Safety Case for the Disposal of Spent Nuclear Fuel at Olkiluoto

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P O S I V A O Y O l k i l u o t o F I - 2 7 1 6 0 E U R A J O K I , F I N L A N D P h o n e ( 0 2 ) 8 3 7 2 3 1 ( n a t . ) , ( + 3 5 8 - 2 - ) 8 3 7 2 3 1 ( i n t . ) F a x ( 0 2 ) 8 3 7 2 3 8 0 9 ( n a t . ) , ( + 3 5 8 - 2 - ) 8 3 7 2 3 8 0 9 ( i n t . )

P o s i v a O y

Safety Case for the Disposal of

Spent Nuclear Fuel at Olkiluoto

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Tekijä(t) – Author(s)

Posiva Oy

Toimeksiantaja(t) – Commissioned by

Posiva Oy

Nimeke – Title

SAFETY CASE FOR THE DISPOSAL OF SPENT NUCLEAR FUEL AT OLKILUOTO

FEP SCREENING AND PROCESSING

Tiivistelmä – Abstract

TURVA-2012 is Posiva’s safety case in support of the Preliminary Safety Analysis Report

(PSAR) and application for a construction licence for a repository for disposal of spent nuclear

fuel at the Olkiluoto site in south-western Finland. This report presents and applies the

methodology by which Posiva’s TURVA-2012 FEP list

as described in

Features, Events and

Processes

and

used in

Performance Assessment

,

Formulation of Radionuclide Release Scenarios,

Assessment of Radionuclide Release Scenarios for the Repository System, Biosphere Assessment

and

Models and Data for the Repository System

is shown to be as comprehensive as necessary

at the current stage of the spent nuclear fuel management programme.

The main part of the work, i.e. screening methodology and processing of the selected FEPs, has

been conducted within earlier safety assessments, and has been applied to TURVA-2012 and to

previous safety assessments, but never formally presented before this report. A full screening of

Nuclear Energy Agency 2.1 FEP database is carried out again for this report and reported in detail

to confirm the comprehensiveness of the TURVA-2012 FEP list. Except for the first stages of the

screening process, surface environment FEPs are, however, not considered in this report.

Avainsanat - Keywords

FEPs, screening, disposal system, regulatory framework, assessment, scenario driver

.

ISBN

ISBN 978-951-652-241-1

ISSN

ISSN 1239-3096

Sivumäärä – Number of pages

148

Kieli – Language

English

Posiva Oy

Olkiluoto

FI-27160 EURAJOKI, FINLAND

Puh. 02-8372 (31) – Int. Tel. +358 2 8372 (31)

Julkaisuaika – Date

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Tekijä(t) – Author(s)

Posiva Oy

Toimeksiantaja(t) – Commissioned by

Posiva Oy

Nimeke – Title

TURVALLISUUSPERUSTELU KÄYTETYN YDINPOLTTOAINEEN

LOPPUSIJOITUKSELLE OLKILUODOSSA - FEPIEN VALINTA JA PROSESSOINTI

Tiivistelmä – Abstract

Posivan rakentamislupahakemukseen liittyen tuotettu PSAR (Preliminary Safety Analysis Report)

-raportti perustuu osaltaan TURVA-2012-pitkäaikaisturvallisuusperusteluun, joka on tehty

käy-tetyn ydinpolttoaineen loppusijoitusta varten Olkiluodon kallioperään rakennettavalle

loppu-sijoituslaitokselle. Tässä raportissa esitetään metodologia, joka on ollut käytössä FEP-listan

(ilmiöt, tapahtumat ja prosessit) muodostamisessa TURVA-2012-turvallisuusperustelua varten.

TURVA-2012:n FEP-lista on kuvattu tarkemmin raportissa

Features, Events and Processes.

FEP-listan käyttö turvallisuusperustelussa on kuvattu raporteissa

Performance Assessment

,

Formulation of Radionuclide Release Scenarios,

Assessment of Radionuclide Release Scenarios

for the Repository System, Biosphere Assessment

sekä

Models and Data for the Repository

System.

Tämän raportin tarkoitus on kuvata FEPien valinta ja prosessointi turvallisuusperustelua

varten ja osoittaa että TURVA-2012:n FEP-lista on riittävän kattava ja vastaa käytetyn

polttoaineen loppusijoitusohjelmassa meneillään olevan vaiheen tarpeita.

Tässä raportissa esitetyn työn pääosa koskee FEP-valintaprosessin metodologiaa, joka on ollut

käytössä myös turvallisuusarvioiden aiemmissa vaiheissa ja jota on käytetty myös

muodos-tettaessa TURVA-2012:n FEP-listaa. Tätä metodologiaa ja prosessointia ei ole kuitenkaan

aiemmin järjestelmällisesti kuvattu. FEPien valinnan pohjana on käytetty NEAn (Nuclear Energy

Agency) 2.1 FEP-tietokantaa. Tässä raportissa esitetään FEPien valinta ja prosessointi, minkä

perusteella on tarkasteltu TURVA-2012:n FEP-listan kattavuutta. Lukuun ottamatta FEPien

valintaprosessin alkuvaihetta, pintaympäristön FEPit eivät ole mukana lopullisessa tarkastelussa.

Avainsanat - Keywords

FEPit, loppusijoitusjärjestelmä, viranomaisvaatimukset, turvallisuusarvio.

ISBN

ISBN 978-951-652-241-1

ISSN

ISSN 1239-3096

Sivumäärä – Number of pages

148

Kieli – Language

Englanti

Posiva Oy

Olkiluoto

FI-27160 EURAJOKI, FINLAND

Puh. 02-8372 (31) – Int. Tel. +358 2 8372 (31)

Julkaisuaika – Date

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TABLE OF CONTENTS

ABSTRACT

TIIVISTELMÄ

 

TERMS AND ABBREVIATIONS ... 3

 

FOREWORD ... 5

 

1

 

INTRODUCTION ... 7

 

1.1

 

Background ... 7

 

1.2

 

The KBS-3 method ... 7

 

1.3

 

Posiva’s programme for developing a KBS-3 repository at Olkiluoto ... 8

 

1.4

 

Regulatory context for the management of spent nuclear fuel ... 11

 

1.5

 

Safety concept and safety functions ... 11

 

1.6

 

TURVA-2012 Safety Case portfolio ... 15

 

1.7

 

Quality assurance ... 17

 

1.8

 

Scope and objectives of the present report ... 19

 

1.9

 

Structure ... 19

 

2

 

METHODOLOGY FOR FEP SCREENING AND PROCESSING ... 21

 

2.1

 

Overall methodology ... 21

 

2.2

 

FEP screening and processing steps ... 22

 

2.3

 

Identification and screening of FEPs for potential significance ... 22

 

2.3.1

 

The initial FEP list ... 22

 

2.3.2

 

Relevance screening ... 22

 

2.3.3

 

Initial aggregation and component-wise classification of the FEPs .. 23

 

2.3.4

 

Significance screening ... 23

 

2.4

 

Mapping remaining Project FEPs to the TURVA-2012 FEP list ... 24

 

2.5

 

Cross-checking ... 24

 

3

 

SCREENING AND PROCESSING OF THE FEPS ... 25

 

3.1

 

FEP lists included in the work ... 25

 

3.2

 

Relevance screening results ... 25

 

3.3

 

Preliminary aggregation of FEPs and classification under disposal system

components ... 25

 

3.4

 

Significance screening results ... 26

 

4

 

MAPPING REMAINING PROJECT FEPS TO THE TURVA-2012 FEP LIST ... 27

 

5

 

CROSS-CHECKING AGAINST OTHER RELEVANT FEP SOURCES ... 29

 

5.1

 

Cross-checking against the Swedish SR-Site ... 29

 

5.2

 

Cross-checking against the Canadian Fourth Case Study ... 32

 

5.3

 

Comparison with FEPs in Process Report 2007-12 ... 34

 

6

 

CONCLUSIONS AND THE WAY FORWARD ... 37

 

6.1

 

Comprehensiveness of TURVA-2012 FEP list ... 37

 

6.2

 

The way forward ... 37

 

REFERENCES ... 39

 

APPENDIX A. FULL TURVA-2012 FEP LIST ... 43

 

APPENDIX B. MAPPING OF THE TURVA-2012 FEPS TO NEA FEPS AFTER

SCREENING PROCESS ... 49

 

APPENDIX C. CROSS-CHECK AGAINST SR-SITE ... 111

 

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TERMS AND ABBREVIATIONS

CLA

Construction Licence Application.

DiP (Government)

Decision-in-Principle.

EBS

EPM

Engineered Barrier System, which includes canister, buffer,

back-fill and closure.

Equivalent Porous Medium.

FEPs

Features, Events and Processes.

GD Government

Decree.

IAEA

International Atomic Energy Agency.

ISAM

Integrated Safety Assessment Methodology.

KBS-3

An abbreviation of

kärnbränslesäkerhet

(nuclear fuel safety)

ver-sion 3. The KBS-3 method for implementing the spent nuclear

fuel disposal concept based on multiple barriers.

KBS-3H

(Kärnbränslesäkerhet 3-Horisontell). Design alternative of the

KBS-3 method in which several spent nuclear fuel canisters are

emplaced horizontally in each deposition drift.

KBS-3V (Kärnbränslesäkerhet

3-Vertikal). The reference design alternative

of the KBS-3 method, in which the spent nuclear fuel canisters are

emplaced in individual vertical deposition holes.

KTM

Finnish Ministry of Trade and Industry.

NDT Non-Destructive

Testing.

NEA

Nuclear Energy Agency.

NWMO

Nuclear Waste Management Organization (in Canada).

OL3 Olkiluoto

3

reactor.

OL4

Fourth reactor to be constructed at Olkiluoto. Expected to be

simi-lar to OL3 in TURVA-2012 safety case.

ONKALO

Underground research facility constructed at Olkiluoto.

OSD

Olkiluoto Site Descriptive model.

POTTI

Database at Posiva with site-investigation data.

PSAR

Preliminary Safety Analysis Report – a part of the construction

licence application.

QA Quality

Assurance.

QC

Quality Coordinator; Quality Control.

R1

Relevance screening criterion 1. The Project FEP is defined by a

heading without any description of what is meant by the heading.

R2

Relevance screening criterion 2. The Project FEP is related to

as-sessment methodology. These FEPs are handled elsewhere in the

TURVA-2012 safety case.

R3

Relevance screening criterion 3. The Project FEP is not relevant

for the context of the TURVA-2012 safety case, especially in

re-spect to the national regulatory requirements and guidelines.

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R4

Relevance screening criterion 4. The Project FEP is not relevant

for the KBS-3V type repository design for spent nuclear fuel

dis-posal.

R5

Relevance screening criterion 5. The Project FEP is not relevant

for the present-day Olkiluoto site characteristics and likely future

site characteristics evolving in response to climatic changes and

other external factors.

Repository

system

Spent nuclear fuel, canister, buffer, backfill (deposition tunnel

backfill + deposition tunnel end plug), closure components and

host rock. Excludes the surface environment.

RSC

Rock Suitability Classification. The aim of the RSC is to define

suitable rock volumes for the repository, deposition tunnels and

deposition holes.

RTD

Research, Technical development and Design.

S1

Significance screening criterion 1. The FEP has insignificant

im-pact on safety functions and radiation protection criteria.

S2

Significance screening criterion 2. The FEP has low probability to

occur and low impact on safety functions and radiation protection

criteria.

S3

Significance screening criterion 3. The FEP itself has considerably

more serious consequences than any potential radiological

conse-quences from the spent nuclear fuel.

SAFCA

Safety Case project.

SKB

Swedish Nuclear Fuel and Waste Management Company.

SR-Site

SR-Site safety assessment for a repository in Forsmark.

STUK

Finnish Radiation and Nuclear Safety Authority.

TEM

Finnish Ministry of Employment and the Economy, previously

Ministry of Trade and Industry (KTM).

TKS-2009

Finnish equivalent for RTD (see RTD). RTD programme for

2010

2012.

TURVA-2012

Posiva’s safety case supporting the construction licence

applica-tion submitted in 2012 for the Olkiluoto spent nuclear fuel

dis-posal facility. TURVA means safety.

VAHA

Requirements management system at Posiva.

VVER-440 Pressurised

water

reactor type at Loviisa.

YJH

Finnish abbreviation for Nuclear Waste Management.

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FOREWORD

The participants in the project group for screening in/out discussions in this report are

listed below:

Hagros, Annika (Saanio & Riekkola, SROY)

Hellä, Pirjo (SROY)

Hjerpe, Thomas (Facilia AB)

Pitkänen, Petteri (Posiva Oy)

Koskinen, Lasse (Posiva Oy)

Laine, Heini (SROY)

Marcos, Nuria (SROY)

Pastina, Barbara (SROY)

Snellman, Margit (SROY)

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1 INTRODUCTION

1.1 Background

On assignment by its owners, Fortum Oyj and Teollisuuden Voima Oyj, Posiva Oy will

manage the disposal of spent nuclear fuel from the Loviisa and Olkiluoto nuclear power

plants. At Loviisa, two pressurised water reactors (VVER-440) are in operation; at

Olkiluoto, two boiling water reactors are operating and one pressurised water reactor is

under construction. Plans exist also for a fourth nuclear power unit at Olkiluoto. At both

sites there are facilities available for intermediate storage of the spent nuclear fuel

be-fore disposal.

In 2001, the Parliament of Finland endorsed a Decision-in-Principle (DiP) whereby the

spent nuclear fuel generated during the operational lives of the operating Loviisa and

Olkiluoto reactors will be disposed of in a geological repository at Olkiluoto. This first

DiP allowed for the disposal of a maximum amount of spent nuclear fuel corresponding

to 6500 tonnes of uranium (tU) initially loaded into the reactors. Subsequently,

addi-tional DiPs were issued in 2002 and 2010 allowing extension of the repository (up to

9000 tU) to also accommodate spent nuclear fuel from the operations of the OL3 reactor

and the planned OL4 reactor. OL4 spent nuclear fuel is handled in the TURVA-2012

safety case assuming it to be similar to OL3 spent nuclear fuel.

1.2 The KBS-3 method

The 2001 DiP states that disposal of spent nuclear fuel shall take place in a geological

repository at the Olkiluoto site, developed according to the KBS-3 method. In the

KBS-3 method, spent nuclear fuel encapsulated in water-tight and gas-tight sealed

me-tallic canisters with a mechanical load-bearing insert is emplaced deep underground in a

geological repository constructed in the bedrock. According to the DiP, the repository

shall be located at minimum depth of 400 m. In Posiva’s current repository design, the

repository is constructed on a single level and the floor of the deposition tunnels is at a

depth of 400

450 m in the Olkiluoto bedrock.

Posiva’s reference design in the construction licence application is based on vertical

emplacement of the spent nuclear fuel canisters (KBS-3V; Figure 1-1). Currently, an

alternative horizontal emplacement design (KBS-3H) is being jointly developed by the

Swedish Nuclear Fuel and Waste Management Company (SKB) and Posiva.

The KBS-3V design is based on a multi-barrier principle in which copper-iron canisters

containing spent nuclear fuel are emplaced vertically in individual deposition holes

bored in the floors of the deposition tunnels (see inset in Figure 1-1). The canisters are

to be surrounded by a swelling clay buffer material that separates them from the

bed-rock. The deposition tunnels and the central tunnels and the other underground openings

are to be backfilled with materials of low permeability.

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Figure 1-1. Schematic presentation of the KBS-3V design.

1.3 Posiva’s programme for developing a KBS-3 repository at Olkiluoto

The Olkiluoto site, located on the coast of south-western Finland (Figure 1-2), has been

investigated for over 20 years. During the past few years, key activities in the

pro-gramme have been related to:

completion of the investigations for site confirmation at Olkiluoto both through

analyses of data from surface-drilled characterisation holes and surveys and studies

carried out in the ONKALO underground research facility,

the design of required surface and disposal facilities,

the development of the selected disposal technology to the level required for the

construction licence application, and

demonstration of the long-term safety of the disposal of spent nuclear fuel including

the preparation of a safety case (Section 1.6) presented as a portfolio of reports,

including the present report.

Posiva’s ongoing RTD (research, development and technical design) phase has been

introduced in the TKS-2009 report (Posiva 2009) for the years 2010

2012, which also

provides insight into developments from previous RTD phases. In 2012 a new RTD

programme (YJH-2012) for 2013

2015 was published (Posiva 2013). In Figure

1-3, a

general timeline of Posiva’s programme is presented.

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Figure 1-2. Olkiluoto Island is situated on the coast of the Baltic Sea in south-western

Finland. Photograph by Helifoto Oy.

Figure 1-3.

Overall schedule for nuclear waste management relating to the Loviisa and

Olkiluoto reactors until 2020. The target is to begin disposal of spent nuclear fuel around

2020.

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The repository will be located in the bedrock of Olkiluoto Island taking into account the

host rock properties as well as the restrictions set by urban planning in the Eurajoki

Municipality. In Figure 1-4 the current reference layout is presented.

Figure 1-4. The current reference layout (green). Dark grey areas are not suitable for

deposition tunnels based on Rock Suitability Classification (RSC), which has been

de-veloped by Posiva. Red ovals denote respect distances to drillholes. The red line

sur-rounding the repository shows the area reserved for the repository in urban planning.

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1.4 Regulatory context for the management of spent nuclear fuel

According to the law, the Finnish Ministry of Employment and the Economy (TEM;

previously the Ministry of Trade and Industry, KTM) decides on the principles to be

followed in waste management of spent fuel and other nuclear waste.

The schedule for the disposal of spent nuclear fuel was established in the KTM’s

Deci-sion 9/815/2003. According to this DeciDeci-sion, the parties under the nuclear waste

man-agement obligation shall, either separately, together or through Posiva Oy, prepare to

present all reports and plans required to obtain a construction licence for a disposal

fa-cility for spent nuclear fuel as stated in the Nuclear Energy Decree by the end of 2012.

The disposal facility is expected to become operational around the year 2020.

The legislation concerning nuclear energy was updated in 2008. As part of the

legisla-tive reform, a number of the relevant Government Decisions were replaced with

Gov-ernment Decrees. The Decrees entered into force on 1

st

December 2008. The

Govern-ment Decision (478/1999) regarding the safety of disposal of spent nuclear fuel, which

particularly applied to the disposal facility, was replaced with Government Decree

736/2008, issued 27 November 2008.

Currently, the valid Regulatory Guides pertaining to nuclear waste management are

Guides YVL D.1

D.5 issued by the Radiation and Nuclear Safety Authority (STUK) in

2013. Guide YVL D.1 deals with nuclear non-proliferation control, D.2 with the

trans-port of nuclear material and nuclear waste, D.3 with the processing, storage and

encap-sulation of spent nuclear fuel, D.4 with nuclear waste management and

decommission-ing activities and D.5 with the disposal of nuclear waste. As these Guides were

pub-lished in late 2013, the version of YVL D.5 used in the preparation of the TURVA-2012

safety case (see Section 1.6) was Draft 4 (17.3.2011, in Finnish only).

1.5 Safety concept and safety functions

The long-term safety principles of

Posiva’s

planned repository system are described at

Level 2 of the VAHA (VAHA is

Posiva’s

requirement management system) as follows:

1.

The spent nuclear fuel elements are disposed of in a repository located deep in the

Olkiluoto bedrock. The release of radionuclides is prevented with a multi-barrier

disposal system consisting of a system of engineered barriers (EBS) and host rock

such that the system effectively isolates the radionuclides from the living

environ-ment.

2.

The engineered barrier system consists of

a)

canisters

to contain the radionuclides for as long as they could cause significant

harm to the environment,

b)

buffer

between the canisters and the host rock to protect the canisters as long as

containment of radionuclides is needed,

c) deposition

tunnel backfill and plugs

to keep the buffer in place and help restore

the natural conditions in the host rock,

d) the

closure

, i.e. the backfill and sealing structures

to decouple the repository from

the surface environment.

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3.

The host rock and depth of the repository are selected in such a way as to make it

possible for the EBS to fulfil the functions of containment and isolation described

above.

4.

Should any of the canisters start to leak, the repository system as a whole will hinder

or retard releases of radionuclides to the biosphere to the level required by the

long-term safety criteria.

The safety concept, as depicted in Figure 1-5, is a conceptual description of how these

principles are applied together to achieve

safe disposal

of spent nuclear fuel in the

con-ditions of the Olkiluoto site. Due to the long-term hazard of the spent nuclear fuel, it has

to be isolated from the surface environment over a long period of time. The KBS-3

method provides

long-term isolation and containment

of spent nuclear fuel by a

sys-tem of multiple barriers, both engineered and natural, and by ensuring a sufficient depth

of disposal (the key safety features of the system in Figure 1-5). All of these barriers

have their roles in establishing the required long-term safety of the repository system.

These roles constitute the

safety functions

of the barriers (see Table 1-1). The surface

environment is not given any safety functions; instead it is considered as the object of

the protection provided by the repository system.

Most radionuclides in the spent nuclear fuel are embedded in a ceramic matrix (UO2)

that itself is resistant to dissolution in the expected repository conditions. The slow

re-lease of radionuclides from the spent nuclear fuel matrix is part of Posiva’s safety

con-cept. Moreover, the near-field conditions should contribute to maintain the low

solubil-ity of the matrix.

Figure 1-5. Outline of the safety concept for a KBS-3 type repository for spent nuclear

fuel in a crystalline bedrock (adapted from Posiva 2003). Orange pillars and blocks

indicate the primary safety features and properties of the disposal system. Green pillars

and blocks indicate the secondary safety features that may become important in the

event of a radionuclide release from a canister.

Retention and retardation of radionuclides S lo w t ran sp o rt i n t h e g e os ph e re S lo w re le ase fr o m th e spe n t f u el m at ri x S low di ff u s ive tra n s p o rt in t h e b u ffe r SUFFICIENT DEPTH F AV O URABL E NE AR -F IE L D CO NDI T IO NS F O R T HE CANI S T E R P ROV E N T E CHNI CAL QUAL IT Y O F TH E E B S

SAFE DISPOSAL

LONG-TERM ISOLATION AND CONTAINMENT

FAVOURABLE, PREDICTABLE BEDROCK

AND GROUNDWATER CONDITIONS WELL-CHARACTERISED MATERIAL

PROPERTIES

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Implementation of the KBS-3 method entails the introduction of a number of additional

barriers because of engineering, operational safety or long-term safety needs. Long-term

safety needs arise, for example, because implementation involves the construction of a

system of underground openings, including access tunnels and shafts, that would

sig-nificantly perturb the safety functions of the host rock unless backfilled and sealed at

closure of the disposal facility. These closure components with long-term safety

func-tions include:

backfill of underground openings, including the central tunnels, access tunnels,

shafts, and other excavations, and

drillhole plugs, mechanical plugs, long-term hydraulic plugs at different depths and

plugs near the surface.

The safety functions of the engineered barrier system (EBS) components and host rock

are summarised in Table 1-1. In the TURVA-2012 safety case documentation, the spent

nuclear fuel, EBS and the host rock are jointly termed the

repository system

, whereas

the term

disposal system

is used when the repository system and the surface

environ-ment are both considered (see Figure 1-6).

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Table 1-1. Summary of safety functions assigned to the barriers (EBS components and

host rock) in

Posiva’s

KBS-3V repository.

Barrier

Safety functions

Canister

Ensure a prolonged period of containment of the spent nuclear fuel. This

safety function rests first and foremost on the mechanical strength of the

canister’s cast iron insert and the corrosion resistance of the copper

sur-rounding it.

Buffer

Contribute to mechanical, geochemical and hydrogeological conditions that

are predictable and favourable to the canister,

Protect canisters from external processes that could compromise the safety

function of complete containment of the spent nuclear fuel and associated

radionuclides,

Limit and retard radionuclide releases in the event of canister failure.

Deposition

tunnel

backfill

Contribute to favourable and predictable mechanical, geochemical and

hydrogeological conditions for the buffer and canisters,

Limit and retard radionuclide releases in the possible event of canister

failure,

Contribute to the mechanical stability of the rock adjacent to the deposition

tunnels.

Host rock

Isolate the spent nuclear fuel repository from the surface environment and

normal habitats for humans, plants and animals and limit the possibility of

human intrusion, and isolate the repository from changing conditions at the

ground surface,

Provide favourable and predictable mechanical, geochemical and

hydro-geological conditions for the engineered barriers,

Limit the transport and retard the migration of harmful substances that could

be released from the repository.

Closure

Prevent the underground openings from compromising the long-term

isola-tion of the repository from the surface environment and normal habitats for

humans, plants and animals.

Contribute to favourable and predictable geochemical and hydrogeological

conditions for the other engineered barriers by preventing the formation of

significant water conductive flow paths through the openings,

Limit and retard inflow of water to and release of harmful substances from

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Figure 1-6. The components of the disposal system.

1.6 TURVA-2012 Safety Case portfolio

A safety case for a geological disposal facility documents the scientific and technical

understanding of the disposal system, including the safety barriers and safety functions

that these are expected to provide, results of a quantitative safety assessment, the

proc-ess of systematically analysing the ability of the repository system to maintain its safety

functions and to meet long-term safety requirements, and provides a compilation of

evi-dence and arguments that complement and support the reliability of the results of the

quantitative analyses.

As stated in Guide YVL D.5, A01:

Compliance with the requirements concerning

long-term radiation safety, and the suitability of the disposal method and disposal site, shall

be proven through a safety case that must analyze both expected evolution scenarios

and unlikely events impairing long-term safety. The safety case comprises a numerical

analysis based on experimental studies and complementary considerations insofar as

quantitative analyses are not feasible or involve considerable uncertainties

(Govern-ment Decree GD 736/2008).

The TURVA-2012 safety case portfolio is based on the safety case plan published in

2008 (Posiva 2008), which updates an earlier plan published in 2005 (Vieno & Ikonen

2005). In the updated safety case plan, further details are provided on quality assurance

and control procedures and their documentation, as well as on the consistent handling of

different types of uncertainties. Since 2008, the safety case plan has been iterated based

on the feedback received from the authorities, and the contents of the safety case

portfo-lio TURVA-2012 are now as presented in Figure 1-7. In this report, all TURVA-2012

portfolio reports are referenced using the report title in

italics

. The full titles and report

numbers are listed at the beginning of the reference list.

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Main reports

Main supporting documents

Site Description

Biosphere Description

Understanding of the present state and past

evolution of the host rock

Understanding of the present state and evolution of

the surface environment

Models and Data for the

Repository System

Biosphere Data Basis

Description of climate evolution and definition of release scenarios

Models and data used in the performance

assessment and in the analysis of the

radionuclide release scenarios

TURVA-2012

Synthesis

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

Design Basis

Performance targets and target properties for the repository system

Production Lines

Design, production and initial state of the EBS and the underground openings

Description of the Disposal System

Analysis of releases and calculation of doses and activity fluxes.

Complementary Considerations

Supporting evidence incl. natural and anthropogenic analogues

Data used in the biosphere assessment and

summary of models

Biosphere Assessment: Modelling reports

Description of the models and detailed modelling of surface environment

Assessment of Radionuclide

Release Scenarios for the

Repository System

Biosphere Assessment

Summary of the initial state of the repository system and present state of the surface environment

Features, Events and Processes

General description of features, events and processes affecting the disposal system

Performance Assessment

Analysis of the performance of the repository system and evaluation of the fulfillment of performance

targets and target properties

Formulation of Radionuclide Release Scenarios

Figure 1-7. TURVA-2012 safety case portfolio including report names (coloured boxes)

and brief descriptions of the contents (white boxes). Disposal system = repository

sys-tem + surface environment.

(23)

The main reports and supporting documents of the TURVA-2012 portfolio have been

described in the introduction to other main reports and will not be repeated here.

This FEPs screening and processing report is not in the portfolio. The FEP screening

and processing methodology, although applied in TURVA-2012, has not been formally

reported until now, though an auditing of the FEPs taken into account in previous safety

assessment was reported by Vieno & Nordman (1997) and discussions on what FEPs

should be taken into account in a safety case took place during the compilation of

Rasi-lainen (2004) and of Miller & Marcos (2007). This report presents also an audit against

the NEA Version 2.1 Project Databases. The reasoning on why the FEPs are screened

out of the final list is also presented.

In the review of the pre-licensing documentation, STUK emphasises the need for

aggre-gating/disaggregating FEPs, and this has been taken thoroughly into account

.

1.7 Quality

assurance

The quality assurance (QA) procedures for the safety case (SAFCA) portfolio (see

Fig-ure 1-7) have been carried out following

Posiva’s

quality management system, which

complies with the ISO 9001:2008 standard and considers relevant regulatory

require-ments. Even though the quality assurance is based throughout on management

accord-ing to the standard ISO 9001:2008, a graded approach proposed for nuclear facilities is

adopted, i.e. the primary emphasis is on the quality control of the safety case,

particu-larly for those activities that have a direct bearing on long-term safety, whereas standard

quality measures are applied in the supporting work. This means, in practice, that the

main safety case reports are subjected to stricter quality demands than general research

activities. The input from Posiva’s own RTD activities and other research also fulfil the

ISO 9001 quality standards.

The general quality guidelines of Posiva are also applied; the composition and quality

management of portfolio reports and the recruitment of expert reviewers are carried out

according to the respective guidelines. In addition, special attention is paid to the

man-agement of the processes that are applied to produce the safety case and its foundations,

which is the basis for the whole safety case process and organisation of the work. The

purpose of this enhanced process control is to provide full traceability and transparency

of the data, assumptions, models, calculations and results. The safety case production

process is a part of Posiva’s RTD process and is linked to Posiva’s Production lines,

Facility design and other main processes. The main customer is the Strategy process and

the Licensing sub-process. The aim of the safety case production process is to produce

the long-term safety documentation for the construction licence application. The safety

case production process is owned by the research manager of Posiva’s Long-term Safety

Unit in Posiva’s Research Department.

The overall plan, main goals and constraints for the safety case production process are

presented in the Safety case plan (Posiva 2008). The details of how the Safety case plan

2008 is being implemented are described in the SAFCA project plan. The work is

man-aged and coordinated by a SAFCA core group and supervised by a steering group.

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The safety case production process is divided into four main sub-processes:

Conceptu-alisation and Methodology, Data Handling and Modelling, Safety Assessment, and

Evaluation of Compliance and Confidence.

The Data Handling and Modelling sub-process constitutes the central linkage between

Posiva’s main technical and scientific activities and the production of the safety case. It

is a clearinghouse activity between the supply of, and demand for, quality-assured data

for the safety case. Data are produced by Posiva’s planning, design and development

processes for the EBS (Engineered Barrier System), by the site characterisation process

for the geoscientific data and through the biosphere description of the Olkiluoto area.

A SAFCA quality co-ordinator (QC) has been designated for the activities related to the

quality assurance measures applied to the production of the safety case contents. The

QC is responsible for checking that the instructions and guidelines are followed, and

improvements are made in the process as deemed useful or necessary. The QC is also

responsible for the coordination of the external expert reviews, maintenance of

sched-ules, review and approval of the products, and the management of the expert elicitation

process. The QC also leads the quality review of models and data used in the Data

Han-dling and Modelling sub-process. Regular auditing of the safety case production process

is done as part of Posiva's internal audit programme.

Data sources and quality aspects of the sources are documented according to a specific

guideline. Individual data and databases are approved through a clearance procedure

supervised by the SAFCA Quality Co-ordinator. The process owner checks and

ap-proves the data and the QC checks and apap-proves the procedure. Data used may also be

approved using other Posiva databases such as VAHA or POTTI and the respective

ap-proval processes. A clearance procedure has been applied to all key data used in the

performance assessment (i.e. showing compliance with performance targets and target

properties), and in the safety assessment (i.e. radionuclide transport and dose

calcula-tions).

The control and supervision of the safety case products (i.e. main portfolio reports) has

been done in two steps, first an internal review by safety case experts and subject-matter

experts within

Posiva’s

RTD programme and then the second step by external expert

reviewers. A group of external experts covering the essential areas of knowledge and

expertise needed in the safety case production has been set up. The review process is

based on review templates, which record each review comment and how it has been

addressed. Upon completion, this template is checked and approved according to the

quality guidelines of Posiva.

An expert elicitation process has been applied to specific cases when the understanding

or data basis is conflicting and consensus is needed for the selection of key data (e.g.

future climate scenarios, solubility and sorption data). This expert elicitation process has

been initiated, recruited, documented and managed by the SAFCA Quality

Co-ordinator.

QA issues are discussed further in the

Synthesis

. Quality assurance and quality control

measures related to the production and operation of the repository are discussed in detail

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in the Production Line reports (

Canister, Buffer, Backfill, Closure

and

Underground

Openings

).

1.8 Scope and objectives of the present report

This report documents the screening and processing of features, events and processes

(FEPs) starting from NEA Version 2.1 Project Databases that has been carried out

within TURVA-2012. The main objective is the FEP screening process that has been

used to show that Posiva’s FEP list, as described in

Features, Events and Processes

, is

adequate for the current stage of the spent nuclear fuel management programme. The

disposal system, as defined in Figure 1-6 includes the spent nuclear fuel, the engineered

barriers surrounding it, the host rock, and the surface environment. The disposal system

will evolve over time. The evolution of the disposal system will depend on:

-

the initial state of the system (relevant features are summarised in

Description of the

Disposal System

),

-

a number of processes acting within the disposal system, and

-

external influences (events and processes) acting on the system.

The focus of the present report is on the FEPs related to the repository system and

ex-ternal FEPs. The processing for the FEPs related to the surface environment is here

lim-ited to the initial step, the relevance screening (Chapter 3). This is due, on the one hand,

to the lack of resources and, on the other hand, to the emphasis given by the Finnish

regulator STUK, to the FEPs related to the repository system.

1.9 Structure

The structure of the present report is as summarised below.

Chapter 2 presents the overall FEP screening and processing methodology.

Chapter 3 presents the outcome of the relevance and significance screening steps

performed on the NEA Version 2.1 Project Databases.

Chapter 4 presents the further processing of the screened in FEPs and the mapping

of the TURVA-2012 FEP list to the screened in FEPs.

In Chapter 5 a cross-checking of the TURVA-2012 FEP list is performed against

FEP lists developed in other relevant projects and FEPs in Posiva’s 2007 Process

Report (Miller & Marcos 2007).

Chapter 6 concludes on the advantages and challenges of the TURVA-2012 FEPs

classification and provides a discussion on comprehensiveness.

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(27)

2 METHODOLOGY FOR FEP SCREENING AND PROCESSING

2.1 Overall

methodology

A central feature of Posiva’s TURVA-2012 safety case is the formulation and analysis

of a set of scenarios that, collectively, represent the envelope of future evolutions for a

KBS-3V type disposal facility at the Olkiluoto site. The definition and formulation of

scenarios is supported by the identification and consideration of all potentially relevant

features, events and processes (FEPs) that, on the one hand, characterise the system, and

on the other hand might occur during system evolution, and that have the potential to

affect long-term safety. These FEPs are discussed in detail in

Features, Events and

Processes

. Focusing on FEPs when developing the scenarios is in line with international

recommendations regarding the development, operation and closure of disposal

facili-ties and international best practice applied. For example, the Specific Safety

Require-ments on Disposal of Radioactive Waste (IAEA 2011) states in Requirement 15 on Site

characterization for a disposal facility that:

The site for a disposal facility shall be characterized at a level of detail sufficient

to support a general understanding of both the characteristics of the site and how

the site will evolve over time. This shall include its present condition, its probable

natural evolution and possible natural events, and also human plans and actions

in the vicinity that may affect the safety of the facility over the period of interest. It

shall also include a specific understanding of the impact on safety of features,

events and processes associated with the site and the facility.

More specifically, the Specific Safety Guide on The Safety Case and Safety Assessment

for the Disposal of Radioactive Waste (IAEA 2012) states (5.42):

Regardless of the method used for developing the scenarios, all features, events

and processes that could significantly influence the performance of the disposal

system should be addressed in the assessment.

Posiva’s methodology for scenario formulation, related to the repository system, follows

a ‘top-down’ approach in first identifying the safety functions that are required of the

repository system, then considering the effects of single FEPs or combinations of FEPs

on those functions to check that the scenarios are comprehensive (

Formulation of

Ra-dionuclide Release Scenarios

, Section 2.5). However, Posiva’s methodology for the

FEP screening component in the overall FEP processing is more closely related to the

‘bottom-up’ approach for scenario development described, for example, in the ISAM

project (IAEA 2004). When using this method, a comprehensive list of features, events

and processes is developed as a starting point. This may involve the use of generic lists

of features, events and processes (internationally agreed lists, regulations, etc.) and the

determining of site- and system-specific features, events and processes (as discussed

above). This is followed by a screening process to exclude features, events and

proc-esses from further considerations that are either irrelevant for the KBS-3 concept or

considered to have insignificant impact on the long-term safety of the disposal system.

Criteria for screening features, events and processes may include rules relating to

regu-lations and/or to the probability of occurrence or consequences of events and processes.

The sections below describe the step-wise FEP screening method, and further

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process-ing, applied in demonstrating that the TURVA-2012 FEP list for the repository system

and external events and processes is comprehensive enough.

2.2 FEP screening and processing steps

Features, events and processes that might occur, and that have the potential to affect

long-term safety under certain conditions are accounted for in the safety assessment in

the TURVA-2012 safety case. These FEPs are presented and discussed in

Features,

Events and Processes

. This section describes the identification and screening of FEPs

and their further processing and cross-checking that was conducted in order to assess

the comprehensiveness of the TURVA-2012 FEP list. The work has been conducted in a

structured step-wise manner mainly relying on expert judgement. Each step in the

proc-ess is elaborated in the sub-sections below and they are summarised as follows:

1.

Selecting an initial comprehensive FEP list to use as a starting point.

2.

Performing a

relevance screening

based on a set of screening criteria aiming at

screening out FEPs not relevant for the KBS-3 concept or the TURVA-2012 safety

case.

3.

Performing an initial aggregation of FEPs with an identical heading or meaning, and

the classification of the FEPs under the components of the disposal system (or as

ex-ternal if they are exex-ternal to the system).

4.

Performing a

significance screening

based on a set of screening criteria aiming at

screening out FEPs clearly insignificant for long-term safety.

5.

Mapping the FEPs not screened out in previous steps to the TURVA-2012 FEP list.

This step contains, for example, the aggregation and disaggregation of FEPs to

fol-low Posiva’s FEP nomenclature.

6.

Cross-check the final TURVA-2012 FEP list against FEP lists developed in other

relevant projects.

2.3 Identification and screening of FEPs for potential significance

2.3.1 The initial FEP list

The FEP screening is based on the FEP list from NEA 2.1 Project Databases

(NEA 2006), which was the latest NEA FEP database available in 2011 when the FEPs

in

Features, Events and Processes

were compiled.

2.3.2 Relevance

screening

A relevance screening, aiming to screen out FEPs not relevant for a KBS-3V type

re-pository or the TURVA-2012 safety case, is performed on the FEPs in the NEA Version

2.1 Project Databases, below denoted as Project FEPs. A set of criteria has been set out

to facilitate this screening. A Project FEP is screened out if at least one of the five

fol-lowing screening criteria is fulfilled:

R1 The Project FEP is defined by a heading without any description of what is

meant by the heading.

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R2

The Project FEP is related to assessment methodology. These FEPs are handled

elsewhere in the TURVA-2012 safety case.

R3

The Project FEP is not relevant for the context of the TURVA-2012 safety

case, especially in respect to the national regulatory requirements and

guide-lines.

R4

The Project FEP is not relevant for the KBS-3V type repository design for

spent nuclear fuel disposal.

R5

The Project FEP is not relevant for the present-day Olkiluoto site

characteris-tics and likely future site characterischaracteris-tics evolving in response to climatic

changes and other external factors.

2.3.3 Initial aggregation and component-wise classification of the FEPs

The second step in the process includes:

the initial aggregation of the Project FEPs screened in that have identical heading or

meaning. At this stage, the individual project-specific FEP descriptions are,

how-ever, kept in the documentation for the benefit of the experts carrying out the next

screening step (Section 2.3.4).

the classification of the aggregated FEPs under the component(s) of the disposal

system, i.e. spent fuel, canister, buffer, backfill, auxiliary components, geosphere or

surface environment or they are classified as “external” if they are related to

condi-tions external to the disposal system. A FEP is classified under several components

if it is not obvious that it only relates to one component (e.g. “soil moisture and

evaporation” is only mapped to surface environment, whereas “diffusion” is

classi-fied to all components of the disposal system).

2.3.4 Significance

screening

The third step in the process is to conduct a screening evaluation of the Project FEPs not

screened out in the relevance screening, aiming at screening out FEPs clearly

insignifi-cant for long-term safety. A set of criteria regarding a FEP’s impact on safety functions

and radiation protection criteria (these are doses and activity fluxes; there are FEPs

af-fecting e.g. exposure pathways that have an impact on the end points regarding radiation

protection criteria, but these FEPs have no impact on safety functions) has been defined

to facilitate this screening. A Project FEP is screened out if at least one of the following

significance screening criteria is fulfilled:

S1 The FEP has insignificant impact on safety functions and radiation protection

criteria.

S2 The FEP has low probability to occur and low impact on safety functions and

radiation protection criteria.

S3 The FEP itself has considerably more serious consequences than any potential

radiological consequences from the spent nuclear fuel.

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2.4 Mapping remaining Project FEPs to the TURVA-2012 FEP list

The outcome of the steps in the FEP screening and initial processing described above is

a list of NEA Project FEPs potentially safety relevant for a KBS-3V repository at the

Olkiluoto site. These FEPs have been aggregated and classified under relevant

compo-nents of the disposal system or as external FEPs. This list is mapped to TURVA-2012

FEPs to check that they include all FEPs relevant for the KBS-3V system at Olkiluoto.

The full TURVA-2012 FEP list is presented in Appendix A. An explanation is given,

when necessary, in case a remaining NEA Project FEP has not a clear corresponding

TURVA-2012 FEP.

2.5 Cross-checking

The final step is to cross-check the TURVA-2012 FEP list against relevant sources to

increase the confidence in that no important FEPs have been omitted. Of importance is

to cross-check against FEP lists developed in other relevant projects, especially the lists

underpinning safety assessments performed by SKB for a KBS-3V type repository for

spent nuclear fuel disposal. A cross-check against the FEP list in Miller & Marcos

(2007) is also included.

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3 SCREENING AND PROCESSING OF THE FEPS

3.1 FEP lists included in the work

The screening process was based on the NEA FEP list (NEA Version 2.1 Project

Data-base), which is a compilation of FEPs included in several spent nuclear fuel disposal

programmes around the world (i.e. Goodwin et al. 1994, NAGRA 1994, DOE 1996,

Chapman et al. 1995, Miller et al. 2002, Miller & Chapman 1993, Bronders et al. 1994).

Other FEP lists or sources of information used are discussed in Chapter 5 where the

final list is cross-checked against relevant literature. Cross-checking includes data from

SKB’s SR-Site (SKB 2010a) (Section 5.1), NWMO’s Fourth Case Study (Garisto 2012)

(Section 5.2) and comparison to earlier work done by Posiva (Section 5.3).

3.2 Relevance screening results

Relevance screening was performed following the protocol presented in Section 2.3.2.

The number of Project FEPs in version 2.1 of the NEA FEP database is large, in total

there are 1671 FEPs (Electronic Appendix 1, NEA version 2.1 Project Database). In

order to make the relevance screening more efficient, a workshop exercise was carried

out by a group of safety assessment experts.

This screening process is documented in Electronic Appendix 1 (NEA version 2.1

Pro-ject Databases – Relevance screening_final), where screening decisions based on

R-criteria (see Section 2.3.2) are listed. The final table shows the result of the initial

work-shop as well as including additional screening decisions that were revised during further

steps, i.e. cross-check, of the work.

The relevance screening resulted in 1154 FEPs being screened in and 517 FEPs being

screened out; the latter were divided among the individual screening criteria:

R1: 119 FEPs screened out

R2: 88 FEPs screened out

R3: 89 FEPs screened out

R4: 111 FEPs screened out

R5: 110 FEPs screened out.

3.3 Preliminary aggregation of FEPs and classification under disposal

system components

A preliminary aggregation of the FEPs and their classification under components of the

disposal system (or as external to the system) was done before moving to the

Signifi-cance screening phase. The protocol for the process is described in Section 2.3.3. The

aggregation was done to collate FEPs that were duplicates in the NEA FEP list in order

to simplify the following steps. FEPs were then classified under the following

compo-nents (reflecting those discussed in

Features, Events and Processes

):

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canister

buffer

backfill

auxiliary components

geosphere

surface environment

external FEPs.

The aggregation was documented in an Excel file which was used as a basis for the

Sig-nificance screening. Hence the, aggregation is shown also in the documentation of the

Significance screening results and is not duplicated here (see Section 3.4 and Electronic

Appendix 2, NEA version 2.1 Project Databases – Significance screening and

justifica-tions).

After the preliminary aggregation, the number of FEPs in the list was 735. It should be

noted that some of these FEPs (168 in total) were exclusively related to the surface

en-vironment, and these FEPs were not further processed.

3.4 Significance screening results

The Significance screening was performed in accordance to the protocol presented in

Section 2.3.4. The significance screening requires a deeper process understanding

com-pared with the relevance screening. Hence, the screening involved various subject

mat-ter experts for the different components of the disposal system and exmat-ternal conditions.

Initial screening was carried out by a group of experts in a significance screening

work-shop, and the justifications for screening out FEPs were written later by individual

ex-perts. The components included in the significance screening were all those listed above

(Section 3.3), except for the surface environment.

The Significance screening was documented in an Excel file on top of the initial

aggre-gation of the FEPs (Section 2.3.3). As noted above FEPs that relate only to the surface

environment (168 FEPs in total) are shown in the Excel sheet but they were not further

processed. Thus, 567 FEPs remained to be screened in this phase. The screening

deci-sions based on the Significance criteria and justification for “OUT” screening decideci-sions

are presented in Electronic Appendix 2 (NEA version 2.1 Project Databases –

Signifi-cance screening and justifications).

The significance screening resulted in 491 FEPs being screened in and 76 FEPs being

screened out. The latter were divided among the individual screening criteria:

S1: 55 FEPs screened out

S2: 16 FEPs screened out

S3: 5 FEPs screened out.

See Electronic Appendix 2 for justifications why these FEPs were screened out in this

phase (column “Justification”).

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4 MAPPING REMAINING PROJECT FEPS TO THE TURVA-2012 FEP LIST

After the screening phase (Chapter 3), the resulting FEP list (comprising 491

screened-in FEPs) was divided to component-wise lists, which were then used screened-in the mappscreened-ing

against Posiva’s FEPs to show that the TURVA-2012 FEP list is comprehensive

enough. The full TURVA-2012 FEP list is given in Appendix A.

Initial mapping was done by the project group for each component included in this

phase (spent fuel, canister, buffer, backfill, auxiliary components, geosphere and

exter-nal). The results were cross-checked within the project group. Mapping of the FEPs is

documented in Appendix B (Tables B-1 to B-7). In the mapping, FEP names from the

TURVA-2012 (

Features, Events and Processes

) were used. Project FEPs not included

in the TURVA-2012 FEP list were marked as “NA” (Not Applicable) in the mapping

tables with a note (justification or explanation).

The number of Project FEPs not applicable (NA) to the components was 21 for the

FUEL (FU), 24 for the CANISTER (CA), 11 for the BUFFER (BU), 15 for the

BACK-FILL (BA), 12 for the AUXILIARY COMPONENTS (A), 5 for the GEOSPHERE (G)

and 2 for EXTERNAL (E). The main reasons were that the Project FEP did not occur

in the component itself, being in most cases treated in interaction matrices (e.g. Table

3-4, p. 54 in

Features, Events and Processes

). In other cases the Project FEP was not

found as a TURVA-2012 FEP, but its consequences were treated under other relevant

FEPs of TURVA-2012, belonging to the same component or to others.

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5 CROSS-CHECKING

AGAINST

OTHER RELEVANT FEP SOURCES

In this chapter, the TURVA-2012 FEP list is compared with other relevant FEP lists

produced after the compilation of NEA’s Project Databases Version 2.1 but before the

publication of

Features, Events and Processes

in 2012. The FEP lists considered here

include those related to the following safety assessments for deep geological

reposito-ries in crystalline environments:

Sweden’s SR-Site (SKB 2010a),

Canada’s Fourth Case Study (Garisto 2012).

The purpose of this section is to cross-check whether all FEPs from these safety

assess-ments are also included in the TURVA-2012 FEP list, and if not, the reasons for their

omission are explored. The cross-checking is done by going through the entire FEP list

in question and by mapping the FEPs to one or (if necessary) several FEPs of the

TURVA-2012 FEP list (Tables C-1 and D-1 in Appendices C and D). If a FEP cannot

be mapped to any TURVA-2012 FEP, the reason for the omission is documented.

Fur-thermore, all TURVA-2012 process FEPs (excluding the surface environment FEPs) are

mapped to process FEPs in the above-mentioned assessments (Tables C-2 and D-2 in

Appendices C and D).

5.1 Cross-checking against the Swedish SR-Site

The SR-Site FEP catalogue (SKB 2010a) has been mapped to TURVA-2012 FEPs in

Appendix C to check the comprehensiveness of the TURVA-2012 FEP list. All SR-Site

FEPs that could not be mapped directly to any TURVA-2012 FEP are shown in Table

5-1. It came out that the FEP lists are fairly similar with the few exceptions mentioned

in Table 5-1. Differences are mainly due to the fact that assessment methodology issues

(including quality control issues) are not treated as FEPs in TURVA-2012 but are

han-dled elsewhere in the safety case and/or in other documents presented for the

construc-tion licence applicaconstruc-tion (CLA). Also, a few irrelevant FEPs (e.g. earth currents,

lique-faction of bentonite) have been excluded from Posiva’s FEP list already before

TURVA-2012, but they are included in the SR-Site FEP catalogue, even if concluded to

be irrelevant in the assessment.

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Table 5-1. SR-Site FEPs (SKB 2010a, Tables 5-1...5-12, Sections 5.6, 5.7 and 5.8 and

Appendix 2) that were not found in the TURVA-2012 FEP list (see Table C-1). FEPs

that were excluded from the SR-Site assessment (shown in grey in Table C-1) are not

included here, nor any surface environment FEPs.

FEP

number in

SR-Site

FEP name in SR-Site

Note

ISGen02

Effects of phased

op-eration

Operation schedule is handled elsewhere in TURVA-2012 (e.g.

waste emplacement schedule used in thermal dimensioning).

ISGen03

Incomplete closure

Out of the scope of the post-closure safety case TURVA-2012 that

assumes the disposal facility to be properly closed.

ISC01

Mishaps – canister

Canister handling accidents discussed in

Performance

Assess-ment

but not included as a FEP, as any canister damaged during

operation is assumed to be replaced. Operational safety is outside

the scope of TURVA-2012.

ISC02

Design deviations –

canister

Initial penetrating defect(s) assumed in several radionuclide re-

lease scenarios.

ISBu01

Mishaps – buffer

Out of scope of TURVA-2012. It is assumed that quality control

(QC) measures are successfully applied to buffer production and

emplacement. QC issues are related to assessment methodology

and are handled elsewhere in TURVA-2012.

ISBu02

Design deviations –

buffer

Out of scope of TURVA-2012. It is assumed that quality control

(QC) measures are successfully applied to buffer production and

emplacement. QC issues are related to assessment methodology

and are handled elsewhere in TURVA-2012.

ISBfT01

Mishaps – backfill in

tunnels

Out of scope of TURVA-2012. It is assumed that quality control

(QC) measures are successfully applied to backfill production and

emplacement. QC issues are related to assessment methodology

and are handled elsewhere in TURVA-2012.

ISBfT02

Design deviations –

backfill in tunnels

Out of scope of TURVA-2012. It is assumed that quality control

(QC) measures are successfully applied to backfill production and

emplacement. QC issues are related to assessment methodology

and are handled elsewhere in TURVA-2012.

ISBP01

Mishaps – bottom plate

in deposition holes

The bottom plate is not a component in Posiva’s current repository

design.

ISBP02

Design deviations –

bottom plate in

deposi-tion holes

The bottom plate is not a component in Posiva’s current repository

design.

ISPg01

Mishaps – plugs

Out of scope of TURVA-2012. It is assumed that quality control

(QC) measures are successfully applied to the production and

emplacement of closure plugs (auxiliary components). QC issues

are related to assessment methodology and are handled

else-where in TURVA-2012.

ISPg02

Design deviations –

plugs

Out of scope of TURVA-2012. It is assumed that quality control

(QC) measures are successfully applied to the production and

emplacement of closure plugs (auxiliary components). QC issues

are related to assessment methodology and are handled

else-where in TURVA-2012.

Figure

Updating...

References

Updating...