In-Process ECP Monitoring at BWR Utilizing OLNC for ...envdeg2015.org/final-proceedings/ENVDEG/presentations/ENVDEG_P… · One Pt ECP probe in external monitoring system (MMS - Mitigation

© 2015 Electric Power Research Institute, Inc. All rights reserved.

Susan Garcia, EPRI [email protected]

Environmental Degradation Conference August 2015

In-Process ECP Monitoring at BWR Utilizing OLNC for

Mitigation of IGSCC

mailto:[email protected]

2 © 2015 Electric Power Research Institute, Inc. All rights reserved.

BWR IGSCC Mitigation

Hydrogen Water Chemistry (HWC) was implemented to protect BWR reactor vessel, internals and piping from intergranular stress corrosion cracking. – At moderate hydrogen injection rates (1-2 ppm FW H2), mitigation of

stress corrosion cracking is achieved when the electrochemical corrosion potential (ECP) of reactor vessel, piping and internals is <-230 mV(SHE). (1982 – current)

– Lower hydrogen injection (<0.5 ppm), combined with noble metal injection, also reduces ECP, two generations of noble metals exist: Noble Metal Chemical Addition (NMCA) – applied during shutdown

every 4-6 years (1996 – 2008) On-Line NobleChem™ (OLNC) – applied during full power

operation every 11-16 months (2005 – current)


U.S. BWR Chemistry - History

0

5

10

15

20

25

30

35

1985 1990 1995 2000 2005 2010 2015 2020

Num

ber o

f U.S

. BW

Rs

Zn Injection NMCA+HWC HWC (no NMCA) OLNC

Zn addition for shutdown dose control

Mitigation Technologies


Monitoring of IGSCC Mitigation with OLNC

Demonstration of the effectiveness of OLNC was limited to Electrochemical Corrosion Potential (ECP) probes mounted in external piping and monitoring skids. – Chemistry conditions at these locations are not as

aggressive as in the lower vessel head region. Lower oxidant concentration as distance from the core increases. H2O2 decomposition is also known to occur.

Prior to recent Brunswick-1 experience, there had been no direct in-vessel ECP measurements during OLNC application/operation in the lower vessel head region. – At this location, oxidant concentrations are elevated

compared to recirculation loops and external monitoring skids.


Brunswick-1 Mitigation Monitoring

Two platinum probes and a pre-oxidized stainless steel billet were installed in a modified local power range monitor (LPRM). Coolant flow holes for LPRM were shifted down to coincide

with a flow hole, allowing coolant from below the core plate to flow past the probes.


Location of Brunswick-1 ECP Probe


Brunswick-1 Mitigation Timeline

Moderate HWC from 1989 – August 2014 LPRM ECP modification completed during March 2014

refuel outage Hydrogen benchmark completed in May 2014 under

Moderate HWC conditions Initial OLNC application in August 2014 Hydrogen benchmark completed in October 2014 for OLNC

conditions Benchmark Testing provides valuable IGSCC mitigation data

M-HWC (25 years) Installation of LPRM

ECPs Benchmark

Test OLNC

Application Benchmark

Test


Brunswick-1 ECP Response during HWC-M Ramp Test

Platinum to LPRM surface potential difference shown as "Pt1(2)-GND". Platinum to stainless steel electrode

potential difference shown as "Pt1(2)-SS".


Brunswick-1 LPRM ECP Data vs Feedwater Hydrogen

Platinum to stainless steel electrode potential difference shown as "Pt1(2)-SS".


Brunswick-1 LPRM ECP Response during OLNC Application

Platinum to LPRM surface potential difference shown as

"Pt1(2)-GND".

Current OLNC vendor recommendation is OLNC injection 60-90 days after startup

Rapid response of LPRM ECP

due to noble metal deposition on surfaces


Nine Mile Point-1 Experience

Two Pt ECP probes in decontamination flange of reactor recirculation system (RRS) loop. One Pt ECP probe in external monitoring system (MMS -

Mitigation Monitoring System) that takes flow from reactor water cleanup (CU) loop. HWC benchmark test performed June 2013

– Feedwater hydrogen reduction from 6 scfm to 2.7 scfm – No change in MMS ECP readings while RRS ECP raw

values became more negative – All probes indicated a shift in values at 2.7 scfm when the

molar ratio of hydrogen to oxidants was less than 2:1

javascipt:void(0)


Nine Mile Point-1 HWC Ramp Test Data

RGnd = Recirculation ECP

CUGnd = MMS ECP


Hatch-1 Experience

Host site of ECP measurement study by Japanese Owners Group in late 1990s and 2000s. ECP probes in multiple locations:

– LPRM – MMS (external system) – Bottom Head Drain Line (BHDL)

Data collected pre-NMCA and post-NMCA LPRM and BHDL ECP data indicated that HWC-M and

NMCA were both effective for IGSCC mitigation LPRM ECP electrodes are no longer used at plant, but the

station continues to monitor ECP at the BHDL and MMS


Hatch ECP Response at BHDL and LPRM Pre- and Post-NMCA


Hatch-1 Experience

In late 2000s, a difference between “as-read” ECP measurements at the BHDL and MMS locations was noted, with a gradual increase at the BHDL starting in 2009. The increase in ECP at the BHDL location was expected

since it had been four years since an NMCA application. Not expected…MMS ECP remained low and stable several

years after NMCA and in between future OLNC applications. MMS ECP manifold was replaced and confirmed that a low

oxygen environment within the MMS was contributing to false low ECP measurements and may not be indicative of ECP measurement of reactor vessel internals. Considerations for ECP monitoring in MMS now being

evaluated, with counter measures being recommended.


Hatch-1 ECP Data in MMS and BHDL


Conclusions

Brunswick-1 experience demonstrated that OLNC can be effective for mitigation of IGSCC in an aggressive environment. Nine Mile Point-1 experience demonstrated that ECP can be

used to indicate when molar ratio of hydrogen to oxidant is less than 2:1. Hatch-1 LPRM and BHDL ECP demonstrated effectiveness

of HWC-M and NMCA regimes for IGSCC mitigation. In-reactor ECP monitoring can provide better trending to

show the effect of plant changes or local losses of catalytic activity. – LPRM and BHDL locations are unaffected by radiation

from the core, which drives recombination reactions. – Monitoring at these locations has great value.


Brunswick Chemistry, Engineering, and Major Projects personnel – Steve Williams, Larry Yemma, Kurt Crytzer, Joel McLean,

John Piepmeyer, Kristi White, Pat Godsey and Terri Jones Nine Mile Point’s and Hatch Nuclear Plant’s Chemistry

Departments – Collin Custer (NMP) and Brian Colson (Hatch)

General Electric – Hitachi – Juan Varela and Bert Huie

Acknowledgements


Together…Shaping the Future of Electricity

Documents

In-Process ECP Monitoring at BWR Utilizing OLNC for ...envdeg2015.org/final-proceedings/ENVDEG/presentations/ENVDEG_P… · One Pt ECP probe in external monitoring system (MMS - Mitigation