lec 4:regulatory reqs Flashcards
- International Guides
✓IAEA-TECDOC-1791, Considerations on the Application of the International
Atomic Energy Agency (IAEA) Safety Requirements for the Design of Nuclear
Power Plants
✓IAEA document SSR-2/1, Safety of Nuclear Power Plants,
- United States Regulations
✓Appendix A to Part 50—General Design Criteria for Nuclear Power Plants,
United States Nuclear Regulatory Commission (USNRC)
- Canadian Regulations
✓Design of Reactor Facilities: Nuclear Power Plants”, Regulatory Document
REGDOC2.5.2, Canadian Nuclear Safety Commission (CNSC), 2014. (A short
version by me on Brightspace for you)
✓Other REGDOCs available example, REGDOC 2.4.1 and 2.4.2
IAEA document
SSR-2/1, Safety
of Nuclear Power
Plants: Design
Publication used primarily for land based
stationary nuclear power plants with
water cooled reactors designed for
electricity generation or for other heat
production applications (such as district
heating or desalination).
* May also be applied, with judgement, to
other reactor types, to determine the
requirements that must be considered in
developing the design
* Canadian Regulator makes reference to
SSR-2/1
Canadian Nuclear Regulator
Canadian Nuclear Safety Commission (CNSC)
Established May 2000, under the Nuclear Safety and
Control Act (NSCA)
✓Replaced the AECB, established in 1946, under the
Atomic Energy Control Act
▪ Established same time as Atomic Energy Act of
1946 in US (Why 1946?)
Canadian Nuclear Regulator
Canadian Nuclear Safety Commission (CNSC) purpose
- The CNSC regulates all nuclear-related facilities and
activities
✓Does not promote any nuclear technology
✓Ensure nuclear facilities and/or activities are safe
CNSC Mission
- To protect the health, safety and security of persons and the
environment; and to implement Canada’s international
commitments on the peaceful use of nuclear energy
✓ The licensee is the cornerstone of safety and is held
accountable by their licence
Accountability of Licensee/Proponent: * No licence may be issued, renewed, amended or replaced
unless, in the opinion of the Commission, the applicant:
- Section 24(4) of the Nuclear Safety and Control Act
✓is qualified to carry on the activity that the licence will
authorize the licensee to carry on; and
✓will, in carrying on that activity, make adequate
provision for the protection of the environment, the
health and safety of persons and the maintenance of
national security and measures required to implement
international obligations to which Canada has agreed
CNSC
Regulatory
Framework : SLIDE 13
Nuclear safety and Control Act: Class I Nuclear Facilities Regulations
Provide requirements for site preparation licence applications,
personnel certifications, record-keeping and sets timelines for
regulatory reviews.
Apply to: Class 1A and Class 1B nuclear facilities including
nuclear reactors, large particle accelerators, nuclear processing
plants, fuel fabrication plants and waste disposal facilities
CNSC Design
Requirements
CNSC expects the applicant to demonstrate their safety case is
commensurate with the risks posed by the facility.
* For any size reactor, this allows for the use of a graded approach to safety.
* CNSC have regulated NPPs to small reactors using this approach. This is
consistent with IAEA standards
slide 16
Nuclear power plant (NPP):
a fission
reactor with a thermal power approx.
greater than 200 MWt (about 75 MW
electrical output)
Small reactor
a fission reactor
with a thermal power approx.
less than 200 MWt
Concept of Graded Approach In Regulation
Factors to be considered in applying graded approach include:
- reactor power
- reactor safety characteristics
- passive safety features
- amount and enrichment of fissile material
- fuel design
- type and mass of moderator, reflector and coolant
- presence of high-energy sources and other radioactive and
hazardous sources - safety design features
- source term (release in case of accident)
- intended utilization of the reactor
- siting/proximity to populated areas
- proven design (knowledge and experience)
Graded Approach - Examples
- Requirements are not gradable; fulfilling fundamental safety
functions, such as shutting down the reactor, core cooling and
containment of radioactive material, are not gradable. - The way in which the requirement is met may be graded.
Graded approach may be applied to:
✓design of shutdown means
✓confinement/containment features depending on the
safety characteristics of the reactor design
✓For example in safety analyses
▪ the scope, extent and detail of these analyses may
be significantly reduced because certain accident
scenarios may not apply or may need only a limited
analysis
General Nuclear Safety Objective
- Nuclear power plants (NPPs) must be designed and operated in a manner that will protect
individuals, society and the environment from harm - The general nuclear safety objective is supported by three complementary safety objectives:
General Nuclear Safety Objective
SLIDE 20
Technical Safety Objective
see slide 21 AND 22
Three types of safety assessments shall be carried out
✓ To identify all sources of exposure in order to evaluate potential radiation doses to
plant workers and the public, and the effects on the environment
hazard
deterministic safety (DSA)
Probabilistic saFety (PSA)
SAFETY GOALS
Protection such that there is no
significant additional risk to the life
and health of individuals
Safety goals
Societal risk comparable to or less than
the risks of generating electricity by
viable completing technologies
Core damage frequency: <10-5
/year
Small release frequency (>1000 TBq of
I-131): <10-5
/year
Large release frequency (>100 TBq of
Cs-137): <10-6
/year
Defence in
Depth
Principle: * As per CNSC REGDOC-2.5.2, Design of Reactor
Facilities:
✓ defence in depth is to ensure overlapping
provisions are applied to all
organizational, behavioural, and designrelated safety and security activities
✓ provisions for all five levels of defence
(later in presentation)
✓ balanced provisions for prevention and
mitigation
▪ imbalance: e.g., prevention with
inadequate mitigation or mitigation
with little prevention
Fundamental
Safety
Functions of a
Nuclear Reactor
Control of reactivity
Removal of heat from the fuel
Confinement of radioactive material
Shielding against radiation
Control of operational discharges and
hazards substances, as well as
limitation of accidental releases
Monitoring of safety-critical
parameters to guide operator actions
REGDOC 2.5.2: Document present the requirements in a hierarchy manner
- Safety objectives
- Safety criteria
- Safety management
- Design and engineering principles
- General system requirements
- System specific requirements
REGDOC 2.5.2: Allows alternative approach especially for small reactors
- Graded approach
REGDOC 2.5.2: * Provide the requirements for various aspects of the design including:
✓Environment protection
✓Radiation protection
✓Ageing
✓Human factors
✓Security
✓Safeguards
✓Transportation
✓Accident and emergency response planning
✓Safety analysis
REGDOC 2.5.2: Design requirements have been extended from past CNSC practice, e.g.,
✓Safety classification of SSCs
✓Classification of events (next slide)
✓Adoption of quantitative safety goals
✓Design for severe accidents
✓AOOs to be handled by the control systems
✓Design for reliability (safety systems and safety support systems)
✓Technical Specifications (Operating Limits and Conditions)
✓Consideration of malevolent acts in the design
classification of events
Normal operation
* Anticipated Operational Occurrence (AOO)
✓Frequency of occurrence > 10-2
/y
* Design basis accident (DBA)
✓Frequency of occurrence, 10-2
/y to 10-5
/y
* Design extension conditions (DEC) including severe accidents
✓Frequency of occurrence < 10-5
/y
✓We shall not consider this classification
Plant Design Envelope slide 29
Safety CriteriaL * Dose acceptance criteria
- ≤ 0.5 mSv for any AOO
- ≤ 20 mSv for any DBA
safety CriteriaL * Quantitative safety goals
Core-Damage Frequency: the sum of frequencies of all event sequences
that can lead to significant core degradation < 10-5
/y
* Small-Release Frequency: the sum of frequencies of all event sequences
that can lead to a release to the environment of more than 1015 Bq of I131 <10-5
/y
* Large-Release Frequency: the sum of frequencies of all event sequences
that can lead to a release to the environment of more than 1014 Bq of Cs137 <10-6
/y
Design for
Reliability
To design for common cause failures, the
principles of diversity, separation, and
independence are applied to achieve the
necessary reliability
The safety systems and their support systems
shall be designed to ensure that the probability
of system failure on demand from all causes is
lower than 10-3
.
All safety systems and their safety support
systems meet the single failure criterion.
Each safety group perform all safety functions
required for a Postulated Initiating Events
(PIE) in the present of any single component
failure (single failure criterion).
Each safety group can perform the required
safety functions under the worst permissible
systems configuration
* considering maintenance, testing, inspection and
repair, and allowable equipment outage times (single
failure criterion).
✓(To be discussed later under defence in depth)
Regulatory Challenges
New designs that are non-water water cooled
reactors
Sodium, Lead
* Helium, Carbon Dioxide
* Molten Salts
Example
* REGDOC 2.5.2 for PHWRs and later
all water-cooled
* Sodium Cooled Fast Reactor Design
Criteria
* Modular High Temperature GasCooled Reactor Design Criteria
* FOAK Reactor
CNSC Regulations being updated to
address all designs
Post-Fukushima
Design Requirements
REGDOC 2.5.2
✓ Used for CNSC’s vendor pre-project reviews
and for the review of application for a licence
to prepare site for new builds.
▪ None yet
✓ Docment adequate design requirements at
an overall level for severe accidents such as
the Fukushima event.
* REGDOC 2.5.2 has been revised to consider
detailed lessons learnt from the Fukushima event
✓ multi-unit accidents,
✓ complementary design features for
irradiated fuel bays,
✓ margins to cliff edges
✓ reliable monitoring
Alternative
Approaches
The requirements are
technology neutral.
* specific technologies may use
alternative approaches.
Alternative approaches will
be considered as acceptable
* provided that an equivalent level of
safety can be demonstrated.
Examples of
Challenges: Two means of shutdown
systems
- Independent shutdown systems
- Inherent designed shutdown
systems
Examples of
Challenges: Containment
- Definition of containment
- Means of containment
- Containment function
- Containment system
