(140714) [park] safety assessment for radioactive waste disposal

Safety Assessment for

Radioactive Waste Disposal : Recent status and Wolsong LILW Disposal Facility

14 July 2014

Jin Beak Park (KORAD) [email protected]

http://www.korad.or.kr

Definitions

• Safety

the protection of people and the environment against

radiation risks, and the safety of facilities and activities

that give rise to radiation risks.

• Assessment

The process, and the result, of analysing systematically

and evaluating the hazards associated with sources and

practices, and associated protection and safety

measures.

• Disposal

Emplacement of waste in an appropriate facility without

the intention of retrieval.

Overall aim of radioactive waste disposal

• Safety Disposal of radioactive waste for required

long period of time

Things have to be considered

• How does one measure the safety of disposal

facility?

Measuring criteria

• Who define the measuring criteria?

• Who develops the method required to derive the

measuring the safety of disposal facility?

• Who check the work that results in measuring the

safety?

• What does “required long period of time” mean?

Progress

• No universally accepted definitions exist

e. g. Safety assessment, safety case

Definition may change in the course of time

Guidance exists on possible definition of key terminology

• NEA, IAEA, Safety report compiled within national program

• It is important to clearly define key terminology in

each new safety report during your staying in

graduated school.

My experiences

• Why there is progress?

Their experiences

Progress in safety assessment

• Progress in methodology

Early days : verification → benchmarks

Then : validation → model testing (importance

of experience with URL and lab testing)

A more integrated approach with Robustness,

confidence and defense in depth

Today : Safety Case

• Overall system development approach

• Phenomenological analysis

• Role of safety function

• Quantitative and qualitative argument

• Stepwise repository implementation

• Strategy

Progress in science & technology (Knowledge

basis)

• Growing geological information basis & improved

understanding

Regional and site-specific investigation, URLs)

• Improved understanding of engineered barrier

system

• More detailed design concepts

• In many other areas

Waste characterization, geochemistry etc.

Progress and Increase in complexity

Safety Case

Introduction to the Safety Case

• Radioactive waste must be managed in such a way as to avoid imposing an undue burden on future generations

• The generations that produce the waste have to seek and apply safe, practicable and environmentally acceptable solutions for its long term management

• IAEA safety requirements for radioactive waste disposal require that a safety case (including a supporting safety assessment) be developed


• The safety case is:

the collection of scientific, technical, administrative and managerial

arguments and evidence in support of the safety of a disposal

facility

• The arguments cover the suitability of the site and the design,

construction and operation of the facility, the assessment of radiation

risks and the assurance of the adequacy and quality of all of the safety

related work associated with the disposal facility

a well-defined, formal set of documents produced by the operator

and reviewed by the regulator


• Safety assessment is an integral part of the safety case

It provides an understanding of the behaviour of the disposal facility

under normal conditions and disturbing events, considering the time

frames over which the radioactive waste remains hazardous

It includes a systematic quantification of radiation doses and risks

that may arise from the disposal facility for comparison with dose

and risk criteria


• For disposal facilities the operator shall:

Develop and maintain the safety case

Carry out safety assessment

Carry out all necessary activities for site selection and evaluation,

facility design, construction, operation, closure and, if necessary,

surveillance after closure

These activities shall be done in accordance with national strategy,

legal and regulatory requirements


• For disposal facilities the regulator shall:

Establish regulatory requirements for the development of different

types of disposal facility for radioactive waste

Set out the procedures for meeting the requirements for the various

stages of the licensing process

Set conditions for the development, operation and closure of each

individual disposal facility

Carry out such activities as are necessary to ensure that the

conditions are met


• IAEA Requirements (SSR-5):

The safety case for a disposal facility shall describe all safety

relevant aspects of the site, the design of the facility, and the

managerial control measures and regulatory controls

The safety case and safety assessment shall:

• Be prepared and updated by the operator, as necessary, at each step

in the development of a disposal facility

• Be submitted to the regulatory body for approval

• Be sufficiently detailed and comprehensive to provide the necessary

information for the regulatory body and the decisions at each step

• Demonstrate the level of protection of people and the environment

provided and provide assurance to the regulatory body and other

interested parties that safety requirements will be met


• The disposal facility shall (SSR-5):

Be constructed in accordance with the design described in the

approved safety case and supporting safety assessment

Be operated in accordance with the conditions of the licence and the

relevant regulatory requirements so as to maintain safety during the

operational period and in such a manner as to preserve the safety

functions assumed in the safety case that are important to safety

after closure

• Waste packages and unpackaged waste accepted for emplacement in

a disposal facility shall conform to criteria that are fully consistent with,

and are derived from, the safety case

• Plans shall be prepared for the period after closure to address

institutional control and the arrangements for maintaining the availability

of information on the disposal facility

Safety Case Components (IAEA, 2012)

Safety Case Components (NEA, 2012)

Safety Case Context : General

• The safety case context comprises:

Regulatory requirements and criteria for the safety case

The particular decision step in the lifecycle of the disposal facility

Key disposal system characteristics

• e.g. the nature of the waste and the site

The purpose of the safety assessment

The assessment timeframes (e.g. hundreds to many thousands of

years), philosophy (e.g. conservative, realistic) and end-points (e.g.

dose, risk, others)

Safety Case Context : Safety Approach

Safety Strategy : General

• The safety strategy comprises:

A high-level integrated approach adopted for achieving safe

disposal of radioactive waste

An overall management strategy for the activities required in

planning, operation and closure of a disposal facility

Should identify the intended safety functions, the timeframes over

which they will be available and how degraded performance of one

barrier will be compensated for by another mechanism or

component of the disposal system (robustness, defence in depth)

The preferred strategy for the management of all radioactive waste

is to contain it and isolate it from the accessible biosphere [SSR-5]

Safety Strategy : KORAD

Iterative Process Robustness

Demonstrability Multiple lines of

evidence

Safety Strategy

System Description : General

• The system description:

Provides information on the disposal system

Demonstrates system understanding

Provides the basis for safety assessment

Helps to determine needs for further system characterisation and

facility design work

• Related terms:

The system description includes much of what is sometimes called

the “assessment basis”

Also closely related to the “site descriptive model”

System Description : General

• The system description should provide information on:

The facility design and the reasons for its selection

The near-field – including:

• The wastes (e.g., origin, nature, quantities and properties, radionuclide

inventory),

• System engineering (e.g., waste conditioning and packaging, disposal

units, engineered barriers, disposal facility cap or cover, drainage

features)

• The extent and properties of the zone disturbed by excavations

The far-field - e.g., geology, hydrogeology, geochemistry, tectonic

and seismic conditions, erosion rates

The biosphere - e.g., climate and atmosphere, water bodies, human

activities, biota, near-surface geology, topography, geographical

extent and location

System Description : Geology

• Hydraulic Rock Domains vs. Hydraulic Conductor

Domains

System Description : Waste Characteristics

• Type and quantity of waste packages for each

waste producer


• Waste containers

Type and physical characteristics of waste containers

• 200 L Miscellaneous solid waste : Dry Active

Waste (DAW)


• 320L Super compacted Waste


• 200L Spent Cartridge Filter


• 200L Concentrated resin waste


• High Integrity Container (HIC) Spent Resin : Completely Dried


• Circular Concrete Containers used in Ulchin #1 and #2

Type A

Type B

Type C

Type D


• Facility Profile

System Description : Facility Design

• Disposal Silo


• Disposal Silo after closure


• Disposal Container for 200L and 320L


Safety Assessment : General

• Based on IAEA ISAM FEPs, post-closure

assessment scenarios were developed.

• Total seven individual scenarios

Scenario Class Scenario Name Criteria

Reference Scenarios BS-1 Dose (mSv/yr)

BS-2 Dose (mSv/yr)

Alternative Scenarios ES-1 Risk (/yr)

ES-2 Risk (/yr)

Human Intrusion Scenarios

HS-1 Dose (mSv/yr)

HS-2 Dose (mSv/yr)

HS-3 Dose (mSv/yr)

Safety Assessment : Scenario

• BS-1 Reference Scenario


• ES-1 Alternative Scenario


• ES-2 Alternative Scenario


• HS-1 Human Intrusion Scenario


• HS-2 Human Intrusion Scenario


• HS-3 Human Intrusion Scenario (well scenario)


• Groundwater flow modeling

3-D groundwater flow based on equivalent porous

medium

Calculate the groundwater travel time and travel path

from each silo to the Geosphere Biosphere Interface

(FEFLOW)

• Radionuclide transport modeling

1-D radionuclide transport model (MASCOT)

Calculate the radionuclide flux and dose profiles

• Biosphere modeling

Pathway specific flux-to-dose conversion factors within

both ocean and well biosphere (AMBER)

Safety Assessment : Modeling


• 1-D radionuclide transport model (MASCOT)

• Result of post-closure safety assessment (BS-1)

100

101

102

103

104

105

106

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

3.74E-3 mSv/yr

at 3600 yr

BS1 H-3

C-14

Ni-59

Nb-94

Tc-99

I-129

Total Alpha

Total Dose

Do

se (

mS

v/y

r)

Time after closure (yr)


• Result of post-closure safety assessment (ES-1,2)

100

101

102

103

104

105

106

10-20

10-19

10-18

10-17

10-16

10-15

10-14

10-13

10-12

10-11

10-10

10-9

10-8

10-7

10-6

6.04E-8 /yr at 1 yrES-1A + ES-1B + ES2B

ES-1A

ES-1B

ES-2B

TOTAL

Ris

k (

yr-1

)




• Result of post-closure safety assessment (HS-3)

102

103

104

105

106

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

8.54E-1 mSv/yr

at 2040 yr

HS3-well 2 H-3

C-14

Ni-59

Nb-94

Tc-99

I-129

Total Alpha

Total Dose

Do

se (

mS

v/y

r)


Iteration and Design Optimisation

Uncertainty

• Scenario uncertainty

Uncertainty in the broad evolution of the facility

• Time scale of concern, Treatment of the biosphere, Treatment of

future human action

• Model uncertainty

Uncertainty in the assumptions or conceptual model

used to represent a given scenario

• Parameter uncertainty

Uncertainty in parameter values used in a model

Limits of predictability of the different element of

a disposal system

Structuring safety assessment calculations

Type of Modeling and calculation

• Dose and risk calculations using “PA Model”

• Calculation relevant to system evolution and

calculations used to derive input parameters for

dose and risk calculations “Process Model”

• Insight modeling to build system understanding

Example of Modeling Structure (KORAD)

PICK YOU UP the topic of your master program!

PA Models

Process Models

Process Models

Site, Waste & System Characteristics

Engineered Barrier

Behavior

Biosphere Behavior

Groundwater Behavior



Consequence Analysis

Radionuclide Release (Near-Field)

Radionuclide Transport (Near-Field)

Radionuclide Release (Far-Field)

Dose

Example of Modeling Structure (SWISS)

Limits, Controls and Conditions

• The safety case should be used to assist in the

establishment of limits, controls and conditions, e.g:

Site-specific limits on the total waste inventory, on acceptable

concentration levels for specific radionuclides in the waste, and

other waste acceptance criteria (WAC)

• Particularly relevant for near-surface disposal facilities

Controls and conditions on repository construction and on the

manufacture, materials and quality of engineered barriers and their

emplacement

Conditions for a monitoring and surveillance programme

Integration of Safety Arguments

• Simply showing that safety assessment results comply with quantitative

regulatory criteria is not sufficient - multiple lines of reasoning should

be used to compliment quantitative assessments

• These lines of reasoning may include discussion of:

The use of best available techniques

The history of design optimisation

Consideration of radiological protection principles

Waste isolation and containment

Passive safety

Robusness and defence in depth

QA and peer review

Conservatisms in safety assessment

Application of limits, controls and conditions

Integration of Safety Arguments

• In summary, the safety case should:

provide a synthesis of the available evidence, arguments and

analyses

acknowledge any limitations of currently available evidence

highlight the principal reasons why planning, development and use

of the disposal system should continue

describe an approach to the management of uncertainty through

which any open questions and uncertainties with the potential to

undermine safety will be addressed

Examples of Recent Safety Cases

Concluding Remarks

• To understand the stakeholder of disposal facility, a report documenting

a safety case should include

A description of motivation/background/boundary conditions

A summary of the regulatory guidelines and other guidance

A description of the methodology used

A description of the system and its possible evolutions

A summary of system understanding

A list of scenarios and assessment cases

The results of the analysis of the assessment case vs. regulatory

guidelines

A statement of confidence and unresolved issues

Guidance for future work

• Overall aim of radioactive waste disposal

Safety disposal of radioactive waste over required long period of time

<Construction tunnel> <Operational tunnel> <Waste loading tunnel>

<Disposal Silo> <Disposal Silo> <Visiting Center>

http://www.korad.or.kr

(140714) [park] safety assessment for radioactive waste disposal

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