1 Operational Safety Bon Hyun Koo e-mail : [email protected] KINS-IAEA-ANNuR-ANSN-FNBRA Joint Workshop on BPTC 4-15 May, 2015, Tunis, Tunisia
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Operational Safety
Bon Hyun Koo e-mail : [email protected]
KINS-IAEA-ANNuR-ANSN-FNBRA Joint Workshop on BPTC
4-15 May, 2015, Tunis, Tunisia
Operational Safety
OEF Tools
Safety Requirements for Operation
Operating Experience Feedback
Accidents V
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Status and Issues in Nuclear Safety Regulation
I. Operational Safety
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Safety
Safety Safety is a condition or a state with no risk or no
concern with an accident.(Korean Dictionary)
Constituents of Nuclear Safety Hardware
Software
Human Factor(Safety Culture, Management System)
Meaning of Safety 'Safety' is the achievement of proper operating
conditions, prevention of accidents and mitigation of
accident consequences, resulting in protection of
workers, the public and the environment from undue
radiation hazards. (IAEA Safety Glossary)
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Safety
NPP Safety shall be ensured by means of the
followings; proper SITING, DESIGN, CONSTRUCTION and
COMMISSIOING,
followed by the proper MANAGEMENT and OPERATION.
in a later phase, proper DECOMMISSIONING is required
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Safety Analysis Report
SAR(Safety Analysis Report) is the basic Licensee
documents and is based on specific safety
analysis and shall be submitted to the Regulatory
Body for authorization
Licensee describes the results of safety analysis in
the SAR based on approved experiments,
approved analysis codes or Industrial Code & Std.
Regulatory Body should verify the conservatism
and safety margin contained in the SAR based on
its own audit calculation and/or in-depth review
and inspection.
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Safety-concerned Parties
So, the SAFETY shall be maintained during normal
operation and accident condition.
Licensee shall show(substantiate) the safety of its facility
via documents, i.e. SAR, RSE, TR.
Regulatory Body shall confirms the safety via Safety
Review and Safety Inspection.
Stakeholders and NGOs are monitoring all the above
activities.
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Safety Review
RB/TSO are responsible for the review and
evaluation for the Safety of NPP and Nuclear
Facilities.(IAEA-NS-R-2 Safety of NPP: Operation) PSAR for Construction Permit (CP)
FSAR for Operating License (OL)
PSR for the next 10 year’s safe operation
RTSR (Reload Transition Safety Report) for new Fuel Loading or Steam Generator Replacement
RSE (Reload Safety Evaluation) for every reload core as the Reactor Core configuration is different for every reload core.
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Operational Safety
IAEA proposes the following 10 topics to ensure the safe operation of NPP(NS-R-2 Safety of NPP : Operation)
1) Operating Organization (including OEF) 2) Qualification and Training of Personnel 3) Commissioning Program for the Plant 4) Plant Operations: OLC/ Operating instructions and
procedures/ Core management and fuel handling 5) Maintenance, Testing, Surveillance and Inspection of
‘SSCs important to Safety’ 6) Plant Modifications 7) Radiation Protection and Radioactive Waste
Management 8) Records and Reports 9) Periodic Safety Review
10) Decommissioning
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Responsibility on NPP Safety
Licensee has the ultimate responsibility on NPP safety. May outsource some parts of NPP operation, e.g.,
maintenance. But licensee has the prime responsibility on it. Must provide the necessary resources and support
RB and TSO confirms the safety of facilities permeated in the Licensee document and all the activities performed by the Licensee.
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Status and Issues in Nuclear Safety Regulation
II. Safety Requirements for Operation
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IAEA Convention on Nuclear Safety (1)
Convention on Nuclear Safety [Art. 19. “Operation”]
(1) the initial authorization to operate a nuclear installation is based upon the
safety analysis and a commissioning program demonstrating that the
installation is consistent with design and safety requirements;
(2) operational limits and conditions(OLC) derived from the safety analysis,
tests and operational experience are defined and revised as necessary for
identifying safe boundaries for operation;
(3) operation, maintenance, inspection and testing of a nuclear installation are
conducted in accordance with approved procedures;
(4) procedures are established for responding to anticipated operational
occurrences (AOO) and to accidents;
(5) necessary engineering and technical support in all safety related fields is
available throughout the lifetime of a nuclear installation;
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Nuclear Industries in Korea
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KPS / SEC
PLANT MAINTENANCE
KAERI / KEPRI
R & D
DOOJUNG DOOSAN HEAVY INDUSTRIES CO.
MAIN EQUIPMENT SUPPLY
KOPEC KOREA POWER ENGINEERING CO.
NSSS DESIGN + A/E
ENGINEERING
KHNP
OPERATION &
CONSTRUCTION
KNFC
KOREA NUCLEAR FUEL CO.
NUCLEAR FUEL SUPPLY
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IAEA Convention on Nuclear Safety(2)
(6) incidents significant to safety are reported in a timely manner by the
licensee to the regulatory body;
(7) program to collect and analyze operating experience(OEF) are
established, the results and conclusions are acted upon and that
existing mechanisms are used to share important experience with
international bodies and with other operating organizations and
regulatory bodies;
(8) the generation of radioactive waste resulting from the operation of a
nuclear installation is kept to the minimum practicable for the
process concerned, both in activity and in volume, and any
necessary treatment and storage of spent fuel and waste directly
related to the operation and on the same site as that of the nuclear
installation take into consideration conditioning and disposal.
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IAEA NS-R-2 ‘Safety of NPP: Operation’ stipulates 10 requirements for the Operational safety;
I. Operating Organization (including OEF)
II. Qualification and Training of Personnel
III. Commissioning Program for the Plant
IV. Plant Operations: Operational limits and conditions/ Operating instructions and procedures/ Core management and fuel handling
V. Maintenance, Testing, Surveillance and Inspection of Structures, Systems and Components important to Safety
VI. Plant Modifications
VII.Radiation Protection and Radioactive Waste Management
VIII.Records and Reports
IX. Periodic Safety Review
X. Decommissioning
IAEA Safety Requirement for Operation
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Operating Organization(1)
The Operating Organization(Licensee) shall have the responsibility for the safe operation of NPP
The licensee shall consider the following management functions in establishing the organizational structure; Policy making function, Operating functions,(operation) Supporting
functions and, and Reviewing functions
The organizational structure shall be clearly structured & documented so as to ensure that the following responsibilities are discharged to achieve safe operation; Responsibilities shall be allocated and authority shall be delegated
within the organization. Adequate training for personnel shall be provided Liaison shall be established with the RB and with public authorities, with
domestic and international organization.
Safety related activities shall be performed by qualified and experienced persons and certain activities may be performed by contractors if properly qualified, approved, controlled and supervised by the plant staff.
General Requirements
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Interface with Regulatory Body
Operational safety shall be subject to surveillance by a RB
independent of the Operating Organization(licensee); there should be mutual understanding and respect between the
bodies with frank and open, but formal relationship
Licensee shall give the RB all the necessary assistance,
information and access to the plant and documentation; if required, undertake special analysis, tests and inspections
Licensee shall submit or make available documents and other
information in accordance with the legal requirements
• Licensee shall develop and implement a internal procedure for
reporting abnormal events to the RB in accordance with the
established criteria
Operating Organization(2)
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Feedback of Operating Experience
OE shall be evaluated in a systematic way for correct
investigation of direct and root cause, recommendation, and
proper corrective actions
Other plants OE shall be properly collected and evaluated to
derive Lessons Learned. Exchange of OE between national and
international organization is of great importance.
All plant personnel shall be required to report all events and
shall be encouraged to report any ‘near miss’ relevant to the
safety.
Operating Organization(3)
Fire Safety
Physical Protection
Quality Assurance
Emergency Preparedness
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Qualification and Training(1)
The operating organization shall define the qualifications and
experience necessary for personnel performing safety-related duties.
These qualifications and experience shall be approved by the
regulatory body. Persons performing certain functions important to
safety shall be required to hold a formal authorization; this may be
issued or acknowledged by the regulatory body
A suitable program shall be established and maintained for the
training of personnel before their assignment to safety related duties.
The training shall emphasize the paramount importance of safety in
all aspects of plant operation.
All personnel responsible for safety-related duties shall have
sufficient understanding of the plant and its safety features.
The training program shall include periodic confirmation of the
personnel competence and refresher training.
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Qualification and Training(2)
Performance based program shall be developed and put in place for each
major group.
Training instructor shall be technically competent
Representative simulator facilities shall be used for the training of operating
personnel
Plant staff shall receive instructions in the management of accidents beyond
the design basis. The training of operating personnel shall ensure their
familiarity with the symptoms of accidents beyond the design basis and with
the procedures for accident management.
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Specific approval by the regulatory body shall be required before
the start of normal operation. Such approval will be granted on the
basis of an appropriate safety analysis report and a commissioning
program. The commissioning program shall provide evidence that
the installation as constructed meets the design intent and complies
with the safety requirements.
A sufficient number of qualified operating personnel, at all levels
and in all areas, shall be directly involved in the commissioning
process.
To confirm the applicability and quality of the operating procedures,
they shall be verified to ensure their technical accuracy and
validated to ensure their usability with the installed equipment and
control systems, as far as possible prior to fuel loading.
Commissioning(1)
Commissioning program for the NPP
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The operating organization shall ensure that the commissioning
program includes all the tests necessary to demonstrate that the
plant as installed meets the requirements of the safety analysis
report and satisfies the design intent, and consequently can be
operated in accordance with the OLCs.
Initial fuel loading shall not be authorized until all pre-operational
tests deemed necessary by the operating organization and the
regulatory body have been performed and results acceptable to
both parties have been obtained.
Reactor criticality and initial power raising shall not be authorized
until all tests deemed necessary by the operating organization and
the regulatory body have been performed and results acceptable to
both parties have been obtained.
Commissioning(2)
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Plant operations(1)
OLC is a set of rules setting forth parameter limits, the functional
capability and the performance levels of equipment and
personnel.
The purpose of OLC is:
(1) Prevention of situations which could lead to accidents;
(2) Mitigation of the consequences of any such accidents, if they
do occur.
OLC shall be developed to ensure that the plant is operated in
accordance with the design assumptions and intent.
The OLC shall be based on an analysis of the individual plant and
its environment, in accordance with the provisions made in the
design. The necessity for each of the operational limits and
conditions shall be substantiated by a written statement of the
reason for its adoption.
Operational Limits and Conditions
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Plant operations(2)
The operational limits and conditions shall be reviewed
over the operating life of the plant in the light of
experience, developments in technology and safety, and
changes in the plant, and shall be modified if this is
required by the RB or if it is considered appropriate by
the operating organization and approved by the RB.
Plant, prior to the initial fuel loading, shall prepare the
OLC and it shall be approved by the RB before
commencement of operation.
Operational Limits and Conditions
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Plant operations(2)
The OLC is composed of; General Principles for Use & Application of TS
Definitions, Logical Connectors, Completion Times, Freq.
Safety Limits (SL) to assure the integrity of Core & RCS
Pressure, Temperature, Thermal Power
Limits on Safety System Settings
Limiting Conditions for Operation (LCO)
LCO, Applicable Modes, Actions, Surveillance Requirement.
Design Features
Site Location, Reactor Core, Fuel Storage
Administrative Controls
Organization & Responsibility, Staff Qualifications, Procedures,
Programs and Manuals, Reporting Requirements
Operational Limits and Conditions
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Typical Operational Modes
Operational Limits and Conditions
Plant operations(3)
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Operating procedures shall be developed which apply
comprehensively for normal, abnormal and emergency conditions, in
accordance with the policy of the operating organization and the
requirements of the regulatory body. Strict adherence to written
operating procedures shall be an essential element of safety policy.
It shall be ensured that operating personnel are knowledgeable of,
and have control over, the status of plant systems and equipment for
all operational states. Only designated and suitably qualified members
of the operating personnel shall control or supervise any changes in
the operational states of the plant. No other person shall interfere in
their decisions relevant to safety.
If there is a need to conduct a non-routine operation, test or
experiment, it shall be the subject of a safety review. The specific
operational limits and conditions shall be determined and a special
procedure shall be prepared.
Plant operations(4)
Operating instructions and procedures
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Procedures for General Managements; QA Procedures, Technical Admin. Procedures, Radiation Protection
for Normal operations; System Operating Procedures, General Operating Procedures, Chemistry,
Maintenance, Testing, Surveillance and Inspection…
for Abnormal & Emergency Operations; AOP, EOP
for Severe Accidents Conditions; Severe Accidents Management Guideline (SAMG)
for Emergency Preparedness; Emergency Planning
• Response to Abnormal and Emergency Operational State;
Application of appropriate procedures as far as possible.
However, Operators in some cases, should have the authority to take
corrective actions according to their judgment
(e.g., Radiation Emergency declaration during the night shift)
Plant operations(5)
Operating instructions and procedures
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The operating organization shall be responsible and shall make
arrangements for all the activities associated with core management and
on-site fuel handling in order to ensure the safe use of the fuel in the
reactor and safety in its movement and storage on the site. Provisions
shall be made to ensure that in each reactor only fuel whose design and
enrichment have been approved by the regulatory body for use with that
reactor is loaded.
Following batch refueling, tests shall be performed before and during
startup to confirm that the core performance meets the design intent.
Core conditions shall be monitored and the fuelling program shall be
reviewed and modified as necessary.
For fuel and core components, handling procedures shall be written
which include the movement of unirradiated and irradiated fuel, storage
on the site and preparation for dispatch from the site.
Plant operations(6)
Core Management and Fuel Handling
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Status and Issues in Nuclear Safety Regulation
III. OEF
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Why do we study Operating Experience ?
Can not get similar OE for the plant itself
Can acquire Valuable Lessons from expensive Experiences
Can feedback the collected lessons/inspirations to our facilities
How do we manage valuable Information from the
Operating Experience ?
Collect/ Exchange/ Share domestic & foreign Operating
Experiences
Establish an OEF system for Storage/ Analyze/ Evaluate/ Apply
the OE-related information
OEF Systems [necessity]
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IAEA Convention on Nuclear Safety Article 19 :
Safety significant incidents are reported by the
licensee to the regulatory body
Program to collect and analyze operating experiences
are established
That results obtained and conclusions drawn upon
and
Mechanisms are used to share important experience
between international bodies, other operating
organizations and regulatory bodies
OEF Systems [requirements]
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Safety Fundamentals (No. 110) Principle 21 : Operating organization shall report safety significant
incidents to the regulatory body
Operating organizations and regulatory body shall
establish complementary programs to analyze
operating experience, to ensure lessons are learned
and acted upon;
Such experience shall be shared with relevant
national and international bodies
OEF Systems [requirements]
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National level OEF System
Purpose
Prevent recurring of similar events by management
& incorporating related information and thus
Reduce the potential hazards of events reflecting OE
to the design, operation and maintenance
Related Documents
Convention on Nuclear Safety Article 19. “Operation”
A System for the Feedback of Experience from
Events In Nuclear Installations, NS-G-2.11, 2006
Related Requirement including Reporting (IRS
Guideline)
OEF Systems [RB OEF]
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Collection
Screening
Communication Immediate
Actions
Evaluation / Application
Regulatory Action
Tracking
Storage
Dissemination
• NSSC Notice • IRS, INES • US NRC IN, GL, etc.
• By OE Department • By Technical Groups (9 fields)
• Investigation
• Corrective Actions
• CATS
• Inspections • Safety Reviews
• OPiS • DIOS
- Reference : IAEA Safety Guide No. NS-G-2.11 “A System for the Feedback of Experience from Events in Nuclear Installations”
Overall Program [OEF Process]
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Overall Program [OEF Tools]
IAEA OEF Process Domestic OEF Process Tools
Reporting
Collection
- NSSC Notice 2009-37
- IAEA IRS, Web Site
- USNRC IN, EN, Bulletin etc.
- JNES PRI, etc.
Screening
Immediate Actions Investigation and
Analysis
- KINS Expertism
- e-FAST Investigation
Corrective Actions Corrective Actions - CATS
Trending and
Review
Classification
- Coding System for the Public
- HuRAM
- IAEA IRS
Dissemination and
Review
Dissemination - DIOS
- OPIS
Monitoring of
Effectiveness
Monitoring of
Effectiveness
- Review and Inspection, Audits
- Feedback on Regulatory Activities
and Annual Workshop on OEF QA
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OEF Tools [reporting]
Analysis/ Screening
Event Reporting 1st Investigation
Event review
2nd Investigation
Recommendation Corrective Action
CA Evaluation
Self-Assessment
Fe
ed
bac
k
for S
ys
. Imp
rove
me
nt
Information
Dissemination
Process for the Event Management
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Status and Issues in Nuclear Safety Regulation
V. OEF Tools
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OPiS [Background]
Background
NPPs and its related facilities are becoming nationally
concerning facilities in Korea.
The Public, NGOs and many Stakeholders want to know safety-related information about NPP and those incidents and failures instantly.
OPiS fulfills these demands, and promotes the public confidence in nuclear safety.
OPiS also implements those functions of the OEF by Disseminating and Storing the information.
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OPiS [Development]
First Version of OPiS Developed in Jan. 2004 for Korean version only
Main contents were NPP Status, NEED, INES and SPI
Became very useful website for the RB and also for many stakeholders
Urged to develop an improved version which could include the English version
Second Version of OPiS Developed in Oct. 2006 for a year
Korean version with English version optional
Improved the functions of NEED, INES and SPI
Includes the abstract of all events in English
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OPiS [Main Pages]
Main Pages NPPs Status
Location of Worldwide NPPs
Specific and Licensing Information about NPPs
NEED (Nuclear Event Evaluation Database)
INES (International Nuclear Event Scale)
SPI (Safety Performance Indicator)
[Website : http://opis.kins.re.kr]
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OPiS [NPPs Status]
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OPiS [NEED]
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OPiS [Incident Information]
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OPiS [INES]
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OPiS [INES]
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SPI [Structure]
Area Category Indicator Remark
Reactor
Safety
Operational Safety Unplanned Reactor Scram URS
Unplanned Power Reduction UPR
Multiple Barriers
Fuel Reliability FR
Reactor Coolant Leakage RCL
Containment Reliability CR
Emergency Preparedness EP
Safety System
SIS Availability SI
EDG Availability EDG
AFWS Availability AFW
Radiation
Safety
On-site Rad.
Safety Radiation Collective Dose RCD
Off-site Rad.
Safety Public Dose/Environmental Rad. PD/ER
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OPIS [SPI]
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Effectiveness of OEF
NSSC/KINS are consistently implementing the national OEF
program since 1990’s
Number of Reportable Events is being stabilized and decreased. It
was just 0.35 in 2013 while it was 1.38 in 2001.
Frequency was less than 1.0 during the last 4 years consecutively.
In 2013, the frequency decreased to 0.35 and a value less than 0.5 is anticipated in 2014.
The proper implementation of OEF program is the best and the most positive way to enhance the operational safety and the efficiency of NPPs.
Web-based OEF Tools is necessary and inevitable for the proper
and prompt implementation of the OEF process.
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Status and Issues in Nuclear Safety Regulation
V. Accidents
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Accidents
3 NPPs have experienced tragic nuclear accidents TMI-2 Accident in March 28,1979
Chernobyl Accident in April 26, 1986
Fukushima Accident in March 11, 2011
A lot of Lessons-Learned and Action Plans were drawn
and have been implemented in all NPP operating
countries to prevent similar accidents and now
Fukushima Action Plans and several Stress Tests are
in progress.
After the TMI-2 Accident, the World Nuclear Society
have recognized, acknowledged and studied the
importance of OEF
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TMI-2 Accident [milestones]
located in Harrisburg in Pennsylvania State of the
USA
Babcock & Wilcox (B&W) designed PWR
thermal power 2,772MWth, electric power 906MWe
milestones 1978.3 first criticality
1978.12.30 commercial operation
1979.3.28 small LOCA thru the PZR PORV occurred
permanent shutdown and decommissioned
1979.7 TMI-2 Lessons Learned Task Force Status Report and
Short-Term Recommendations(NUREG-0578)
1980.11 Clarification of TMI Action Plan Requirements
(NUREG-0737)
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TMI-2 Accident [Plant Overview]
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TMI Accident [Synopsis]
Sequence of Event Condensate Pp stop → Main Feed Water Pp trip → TBN Trip
→ Reactor Trip due to RCS high Pr. → PZR PORV opened but
unidentified → AFW Pp actuated but failed to supply water due to
valve spuriously closed → S/G dryout → ECCS actuated → PRT
Tank rupture disk opened → Block HPSI due to PZR high level →
RCS became saturated state → Cont’t Sump Pp start → Zr-Water
reaction and H2 generated(locally might be H2 explosion) → close
PORV (after 140 min.) → 12 ton of molten corium pool moved to
Reactor Vessel lower head → Core cooling recovery (after 300
min.)
Compounded by the initial mistakes of operators and
human factor problems(MCR indication)
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Results of the TMI-2 Accident
Core melt-down & relocation
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Results of the TMI-2 Accident
Environmental release of Radioactive material • Noble gas 2,500,000 Ci( 5% of noble gas of the core)
• Iodine 15 Ci
Radiation exposure of the publics : negligible
• Collective dose 33 man-Sv
• Average exposure per person: ~0.1mSv(1mrem)
(Max.<100mrem)
[X-ray(~6mrem), natural background dose (~100mrem/yr)]
Increase in Cancer Occurrence : negligible
• Increase 1/50,000 rate (add 1 to 325,000 cancer death )
INES Rating : Level 5
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TMI Action Plans
Short term Action Plan(NUREG-0578) Control Room Design Review
Safety Parameter Display System
Emergency Response Facility
Post Accident Sampling System
Probabilistic Reliability Analysis
Emergency Operating Procedure, etc.
Long term Action Plan(NUREG-0737) Reactor Head Vent valve
H2 Re-combiner, RVLIS, SCMM, ICC
Technical Support Center & Operating Support Center
BE Analysis and revise EOP
Immediate upgrading of RO & SRO training and qualifications
AFW system evaluation
Emergency power for pressurizer heaters
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Action Plan I.A.1.l STA
NRC Position
Each licensee shall provide an on-shift technical advisor to the shift
supervisor.
The shift technical advisor (STA) may serve more than one unit at a
multiunit site if qualified to perform the advisor function for the
various units.
The STA shall have a bachelor's degree or equivalent in a scientific
or engineering discipline and have received specific training in the
response and analysis of the plant for transients and accidents. The
STA shall also receive training in plant design and layout, including
the capabilities of instrumentation and controls in the control room.
The licensee shall assign normal duties to the STAs that pertain to
the engineering aspects of assuring safe operations of the plant,
including the review and evaluation of operating experience.
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Chernobyl Accident
located in Pripyat, Ukraine
designed and built by the former USSR
RBMK-1000 (Boiling Water Reactor
moderated by graphite)
4 Reactors produced about 10 % of
Ukraine’s electricity April 26,1986, Chernobyl disaster
happened.
A level 7 event (the maximum
classification) on the INES.
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RBMK [Reactor]
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RBMK [Plant Overview]
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Chernobyl NPP after the disaster
Chernobyl power plant in 2003 with the sarcophgus
containment structure
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Chernobyl Accident
intended to perform an experiment of bridging power gap
between the Loss of Offsite Power (LOOP) and the full
availability of the Emergency Diesel Generator (EDG)
failed the test 3 times already and 4th time test was
attempted in April 26, 1986 but resulted in a catastrophic
disaster
positive reactivity ( + ρ) was inserted due to the positive
void coefficient (during low reactor power level), extreme
power excursion occurred, and the reactor vessel
ruptured
INES level 7
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NPPs in Japan
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Unit 1
Unit 2
Unit 3
Unit 4
Units 5, 6
At the Time of Earthquake - Reactors 1, 2 and 3 operating - Reactors 4, 5 and 6 shutdown for maintenance, inspection and refueling
Fukushima Daiichi NPPs
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Fukushima NPPs after Disaster
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Fukushima NPPs against Tsunami
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Fukushima Accident [Synopsis]
external hazard induced accident, i.e. earthquake and
tsunami.
the magnitude of historical earthquake or tsunami was
not sufficiently considered in the design stage during
construction.
the volumetric capacity of BWR containment was found
to be inferior to PWR containment during accident.
the importance of ultimate and fundamental bastion and
barrier was realized again and now STRESS TEST to
overcome such things is being implemented. heat sink, emergency electrical power, decay heat
radiation, natural disaster
INES level 7 event
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Fukushima Accident [Chronicle Sequence]
Date Event and Failure Remarks
2011.3.11 14:46 (Friday Afternoon)
- Fukushima-1,2,3 Reactor Trip due to Earthquake
- Unit-1,2,3 experienced Station Black Out(15:40)
- Emergency declared(19:03)
2011.3.12 - Unit-1 Hydrogen explosion(15:36)
- Sea Water to Unit-1 Reactor
1st H2 explosion
2011.3.14
- Unit-3 Hydrogen explosion(11:01)
- Sea Water to Unit-2 Reactor
2nd H2 explosion
2011.3.15
- Unit-2 Containment failure and large radiation
release to environment
- Unit-4 Hydrogen explosion(06:10)
3rd H2 explosion
SFP suspicious
2011.3.16 - Rad. Level increased to 1,000mSv/h temporarily
2011.3.17~19 - Unit-5,6 recovered RHR System Operability
2011.3.20~31 - Units recovered Offsite Power
- Fresh Water injected to all Units
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Thank you for your attention! شكرا