potassium hydroxide for pwr primary ph control …...epri has initiated a number of activities to...

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

Keith FruzzettiTechnical Executive

International Light Water Reactor Materials Reliability Conference and Exhibition 2016

August 1 - 4, 2016Chicago, IL

Potassium Hydroxide for

PWR Primary Coolant pHT

ControlFeasibility Assessment

Co-authors:

Chuck Marks and Jeff ReindersDominion Engineering, Inc.

Joel McElrath, Daniel M. Wells, Paul Frattini, Al Ahluwalia, Ryan WolfeEPRI

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

PWRs Currently Need Highly Enriched Li-7

pHT required to be ≥ 7.0 during cycle

operation

– Maintained by proper Li concentration

Natural lithium is mostly Li-7 and Li-6

– But Li-6 neutron activation

generates tritium

36𝐿𝑖 + 𝑛 → 2

4𝐻𝑒 + 13𝐻

– Need enriched Li-7 (99.99%)

Li-7 is generated in coolant via

neutron reaction with B-10

– 510𝐵 + 𝑛 → 3

7𝐿𝑖 + 𝛼

Isotope Abundance (at%)

Li-6 7.59

Li-7 92.41

Natural Lithium


Vulnerability of Li-7 Supply Realized

United States Government Accountability Office 2013 report identified the concern that the required Li-7 may at some point be in short supply1

– “In a new report the Government Accountability Office (GAO) raises serious concerns about the future U.S. supply of Lithium-7, a critical radioactive isotope required for the safe operation of more than half of the nation’s nuclear power plants.”2

In 2015, some plants (U.S. and non-U.S.) reported an inability to procure Li-7

– Still feeling the effect as full supply is being re-established

The US Department of Energy (DOE) has been preparing an emergency reserve

EPRI has initiated a number of activities to address this vulnerability

1 GAO-13-716, “Managing Critical Isotopes: Stewardship of Lithium-7 Is Needed to Ensure a Stable Supply”, Sep. 2013.

2 Press Release, House Committee on Science, Space, & Technology, “GAO Raises Questions about Adequate Supply of Lithium-7 for Nuclear Power Reactors”, Oct 9, 2013.


EPRI Li-7 Strategy

Co-funding from DOE in 2015 and 2016

Usage Reduction and Plant Impacts

• Summarize impacts on plant

• Establish methods to reduce cycle usage

• Document in white paper

Lithium Recovery

• Continue to evaluate recovery/recycle options

• End goal – full scale demonstration

Alternative for pH Control

• KOH Feasibility Gap Assessment

• KOH Materials/Fuels Evaluations

• Incorporation of KOH into MULTEQ

Feasibility analysis of KOH use (3002005408) and

gaps identified

High temperature KOH Chemistry for MULTEQ and

pH calculation

Literature review and experimental scope development

for impact on Zircaloy cladding

Develop technology for Li-7 recovery

from spent resin

Demonstration Li-7 recovery for industry

Survey of industry usage

White paper– Assesses the impact of Li-7 supply loss for a typical

PWR plant and options for mitigating the impact

Evaluation of Lithium Addition on Plant Startup– EPRI report 3002008184


Feasibility of KOH vs LiOH for PWR Primary pH ControlPublished October 2015 (3002005408)

Important differences between VVER and Western-PWR experiences

– Materials: Titanium-stabilized SS (VVER) vs nickel-based alloys (PWR)

– Fuel cladding: Both zirconium alloy (KOH less corrosive), but low crud and lower boiling (VVER)

– Chemistry: Ammonia for hydrogen (VVER) vs dissolved hydrogen gas (PWR), Li/K new to PWRs

– Worker dose & Radwaste: Potassium activation products (VVER)

Key Gaps

Materials

• SCC of austenitic SS reactor internals & pressure boundary (including IASCC)

• SCC initiation and CGR of nickel based alloys

Fuels

• Corrosion and/or hydriding of zirconium fuel cladding – with crud and boiling

Chemistry

• Management of Li/K ratio (e.g., pHT

control, resin management)

• Including Li-7 production rate B-10 Li-7

Radiation Safety & Radwaste

• Activation of Potassium and impurities (i.e., sodium)

• 42K – external dose

• 40K – internal dose

• Waste classification

Appears feasible. Initiated next steps. More detailed multi-year plan developed.


Historical Use of KOH

KOH used for pH control at Trino Vercellese (Northern Italy)

– Westinghouse 270 MWe PWR

– Operated from 1964 to 1988

– Fuel clad and SG tubing was stainless steel

– However, very little to no data is now available

KOH used in Russian-designed VVERs*

* VVER = WWER = Water-Water Energetic Reactor, i.e., a PWR


Observations from VVER Operation

General Observations

– Successful use of KOH for over 40 years

– Generally low corrosion

– No observed Crud Induced Power Shift (CIPS)

– Very low radiation fields

– No unique waste or radiation field issues

Challenges

– Alloys are somewhat different

– Higher fuel boiling duty in PWRs

– Management of Li-7 production on pHT is a known challenge

VVER experience indicates it can be managed

– Activation pathways of potassium

– Other chemistry differences

Ammonia added for ECP control instead of hydrogen

VVER 1000 – Primary Circuit


VVER Overview

Operated in former USSR and Eastern Europe(plus China and India)

– 58 in operation, 25 under construction

Several types built

– Mainly VVER-440 & VVER-1000

Primary System Materials

– Ti-stabilized Stainless Steel

Main coolant pumps, SG tubes

– Low Alloy Steel

Main loop piping (clad with SS),

RPV (usually clad with SS)

– Carbon Steel

RPV Head and Pressurizer (clad

with SS), Nozzles

Fuel Cladding

– Zr-1%Nb

Some designs also have Zr-2.5%Nb sheath surrounding the assemblies

1 Higher concentrations may be used for limited duration (with fuel vendor concurrence)2 No EPRI limit. This is the molar equivalent based on 3.5 ppm Li

ParameterValues During Full Power Operation

VVER EPRI Guidelines

pH

pH at 300°C:

VVER-440: 7.1 to 7.3

VVER-1000: 7.0 to 7.2

≥ 7.0 at Operating

Temperature

Li (ppm) --- Typically ≤ 3.5 (1)

K (equivalent) (ppm) 0.8 to 20 ≤ 19.55 (2)

NH3 (ppm) ≥ 5 (normally 10) diagnostic

H2 (cc/kg) 30 to 60 25 to 50


Base Metal

Chromium Depleted Metal

Inner Oxide

Outer Oxide

Cr-rich

Fe-rich

Materials CompatibilityGeneral Corrosion – Stainless Steel

Typical Oxide StructureFrom Primary Circuit of Temelin (VVER)

(10x Cr as outer oxide)

Comparison of oxide films from VVERs and PWRs show similar structures and thicknesses

Baffle-former bolt at Tihange (PWR)

T. Grygar and M. Zmitko, “Corrosion Products Behavior Under VVER Primary Coolant Conditions,”

Chemistry 2002: International Conference on Water Chemistry in Nuclear Reactors Systems -

Operation Optimization and New Developments, Avignon, 2002. (NPC 2002)

Analytical Transmission Electron Microscopy (ATEM) Characterization of Stress-Corrosion Cracks in LWR-

Irradiated Austenitic Stainless Steel Core Components—Revision 2. EPRI, Palo Alto, CA: 2006. 1014511.


Materials CompatibilityGeneral Corrosion – Nickel Based Alloys

Oxide layer is similar

Corrosion product release kinetics appear similar

BOREAL test loop of Alloy 690 tubing

Typical Oxide Layer on Nickel Alloy in a PWRBut…

• Short term test

• Does not consider possible

restructuring, i.e., from Li to K

pHT is likely controlling factor rather than ion-specific effect

D. Morton, N. Lewis, M. Hanson, S. Rice, and P. Sander, Nickel Alloy Primary Water Bulk Surface and

SCC Corrosion Film Analytical Characterization and SCC Mechanistic Implications, Lockheed Martin

Corporation, Schenectady, NY: 2007. LM-07K022.

Effect of Boron Concentration on Alloy-690 Corrosion Product Release Rates - Results at 325°C and

285°C. EPRI, Palo Alto, CA : 2001. 1011744.


Materials CompatibilitySCC – Stainless Steel

PWSCC

– Chemistry has only a small effect within normal ranges

– Good performance of similar materials in VVERs

Austenitic stainless steels (no nickel alloys)

Irradiation Assisted Stress Corrosion Cracking (IASCC)

– Time to failure decreases when exposed to higher Li concentrations

EDF work (limited to ten specimens, and 2.2 vs 3.5 ppm Li)

EPRI MRP preliminary work

O-ring

Uniaxial Constant Load (UCL)

Evaluate effect of potassium on SCC of stainless steel (including IASCC)

• Li = 2.0 or 8.0 ppm

• pH300°C = 7.2 (Boron)

• Irradiated specimens at ~ 60 or 100 dpa

• 21 specimens tested

EPRI MRP Preliminary Testing (at 340°C)


Materials CompatibilityPWSCC – Nickel Based Alloys

Li has little to no effect on initiation (Metastudy)

– However, two individual studies (considering smaller concentration ranges) have reached a different conclusion

About 40% reduction in time to initiation going from about 2.2 to 3.5 ppm Li

Evaluate effect of potassium on PWSCC Initiation of nickel based alloys

Li has no measurable effect on crack growth rate

– Constant pHT

2 ppm Li → 7 ppm Li → 2 ppm Li → 0.3 ppm Li

Initiation Testing

CGR Testing

Pressurized Water Reactor Primary Water Chemistry Guidelines, Volume 1, Revision 7. EPRI, Palo Alto,

CA: 2013. 3002000505.

Materials Reliability Program: Effects of B/Li/pH on PWSCC Growth Rates in Ni-Base Alloys (MRP-217).

EPRI, Palo Alto, CA: 2007. 1015008.


Summary of Needed Materials Testing for Qualification of KOH

Trial Application*

Crack Initiation Testing

– Non-irradiated testing

Alloy 600 (or weld metal)

– Cold work (at or near yield stress)

– 1 material, 3 chemistries (including “crevice” chemistry)

Stainless steel

– Sensitized, cold work

– 1 material, 1 chemistry (“crevice” chemistry)

– Irradiated testing

Stainless steel (similar to current MRP testing with Li)

Crack Growth Rate Testing using “On the fly” DCPD technique

Reference LiOH #1 KOH-chemistry #1




– Non-irradiated testing

Alloy 600 MA or SA and 182

Stainless steel (CW and sensitized)

LAS

– Irradiated testing

Stainless steel

*Thank you to Peter Chou (EPRI) for developing the detailed materials testing plan


Fuel CladdingOverview

Long history of good performance of Russian alloys in VVERs

Recent history of good performance of “Western” alloys in VVERs

– Westinghouse supplied fuel in Ukraine and Czech Republic

However, for VVERs:

– Boiling duties not particularlyhigh

– Deposit loading is typically much lower

– No zinc

– Ammonia is another chemistrydifference

“Western” Russian

Fuel Type Zircaloy-2 Zircaloy-4 Zirlo® M5® Zr-1Nb Zr-2.5Nb

Element Wt% Wt% Wt% Wt% Wt% Wt%

Nb 0.94-0.98 1.0 1.0 2.4-2.8

Sn 1.2-1.7 1.2-1.7 0.97 <0.01

Fe 0.07-0.2 0.18-0.24 0.1 <0.05

Cr 0.05-0.15 0.07-0.13 <0.015

Ni 0.03-0.08

O 0.13 0.11-0.13 0.12 0.14 0.06 0.09-0.13

(Table adapted from 3002004140 and 3002005408)


Fuel CladdingSolubility impact on CIPS

Precipitation of alkali-borate and alkali-borate-nickel compounds are

a concern for inducing Crud Induced Power Shift (CIPS)

– Not known whether this will be an issue for KOH

Very likely that potassium compounds are much more soluble

Developing MULTEQ entries for important species

– Currently under development

mol/Kg ppm mol/Kg ppm mol/Kg ppm

(BO2)-1 36.6 750,000 27.6 693,000 0.1 9,325

(B4O7)-2 (1) 17.1 800,000 11.0 720,000

(B5O8)-1 18.1 800,000 15.1 770,000

Notes:

(1) - Solubility is for K2B4O7 and Na2B4O7

K+ Na+ Li+

MULTEQ entries for KOH and K-borate system

(soluble and solid species) to be incorporated in 2016


10

100

1000

10000

1 10 100 1000 10000 100000

Corr

osio

n Ra

te (m

g/dm

2 )

Concentration of Cations (ppm)

Zircaloy 2

NaOH

LiOH

KOH

Corr

osio

n R

ate

(m

g/d

m2)

1000

Fuel CladdingCorrosion and Hydriding

Fuel cladding corrosion expected to be much smaller with KOH chemistry

– Although increased solubility could lead to much higher cation concentrations at the fuel cladding surface when significant crud is present

Dominant source of hydrides in zirconium based alloys are from hydrogen released as a result of the cladding corrosion process

Hydrogen pick up fraction (HPUF)

– Fraction of corrosion generated hydrogen that is absorbed into the cladding

Corrosion Rate of

Zircaloy 2 at 360°CNaOH

LiOH

KOH

10000

100

10101

Concentration of Cation (ppm)

102 103 104 105

Corrosion and HPUF is expected to be lower with KOH than with LiOH

H. Coriou, L. Grall, J. Neunier, M.

Pelras, and H. Willermoz, “The

Corrosion of Zircaloy in Various

Alkaline Media at High

Temperature”, Corrosion of

Reactor Materials, Vol. II, 193,

IAEA, Vienna (1962).

Y.H. Jeong, J.H. Baek, S.J. Kim, H.G. Kim, and H.

Ruhmann, “Corrosion Characteristics and Oxide

Microstructures of Zircaloy-4 in Aqueous Alkali

Hydroxide Solutions,” Journal of Nuclear Materials

270:3, 1999.


Chemistry ChallengepHT Control

Li-7 generation expected to be comparable to VVERs

–

– Needs to be calculated for specific cycle/core designs

10 7( , )B n Li

Detailed analysis needed− Actual PWR generation rates of 7Li

− Potassium addition rates (pHT program)

− Selectivity of resins

− Effect of ammonia

− Demineralizer capacity

− …

Simultaneous control of Li and K required. This work is underway.Boric acid concentration, g/l

Pota

ssiu

m c

oncentr

atio

n,

ppm

Lithiu

m c

oncentr

atio

n,

ppm

0.6

43210

18

16

14

12

10

8

6

4

2

0

0.5

0.4

0.3

0.2

0.1

0

65

Potassium

Lithium

Pressurized Water Reactor Primary Water Chemistry Guidelines, Volume 1, Revision 7. EPRI,

Palo Alto, CA: 2013. 3002000505.

Potassium Hydroxide: A Potential Mitigation for AOA. EPRI, Palo Alto, CA: 1999. TE 114158.


Radiation Safety & Radwaste Challenges

For reactions reviewed, 42K is the candidate most likely to be problematic

– High energy gamma (1.5 MeV), half-life of 12.3 hours

– VVER operating experience indicates 42K is a significant contributor to radiation fields during operation

Could be significant benefits to tightening specifications on impurities in bulk KOH (e.g., Na)

Worker dose and waste issues must be addressed

– Internal dose from 40K (now that it’s produced by reactor operation)

– Impact on waste classification and disposal

IsotopeAbsorption Cross

Section (barn)

Natural

Abundance6Li 940 7.57Li 0.045 92.5

Li (1) 70.5 -

39K 2.1 93.340

K 35 0.0141

K 1.46 6.73

K (1) 2.1 -

Na (2) 0.53 -

42Ca 0.68 (3)

Notes

(1) Average cross section based on natural abundance

(2) 23Na is the only stable isotope of sodium

(3) 42

Ca is produced through the activation of 41

K

Activation pathways and production of important isotopes

needs to be addressed

39 40( , )K n K

39 38( , )K n p Ar

40 41( , )K n K

40 40( , )K n p Ar

41 42( , )K n K

42 42K Ca

23 24( , )Na n Na

23 22( , )Na n p Ne

Some Nuclear Reactions to Consider:


Qualification PlanShortest

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