IGSCC Mitigation Experience and Application for New Design ... · * Tests occurred at KKP-1 up to...

© 2016 Electric Power Research Institute, Inc. All rights reserved.

Susan GarciaEPRI – Principal Technical Leader

(with acknowledged support from Finetech: Joe Giannelli, Jeremie Varnam, Jim Tangen, Jen Jarvis and J. Sundberg)

International Light Water Reactor Materials Reliability Conference and Exhibition 2016

August 1 – 4, 2016

IGSCC Mitigation

Experience and Application

for New Design BWRs

2© 2016 Electric Power Research Institute, Inc. All rights reserved.

Optimized Water Chemistry Needed

Conditions for IGSCC & Potential Mitigating Actions

Presence of susceptible material, e.g. sensitized material, cold work, irradiation,

tensile stresses

High coolant “bad” conductivity high crack growth rates

Presence of BWR oxidants such as O2, H2O2, Cu2+, etc.

BWR operating temperature, e.g., ~ 288C

High level of oxidants high ECPs high crack growth rates

Low level of oxidants low ECPs low crack growth rates

Materials

EnvironmentStress

Reference: BWR Water Chemistry Guidelines - Volume 2 Technical Basis (3002002623)


BWR Chemistry…a history of changes

Pure water

Hydrogen injection

Zinc addition

Noble Metal injection (NMCA)

Online Noble Metal injection

(OLNC)

Early Hydrogen injection (EHWC)

Original

Design

Operation

1983

1995

2006

2011

Chemistry control at BWRs

has changed significantly over time

0

10

20

30

40

50

200

5

200

6

200

7

200

8

200

9

201

0

201

1

201

2

201

3

201

4

201

5Nu

mb

er

of

BW

Rs

NMCA+HWC OLNC HWC (no noble metals)

What is next and what is

needed for new BWR designs?


Electrochemical Corrosion Potential (ECP)

IGSCC Initiation “Threshold” = -230

mV(SHE)

0 0.1 0.2 0.3 0.4 0.5 0.6

-600

-500

-400

-300

-200

-100

0

100

200

Conductivity (µS/cm)

Elec

troc

hem

ica

l Pot

entia

l (V

, SH

E)

No IGSCC

IGSCC

BWR Data Sources Dresden 2 FitzPatrick Ringhals 1 Nuclenor Hatch 1 Hope Creek NMP 1

IGSCC

NO IGSCC

Pure

Water

EC

P,

mv(S

HE

)

Goal: maintain < -230 mV(SHE) ECP values


Stress Corrosion Cracking Mitigation with Hydrogen Water

Chemistry (HWC)

1.4 x 10-7 mm/s

<4 x 10-9 mm/s

<4 x 10-9 mm/s

Crack Growth Rate studies show significant reductions with HWC

Reference: BWR Water Chemistry Guidelines - Volume 2 Technical Basis (3002002623)


STEAM

FEEDWATER

HIGH PRESSURE TURBINE

LOW PRES TURBINE

GENERATOR

Feedwater Hydrogen Concentration (PPM)

Normalized Main Steam Line Activity

H2 Addition to Feedwater (HWC)

Mitigates IGSCC, but Main Steam

Dose Rate increases

Due to N-16

Area Dose

Rate

Increase

HWC Side Effects and

Benefits of NMCA/OLNC

HWC Operating

Regime

NC/OLNC Operating Regime


On-Line NobleChem™ (OLNC)

Platinum catalyzes recombination reactions between hydrogen and oxidants

Criteria:

– Requires a molar ratio of hydrogen to oxidants ≥2 (oxygen equivalent) at the most limiting location at which mitigation is targeted. For conservativism, many plants target molar ratios of ≥ 3 or ≥ 4

– Requires sufficient noble metal coverage on the surfaces

Less hydrogen required, typically 0.15-0.4 ppm feedwater hydrogen so MSLRM dose rates remain low

Mitigation is not claimed in:

– boiling regions (cannot achieve required molar ratio)

– the upper downcomer - incomplete mixing between feedwater and discharge from the steam separators is assumed

Significant BWR operating experience demonstrating effectiveness

Reference: BWRVIP-99-A Crack Growth Rates in Irradiated Stainless Steels in BWR Internal Components (1016566)


BWR Internals Mitigation with HWC and Noble Metals

NM

CA

pro

tect

ed re

gion

s

HW

C p

rote

cted

regi

ons

HWC-Moderate

• ECP reduction in the upper shroud annulus as gamma from the core

recombines H2 and O2

• ECP reduction depends on H2

injection amount

• Typically <-230 mV(SHE) around upper jet pump

• Hydrogen injection rates are >1ppm

Noble Metals + HWC

Noble metals (Pt alone or Pt+Rh)

needed on wetted surfaces

ECP reduction achieved as soon

as feedwater and separator/dryer

return flow are fully mixed to create

>2:1 H2 to oxidant molar ratio

Additional areas of protection with

NMCA – upper, outer shroud

regions (red region)

Hydrogen injection rate is <0.3 ppm


BWR-4 ECP Response following 2 OLNC Applications

2 Pt reference electrodes in modified

LPRM string (lower plenum)

OLNC Applications

– August 6, 2014 and July 24, 2015

Increase in ECP from -490 mV(SHE) to

~380 mV(SHE) after 1st OLNC

Reduction in ECP from ~-380 mV(SHE)

to ~-490 mV(SHE) during 2nd OLNC

Following 2nd application, gradual

increase in ECP values, similar to

experience after 1st OLNC application

ECP values recovering after November

2015 mid-cycle outage to repair

recirculation pump seal

Mid

-Cycle

Ou

tag

e

HWC-M

-550

-500

-450

-400

-350

-300

-250

5/1/2014 10/28/2014 4/26/2015 10/23/2015

Ele

ctr

och

em

ical

Co

rro

sio

n P

ote

nti

al, m

V(S

HE

)Pt-1 Pt-2 OLNC


Return to moderate HWC

– One U.S. BWR-2 has returned to M-HWC

2 NMCA applications (2003 and 2009)

Economic decision to not apply OLNC (plant to shutdown in 2019)

Earlier OLNC

– Original guidance to apply 90 days after startup (fuel concerns)

– Reduced to 60 days with fuel vendor concurrence

– Evaluating 30 day application hold period

– Swiss BWR will be the first to apply sooner, and has applied several mini-applications in place of annual applications

Methanol Injection

– Applied at German BWR in 2003/2004 at full power

– Startup application at U.S. BWR in March 2016 (data evaluation indicates mitigation not achieved)

TiO2 Injection

– Applied at Japanese BWR in 2010 (plant shutdown in 2011)

– Being considered at U.S. BWR that will shutdown in 2019

Mitigation Technologies – Recent Changes


How Does OLNC Mitigation Experience Apply to

New Design BWRs?


Comparison of Reactor Vessels

Extended

Chimney

Active Fuel

height is shorter

Taller

Downcomer

External

Recirculation loop

No external recirc.

loop

BWR 3-6 ABWR ESBWR

No external recirc. loop;

natural circulation

Jet pumps

10

RIP


Comparison of Design Parameters Affecting Radiolysis

Property BWR 6 ABWR ESBWR

Core Thermal Power (MWt) 3579 3926 4500

Core coolant flow rate (kg/s) 13104 145028763-

10376

Feedwater flow rate (kg/s) 1936 2118 2451

Max. Exit void fraction within

assembly0.79 0.751 0.9

Core average void fraction in active

coolant0.414 0.408 0.53

Core average inlet velocity (m/s) 2.13 1.96 1.12

Max. core inlet velocity (m/s) 2.6 2.29 1.15

Active Fuel Height (m) 3.7 3.7 3.0

RPV Diameter (m) 6.4 7.1 7.1

RPV Height (m) 21.8 21.1 27.7

Higher void

fraction

FW to Core

flow rate

higher

0.24 - 0.28 vs.

0.14

Shorter

active fuel

Larger radius

and taller RPV


Void Fraction in Average Channel of the ESBWR and ABWR

[Data from Ch 4 ABWR Design Control Doc. Rev. 4, Ch 4 ESBWR DCD Rev 10, and BWRVIA]

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Vo

id f

racti

on

Axial Height from bottom of Active Fuel (m)

ABWR ESBWR BWR6

Bulk boiling in

ESBWR starts at

a lower elevation

ESBWR Core is

shorter, and exit

void fraction is

higher


Summary of IGSCC Mitigation OptionsTechnology Type of Method Operating

Experience?

Increase in

MSLR Dose?

Other Notes, Requirements, Limitations

NWC (Non-additive) - - Yes -More frequent monitoring, careful control of

water chemistry required

HWC-Moderate x Yes Yes Volatile

NobleChem™/OLNC +

Low HWCx x Yes Minimal Volatile

Hydrazine or

Carbohydrazidex No

Decomposes at operating temperatures

(applicable to startup only)

Methanol x Limited*Likely,

if used alone

Volatile, less than H2

Kinetics of methanol-oxidant reactions may be

slow; UV light may be required to catalyze

TiO2 x Limited **

Does not require H2 if there is sufficient UV

light at the surface (small amount of H2 needed

for regions with insufficient UV) Compatibility

with noble metal treatment, methanol, and

depleted zinc oxide (DZO) is not known

* Tests occurred at KKP-1 up to 0.8 ppm FW injection during full power operation and LAS1 during startup. (both insufficient for IGSCC mitigation)

** Application and partial cycle operation at 2F-1. No ECP measurements.


IGSCC Considerations for Advanced BWR Designs

ABWR

– Hydrogen mini-tests and radiolysis modeling indicate that the response to hydrogen is similar for ABWRs and BWR 2-6:

Regions/components mitigated and amount of feedwater hydrogen required will be very similar.

ESBWR

– Radiolysis and water chemistry have not been modeled.

– Significantly more boiling than BWR 2-6 and ABWR. Core is shorter, downcomer is longer.

Hydrogen may not be as effective

Extended chimney piece above core (may be difficult to mitigate)

Longer downcomer, with shorter active core height, may lead to less exposure to high gamma rates to encourage recombination.


Hydrogen Water Chemistry and Noble Metal Treatments

Hydrogen Mini-Test at K7 and radiolysis models suggest that the ABWR responds

similarly to hydrogen injection as BWR 2-6.

Molar ratios in Lungmen ABWR

calculated with DEMACE

radiolysis code

-0.7

1.3

3.3

5.3

7.3

9.3

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Hyd

rog

en

: O

xid

an

ts M

ola

r R

ati

o

FFW H2 (ppm)

Upper Plenum Outlet

Top DC

Downcomer Outlet

Reactor Internal Pump Outlet

Bottom Lower Plenum Outlet

Molar ratios in an ABWR

calculated with BWRVIA[BWRVIA Modeling of Advanced Boiling Water Reactor. EPRI, Palo Alto, CA: 2011. 1023003]

[M. Wang, T.K. Yeh, Nucl. Sci. Eng. 180 (2015) 335–340]


Hydrogen Water Chemistry and Noble Metal Treatments

MSLR dose rate increase at K-7 with feedwater hydrogen-

increase is similar to those at BWR 2-6.

0

1

2

3

4

5

6

0.0 0.5 1.0 1.5 2.0 2.5

Main

Ste

am

Lin

e D

os

e R

ate

In

cre

ase

Feedwater DH (ppm)

OLNC+HWCModerate HWC

[Murai et al. 7th Int. Conf. Nucl. Eng., JSME, Tokyo, Japan, 1999]


Alternate Mitigation Technologies for ABWR Application

Limited BWR experience with Methanol or TiO2 but no ABWR experience

Hydrogen response is similar for the ABWR and BWR 2-6. It is likely that

methanol in an ABWR would be similar to that in a BWR 2-6.

– Tests with Methanol alone indicate it may take high concentrations

May be better when used with NMCA/OLNC.

– TiO2 could offer mitigation in more of the reactor vessel (upper plenum, upper

downcomer, etc.).

Dependent on coverage, UV intensity. Because the reactor vessel design is

different (RIP vs. jet pumps and recirculation loop), the required surface

loading in the downcomer may be different from that for a BWR 2-6. No

recirculation loop to mitigate.

Radiation Field Dose Rates: It is not known if methanol or TiO2 can produce the

very low ECP (-500 mV(SHE)) which is beneficial for dose rates due to incorporation

of activated corrosion products in oxide layers (when used with DZO).


Alternate Mitigation Technologies for ESBWR Application

Methanol: may provide some advantage over hydrogen

– Less volatile than hydrogen. However, methanol has not yet been proven to

mitigate IGSCC in BWRs, demonstrations had limited monitoring.

TiO2: since all of the vessel cannot be mitigated with HWC-M or NMCA/OLNC-

HWC, TiO2 may be useful for mitigation in oxidizing regions (top of the

downcomer, chimney, upper plenum, etc.).

Other considerations: would it be better to design the ESBWR chimney piece to

avoid IGSCC, or plan on replacing it (material selection, manufacturing)?

Summary:

IGSSC mitigation experience with BWR 2-6 designs may be applicable to ABWRs

Further radiolysis and water chemistry modelling required for ESBWRs


Together…Shaping the Future of Electricity

IGSCC Mitigation Experience and Application for New Design ... · * Tests occurred at KKP-1 up to...

Documents

Transcript of IGSCC Mitigation Experience and Application for New Design ... · * Tests occurred at KKP-1 up to...