:

Annika Hagros, Saanio & Riekkola Oy annika.hagros@sroy.fi

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