safety and environment studies for a european demo power plant meeting... · safety and environment...
TRANSCRIPT
Outline
• Background
• Safety and environmental potential of fusion
• Aims and objectives of Safety and Environment project for EU DEMO
• Earlier studies
• Design and licensing requirements
• Safety approach and safety functions; minimizing inventories; confinement
• Licensing – what do we know?
• Integrated Safety Analyses / Source Terms / Models & Codes
• Experiments for code and model validation; neutronics; accident analysis
• Radioactive Waste Management
• Detritiation of solid waste
• Interaction with other Work Packages in the EU DEMO project
Research Units participating in the Safety and Environment project:
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 2
Potential for excellent safety performance of
fusion
• No climate-changing emissions
• Power excursions self-limited by
inherent processes
• Products of fusion reaction are not
radioactive
• Structures are activated by
neutrons but:
• Low power density (“decay
heat”) after termination of burn
• rapid decay of radiotoxicity
• No fissile or fertile material, no
actinides or fission-products
• Radioactive inventory
• Tritium
• Will require licensing like
any other nuclear facility
However…
A Demonstration Power
Plant should demonstrate
that these characteristics
lead to excellent Safety and
Environmental
performance.
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 3
EUROfusion Safety and Environment (SAE)
project: The aims
• To ensure that design choices take into account safety considerations
from the beginning
elaborate safety requirements
optimize safety provisions – iterative process with designers
define safety classification of systems, structures and components
• To ensure that DEMO will be licensable
understand the likely regulatory regime
• To resolve outstanding issues in safety and environment
perform R&D to resolve issues
develop and validate safety models and codes for DEMO
preliminary safety analyses, including accident consequences
• To minimize environmental impact of fusion
develop radioactive waste management techniques
identify and minimize contributions to routine releases
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 4
Eurofusion SAE Project Objectives (1)
1. To ensure that the safety approach for DEMO is well-founded
and takes maximum benefit from earlier work;
2. To ensure that the safety requirements for DEMO are soundly
specified and well understood, and that the design properly
takes into account these requirements and includes all
necessary safety provisions;
3. To ensure that design choices are made with due regard to
safety and environmental factors, so as to optimize safety
performance and to minimize the environmental impact;
4. To facilitate the eventual licensing of DEMO by understanding
the likely regulatory regime and discerning any requirements
that arise;
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 5
Eurofusion SAE Project Objectives (2)
5. To identify outstanding issues in safety and environment areas, and
to plan and perform R&D to resolve these issues;
6. To develop and validate safety models and codes needed for safety
analyses of DEMO, and to perform preliminary safety analyses,
including the evaluation of the consequences of a set of
representative accident scenarios;
7. To develop techniques to reduce the impact of radioactive waste
from fusion plant, in particular through the development of methods
for the detritiation of tritium-contaminated components and by
establishing the practical feasibility of methods for the recycling of
activated materials;
8. To minimize the environmental impact of the operation of DEMO by
identifying contributions to radioactive gaseous and liquid effluent
and proposing strategies to limit these releases.
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 6
Background – Previous studies
Earlier work that helps to support EU DEMO safety studies:
• Safety and Environmental Assessment of Fusion Power (SEAFP) • SEAFP 1992 – 95 • SEAFP2 1996 – 98 • SEAFP99 1999 • SEAL 2000 • All summarised in SEIF report (2001)
• Power Plant Conceptual Study (PPCS), 2001 – 05
• ITER Safety and Licensing • NSSR, 1996; NSSR2, 1998 • GSSR, 2001, 2004 • DOS, 2002 • RPrS, 2008, 2010, 2011
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 7
PPCS bounding accident analysis
Three areas of work in SAE project
1. Design and Licensing Requirements
2. Integrated Safety Analyses / Source Terms /
Models & Codes
3. Radioactive Waste Management
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 8
SAE Main Activities (1)
Design and Licensing Requirements
• Establish the safety approach and fundamental safety strategies (such as the confinement strategy) General Safety Principles
• Safety requirements are drafted and elaborated as the design concepts are developed Plant Safety Requirements Document
• Safety criteria are to be set and the safety impact of fundamental design choices (materials, coolant, etc.) are to be assessed.
• A review of the possible licensing regimes for DEMO is to be carried out, and implications for safety requirements determined.
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 9
Safety Approach for DEMO
• To protect workers, the public and the environment from harm;
• To ensure in normal operation that exposure to hazards within the
facility and due to release of hazardous material from the facility is
controlled, kept below prescribed limits and minimized to be as low as
reasonably achievable;
• To ensure that the likelihood of accidents is minimized and that their
consequences are bounded;
• To ensure that the consequences of more frequent incidents, if any,
are minor;
• To apply a safety approach that limits the hazards from accidents such
that in any event there is no need for public evacuation on technical
grounds;
• To minimize radioactive waste hazards and volumes and ensure that
they are as low as reasonably achievable.
ALARA Defence in depth Passive safety
Top-level safety objectives
Employ established safety principles
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 10
• To protect workers, the public and the environment from harm;
• To ensure in normal operation that exposure to hazards within the
facility and due to release of hazardous material from the facility is
controlled, kept below prescribed limits and minimized to be as low as
reasonably achievable;
• To ensure that the likelihood of accidents is minimized and that their
consequences are bounded;
• To ensure that the consequences of more frequent incidents, if any,
are minor;
• To apply a safety approach that limits the hazards from accidents such
that in any event there is no need for public evacuation on
technical grounds;
• To minimize radioactive waste hazards and volumes and ensure that
they are as low as reasonably achievable.
Main safety function is confinement of radioactivity,
achieved by multiple layers of protection:
Prevention of accident progression,
mitigation of consequences
Control of accidents within design basis
Control of abnormal operation and
detection of failures
“Defence in Depth” approach to safety
Prevention of abnormal
operation and failures
Fifth level: Mitigation of consequences of significant releases of radioactive material
Off-site emergency response (e.g. evacuation) – should not be necessary for fusion
• Natural shutdown
• Small inventories
• Conservative design
• High quality
construction
• Multiple barriers
(inherent in design)
• Extensive monitoring
• Redundant and
diverse safety
systems
• Safety systems
• Use of passive
means wherever
possible
• Multiple barriers
• Filtering and
detritiation systems
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 11
Adopted accident dose limits for DEMO
Anticipated
events /
Incidents
Unlikely
events
Extremely
unlikely events
Hypothetical
events
Accident
Frequency
/year
f > 10-2 10-2 > f > 10-4 10-4 > f > 10-6 f < 10-6
On-site Dose
5mSv/year
20mSv/event
Off-site Early
Dose 10mSv/event 50mSv/event
Off-site
Chronic
Dose
1mSv/year 5mSv/event 50mSv/event
No cliff-edge
effects.
Countermeasures
limited in time and
space.
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 12
Adopted normal operation dose limits
DEMO Dose
Design Target
DEMO Dose
Limit
Normal Operations
Off-Site Dose
(mSv/year)
0.1 1
Normal Operations
On-Site Dose
(mSv/year)
5 50
On-Site Dose
(mSv/5 years) 100
Meeting limits is not sufficient: all doses must be As Low As Reasonably Achievable
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 13
Limits are based on international guidelines, may be revised (downwards) later.
Safety Functions defined for European DEMO
• Confinement of radioactive and hazardous materials
• Limitation of exposure to ionizing and electromagnetic radiation
• Limitation of the non-radiological consequences of conventional
hazards
• Limitation of environmental legacy
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 14
Fundamental
safety
functions
Supporting
functions
Functions in support of confinement:
• Control of plasma energy
• Control of thermal energy
• Control of confinement pressure
• Control of chemical energy
• Control of magnetic energy
• Control of coolant energy
Functions to support personnel and the environmental protection:
• Limitation of radioactive and toxic material exposure to workers
• Limitation of airborne and liquid operating releases to the environment
• Limitation of electromagnetic field exposure to workers
• Limitation of other industrial hazards
Supporting functions to limit environmental legacy:
• Limitation of waste volume and hazard level
• Facilitation of clean-up and the removal of components
Location of radioactive material inventories
tritium
• in fuel cycle equipment (fuelling, pumping, processing)
• in breeder blankets and T extraction system
• retained in the vacuum vessel
adsorbed on surfaces
permeated into the structure of in-vessel components (IVCs)
absorbed in dust
• in RM equipment used to remove and transport IVCs
• in storage of IVCs awaiting maintenance or disposal
• in the Active Maintenance Facility
• in coolants, due to permeation
• in atmospheres of rooms containing contamination
products of neutron activation
• structure of plasma-facing components
• in-vessel dust from plasma-facing surface erosion
• activated corrosion products (ACP) in water or
lead-lithium coolant
• vessel and ex-vessel components (at lower level)
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 15
Minimizing inventories
In-vessel inventory limits for ITER
• Tritium: 1 kg
• Dust: 1000 kg
Can we reduce these for DEMO?
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 16
Tritium Higher throughput but: • No cryopumps (accounts for 180g
of inventory in ITER) • No plasma-facing Be, no Be dust.
W may have lower T retention. • Higher operating temperature
(>500°C compared with 140°C) • Reduced uncertainties?
Dust Higher fusion power, higher duty cycle but: • W instead of Be as plasma-facing
surface Lower erosion rate?
• Different plasma edge conditions? • Reduced uncertainties?
Confinement: in-vessel inventory
Confinement strategy:
• Two confinement systems
• each with one or more static
barriers and/or dynamic
systems
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 17
Tritium
(on plasma-facing surfaces,
permeated into components,
and in dust)
Active dust
(tungsten eroded from
plasma-facing surfaces)
Activated corrosion
products
(in accidents with in-vessel
loss of water coolant)
First confinement system
Vacuum vessel and its
extensions
Second confinement
system
Building walls and slabs
surrounding tokamak, rooms
served by ventilation with
filtering and detritiation
systems.
Other boundaries (e.g.
cryostat)
ITER experience: vacuum vessel and extensions
as first confinement
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 18
Penetrations
• neutral beams
• cooling pipes
• RF heating systems waveguides
• diagnostics systems
• vacuum pumping lines
• fuelling systems
• feeders for in-vessel coils
Confinement barrier includes
• seals
• bellows
• windows (including non-metallic)
• isolation valves
• pipes, ducts, waveguides
All must remain leak-tight in all
normal and accident situations, and
all are Safety Importance Class
ITER Vacuum Vessel:
• Robust, double-walled.
• Design loads include electromagnetic
loads in plasma events such as Vertical
Displacement Events
had to show that these loads are
enveloping
• Design pressure limit must be observed
pressure limited by relief system
with rupture discs
• Subject to nuclear pressure equipment
regulation (ESPN)
Proposed EU-DEMO confinement concept (HCPB)
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 19
In-vessel components of future Fusion Power
Plant
• High availability will be essential
• interruptions to electricity generation
unacceptable
• High reliability required of all components
• In-vessel components must not fail
• May be possible to give them full safety
credit for the confinement function
• This would simplify part of the
confinement strategy
• Can’t do this for DEMO.
But how far can we go?
Assessments and discussions are
ongoing.
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 20
Licensing of a future nuclear fusion facility
• ITER is licensed in France as a basic nuclear installation
(Installation Nucléaire de Base, INB)
under same law as all other nuclear facilities
• In other countries, and for a plant on the scale of DEMO, new
legislation may have to be created
An important regulatory principle:
Regulations should be
targeted
proportionate
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 21
Future trends in nuclear regulation
• Regulators are reluctant to voice
opinions until they have a firm proposal
in front of them
• How will nuclear regulation develop?
• In Europe, efforts towards harmonization
of regulatory approaches in different
countries, through the Western
European Nuclear Regulators
Association (WENRA).
• Although focussed on fission plant,
adaptation of approach to fusion is
possible
• WENRA emphasizes Defence in Depth
and independence of levels
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 22
Future trends in nuclear regulation
Changes may occur in reaction to unforeseen events
• WENRA specified “stress tests” applied to all European
nuclear plant after Fukushima accident
• In reaction to Fukushima, more emphasis on protection
against combinations of external aggressions
• Additional safety analysis of “design extension conditions”
featuring multiple independent failures
• focussed on conditions that could cause core melt in a
fission reactor, but still could apply to fusion facilities
• pay attention to common cause and common mode
failures
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 23
Nuclear regulation – what will not change
• Need to provide and defend a safety case that demonstrates
• acceptable safety objectives have been set and are achieved
• impact on public safety is minimized
• impact on personnel safety is minimized
• environmental impact is minimize
• Demonstration must be
• fully justified
• fully comprehensive (all conceivable
accident scenario are covered)
• where based on computer models,
that these are fully verified and
validated
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 24
SAE Main Activities (2)
Integrated Safety Analyses / Source Terms / Models & Codes
• Determine accident scenarios to be taken into account in the safety analyses, using Functional Failure Modes and Effects Analysis (FFMEA)
• Determine needs for code development for safety analyses and the validation experiments that are required for these
• Develop safety analysis tools, codes and models
• Perform tests as needed to validate the codes and models
• Perform full safety analyses including transient and accident analyses for Design Basis, Design Extension and selected Beyond Design Basis Events
• Assess the needs for source term development, dependent on fundamental design choices
• Perform R&D needed to improve quantification of source terms, evaluate inventories (e.g. ACPs)
• Assess environmental releases (liquid and gaseous) in normal operation, develop strategies for minimizing these
• Identify major contributions to Occupational Radiation Exposure, develop strategies for minimizing these, particularly in design choices
• Development of methods for computation of Shutdown Gamma Dose Rate, with the aim of establishing one common EU approach
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 25
Examples of experiments for code validation
• Simulations of LOFA and LOCA in blankets (KIT)
• Measurements of tritium permeation from beryllium pebbles and structural materials
(KIT)
• Measurements of tritium transport in ceramic breeder blanket (KIT)
• Chemical reactivity of Be with steam and air (ENEA)
• Measurement of liquid lithium-lead/steam reaction rates (ENEA)
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 26
27
T-release from pebbles after thermal loading
400 600 800 1000 1200
500
1000
1500
2000
2500
3000
3500
Rele
ase R
ate
(B
q/s
/g)
Temperature (K)
>100 mkm
30-60 mkm
10-30 mkm
IG
NGK 1mm
15000 20000 25000 30000
Time, s
400
600
800
1000
1200
1400
0 5000 10000 15000 20000 25000 30000
Time, s
Tem
pera
ture
(K
)
5K/min
7K/min
IG
>100µm
NGK
1mm
Bochvar
10-30 µm
Bochvar
30-60 µm
Bochvar
> 100 µm
Neutronics and activation analysis in support of
accident modelling
• Example: decay heat for DEMO based on HCPB blanket
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 28
HCPB Entire reactor
Cooling Time
1 s 1 h 1 day 1 week 1 month 1 year 10 years 100 years
Name of Zone length of zone
material fraction (*)
volume [cm3]
Nuclear heating
Decay heat
mm % MW/m3 MW/m3
First Wall (FW)
W 100% 2.45E+06 - 5.33E-01 4.03E-01 2.12E-01 1.39E-02 8.76E-03 5.00E-04 1.11E-08 2.33E-10
Eurofer 74.3% Eurofer + void
2.93E+07 - 2.00E-01 1.43E-01 5.47E-03 1.64E-03 1.35E-03 2.70E-04 1.46E-06 1.80E-10
Breeder module (BM)
- - - - - - - - - -
BM caps and lateral walls
74.3% Eurofer + void
4.66E+07 - 3.06E-02 2.25E-02 2.32E-03 5.60E-04 4.57E-04 7.24E-05 4.48E-07 5.60E-11
BM material mxiture
11.76% Eurofer + 37.9% Be +13.04% Li4SiO4 + void
7.65E+08 - 1.62E-02 4.27E-03 2.02E-04 4.87E-05 3.84E-05 8.14E-06 1.80E-07 6.87E-10
BM backwall 100%+ Eurofer
4.36E+07 - 3.08E-03 2.44E-03 6.14E-04 1.25E-04 1.01E-04 1.39E-05 9.84E-08 1.07E-11
BM back support /manifold
55.4% Eurofer + void
3.11E+08 - 7.97E-04 6.60E-04 2.28E-04 4.20E-05 3.37E-05 4.44E-06 2.89E-08 2.84E-12
Sum [MW] - - 2.13E+01 9.79E+00 1.04E+00 1.64E-01 1.26E-01 2.07E-02 2.15E-04 5.36E-07
Accident analyses
Initiating events
identification
Accident scenarios
Selection of representative
events
Modelling of accident
sequences
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 29
Predicted releases
Dispersion and dose modelling
Dose to Most Exposed
Individual
Must be comprehensive Use systematic techniques
e.g. FMEA, HAZOP
Postulate additional failures
Event trees, fault trees
Choose events with consequences that
will envelope others
Model all significant phenomena.
e.g. thermal-hydraulic
Calculate maximum environmental release
in worst case
Direct exposure plus ingestion and inhalation. All pathways considered.
Dose uptake for conservative
exposure scenario
Design information Failure rate data
Safety design information
Neutronics/activation data (source terms, decay heat etc.)
More detailed design info
Site characteristics Weather conditions
Consequences
Radioactive Waste Management
• A review of clearance indices for radioactive material to set an approach to
defining a fusion-specific set of limits, and to define these limits.
• A feasibility study of waste recycling to establish if viable and economic
recycling processes are possible; criteria to be defined
• Development of technologies for large-scale recycling
• Techniques for detritiation of solid waste have been reviewed
• A programme of R&D to develop techniques for the detritiation of solid
radioactive waste is starting
• Materials composition limits will be
established to minimize the
radiological impact of activation and
strategies developed to minimize
the quantity of waste. Simple recycle
36%
Cleared
49%
Hands-on
5%
Complex
recycle
10%
Permanent
waste
0%
SAE Main Activities (3)
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 30
PPCS results
H2020 Progress meeting 18 June 2015 31
Extract from Detritiation techniques review
Disposal ( 1 possibly suitable, 2 strong suitability):
Method In
vessel
IVC
transfer
area
Storage
facility
IVC
process
cells
Waste
and
recycling
RH
equipment
maintenance
Other
waste
treatment
3H plant
clean-up
Melting (3) 1 2 2 2 2
Thermal
treatment (7)
1 2 2 1 2 2
Cold crucible 1 1
Molten salt
oxidation
1 1
Interim
storage
1 2 2 1
Surface
abrasion
1 2
Evaporating
and
solidification
line
1 1
Incineration 2
Safety Requirements Document Safety Guidelines
Safety Importance Classification
Radioactive Waste Management
Materials composition limits
Work Packages concerned with design and materials
safety functions and required
safety provisions design optimisations
Safety analyses Accident analyses
Occupational Radiation Exposure studies
Study of effluents in normal operation
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 32
Interactions with other DEMO Work Packages – every WP has a Safety Liaison Officer
Summary
• The Safety and Environment project for EU DEMO is focussed on
• Setting a safety approach and developing requirements in cooperation
with the design teams
• Developing and validating safety models and codes, and applying these
to preliminary safety analyses
• Finding solutions to some key radwaste management issues
• Licensing requirements of the future are uncertain but
• Harmonisation of European regulatory approach is useful
• Defence in Depth is key
• Safety functions for DEMO have been defined
• Confinement of radioactive inventories is the most important
• Every opportunity must be taken to minimize inventories
• Safety considerations must be central to design activities from the beginning
• Dialogue is maintained between safety specialists and design teams
Neill Taylor | EU DEMO safety | 1st IAEA Technical meeting on Safety, Design and Technology of Fusion Power Plants | 3-5 May 2016 | Page 33