(140714) [park] safety assessment for radioactive waste disposal
DESCRIPTION
Safety Assessment for Radioactive Waste Disposal : Recent status and Wolsong LILW Disposal FacilityTRANSCRIPT
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
Introduction to the Safety Case
• 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
Introduction to the Safety Case
• 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
Introduction to the Safety Case
• 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
Introduction to the Safety Case
• 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
Introduction to the Safety Case
• 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
Introduction to the Safety Case
• 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
System Description : Waste Characteristics
• Waste containers
Type and physical characteristics of waste containers
• 200 L Miscellaneous solid waste : Dry Active
Waste (DAW)
System Description : Waste Characteristics
• 320L Super compacted Waste
System Description : Waste Characteristics
• 200L Spent Cartridge Filter
System Description : Waste Characteristics
• 200L Concentrated resin waste
System Description : Waste Characteristics
• High Integrity Container (HIC) Spent Resin : Completely Dried
System Description : Waste Characteristics
• Circular Concrete Containers used in Ulchin #1 and #2
Type A
Type B
Type C
Type D
System Description : Waste Characteristics
• Facility Profile
System Description : Facility Design
• Facility Profile
System Description : Facility Design
• Facility Profile
System Description : Facility Design
• Disposal Silo
System Description : Facility Design
• Disposal Silo after closure
System Description : Facility Design
• Disposal Container for 200L and 320L
System Description : Facility Design
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
Safety Assessment : Scenario
• ES-1 Alternative Scenario
Safety Assessment : Scenario
• ES-2 Alternative Scenario
Safety Assessment : Scenario
• HS-1 Human Intrusion Scenario
Safety Assessment : Scenario
• HS-2 Human Intrusion Scenario
Safety Assessment : Scenario
• HS-3 Human Intrusion Scenario (well scenario)
Safety Assessment : 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
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)
Safety Assessment : Modeling
• 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
)
Time after closure (yr)
Safety Assessment : Modeling
Safety Assessment : Modeling
• 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)
Time after closure (yr)
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
Groundwater 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