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1 | Survey of Vattenfall's Experience with Mixed Cores in Ringhals PWRs | Gabrielsson, Stepniewski | 2011.12.12

Survey of Vattenfall’s Experience with Mixed Cores in Ringhals PWRs

IAEA Technical Meeting on Fuel Design and Licensing of Mixed Cores for Water Cooled Reactors 2011-12-12 Petter Gabrielsson, Marek Stepniewski, David Schrire, Jan Almberger Vattenfall Nuclear Fuel

Vattenfall - Markets and Position in Europe

Offshore wind power no. 2 955 MW on land 772 MW offshore

Technological development Wave energy & CCS

Hydro power no. 3 34.6 TWh

Biomass no. 5 1 TWh

Electricity production no. 6 159 TWh inc. 41.5 TWh nuclear

Trading no. 5 Presence in the most important trading markets

Heating production no. 1 37.9 TWh

Electricity distribution no. 6 7.5 million private customers 5.6 million network customers

Core markets

Ringhals NPP

Ringhals 2 Westinghouse 3-loop PWR 15x15

Siemens/KWU SG 1989 Commissioned in 1975 2652 MWt / 866 MWe


AREVA SG 2011 Commissioned in 1983 2775 (3300) MWt / 935 MWe


Framatome/Siemens SG 1995 Commissioned in 1981 3144 MWt / 1043 MWe

Ringhals 1 ASEA-ATOM BWR Commissioned in 1976 2540 MWt / 840 MWe


Presentation Outline

1. Vattenfall’s Strategy for Purchase and Qualification of New Fuel

2. Mixed Core Considerations for Qualification of New Fuel

3. Survey of Past and Present Mixed Core Situations in Ringhals PWRs

4. Conclusions


1. Vattenfall’s Strategy for Purchase and Qualification of New Fuel


Strategy for Fuel Purchase

• Fuel manufacturing for all Vattenfall’s 7 reactors in Ringhals and Forsmark is purchased by Vattenfall Nuclear Fuel (VNF) every 4 years - Economy of scale - Competition between the vendors

• Reload fuel is chosen on commercial basis, given that offered fuel

designs fulfill the technical requirements - Functional compatibility with the plant - Licensability

• The main goals are

- Improved fuel performance - Competitive price

• As a result, mixed core situations are frequently recurring

Strategy for Fuel Qualification

• In the past Fuel Purchase projects always resulted in a need for several parallel projects for Qualification of New Fuel - Heavy work load - Licensing risks

• To avoid this situation Vattenfall’s modified strategy is to have all

potential reload fuel designs qualified in advance of Fuel Purchase - Several Lead Use Assembly (LUA) projects now ongoing - In line with requirement from the Swedish Radiation Safety Authority

(SSM) for new fuel designs • At least 2 years Lead Use before Reload


Qualification process

Vendor design

VNF review

Ringhals review

SSM review


2. Mixed Core Considerations for Qualification of New Fuel

• Fuel Performance in mixed core - Fuel operating experience and design evaluations - Geometrical compatibility - Mechanical design

• Safety Margins in mixed core - Thermal-hydraulic design - Fuel rod design - LOCA hot rod analysis


Scope of Vendor’s Mixed Core Evaluations


• Fuel operating experience - Previous evidence of Functional Compatibility in mixed core - Signs of Flow Induced Vibrations - Fuel handling issues

• Geometrical compatibility with - Resident fuel

• Axial location of spacers and IFMs • Assembly growth • Lateral gaps • Risk for grid snagging • Length and position of fuel column

- Vessel internals - Handling equipment and procedures - Core instrumentation - Control rods - Dry and wet storage racks

Fuel Performance Evaluation (1)

Fuel Performance Evaluation (2)

• In Mechanical Design evaluations, the following mixed core aspects need to be considered: - Flow redistribution impact on

• Hydraulic Lift Forces / Mechanical Hold-down Margin - Risk for Lift-off vs. Risk for increased Fuel Assembly (FA) bow

• Cross Flows - Risk for Flow-Induced-Vibrations and Fretting wear

- Differences in FA stiffness and spacer positions may impact on • Propagation of forces on FAs from postulated LOCA + earthquake

- Risk for impact on Core Coolability


Safety Margins Evaluation

• Safety Margins are evaluated with respect to: - Parity with reference fuel in the Safety Analysis Report (SAR)

• Based upon Safety Analysis boundary conditions provided in the Interface Document for Fuel Licensing (IDFL)

- Impact of flow redistribution in mixed core • Based upon Fuel Data for resident fuel, disclosed by vendor • Pressure Loss Coefficients (PLC) are crucial inputs for the evaluation

- Comparability between fuel designs and vendors must be ensured • Flow test set-up and post-processing of experimental results

Need to establish PLC standardization requirements for vendors

Availability and completeness of the IDFL is a prerequisite

Mixed core flow tests would be useful


Safety Parameters Affected by Use of New Fuel Design

Affected Safety Parameters • Core flow • Bypass flow • Critical Heat Flux:

- SAL-DNBR, - Core Thermal Limits, - Transient minDNBR

• Linear heat rate limits • RIA enthalpy limits

• LOCA PCT, LMO, CWO

Provisions in Safety Analysis Report • Flow operating window ±2% • Bounding GT bypass assumed (4%)

- 5-10% generic DNB margin

• None required, verified only in RSE • None, low oxidation material required

• None, except SAR margin to criteria


Mixed Core Penalties

• Mixed core penalty on DNBR is determined based upon - Conservative mixed core configuration - Bounding thermal-hydraulic conditions from IDFL

• If DNBR Mixed Core Penalty > Generic DNB margin - Define reduction of allowable radial peaking factor (FΔH) or - Renew bounding safety analyses with revised assumptions and/or more

advanced methods • Mixed core penalty on LOCA PCT is determined based upon

- LOCA hot rod calculation or partial LOCA reanalysis • If PCT Mixed Core Penalty > Available PCT margin in the SAR

- Define reduction of allowable total peaking factor (FQ) or - Define reduction in power level or - Renew LOCA analyses with revised assumptions and/or more advanced

methods

Generic margins in the SAR are recommended for flow, DNB and PCT


3. Survey of Past and Present Mixed Core Situations in Ringhals PWRs


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

Year

Frac

tion

KWU

W P+IFMTP removalZIRLOBE LOCA

AFA 3G/AGORA 5A

W 15x15 UPGRADE

AGORA 5A/Q12

Ringhals 2 Core Composition (schematic)


Transition from KWU to Performance+ Fuel Design

• KWU 15x15 fuel - Ringhals 2 reload fuel until 1994

• Westinghouse’s Performance+

- Ringhals 2 reload fuel from 1995 to 2002 - Novelties: IFMs - SAR update for Increased Peaking Factors and Thimble Plug removal

• FΔH increased from 1.65 to 1.75 • 10% generic DNB margin to offset mixed core penalty • Best Estimate LOCA analysis, FQ increase 2.34 to 2.50

- Total PLC almost 20% higher than for KWU • Significant cross flows • Low lift force and excessive hold-down force on Performance+ ► Possible contribution to development of FA bow • FA bow confirmed during outage 2000

Transitions to AFA-3G/AGORA 5A and 15x15 Upgrade

• Framatome/AREVA’s AFA 3G/AGORA 5A - Ringhals 2 reload fuel from 2003 to 2011 - Novelties: All M5 construction - Important similarities with Performance+:

• Same CHF correlation (WRB-1) • Similar PLCs

►No severe mixed core effects

• Westinghouse’s 15x15 Upgrade - Ringhals 2 reload fuel from 2012 - Novelties: Optimized Zirlo cladding - Important similarities with AFA 3G/AGORA 5A

• Same CHF correlation (WRB-1) • Similar PLCs

►No severe mixed core effects



0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

Year

Frac

tion

AFA 2G

Optimized AFA 2GLow er hold-dow nStronger guide tubesReinforced dashpot

AFA 3GIFMMonoblocM5

HTPDuplexM5Monobloc

RFA-2

GAIA




0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

Year

Frac

tion

AFA 2G

Optimized AFA 2GLow er hold-dow nStronger guide tubesReinforced dashpot

AFA 3GIFMMonoblocM5TP removal HTP

DuplexM5MonoblocAll M5 LFA RFA-2

NGF

Transition from AFA-2G to AFA-3G Fuel Design

• Framatome’s AFA-2G - Ringhals 3/4 reload fuel until 1998

• Framatome’s AFA-3G

- Ringhals 3/4 reload fuel from 1999 to 2002 - Novelties: IFMs, M5 cladding - No SAR update - Total PLC around 5% higher than for AFA-2G - Mixed core penalty offset by improved thermal performance with IFMs

• Plus additional DNB margin exceeding 10%

- LOCA analyses revisited for investigation of M5 cladding behavior • Small PCT penalty

- Cross flows measured in flow tests with AFA-2G • Confirmed within bounds for risk of Flow Induced Vibrations

►Clean case, Framatome vendor of both designs and safety analyses


Transition from AFA-3G to HTP Fuel Design

• Siemens/Framatome-ANP/AREVA’s HTP X5/M5 - Ringhals 3/4 reload fuel from 2003 to 2010/2011 - Novelties: SNP-1 CHF correlation, resistance to FA bow - In 2003 HTP was thought to have lower PLC than AFA 3G

• New vendor measurements resulted in the opposite ► PLC non-conformance • Impact on DNB, PCT and lift forces reevaluated in 2006

- In 2007 Ringhals 3 SAR analyses were updated to cover 13% power uprate, peaking factor increase, thimble plug removal, FA bow • Safety Analyses performed by Westinghouse for RFA-2 as reference fuel • AREVA had to show safety margin parity for HTP ► Limiting DNB and PCT evaluated based on IDFL ► FΔH penalty on HTP avoided by reanalysis of two limiting transients


Transition from HTP to RFA-2 Fuel Design

• Westinghouse’s RFA-2 - Ringhals 3/4 reload fuel from 2011/2012 - Novelties: WRB-2M CHF correlation - In 2011 Ringhals 4 SAR analyses were updated to cover Steam

Generator (SG) Replacement, 18% power uprate, peaking factor decrease, thimble plug removal, FA bow • Analyses performed by AREVA for AGORA-7H (=HTP all M5) • Westinghouse (W) has to show safety margin parity for RFA-2 ► IDFL did not support W’s LOCA Hot Rod PCT analysis ► Low PCT margin in the SAR < Mixed core penalty ? • Possible solutions are being discussed with W

- Inconsistencies in calculation of PLCs identified and adjusted • Mixed core DNB penalty on HTP evaluated by Vattenfall ► Generic margin and power margin credited for HTP



4. Conclusions

Outcome of Mixed Core Operation in Ringhals

• Vattenfall’s ability to qualify fuel for mixed core operation enables selection of the fuel designs that - Are most economical and/or - Provide most significant improvements in fuel performance

• There are no confirmed negative consequences of mixed core

operation in Ringhals PWRs - Occurrences with spacer damages not primarily connected to

differences in spacer designs. - Mixed core conditions may however have assisted the development of

FA bow in Ringhals 2



Measures For Successful Mixed Core Qualification

• To facilitate verification of parity with the reference fuel in the SAR, an Interface Document for Fuel Licensing (IDFL) is necessary. - Completeness and usefulness for other vendors must be ensured.

• To allow offsetting minor differences in thermal performance, and mixed core penalties, Generic DNB and PCT Margins should be included in the SAR, as well as provision for variations in core coolant flow.

• To ensure unbiased thermal-hydraulic evaluations, a standardized procedure for definition of Pressure Loss Coefficients for Mixed Core Studies is suggested.

• To confirm analytical results regarding cross flow/flow redistribution, Mixed Core Flow Tests would be useful.

• To enable safety margin verifications, Competing Vendors should not unnecessarily withhold crucial fuel or analysis data from each other.

• Active Design Review, including independent calculation of key data.

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