French NPPs Filtered Containment Venting Designisnatt.org/Conferences/33/Monday/French NPPs Filtered...

International Society for Nuclear Air Treatment Technologies33rd Nuclear Air Cleaning Conference ● June 22-24, 2014 ● St. Louis, MO ABC Company

French NPPs Filtered Containment Venting Design

Serge M. GuieuElectricité de France, Service Etudes et Projets Thermiques et Nucléaires

Villeurbanne, France

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Content• Brief Historical • Research and development

– PITEAS and FUCHIA programs– Metallic pre-filter R&D– Present R&D

• Design– Basic design requirements– Complementary design requirements– Situation following Fukushima Daiichi

• Conclusion: FCVS installed on NPPs

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Brief Historical (1/2)

Filtered Containment Venting is a long-story in France (roughly 40 years)

• Oct. 1975: “Rasmussen Report” (WASH 1400 – “Reactor Safety Study”) publication– 5 potential modes for containment rupture

risk, in particular by slow internal pressurization ( mode)

– Beginning of French studies (CEA) and R&D (CEA and EDF) concerning Severe Accidents

• March 1979: TMI 2 accident3


Brief Historical (2/2)• April 1986: Chernobyl 4 accident

– EDF decision to install FCVS on all NPPs (letter to ASN dated July 31st, 1986)

• To limit ground long-term contamination by caesium (especially Cs-137, half-life ~ 30 years)

• ~1995– FCVS installation completed on all NPPs

• March 2011: Fukushima Daiichi accident– Re-interrogation concerning FCVS pertinence

and design Note: no FCVS is installed on French EPR in construction at Flamanville

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Research and Development

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General overview• Validation of sand bed filter

‒ PITEAS Program: determination of sand bed filtration parameters (1982-1986)

• Tests performed at small / intermediate scale

‒ FUCHIA Program: validation of FCVS at full scale (1990)

Tests performed at Cadarache CEA Research Centre

• Validation of metallic pre-filter– Determination and design of filtering media

(1990-1993)Tests performed at Saclay CEA Research Centre

and PALL Laboratories (Portsmouth, UK)

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PITEAS Program (tests conditions)• DF objective

‒ For aerosols: DF > 10• Main tests conditions

– Filtration medium: sand (0.45 to 1.6 mm diameter)• Height: 80 cm• Diameter: 20 cm (laboratories / small scale tests), 1 m (pilot

loop / intermediate scale)

– T: 140°C, P: ~ atmospheric– Gas (mass) composition: 68% air, 32% steam– Filtration speed: 10 cm/s (reference value)– Aerosols: Cs2CO3 (AMMD: between 0.6 and 1.5 m)– Filter pressure drop: max 100 hPa

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PITEAS Program (results)

• Sand so-called “from Cattenom” with mass median diameter 0.6 mm and standard deviation less than 2 is selected:– Minimum DF objective for aerosols (10)

including transient operating conditions with filtration speed between 7 and 14 cm/s

– Filter pressure drop less than 100 hPa

Note (trapping of molecular iodine - I2 -)Unique test performed cannot support justification for sand bed capacity to trap I2

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Typical results for steady-state conditions



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Typical DF variation during transient operating conditions(68% air, 32% steam, aerosols 2.15 m AMMD)


FUCHIA Program (test conditions)Full scale test of FCVS as installed on sites (without preheating nor pre-filter)

• Gas mixture– Composition (mass): 35% air, 65% steam– Flow rate: 3.03 kg/s (17,800 m3/h at 0.1 MPa, 140°C)– 0.5 MPa, 140°C at the entrance of the system

• Sand bed– Height: 80 cm, average diameter: 0.6 mm– Filtration velocity: 11.8 cm/s

• Aerosol: CsOH (AMMD ~1m)

• Molecular iodine

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FUCHIA Program (schematic diagram)

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FUCHIA program (facility)

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FUCHIA Program (facility)

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FUCHIA Program (General Aim 1/2)• Thermo-hydraulic tests with nominal flow

rates of steam and air without aerosols nor iodine (24 hours)

• Efficiency tests with nominal flow rates of steam and air with aerosols and iodine (50 hours: 25 hours with CsOH and I2, 25 hours without)Note: At this time, no pre-filter has been designed, so two configurations has been tested: (1) system fully insulated (final situation on NPPs), (2) sand bed filter partially insulated (only up to sand bed upper level) in order to allow natural residual heat removal after FCVS closure

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FUCHIA Program (General Aim 2/2)• Thermal tests

– Fully insulated: constant decay heat (simulated) and air sweeping (2 t/h)Salting out measurement (12 days)

– Partially insulated: decreasing decay heat (simulated) and no air sweeping (12 days)Only thermal behavior

– Partially insulated: decreasing decay heat (simulated) and air sweeping (1.65 t/h)Salting out measurement (~3 months)

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FUCHIA Program (Main Results)

• Thermo-hydraulic tests– PITEAS results confirmation: no clogging during

steam condensation, sand pressure drop < 100 hPa

• Efficiency tests– DF > 100 for aerosols – DF for I2: 27 fully insulated, 9 partially

• Salting out results– Very low for CsOH, significantly higher for I2

• 2 / 4% (12 days tests), 19% (3 months test, but I-131half-life ~ 8 days)

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Metallic Pre-filter (1/3)

• Main result– Particular behavior of metallic media when

filtering hygroscopic aerosols such as CsOH• In dry air: low and linear increase of pressure drop

versus collected mass• In air plus steam mixture: very low pressure drop

at the beginning followed by strong increase leading to flow rate blockage

– With insoluble aerosols such as TiO2: same behavior with dry air and air plus steam mixture (low and linear increase)

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Hygroscopic aerosol behavior Insoluble aerosol behavior



• Aim of R&D– According to main experimental result and

additional computer calculations (see “design part”)• To determine type and filtering area

Tests performed at Saclay CEA Research Centre and Pall Laboratories (Portsmouth, UK)

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Present R&D on FCVS• Since the beginning of 2013, EDF participates to

EU Project PASSAM coordinated by IRSN – To explore potential enhancement of existing source-

term mitigation– To demonstrate the ability of innovative systems to

achieve larger source-term attenuation– Concerning French FCVS: experimental tests

program performed by IRSN• To check the efficiency of sand bed filters and metallic pre-

filters to trap gaseous iodine (particularly ICH3) during FCVS representative conditions

• To check the performance of those retention media in the mid and long term (stability of trapped FP, particularly iodine)

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Design

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Basic Design Requirements (1/4)• Historically from CEA SA calculations (AB

and TLMB sequences) at the end of 70’s for PWR 1300 MWe

• Basic data (1/2)– Maximum gas flow rate: 3.5 kg/s– RB pressure: 0.5 MPa abs. (design pressure)

– RB temperature: 140°C– Density (at 0.5 MPa): 4 kg/m3

– Gas composition (mass): 33% air, 29% steam, 33% CO2, 5% CO

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Basic Design Requirements (2/4)• Basic data (2/2)

– Aerosols:• Mass in containment atmosphere: 5 kg (FP without

MCCI)• AMMD: 1 – 5 m

Although data available for SA sequences have been considerably improved the above set of data remains the “reference design value” for French FCVS (except for aerosols which needs to take into account MCCI, for pre-filter design for example)

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Basic Design Requirements (3/4)• System design requirements (mid-1986, just

before decision of installation) (1/2)– Sufficient DF for aerosols to limit ground long-term

contamination (initially > 10 according to PITEAS R&D program)

– To avoid in steady-state conditions any condensation (to avoid clogging and water storage and treatment)

• Expansion of the mixture very upstream in the system

• Thermal insulation• Gas exhaust via an independent small diameter

duct (400 mm) inside the normal stack

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Basic Design Requirements (4/4)• System design requirements (mid-1986, just

before decision of installation) (2/2)

– No incidence of FCVS on Plant normal operation

– Use of electrical sources kept to a strict minimum level (only when technically necessary)

– Monitoring of radioactivity release– Conditioning of the circuit during normal

operation (corrosion protection)

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Complementary Design Requirements(general)

• Detailed design phase following decision of installation– Hydrogen combustion transient risk at the

opening– Sand bed filter being located on the roof of an

auxiliary building, important FP mass trapped in the sand

• Important radiation dose rate on the site (particularly by “skyshine effect”)

• Natural evacuation of heat generated not possible after closure of FCVS (if totally insulated)

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Complementary Design Requirements(Hydrogen risk at the opening 1/2)

• Originally: condensation on cold structure could lead to H2 enrichment and the mixture could become combustible– Although combustion is not obvious (lack of

explicitly identified ignition source) decision (1988) to install an electrical preheating system prior to opening at the beginning of FCVS installation

Note: PARs installation has drastically reduced (quite eliminated) this risk but in a deterministic way it could subsist for particular SA sequences (late loss of core cooling before FCVS opening)

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Complementary Design Requirements(Hydrogen risk at the opening 2/2)

• After PARs installation: additional transient combustion risk at the opening – In case of “sufficient” MCCI PARs recombination

process could be stopped due to lack of Oxygen• At FCVS opening risk of H2 (and CO) transient

combustion risk due to mixing of H2 and CO with FCVS atmosphere containing O2

– Very transient situation (~ 1 min compared to ~ 1 hour for the previous situation)

– Studied in the general frame of limiting and possibly avoiding base mat penetration by MCCI

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Complementary Design Requirements(To reduce FP trapped in sand bed filter 1/2)

• Solution: metallic pre-filter installed inside RB– Design objective (and advantage for off-site

releases which explains the choice of this technical solution)

• DF for aerosols > 10– Designed using R&D program (hygroscopic

aerosols behavior) completed by SA calculations performed by IRSN using AEROSOLS B2 code

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Complementary Design Requirements(To reduce FP trapped in sand bed filter 2/2)

• Two typical SA sequences considered– SA sequences without MCCI conservatively modeled

(for filtration purpose) by hygroscopic aerosols• To trap a mass of FPs supposed to be only CsOH far

away from flow rate blockage risk– SA sequences with MCCI: aerosols are composed

mainly with (non active) non hygroscopic aerosols (from MCCI) mixed with hygroscopic aerosols (modeling active FP)

• To trap sufficient mass of aerosols so that FP content in the containment atmosphere has been divided by 10. After the pre-filter can be by-passed

Practically the pre-filter is not by passed untill pressure drop reaches 0.1 MPa

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Situation following Fukushima Daiichi

• ASN requirements following stress tests”(Particularly “ECS-29”)– EDF letter dated December 19th, 2013

• To keep a closed containment even in case of SA including core melt for limiting as much as possible radiological releasesPractically: to implement dedicated means to remove decay heat from the containment with a recirculation loop cooled by a dedicated heat sink

• In the frame of “defense in depth”, to ensure ultimate protection of containment, seismic resistance of FCVS presently installed will be increased

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Conclusion: FCVS installed on French NPPs

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FCVS schematic diagram

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Sand bed filter

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EDF patented diameter: 7.32 m, height: 4 mWeight: 12 metric tons (empty), 92 metric tons (operational)


Filtration efficiency• Following all R&D programs

– DF for aerosols > 1000 (> 100 for sand bed filter, > 10 for metallic pre-filter)(value taken into account in safety studies)

– DF for I2 > 10• Detailed analysis of FUCHIA results has shown that I2

is mainly trapped by deposition on the internal surfaces of pipes. The minimum value of 10 takes into account minimum existing pipe length (practically, for all plants, DF is between > 10 and > 100)This minimum value takes also in account experimental uncertainties during FUCHIA program and salting out

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Associated Operating Procedure (“U5”) (1/2)

• General philosophy– To practically eliminate containment failure risk due to

slow pressurization following loss of Safeguard Systems and ground long-term contamination

• Opening of FCVS when internal absolute pressure reaches a value between design value (~ 0.5 MPa) and “ultimate resistance” (0.6 to 0.7 MPa including all singularities such as hatches)

But safety is fundamentally based on the confinement of FP in containment and this not modified by FCVS installation

• Consequently opening of FCVS has to be considered as an ultimate protection of the containment integrity and postponed as long as possible and avoided as much as possible

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Associated Operating Procedure (“U5”)(2/2)

• Main principles– Opening is a concerted action

• In respect to safety general philosophy (see before) • To avoid early (inappropriate) opening due to

transient phenomenon such as H2 combustion(consequently no automatic actuation using, for example, rupture disk)

– Due to important RB free volume opening of FCVS is not necessary before one day after the onset on the accident allowing protection of the population before FCVS opening (sheltering, distribution of non radioactive iodine, evacuation)

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