development of inherently safe technologies for bwrs · development of inherently safe technologies...

© Hitachi, Ltd. 2015. All rights reserved.

Development of Inherently Safe Technologies for BWRs

Hitachi Ltd., Hitachi Research Laboratory

Feb. 17, 2015

Kazuaki Kitou, Naoyuki Ishida, Akinori Tamura, Ryou Ishibashi, Masaki Kanada and Mamoru Kamoshida

IEM-8 IAEA-CN-235-10

Feb. 16-20, 2015, Vienna, Austria


1. Background and objective

2. Overview of the development items

3. Conclusions

Contents

1


1. Background and objective

2


1-1 Safety improvement trends in BWRs

3

Core damage frequencies have been reduced by adding or improving safety systems, considering past accidents.

Countermeasures for large-scale natural disasters have become necessary, considering the Fukushima event.

Ref: GE Hitachi Nuclear Energy, "Safety, constructability, and operational performance of the ABWR and

ESBWR designs", IAEA Technical Meeting on Technology Assessment for Embarking Countries (2013)

10-4

10-3

10-2

10-1

1.0

1970 1980 1990 2000 2010 2020year

ABWR

ConventionalBWR

Our target

ESBWRIncrease safety system division

Passive safety

Norm

aliz

ed c

ore

dam

age

frequency

[-]

Expand redundancy

Core catcherPassive safety

TMI▼

Fukushima▼

Chernobyl▼

Terrorism (9/11)▼

Airplane crashStation blackout

Large-scalenatural disaster


1-2 Fukushima event sequence and development needs

4

Tsunami & station blackout (SBO)

Cooling system stop

Hydrogen explosion

Core melt

Primary containment vessel failure

Development needs were selected considering the Fukushima event sequence.

Recognition of accurate plant status

Long-term cooling system without electricity

Prevention of hydrogen explosion

Sequence Needs


1-3 Objective and development items in the study

5

Objective: Ensure plant safety even under a long-term station blackout

or multiple failures caused by a large-scale natural disaster Development items regarding our innovative cooling system

are mainly reported in this presentation.

Innovative cooling system

Hydrogen explosion prevention system

IC: Isolation Condenser PCCS: Passive Containment Cooling System PAR: Passive Autocatalytic Recombiner PCV: Primary Containment Vessel RCIC: Reactor Core Isolation Cooling RPV: Reactor Pressure Vessel

Abbreviations

Operation support system

RCIC

IC

Air-cooling heat exchanger

PCCS

Reactor building

PCV

RPV Alternative feed-water system

Cover wall Operating floor

SiC fuel cladding

Air-cooling system

PAR

water-cooling systems

Development items

RCIC


Reactor building

PCV

Heat exchanger

Water pool

RPV

Alternative feed-water system


SiC fuel cladding

New water cooling system

Air-cooling system

PAR


Heat exchanger

1-4 New passive water-cooling system

Conventional passive water-cooling systems need a large water pool at a high elevation above the RPV.

The system is devised to improve the seismic design of the water-cooling system.

New passive water-cooling system

Features of the new system

• The water pool can be located below the ground level.

• Steam generated in the RPV flows by the pressure difference between the RPV and the suppression pool.

• Water is supplied to the RPV using turbine driven system (RCIC) or an alternative feedwater system

Steam

RPV

Core

Steam

PCV

Ground level

Condensate

Suppression pool

Choking orifice

RCIC

Water pool

6

Alternative feedwater system

JP Patent No. P05566963 EPO Patent No. 2549484


2. Overview of the development items

7


2-1 Innovative cooling system

8

Elapsed time [day]

0

10

40

5 10 15 0

Air-cooling system

Water-cooling system

20

30

Activation period of both systems

The decay heat for an initial 10 days is removed by both the water- and the air-cooling systems; then it is removed by only the air-cooling system.

We have been developing both the water- and the air-cooling systems to realize the innovative cooling system.

Deca

y heat [M

W]

Capacity of the water pool can be reduced significantly using the air-cooling system.

Infinite-time cooling can be achieved.

(4700M

Wt c

lass

react

or)

RCIC


Reactor building

PCV

Heat exchanger

Water pool

RPV

Alternative feed-water system


New water cooling system

Air-cooling system


0

10

20

30

40

50

60

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Operation range for the new system

1.0 2.0 3.0 7.0

PCCS

IC

0

60

50

40

30

20

10

Inle

t ste

am

velo

city

[m/s

]

Pressure [MPa]0

◆: 27.2 mm O.D.

□: 42.7 mm O.D.

EquivalentRe number

9

Heat transfer data were obtained to design the water-cooling systems, such as IC, PCCS and our new system, using a full-scale single-tube test section.

Multiple-tube tests are also being conducted now.

2-2 Heat transfer tests for water-cooling systems

Test condition map

Steam exhaust

Strain gageCondensation tube

Optical void sensor

Accelerometer

Thermocouples

Water pool

Steam injection tube

Baffle plate

Steam

5.8m

Condensate

DP gage DP

Test section

Tube type S M L

I.D.（mm） 22.2 28.4 35.5

O.D.（mm） 27.2 34.0 42.7

THK（mm） 2.5 2.8 3.6

Detailed TC locations & tube size

Tube

I.D

.O

.D.

Thickness(THK)

TC


0

2

4

6

8

10

12

14

0 2 4 6 8 10 12 14

◆：27.2 mm O.D.■：42.7 mm O.D.

+20%

-20%

10

8

6

4

2

0

12

Boili

ng h

eat tr

ansf

er

coeff

icie

nt

(Experim

ent)

[kW

/(m

2･K

)]

0 2 4 6 8 10 12

14

14Boiling heat transfer coefficient

(Calculation) [kW/(m2･K)]

5.0

674.066.1

bsoso

d

Dqh

5.02146.0 GLb gd

0

100

200

300

400

500

600

700

800

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50.0 0.5 1.0 1.5 2.0 2.5 3.0 3.50

100

200

300

400

500

600

700

8009.3m

7.7m

4.9m

3.3m

27.2mm O.D.

Pressure [MPa]

Ste

am

mass

flo

w r

ate

[kg/h

]

Analysis results

Experimental results

10

The completed condensation length map has been made based on test results[1].

Modified heat transfer correlations have been developed [2].

2-3 Test results for water-cooling systems

Completed condensation length map[1]

TC1 0.1m

TC2 1.7m

TC3 3.3m

TC4 4.9m

TC5 7.7m

TC6 9.3m

The mark means condensation completed between TC3 and TC4.

Developed heat transfer correlation[2]

[1] N. Ishida et al., ICONE22-31007 (2014) [2] H. Hosoi et al., NUTHOS10-1191 (2014)


2-4 Development items for air-cooling system

11

Air-cooling enhancement technologies are key to realize the air cooling system.

Better heat exchanger pipe has been developed.

Reactor building

PCV

RPV


Air-cooling system


Heat exchanger pipe

Heat-transfer fins

Turbulence-enhancing ribs

Micro-fabrication surface

Developed air-cooling heat exchanger pipe

Heat exchanger pipe

Heat-transfer fins

Turbulence-enhancing ribs

Micro-fabrication surface Top view

Cross-sectional view

Developed air-cooling heat exchanger pipe

SEM images of micro-fabrication surface


2-5 Heat transfer tests for air-cooling system

12

Heat transfer tests were conducted to confirm heat transfer and pressure loss characteristics of the developed technologies.

Test apparatus Air-cooling heat exchanger pipe

T

T

F

2400mm

ΔP

950mm

1500mm

T

T

T

300mm

300mm

300mm

P

T

Thermocouple

Air compressor

Reducing valve

Flow control valve

Air heater

Current plates

Insulator

Heat exchanger pipe

A A

B B

100mm 25.4mm

Air

Heat transfer fins

Turbulence enhancing ribs

Micro-fabrication surface

Fin

Rib


2-6 Test results for air-cooling system

13

Nu was increased 140% using the technologies[3]. Pressure loss also increased 70% due to the fins and the ribs.

Nusselt number Pressure loss coefficient

[3] N. Ishida et al., “The concept of passive cooling systems for inherently safe BWRs”, ICMST-Kobe (2014)

0

50

100

150

200

250

300

350

5000 15000 25000 35000 45000 55000 65000

Nu

ssel

t n

um

ber

[-]

Reynolds number [-]

Pipe with developed

technologies

Bare pipe

140%

Dalle-Donne’s Eq. [1973]0

0.2

0.4

0.6

0.8

1

1.2

5000 15000 25000 35000 45000 55000 65000

Pre

ssu

re-l

oss

co

effi

cien

t[-

]

Reynolds number [-]

Pipe with developed

technologies

Bare pipe

70%

Uematsu’s Eq. [1952]N

orm

aliz

ed p

ress

ure

loss

coeffic

ient [-

]

Bare pipe


2-7 Air-cooling performance in a plant

14

The air-cooling performance was estimated using 1D analysis. Heat transfer performance increased 100%[3].

Reactor building

Outer shelter

Air

Air cooling heat exchanger

(HX)

Considered factors in 1D analysis

Inlet loss of HX

Friction loss and acceleration loss

in HX

Outlet loss of HX

Friction loss in air flow path

Outlet loss of air flow path

Draft force of air Air flow rate

Steam generated by decay heat

Condensate

0

50

100

150

200

Ratio o

f heat

transf

er

perf

orm

ance

[％]

Bare pipe Developed pipe

Heat-transfer fin

Micro-fabrication surface and turbulence enhancing rib

65％

36％


2-8 Hydrogen explosion prevention system

15

Hydrogen explosion prevention system consists of using high temperature resistant (SiC) fuel cladding and PARs*.

High temperature oxidation tests for SiC were conducted, and estimated H2 generation using SiC fuel in a plant decreased to one-fifth or less than that using conventional zircaloy fuel[4].

*PAR：Passive Autocatalytic Recombiner

Reactor building

RPV

High temperature resistant fuel

PCV Nitrogen

filling

Leaked hydrogen

Leaked hydrogen gas is recombined by PARs*

[4] R. Ishibashi et al., ICONE22-31139 (2014)

Fuel assembly

Lower hydrogen generation rate under high temperature

conditions during severe accident

Fuel cladding

1) Inner layer:

Metal or alloy

3) Outer layer:

Environment barrier coat

2) Substrate:

SiC/SiC composite


2-9 Operation support system

16

■ The system covers multiple equipment failures, and it has three functions to reduce the occurrence of operators’ false recognitions and human errors.

■ An accident event identification method and a plant simulation code to predict event progress were developed[5].

Operation Equipment

Control panel

Sensors

Operation support system

Operator

Battery

Main control room

Support staff

Technical support center

①Sensor integrity diagnosis

②Accident event identification

③Progress prediction

Process computer

Functions

[5] M. Kanada et al., ICONE22-31104 (2014)


3. Conclusions

17


3-1 Conclusions

18

We have been developing the following inherently safe technologies for BWRs to improve plant safety during large-scale natural disasters.

(1) Innovative cooling system (2) Hydrogen explosion prevention system (3) Operation support system

The development items and results for the innovative cooling

system were summarized in this presentation.

- Heat transfer tests for both the water- and the air-cooling systems were conducted.

- Heat transfer data to design the water-cooling systems were obtained over a wide range of thermal hydraulics conditions.

- The air-cooling enhancement technologies have been developed to realize the air-cooling system.


Hitachi Ltd., Hitachi Research Laboratory

Development of Inherently Safe Technologies for BWRs

Feb. 17, 2015

Kazuaki Kitou, Naoyuki Ishida, Akinori Tamura, Ryou Ishibashi, Masaki Kanada and Mamoru Kamoshida

THE END

19

development of inherently safe technologies for bwrs · development of inherently safe technologies...

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