platinum deposition modeling in bwr systems · epri, palo alto, ca: 2010. 1020875. protection from...

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

Susan Garcia (EPRI)

Joe Giannelli (Finetech), Jim Henshaw (NNL),

International Light Water Reactor Materials

Reliability Conference and Exhibition 2016

August 1 – 4, 2016

Platinum Deposition

Modeling In BWR Systems

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

Background

Majority of US BWRs are applying or planning to apply Online NobleChem™ (OLNC).

OLNC involves addition of a Na-Pt-hydroxide complex to the feedwater line of the system while the plant is at power.

Pt complex is not stable at high temperatures and decomposes to deposit Pt particles on system surfaces.

Pt on surfaces catalyse the removal of O2 and H2O2 by H2 which is also added to the feedwater.

O2 and H2O2 in BWRs can raise the electrochemical corrosion potential (ECP) of 304 and 316 stainless steels in these systems above the -230mV(SHE) required to mitigate stress corrosion cracking (SCC).

With Pt, provided there is molar excess of H2 over O2 + H2O2, the ECP remains < -230mV(SHE)


Background

Pt deposited as 10-50nm sized particles on system surfaces.

SEM Images - BWRVIP-238: BWR Vessel and Internals Project: On-Line NobleChem™ Electrochemical Corrosion Potential and Pt Loading Data Correlation for Plants. EPRI, Palo Alto, CA: 2010. 1020875.

Protection from SCC only where enough Pt deposited.

Important to know where and how much Pt is deposited on ex-core surfaces.

Benchmarked model required to estimate Pt loadings on inaccessible areas.


Plant Sampling Configurations

When injecting most plants monitor coolant Pt levels on the input line to the reactor water clean-up system (RWCU) via the mitigation monitoring system (MMS)

Some plants also sample coolant directly off the reactor recirculation system (RRS) line.


Multi-Box Model Representation of Main Circuit

LP

FC

UP MP

DC

JP RL

IB OB

CU

SL1

FWN FW

SL2

MMS(Mitigation Monitoring System)

BDMSBackup Deposition Monitoring System

LP

FC

UP MP

DC

JP RL

IB OB

CU

SL1

FWN FW

SL2

MMS(Mitigation Monitoring System)

BDMSBackup Deposition Monitoring System

Pt Injection

FC – Fuel Core

IB – Inner Bypass

OB – Outer Bypass

UP – Upper Plenum

MP – Mixing Plenum

FW – Feed Water System

FWN – Feed Water Nozzle

DC – Downcomer

JP – Jet Pump

LP – Lower Plenum

RL – Recirculation Line

CU – Cleanup Unit

SL1 – Sample Line of CU

SL2 – Sample Line of RL

The BWR circuit can be represented as a series of segments with flow in and out.

Model Pt movement between sections and deposition/release to section surfaces


Basis of Model

Initial Assumptions:

– Pt in bulk coolant converts to 10nm sized particles rapidly

– All particles the same size

– Particle size such that inertial transport processes not important (mass transport treated as for molecular type species)

– Deposition rate proportional to concentration of Pt in coolant

– Release rate from surfaces proportional to Pt loading


Initial Multi Box Model Equations

Pt Transport from one reactor section to another +

deposition, represented by the mass balance equation:

iii

i

ii

i

iii AJc

mc

m

dt

dcV

1

1

1

i – Section (e.g. MP, DC….), mi - Mass flow rate, i Water density, Vi - Section volume,

Ai – Section surface area. Ji is the Pt deposition flux to surfaces (gm-2s-1) given by

i

i

i

i

i skckJrd

ii

iii skck

dt

dsrd

si is the surface coverage, and are deposition and release constants.

Pt surface coverage si is then given by

i

dk

i

rk


Multi Box Model Equations – Fuel Cannel

Fuel channel is split into 25 subsections, transport between sections given by

Deposition term in Ji enhanced by boiling

iii

i

ii

i

iiii AJc

)x(c)x(

mdt

dc)y(V

111 1

1

1

yi is the void fraction of the section, xi the flow quality and m the mass flow rate into

the fuel channel


BWR Plant Data for Comparison

Initial focus on plants implementing OLNC with no previous noble metal chemical additions

Plant Initial HWC Initial OLNC

Cofrentes Mar-97 Apr-10

Fermi 2 Sep-97 Mar-11

Grand Gulf May-99 Nov-10

Leibstadt (KKL) Sep-08 Nov-08

River Bend Dec-01 May-10

Model inputs: surface areas, volumes, core/cleanup/feedwater flow rates, core voidage etc.


BWR Plant Data for Comparison

Model compared with several different types of plant data

Coolant Pt measurements v Time (All plants)

Pt loadings on samples in MMS and Backup Deposition Monitor

Fuel clad Pt loadings (KKL)

Surface scrapes from:

– Dry tubes (Grand Gulf)

– N-9 nozzle thermal sleeve (KKM)

– Core Shroud O.D. (LaSalle 1)

– Downcomer Surveillance Capsules (Perry)

– Latch (NMP1)


Modelling Results

Simple Pt particle deposition/release model does not work:- Predict surface coverage correctly then Pt coolant v time predictions incorrect

- Predict Pt coolant v time correctly, surface coverage incorrect.

Had to assume some Pt particles more firmly held than others (two types of Pt particle)

Pt(coolant) + S S-Pt ‘S-Pt

S – surface, S-Pt loosely held Pt, ‘S-Pt tightly held PtMaybe related to two different attachment sites, particle sizes,

growth of Ni/Fe oxide, attachment as particulate Pt(nm sized) or Pt on Fe/Ni particles in coolant


Typical Model - Inputs

BWR section areas/volumes

Pt feed rate: 3g/h

Feedwater flow: 14.1x106 lb/h

Feedwater line: 30m long, 0.3m diameter (no data)

Feedwater nozzle: 0.3m long, 0.025m diameter

Clean up flow: 1.5x105lb/h

Cleanup Line: 100m long, 0.1m diameter

Sample line: length 65ft, diameter 1inch

Sample line flow rate: 0.022kgs-1

Full power core flow: 12.1x103kgs-1

Core power, voidage and quality distributions needed (generic values used)


Model Results – Coolant Pt

Coolant Data at Cofrentes, first OLNC

Decay rate slower than clean-up rate, Pt released slowly after Pt

injection stops

Injection Stops



Coolant Data at Cofrentes, second OLNC application

Injection Stops



KKL Coolant Data


Model Results – MMS Coupon Samples

Cofrentes Steel MMS data

Sample 1 was 84 days exposure, Sample 2 405 days, Sample 3 551 days


Model Results – MMS Coupon Samples

KKL Deposition Monitoring Data

Greater pickup on Backup Deposition Monitor, suggesting significant Pt loss

on cleanup and sample lines to MMS skid


Model Results – Fuel Scrapes

KKL Fuel Clad Deposition Data

Currently model is a crude representation of the core, wouldn’t

expect a reasonable comparison.


Model Predictions of Plant Behaviour

0.00E+00

5.00E-02

1.00E-01

1.50E-01

2.00E-01

2.50E-01

3.00E-01

3.50E-01

4.00E-01

Core Bypass Outer Bypass Upper

Plenum

Mixing

Plenum

Downcomer Recirculation Jet Pump Lower

Plenum

Reactor

Water Clean

Up

Sample Line

1 - RWCU

Location

Su

rface C

overa

ge o

f P

t m

g/c

m2

Relatively even distribution of Pt around ex-core circuit


Summary of Pt Deposition Modelling

OLNC is being increasingly adopted by the BWR industry

Pt is only effective in protecting from SCC where it deposits

Developed Pt transportation deposition-release model

Accumulated significant amount of Pt plant data

Model fitted to OLNC data from Cofrentes, Grand Gulf and KKL

Model comparisons with plant data reasonable

Difficult to account for plant observations with simple deposition-release model, results suggest fraction of Pt held very firmly to surfaces (mechanism unclear)

Gradual increase in coolant Pt consequence of rapid uptake of injected Pt – model indicates a significant fraction of injected Pt deposits in the core

Model suggests on ex-core surfaces Pt relatively evenly distributed around the system

Further development of the model and comparisons with plant data planned


Together…Shaping the Future of Electricity

platinum deposition modeling in bwr systems · epri, palo alto, ca: 2010. 1020875. protection from...

Documents