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Inspection and Validation Activities on
Severe Accident Management in Korea
after the Fukushima Accident
IAEA IEM on Severe Accident Management in the Light
of the Accident at the Fukushima Daiichi N.P.P.
17-21 March 2014, Vienna, Austria
Han-Chul Kim*, Jung-Jae Lee, Sung-Han Lee
Korea Institute of Nuclear Safety
(*E-mail: [email protected])
Outline
1. Introduction
2. Special Safety Inspection for Operating Plants in Korea
3. External Cooling Water Injection
4. Confirmatory Analysis of External Cooling Water
Injection
5. Conclusions
Korea Institute of Nuclear Safety
2
Introduction
 Injection flow paths for emergency cooling water is being installed
at the Korean NPPs following the Government order.
 It was recommended through the Special Safety Inspection
 The objective is to provide cooling water from external
sources to the primary and secondary loops during a
prolonged station blackout accident.
 The effectiveness of this strategy needs to be confirmed through
evaluation of the installed system and on-site verification.
 This presentation shows the background of this installation and the
relevant confirmatory analysis results for APR1400.
Korea Institute of Nuclear Safety
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Introduction
Status of Nuclear Power Plants in Korea
Operation
23 Units
20,716MW
Construction
5 Units
6,600MW
Planning
6 Units
8,400MW
Seoul
Hanul/Shin-Hanul NPP
(PWR)
Operation : 6 units
Construction : 2 units
Planning : 2 units
Wolsong/Shin-Wolsong NPPs
(PHWR/PWR)
Operation :
6 units
Operation : 5 units
Construction : 1 units
Hanbit NPPs
(PWR)
Kori/Shin-Kori NPPs
(PWR)
Operation : 6 units
Construction : 2 units
Planning : 4 units
Korea Institute of Nuclear Safety
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Special Safety Inspection for Operating Plants in
Korea
 A Special Safety Inspection (SSI) was conducted by the Government.
 Seventy-three inspectors from the regulatory organizations,
research institutes, universities, etc. undertook the mission.
 The assumed scenario mirrored the Fukushima accident:
earthquake  tsunami  power loss  extreme severe accident
 They inspected 21 operating NPPs, a research reactor, and fuel
cycle facilities for 5 weeks.
•
•
Site inspection: Mar.21 ~ Apr.15, 2011
Review of findings: Apr.16 ~ Apr.30, 2011
 Hearings for the residents of the nearby towns of NPPs were held
before and after the inspection.
Korea Institute of Nuclear Safety
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Special Safety Inspection for Operating Plants in
Korea
 Major Inspection Points of SSI
Defense-In-Depth
Functions
Major Inspection Points
Extreme Natural
Hazards
Adequacy of the plant design and facilities against natural hazards
- Design against earthquake and seismic capacity
- Design against coastal flooding and inundation protection capability
Prevention of
Severe Accidents
Adequacy of power supply and cooling functions
- Power system and emergency power supply
- Cooling capability in case of station blackout and inundation
Mitigation of
Severe Accidents
Adequacy of countermeasures against severe accidents
- Facilities, guidelines, and strategies against severe accidents
Emergency
Response
Adequacy of emergency response
- Emergency response to multi-units accidents
- Facilities, systems, and infrastructure for the protection of local
residents and workers
Korea Institute of Nuclear Safety
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Special Safety Inspection for Operating Plants in
Korea
 Inspection Results
 Korean NPPs in operation have no imminent risk for the expected
maximum potential earthquake and coastal flooding, based on the
up-to-date investigation/research.
 However, there are needs to implement the long and short-term
improvements in order to secure safety for beyond-design-basis
natural events
Korea Institute of Nuclear Safety
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Special Safety Inspection for Operating Plants in
Korea
 Major Safety Improvements for Korean NPPs
Improvements
Containment
6
Portable
이동형
EDG
발전차
량
2
1
10m
5
Drain
Pump
3
SG
Contro
7
l
PZR rod
Battery
4
E
D
G
원자로용
기
1 Making the coastal barrier higher (Kori site)
2 Preparing a vehicle with a portable
emergency diesel generator at each site
3 Securing the safety of emergency battery
power from flooding
4 Installing watertight doors at major buildings
5 Water-proofing drain pumps
Rx
6 Installing passive H2 removal systems
which operate without electricity [PAR]
7 Installing containment filtered vent or an
alternative depressurizing system
Sea
1 billion USD investment over 5 years
Korea Institute of Nuclear Safety
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Special Safety Inspection for Operating Plants in
Korea
 On-going safety improvements concerning a severe accident
Category
Severe
Accident
Management
Guidelines
Improvements
Strengthening severe accident education and training
Revising severe accident management guidelines (SAMGs)
to enhance their effectiveness
Developing low-power and shutdown SAMGs
Equipment Installation of injection flow paths for emergency cooling
and Facilities water from external sources
Installation of passive hydrogen removal equipment (PAR)
Installation of filtered venting system (CFVS) or
depressurizing facilities in the containment building
Korea Institute of Nuclear Safety
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External Cooling Water Injection
 External cooling water injection stratgegy
 Requirement:
 Some alternative,
direct lineups to
inject emergency
water source to the
primary and
secondary loops
should be provided
as soon as possible.
An additional line to provide emergency cooling water from
outside the reactor containment building to the reactor (A),
auxiliary feed tank (B), and steam generator (C) (KHNP plan)
Korea Institute of Nuclear Safety
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External Cooling Water Injection
 External cooling water for the primary system is injected into the
core through the shutdown cooling line.
 Secondary system injection adopts two different ways:
 Make up the exhausted auxiliary feedwater (AFW) storage tank
through a fire engine
 Inject cooling water directly into the AFW discharge pipe through
a branch line using a fire engine
 Injection is possible when RCS or steam generator secondary
pressure decreases below 15 kg/cm2 (1.47 MPa).
 Minimum required injection flow rates were estimated by the utility.
Analysis of various accident scenarios including station blackout
using MAAP 4.06 showed that they could be achieved.
Korea Institute of Nuclear Safety
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Confirmatory Analysis of Ext. Cooling Water
Injection
 Accident sequence considered: a SBO with external water injection
Time (sec)
Event
Remark
0.0
- Reactor Trip
- Stop to Supply MFW
- Start to Supply TDAFW
900.0
- RCP Seal Leakage
28800.0
- Stop to Supply TDAFW
30600.0
- ADV Manual Open
30 min. after AFWP
trip
Set point :
1st Pressure < 15 kg/cm2
- Injection into the primary
system
Pump performance
curve used
Set point :
2nd Pressure < 15 kg/cm2
- Injection into the secondary Pump performance
system
curve used
Korea Institute of Nuclear Safety
Failure time
assumed
12
Confirmatory Analysis of Ext. Cooling Water
Injection
 Reactor core, primary and secondary system model
 KINS has been developing a MELCOR model with the assistance of a contractor.
IRWST
S/G
Compart.
513
Core
Active Region
512
671
672
511
Lower Plenum
661
667
668
662
660
666
669
663
659
665
670
664
510
509
508
507
506
505
504
503
502
501
673
674
260
130
180 130
652
654
656
658
651
653
655
657
386
385
384
383
396
395
394
393
150
675
676
361
365
364
363
362
371
375
374
Reactor core
Reactor coolant system
Korea Institute of Nuclear Safety
373
372
Steam generator
secondary side
13
Confirmatory Analysis of Ext. Cooling Water
Injection
 Preliminary result: Primary and secondary system pressure change
18
Primary
Secondary
16
Pressure (MPa)
14
RCP Seal Leakage
12
10
ADV Manual Open
8
6
4
Primary injection
2
P/p discharge pressure:
15kg/cm2
0
0
10
20
30
40
50
Secondary injection Time (hrs)
Korea Institute of Nuclear Safety
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Confirmatory Analysis of Ext. Cooling Water
Injection
 Preliminary result: Primary and secondary injection flow rates
2.5
16
External-2nd
External-1st
14
Mass Flow Rate (kg/s)
Mass Flow Rate (kg/s)
2.0
1.5
1.0
12
10
Level control
8
6
4
0.5
2
0.0
0
0
10
20
30
40
50
Time (hrs)
Primary system injection at 19.2 hr
Korea Institute of Nuclear Safety
0
10
20
30
40
50
Time (hrs)
Secondary system injection at 9.1 hr
15
Confirmatory Analysis of Ext. Cooling Water
Injection
 Preliminary result: Core exit temperature
 Reactor core can be sufficiently cooled with an ADV open.
 Further consideration will be given to the cooling rate, which is
higher than the operation limit, 55.6 ℃/h (100℉/h).
SAMG entry condition
CET
600
500
400
Core Exit Temperature
Cooling Limit
320
300
Temperature ( C)
300
280
o
o
Temperature ( C)
340
200
260
240
220
200
100
180
160
8.5
0
0
10
20
30
40
50
8.6
8.7
8.8
8.9
9.0
9.1
9.2
9.3
9.4
Time (hrs)
Time (hrs)
Korea Institute of Nuclear Safety
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9.5
Conclusions
 Injection flow paths for external cooling water are being installed at
the Korean NPPs following a special safety inspection.
 A best-estimate MELCOR analysis to check the effectiveness of
this strategy is being carried out.
 The preliminary analysis results show that this strategy could
successfully cool the reactor core for a station blackout accident
through its effective implementation.
Korea Institute of Nuclear Safety
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Acknowledgments
This work is based on the results from
the Nuclear Safety Research and Development program
of Nuclear Safety and Safeguard Commission.
Korea Institute of Nuclear Safety
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