inspection and validation activities on severe accident

Inspection and Validation Activities on

Severe Accident Management in Korea

after the Fukushima Accident

Han-Chul Kim*, Jung-Jae Lee, Sung-Han Lee

Korea Institute of Nuclear Safety (*E-mail: [email protected])

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

2

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

3

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.


4

Operation

Construction

Planning

23 Units

5 Units

6 Units

20,716MW

6,600MW

8,400MW

Operation :

6 units

Operation : 6 units

Construction : 2 units

Planning : 2 units

Operation : 5 units


Operation : 6 units


Planning : 4 units

Seoul

Hanbit NPPs

(PWR)

Kori/Shin-Kori NPPs

(PWR)

Wolsong/Shin-Wolsong NPPs

(PHWR/PWR)

Hanul/Shin-Hanul NPP

(PWR)

Introduction Status of Nuclear Power Plants in Korea


5

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.


6


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

7


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


8


Korea

Major Safety Improvements for Korean NPPs


4

3

7

Containment

원자로용기

2

10m

Sea

이동형 발전차량

5 Drain Pump

6 Contro

l rod PZR

SG

Rx

Battery

EDG

Portable EDG

1

Securing the safety of emergency battery

power from flooding

Installing passive H2 removal systems

which operate without electricity [PAR]

1

2

3

4

5

6

Installing containment filtered vent or an

alternative depressurizing system

7

1 billion USD investment over 5 years

Improvements

Making the coastal barrier higher (Kori site)

Preparing a vehicle with a portable

emergency diesel generator at each site

Installing watertight doors at major buildings

Water-proofing drain pumps

9


Korea

On-going safety improvements concerning a severe accident


Category Improvements

Severe

Accident

Management

Guidelines Strengthening severe accident education and training

Revising severe accident management guidelines (SAMGs)

to enhance their effectiveness

Developing low-power and shutdown SAMGs

Equipment

and Facilities

Installation of injection flow paths for emergency cooling

water from external sources

Installation of passive hydrogen removal equipment (PAR)

Installation of filtered venting system (CFVS) or

depressurizing facilities in the containment building

10

External cooling water injection stratgegy


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)

Requirement:

Some alternative,

direct lineups to

inject emergency

water source to the

primary and

secondary loops

should be provided

as soon as possible.

External Cooling Water Injection

11 Korea Institute of Nuclear Safety

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.

External Cooling Water Injection

12

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 Failure time

assumed

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

system

Pump performance

curve used

13

Reactor core, primary and secondary system model

KINS has been developing a MELCOR model with the assistance of a contractor.


130 180

150

260

386 385 384 383

396 395 394 393

508

507 506 505 504 503

502

501

130

361

362363364

365

509

371

372373374

375

659

660

661

665

666

667

670

669

668

664

663

662

672

671

652 654 656

651 653 655

658

657

510

511

512

513

IRWST

S/G Compart.

673674

675675 676

Steam generator

secondary side Reactor coolant system

Core

Active Region

Lower Plenum

Reactor core


Injection

14

0 10 20 30 40 50

0

2

4

6

8

10

12

14

16

18

Pre

ssu

re (

MP

a)

Time (hrs)

Primary

Secondary

RCP Seal Leakage

ADV Manual Open

Secondary injection

Primary injection

P/p discharge pressure:

15kg/cm2

Preliminary result: Primary and secondary system pressure change



Injection

15

0 10 20 30 40 50

0.0

0.5

1.0

1.5

2.0

2.5

Ma

ss F

low

Ra

te (

kg

/s)

Time (hrs)

External-1st

0 10 20 30 40 50

0

2

4

6

8

10

12

14

16

Ma

ss F

low

Ra

te (

kg

/s)

Time (hrs)

External-2nd

Primary system injection at 19.2 hr Secondary system injection at 9.1 hr

Level control

Preliminary result: Primary and secondary injection flow rates



Injection

16

0 10 20 30 40 50

0

100

200

300

400

500

600

Te

mp

era

ture

(oC

)

Time (hrs)

CETSAMG entry condition

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).

8.5 8.6 8.7 8.8 8.9 9.0 9.1 9.2 9.3 9.4 9.5

160

180

200

220

240

260

280

300

320

340

Te

mp

era

ture

(oC

)

Time (hrs)

Core Exit Temperature

Cooling Limit



Injection

17

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.


18

Acknowledgments

This work is based on the results from

the Nuclear Safety Research and Development program

of Nuclear Safety and Safeguard Commission.


inspection and validation activities on severe accident

Documents