Latest Results from Source T

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F-

*Corresponding ABSTRACT

Source term research has continued internationally for more than 30 years, with the overall aim of increasing confidence in the methods used in calculating the

radioactive release to the environment after a severe reactor accident. Important data have been obtained

EURATOM studies provide

containment iodine chemistry, which

codes like ASTEC 2.1, MELCOR 2.1 and MAAP such as ISTP

interpreted with a view to further improvements in code capability This paper synthesis

topics, and

discusses ways to proceed, addressing those items considered high priority. The bases for this article come from the

NUGENIA

Two major issues generally affect experimental data from source term research:

analytical exploitation and scale oxidising environmen

103/106, are considered of utmost interest. For transport, potential revolatilisation of fission products embedded in deposits needs further study. Containment iodine chemistry is extensively investigated

evaluation. For mitigation, long term filter

capabilities to remove Ru and the scrubbing capacity of pools undergoing satu further research. Aside from further knowledge

need to assess the source term predictive ability of current system codes.

1 INTRODUCTION

Accurate calculation of the potential radioactive source term to the environment in the event of a severe accident in a nuclear power plant is of vital importance regarding public

Tim Haste*

Centre d'Etudes de Cadarache -13115 St-Paul

tim.haste@irsn.fr

*Corresponding author ABSTRACT

radioactive release to the environment after a severe reactor accident. Important data have been obtained

EURATOM European Framework Program studies provide major

containment iodine chemistry, which

codes like ASTEC 2.1, MELCOR 2.1 and MAAP such as ISTP, EC

interpreted with a view to further improvements in code capability This paper synthesis

, and on source term mitigation. It highlights the knowledge gaps remaining and discusses ways to proceed, addressing those items considered high priority. The bases for this article come from the

NUGENIA technical area 2

analytical exploitation and scale ing environmen

103/106, are considered of utmost interest. For transport, potential revolatilisation of fission products embedded in deposits needs further study. Containment iodine chemistry is

ensively investigated

evaluation. For mitigation, long term filter

INTRODUCTION

Tim Haste*

IRSN

Centre d'Etudes de Cadarache Paul-Lez-Durance, France tim.haste@irsn.fr

author

radioactive release to the environment after a severe reactor accident. Important data have been obtained, mainly under international frameworks such as OEC

European Framework Program

major insights into fission product release and transport and, particularly, containment iodine chemistry, which

codes like ASTEC 2.1, MELCOR 2.1 and MAAP C/PASSAM and

interpreted with a view to further improvements in code capability

This paper synthesises the recent main outcomes from source term research

source term mitigation. It highlights the knowledge gaps remaining and discusses ways to proceed, addressing those items considered high priority. The bases for this article come from the most recent

technical area 2 (Severe Accidents).

analytical exploitation and scale

ing environments potentially leading to increased release of harmful nuclides, like Ru 103/106, are considered of utmost interest. For transport, potential revolatilisation of fission products embedded in deposits needs further study. Containment iodine chemistry is

ensively investigated experimentally evaluation. For mitigation, long term filter

INTRODUCTION

Luis E. Herranz Avda. Complutense 40 ES-28040, Madrid, Spain luisen.herranz@ciemat.es

Centre d'Etudes de Cadarache Durance, France tim.haste@irsn.fr

radioactive release to the environment after a severe reactor accident. Important mainly under international frameworks such as OEC European Framework Program

insights into fission product release and transport and, particularly, containment iodine chemistry, which are

codes like ASTEC 2.1, MELCOR 2.1 and MAAP PASSAM and OECD/BIP&BIP2

es the recent main outcomes from source term research

source term mitigation. It highlights the knowledge gaps remaining and discusses ways to proceed, addressing those items considered high priority. The bases for this

most recent workshop held in 2015 on source (Severe Accidents).

analytical exploitation and scale-up to reactor conditions

ts potentially leading to increased release of harmful nuclides, like Ru 103/106, are considered of utmost interest. For transport, potential revolatilisation of fission products embedded in deposits needs further study. Containment iodine chemistry is

experimentally evaluation. For mitigation, long term filter

Luis E. Herranz CIEMAT Avda. Complutense 40

28040, Madrid, Spain luisen.herranz@ciemat.es

Durance, France

radioactive release to the environment after a severe reactor accident. Important mainly under international frameworks such as OEC European Framework Programmes. In particular, Phébus FP

insights into fission product release and transport and, particularly, are encapsulated in

codes like ASTEC 2.1, MELCOR 2.1 and MAAP-EDF, while data OECD/BIP&BIP2

workshop held in 2015 on source (Severe Accidents).

to reactor conditions

in several OECD projects evaluation. For mitigation, long term filter behaviour

capabilities to remove Ru and the scrubbing capacity of pools undergoing satu

further research. Aside from further knowledge-driven research, there is consensus on the need to assess the source term predictive ability of current system codes.

Luis E. Herranz Avda. Complutense 40

28040, Madrid, Spain luisen.herranz@ciemat.es

Teemu Kärkelä

FI-02044 VTT, Espoo, Finland teemu.karkela@vtt.fi

radioactive release to the environment after a severe reactor accident. Important mainly under international frameworks such as OEC

In particular, Phébus FP

insights into fission product release and transport and, particularly, encapsulated in integral

EDF, while data OECD/BIP&BIP2, THAI&THAI2 interpreted with a view to further improvements in code capability

workshop held in 2015 on source

to reactor conditions. Concerning

in several OECD projects

behaviour regarding fission products, existing capabilities to remove Ru and the scrubbing capacity of pools undergoing satu

driven research, there is consensus on the need to assess the source term predictive ability of current system codes.

Teemu Kärkelä VTT Biologinkuja 7

02044 VTT, Espoo, Finland teemu.karkela@vtt.fi

radioactive release to the environment after a severe reactor accident. Important mainly under international frameworks such as OEC

In particular, Phébus FP

insights into fission product release and transport and, particularly, integral severe accident analysis EDF, while data from international

&THAI2, and STEM interpreted with a view to further improvements in code capability

workshop held in 2015 on source

. Concerning fission product release, ts potentially leading to increased release of harmful nuclides, like Ru 103/106, are considered of utmost interest. For transport, potential revolatilisation of fission products embedded in deposits needs further study. Containment iodine chemistry is in several OECD projects and the net results need

regarding fission products, existing capabilities to remove Ru and the scrubbing capacity of pools undergoing satu

driven research, there is consensus on the need to assess the source term predictive ability of current system codes.

Teemu Kärkelä Biologinkuja 7

02044 VTT, Espoo, Finland teemu.karkela@vtt.fi

Source term research has continued internationally for more than 30 years, with the overall aim of increasing confidence in the methods used in calculating the potential radioactive release to the environment after a severe reactor accident. Important experimental mainly under international frameworks such as OECD/NEA and the In particular, Phébus FP and associated insights into fission product release and transport and, particularly, severe accident analysis

international

and STEM are being es the recent main outcomes from source term research on source term mitigation. It highlights the knowledge gaps remaining and discusses ways to proceed, addressing those items considered high priority. The bases for this term issues under Two major issues generally affect experimental data from source term research:

fission product release, ts potentially leading to increased release of harmful nuclides, like Ru 103/106, are considered of utmost interest. For transport, potential revolatilisation of fission products embedded in deposits needs further study. Containment iodine chemistry is and the net results need regarding fission products, existing capabilities to remove Ru and the scrubbing capacity of pools undergoing saturation need driven research, there is consensus on the

02044 VTT, Espoo, Finland

Source term research has continued internationally for more than 30 years, with the potential experimental D/NEA and the and associated insights into fission product release and transport and, particularly, severe accident analysis international projects are being on these source term mitigation. It highlights the knowledge gaps remaining and discusses ways to proceed, addressing those items considered high priority. The bases for this rm issues under Two major issues generally affect experimental data from source term research:

fission product release, ts potentially leading to increased release of harmful nuclides, like Ru- 103/106, are considered of utmost interest. For transport, potential revolatilisation of fission products embedded in deposits needs further study. Containment iodine chemistry is and the net results need regarding fission products, existing ration need driven research, there is consensus on the

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safety. Research has continued internationally for more than 30 years, with the overall aim of increasing confidence in the methods used in calculating this release, especially with ever more demanding safety requirements in the light of events at Chernobyl and Fukushima.

Important experimental data have been obtained mainly under international frameworks such as OECD/NEA http://www.oecd-nea.org/nsd/, and EURATOM, e.g. the SARNET Network of Excellence under the 7^th Framework programme [2], which included source term studies [3]. Phébus FP and associated studies [4] provide outstanding insights into fission product release and transport and, particularly, containment iodine chemistry, which are encapsulated in recent versions of integral severe accident analysis codes like ASTEC 2.1 [5], MELCOR 2.1 [6] and MAAP-EDF [7], while data from international projects such as ISTP [8], EC/PASSAM [9] and OECD/BIP&BIP2, THAI&THAI2, and STEM [1] are being interpreted with a view to further code improvements. Nevertheless, some issues still remain and need addressing [10]. Generally speaking, forthcoming research should focus on processes yielding airborne radioactive materials hard to be filtered or resulting in unexpected releases in the later phases of severe accidents. Three major drivers for these investigations are:

 Upgrading existing mitigation devices and designing innovative ones on the light of the recent source term outcomes from projects like Phébus FP [4];

 Gathering a thorough understanding of some remaining key source term issues of safety significance, like gaseous iodine dynamics in containment [11], potential radiological impact of ruthenium [12] or pool scrubbing [3];

 Assessing current uncertainties affecting source term predictability when compared to available data [13] and, even further, when modelling severe accidents in nuclear power plants (NPPs).

In Spring 2015, the Source Term community of the SARNET Severe Accident technical area of NUGENIA,www.nugenia.org(this Association has integrated the SARNET network), held a meeting to review the current status of knowledge and to identify and discuss further needs and approaches necessary to implement in the coming years. This paper summarises the main outcomes and succinctly introduces the basic pillars of potential Horizon 2020 (H2020) European projects arising from these discussions. According to the latest structure used to deal with source term research, this is split into: release, transport, in-containment behaviour and mitigation, as dealt with successively below.

2 REMAINING SOURCE TERM ISSUES

2.1 Fission Products (FP) and core materials release

Since the TMI-2 accident this area has been the subject of many international R&D activities. Both separate-effect (HI/VI, AECL/CRL, VERCORS/VERDON, etc.) and integral experiments (PBF-SFD, LOFT-LP-FP, Phébus FP, etc.) have been conducted. Two major outcomes synthesise their results: FP classification according to volatility and identification of key variables for release kinetics [14], [15], [16].

Four groups are presently considered: volatile FPs (noble gases, I, Cs and others), which are released almost completely when reaching fuel melting; semi-volatile FPs (Mo, Ba, Rh and others) whose release potential may be as high as those for volatiles, but are highly dependent on oxygen potential (i.e., Mo shows a high volatility under oxidising conditions whereas Ba does under reducing ones); low-volatile FP (Sr, Ru, U and others), which release fraction is usually less than 10% but under certain circumstances (i.e. oxidising conditions for Ru) it might get to much higher values (30-40%) or even higher; non-volatile FP (Zr, Nd, the actinide Pu and others) that are scarcely released (less than 1%). Several variables govern FP

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release kinetics. Tempera oxygen potential, fuel burn significantly

experiments

environments (from reducing to oxidi

Figure 1:

VERCORS RT3 test normalized to the release reaction at 2200°C

Despite the sound

and coupling of the different phenomena it seem models

issues whose better and deeper knowledge could significantly enhance nuclear safety:

 Semi best s

both from fuel in a reactor core and from spent f

 Release of r would be in

releases from molten pools. This research might entail feedback for post management measures

 Release from MOX fuels, since shown

This issue is being studied in ISTP/VERDON Other data gaps, like volatile FP release under

but considered second order with respect to those mentioned above. Two aspects, however, that should be tackled in the upcoming investigation are data scaling and uncertainties.

Release data mostly come from small

applied to the much more complex configurations of NPP cores. Data are subject to uncertainties and their impact on final source term estimates should be assessed to have an actual measure of their rela

2.2 Fission Products (FP) and core material transport

Radioactive material transport through NPP circuits was largely explored in the past [21] and good knowledge was achieved. However,

and most significant insights as it used irradiated fuel in a scaled facility

Most FPs are transported through the primary circuit as particles (10 However, a fraction of the most volatile ones (I, Cs, Te and Rb) can remain in release kinetics. Tempera

oxygen potential, fuel burn significantly [14].

experiments [17],

environments (from reducing to oxidi

Figure 1: FP release kinetics in the VERCORS RT3 test normalized to the

release reaction at 2200°C Despite the sound

and coupling of the different phenomena it seem ls to improve

Semi- and low

best specific example of

both from fuel in a reactor core and from spent f Release of r

would be in

Release from MOX fuels, since shown that

considered second order with respect to those mentioned above. Two aspects, however, that should be tackled in the upcoming investigation are data scaling and uncertainties.

applied to the much more complex configurations of NPP cores. Data are subject to uncertainties and their impact on final source term estimates should be assessed to have an actual measure of their rela

Fission Products (FP) and core material transport

Radioactive material transport through NPP circuits was largely explored in the past and good knowledge was achieved. However,

and most significant insights as it used irradiated fuel in a scaled ([22] and references therein

Most FPs are transported through the primary circuit as particles (10 However, a fraction of the most volatile ones (I, Cs, Te and Rb) can remain in release kinetics. Temperature i

oxygen potential, fuel burn-up, fuel nature and material interactions that also . These factors are being investigated further

[18] which use environments (from reducing to oxidi

FP release kinetics in the VERCORS RT3 test normalized to the

release reaction at 2200°C

Despite the sound knowledge gathered through and coupling of the different phenomena it seem

prove computing codes used for safety evaluation

and low-volatile FP release under anticipated severe accident conditions. The pecific example of

Release of radioactive materials from configurations other than fuel rods. Examples would be in-vessel and ex

Release from MOX fuels, since that these fuel materials b

applied to the much more complex configurations of NPP cores. Data are subject to uncertainties and their impact on final source term estimates should be assessed to have an actual measure of their relative relevance in the whole set of source term uncertainties.

Fission Products (FP) and core material transport

and most significant insights as it used irradiated fuel in a scaled and references therein

Most FPs are transported through the primary circuit as particles (10 However, a fraction of the most volatile ones (I, Cs, Te and Rb) can remain in

ture is the main one, as shown in Figure

up, fuel nature and material interactions that also These factors are being investigated further

which use highly irradiated UO environments (from reducing to oxidising conditions

FP release kinetics in the VERCORS RT3 test normalized to the¹³⁷

release reaction at 2200°C, after [16]

knowledge gathered through and coupling of the different phenomena it seem

computing codes used for safety evaluation

volatile FP release under anticipated severe accident conditions. The pecific example of this would be

adioactive materials from configurations other than fuel rods. Examples vessel and ex-vessel corium reflooding that might cause Sr leaching of releases from molten pools. This research might entail feedback for post

management measures;

Release from MOX fuels, since the fuel materials b

Release data mostly come from small-sca

applied to the much more complex configurations of NPP cores. Data are subject to uncertainties and their impact on final source term estimates should be assessed to have an

tive relevance in the whole set of source term uncertainties.

Fission Products (FP) and core material transport

and most significant insights as it used irradiated fuel in a scaled and references therein).

s the main one, as shown in Figure

highly irradiated UO ing conditions

137Cs [16]

Figure 2:

Phébus FPT3 knowledge gathered through

and coupling of the different phenomena it seems necessary to develop mechanistic computing codes used for safety evaluation

volatile FP release under anticipated severe accident conditions. The this would be Ru release under oxidi

adioactive materials from configurations other than fuel rods. Examples vessel corium reflooding that might cause Sr leaching of releases from molten pools. This research might entail feedback for post

the database is much scarcer than UO fuel materials behave rather differently regarding This issue is being studied in ISTP/VERDON

Other data gaps, like volatile FP release under

scale tests and they are encapsulated in models that are applied to the much more complex configurations of NPP cores. Data are subject to uncertainties and their impact on final source term estimates should be assessed to have an

Fission Products (FP) and core material transport

and most significant insights as it used irradiated fuel in a scaled

0 1000 2000 3000 4000 5000 6000 7000

-1Cs-137PeakArea/Counts.min 2

s the main one, as shown in Figure

highly irradiated UO2 and MOX samples under different ing conditions, including air

Figure 2:¹³⁷ Phébus FPT3 knowledge gathered through research

necessary to develop mechanistic computing codes used for safety evaluation.

volatile FP release under anticipated severe accident conditions. The Ru release under oxidi

both from fuel in a reactor core and from spent fuel in spent fuel pools;

database is much scarcer than UO ehave rather differently regarding This issue is being studied in ISTP/VERDON [17].

Other data gaps, like volatile FP release under low temperature LOCA condi

s and they are encapsulated in models that are applied to the much more complex configurations of NPP cores. Data are subject to uncertainties and their impact on final source term estimates should be assessed to have an

Fission Products (FP) and core material transport

Radioactive material transport through NPP circuits was largely explored in the past and good knowledge was achieved. However, the Phébus FP project

and most significant insights as it used irradiated fuel in a scaled

2 77 152

N2 Steam

Residual Activity ~11%

slight revaporisation already from 300°C

Revap to 700°C = ~15%

Total Revap after change of gas @ 700°C: 75%

s the main one, as shown in Figure 1. But there are others, like up, fuel nature and material interactions that also

These factors are being investigated further in the IST

and MOX samples under different , including air).

137Cs revaporisation from the Phébus FPT3 vertical line

after [19]

research so far, due to the complexity necessary to develop mechanistic

. Moreover,

volatile FP release under anticipated severe accident conditions. The Ru release under oxidising conditions

in spent fuel pools;

database is much scarcer than UO ehave rather differently regarding

low temperature LOCA condi

Radioactive material transport through NPP circuits was largely explored in the past the Phébus FP project

and most significant insights as it used irradiated fuel in a scaled-down, heavily instrumented Most FPs are transported through the primary circuit as particles (10

However, a fraction of the most volatile ones (I, Cs, Te and Rb) can remain in

227 306 Time / mins

Ar

Residual Activity ~11%

Total revaporisation: ~90%

similar activity loss rates from 300 to 900

52% loss of remaining deposit on switching to reducing gas reducing to 32% in next ~7 mins

1. But there are others, like up, fuel nature and material interactions that also affect FP release in the ISTP/VERDON and MOX samples under different

revaporisation from the cal line V11-X sample

[19]

due to the complexity necessary to develop mechanistic multiscale there are still some issues whose better and deeper knowledge could significantly enhance nuclear safety:

volatile FP release under anticipated severe accident conditions. The ing conditions in spent fuel pools;

adioactive materials from configurations other than fuel rods. Examples vessel corium reflooding that might cause Sr leaching of releases from molten pools. This research might entail feedback for post-

database is much scarcer than UO2and it has been ehave rather differently regarding FP release

low temperature LOCA conditions exist, considered second order with respect to those mentioned above. Two aspects, however, that should be tackled in the upcoming investigation are data scaling and uncertainties.

Radioactive material transport through NPP circuits was largely explored in the past the Phébus FP project provided the latest down, heavily instrumented Most FPs are transported through the primary circuit as particles (10^-1-10

However, a fraction of the most volatile ones (I, Cs, Te and Rb) can remain in vapour

382 457 534

Time / mins

Ar - 6,5%H2 N

Total revaporisation: ~90%

similar activity loss rates from 300 to 900°C

52% loss of remaining deposit on switching to reducing gas reducing to 32% in next ~7 mins

change in revap kinetics?

1. But there are others, like FP release P/VERDON and MOX samples under different

revaporisation from the X sample, due to the complexity

multiscale are still some volatile FP release under anticipated severe accident conditions. The ing conditions [20], adioactive materials from configurations other than fuel rods. Examples vessel corium reflooding that might cause Sr leaching of -accident and it has been FP release [14].

tions exist, considered second order with respect to those mentioned above. Two aspects, however, that should be tackled in the upcoming investigation are data scaling and uncertainties.

Radioactive material transport through NPP circuits was largely explored in the past provided the latest down, heavily instrumented 10² g/m³).

vapour form in

0 200 400 600 800 1000 1200

Temperature/°C

N2

change in revap kinetics?

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the hottest regions and just noble gases and a fraction of iodine enter the containment in gaseous form. Particle composition depends on the core state, but it can be said to be [23]: 1/3 metals (e.g. Ag, In, Cd if these elements are present as control rod materials), 1/3 oxides (e.g.

SnO2, ZrO2, UOx) and 1/3 FP (according to Phébus FPT3, B can reach up to 10% of the mass entering the containment). Generally the phenomena governing FP transport (agglomeration, inertial deposition, sedimentation, thermophoresis etc.) are well characterised [24], but there are some phenomena not fully understood that might strongly affect the source term:

 FP revaporisation from deposits on circuit surfaces. The high likelihood of this phenomenon has been demonstrated experimentally under controlled conditions with deposit samples coming from the Phébus FP tests. Figure 2 shows Cs revaporisation sensitivity to temperature and carrier gas composition [19], [25];

 High temperature chemistry. Studies underway indicate that chemical interactions amongst FPs and with other materials (control rod and structural materials, primary circuit surfaces, air) might yield different speciations, and as a consequence transport properties, from those predicted by simple thermo-chemical calculations. Two specific issues being addressed are the effects of boron on FP transport, highlighted in the FPT3 test (and studied at small-scale in the ISTP/CHIP and VTT EXSI/PC tests), also that of Ag/In/Cd, and the potential Ru transport as a vapour species.

2.3 Containment

As stated in the research priorities defined by the SARNET community [10] most remaining high priority issues regarding in-containment source term are chemistry-related;

while aerosol physics under severe accident conditions in the containment are considered reasonably well understood and encapsulated in models, except for complex phenomena like pool scrubbing under specific conditions.

Up to the Phébus FP project the research done had resulted in a global view of in- containment iodine chemistry that, although still incomplete, seemed sound in its fundamentals [26]. The Phébus data, though, brought up some unexpected evidence that resulted in a new way of looking at iodine chemistry in containment, among them [27] the efficient trapping reaction of iodine and silver, the significant steady concentration of airborne iodine in the long run or the large gas fraction (higher than 80% in the FPT3 test [28]) that might enter containment in the presence of boron. In order to achieve a good understanding of the reasons for those and other observations, many projects have been conducted under the framework of the OECD in the recent years, as summarised in [3].

Good progress has been achieved and a new overall approach of iodine chemistry in- containment has been proposed [29]; a schematic is displayed in Figure 3 (where “aq” denotes the aqueous phase). Although many of these interactions are reasonably well understood, particularly aqueous iodine chemistry, there still persist phenomena that would need additional study to fill knowledge gaps: effects of corrosion and degradation products (i.e., metal cations, anions, organics, colloids, …) existing and/or added (sea water injection) into the aqueous solution; mass transfer between iodine solutions and gas phase for configurations other than pools (droplets, falling films, rivulets, etc.); interactions of iodine oxides (IOx) and metal iodides with surfaces; and some others.

However, the essential focus of research should be on those processes responsible for the presence of airborne iodine species:

 Aerosol stability, in particular iodine oxide, stability in containment atmospheres (i.e., thermal/radiolytic decomposition, interaction of IOx with other particulate matter;

formation from I2and CH3I species);

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 Gaseous iodine production through homogeneous and heterogeneous reactions (aer

Nevertheless

really new as they have been addressed in some OECD projects and elsewhere

[31] and ISTP/EPICUR

In addition to all the iodine above, one should add in

behaviour, from the potential revaporisation from deposits to its persistence in the gas phase once formed. In

exempted from concerns related to representativity of data gathered in bench

uncertainties in iodine chemistry modelling.

2.4 Mitigation

The Fukushima accident highlighted the significance of having effective source term mitigation systems available in case of a severe accident, preferably of a passive type (i.e., no need to supply any power to make them work); containment spr

(LWR)

Most specifically, t

filtering devices, known as FCVS. As a consequence,

decided to install FCVS in addition to those where such measures were already in place, a status report on the matter was issued recently

EC/PASSAM, was launched under the 7

The PASSAM project addresses both existing source term mitigation technologies (i.e., sand/gravel filters, water ponds) and innovative ones (i.e., acoustic agglomerators, high pressure spray

bases and an identification of the existing knowledge gaps for their suitable application in NPPs were done and the outcomes were used as the basis for the project test ma

 Pool scrubbing investigation under conditions hardly explored so far and relevant during severe accidents. This includes aspects like high inlet gas

injection and churn turbulent flow), presence of surfactants and submerged structures in the aqueous bulk or vapour FP absorption by water. Likewise, the “reverse” process of FP re

particular under venting conditions;

 Dry systems (sand/gravel/metallic filters) capabilities for retaining iodine gas, particularly of an organic nature;

 Performance of acoustic aerosol and high pressure agglomerators to enhance potential for particle filtration in the first filter stages under anticipated venting conditions during a severe accident;

 Efficiency and long term

electrostatic precipitators, improved zeolites or metal

under prototypical conditions of severe accident conditions (i.e., high temperature, relative humidity and radiation doses).

Common to all th to iodine species

Gaseous iodine production through homogeneous and heterogeneous reactions (aerosol deposit

Nevertheless

really new as they have been addressed in some OECD projects and elsewhere

and ISTP/EPICUR

In addition to all the iodine above, one should add in

behaviour, from the potential revaporisation from deposits to its persistence in the gas phase once formed. In-containment issues are, again, not exempted from concerns related to representativity of data gathered in bench

uncertainties in iodine chemistry modelling.

Mitigation

NPPs and suppression pools in Most specifically, t

The PASSAM project addresses both existing source term mitigation technologies (i.e., sand/gravel filters, water ponds) and innovative ones (i.e., acoustic agglomerators, high pressure sprays, wet electrostatic precipitators, improved zeolites). A literature review of their bases and an identification of the existing knowledge gaps for their suitable application in NPPs were done and the outcomes were used as the basis for the project test ma

Pool scrubbing investigation under conditions hardly explored so far and relevant during severe accidents. This includes aspects like high inlet gas

injection and churn turbulent flow), presence of surfactants and submerged structures in the aqueous bulk or vapour FP absorption by water. Likewise, the “reverse” process of FP re-entrainment from saturated contaminated water pools i

particular under venting conditions;

Dry systems (sand/gravel/metallic filters) capabilities for retaining iodine gas, particularly of an organic nature;

Performance of acoustic aerosol and high pressure agglomerators to enhance potential for particle filtration in the first filter stages under anticipated venting conditions during a severe accident;

Efficiency and long term

Common to all th

to iodine species highlighted by recent research as a potential source term “enhancer” (CH Gaseous iodine production through homogeneous and heterogeneous reactions

osol deposit stability).

Nevertheless, neither of these two issues is really new as they have been addressed in some OECD projects and elsewhere

and ISTP/EPICUR [32] experiments In addition to all the iodine above, one should add in

behaviour, from the potential revaporisation from deposits to its persistence in the gas phase

containment issues are, again, not exempted from concerns related to representativity of data gathered in bench-scale tests or embedded uncertainties in iodine chemistry modelling.

NPPs and suppression pools in

Most specifically, the accident renewed interest in filtering devices, known as FCVS. As a consequence,

The PASSAM project addresses both existing source term mitigation technologies (i.e., sand/gravel filters, water ponds) and innovative ones (i.e., acoustic agglomerators, high s, wet electrostatic precipitators, improved zeolites). A literature review of their bases and an identification of the existing knowledge gaps for their suitable application in NPPs were done and the outcomes were used as the basis for the project test ma

injection and churn turbulent flow), presence of surfactants and submerged structures in the aqueous bulk or vapour FP absorption by water. Likewise, the “reverse” process

entrainment from saturated contaminated water pools i particular under venting conditions;

Efficiency and long term

Common to all these filtration issues is the interest to check their efficiency with respect highlighted by recent research as a potential source term “enhancer” (CH Gaseous iodine production through homogeneous and heterogeneous reactions

stability).

, neither of these two issues is really new as they have been addressed in some OECD projects and elsewhere [30], like PARIS

experiments

In addition to all the iodine-related issues above, one should add in-containment Ru behaviour, from the potential revaporisation from deposits to its persistence in the gas phase

containment issues are, again, not exempted from concerns related to representativity scale tests or embedded uncertainties in iodine chemistry modelling.

NPPs and suppression pools in boiling water reactors ( he accident renewed interest in

EC/PASSAM, was launched under the 7^th

Efficiency and long term behaviour

filtration issues is the interest to check their efficiency with respect highlighted by recent research as a potential source term “enhancer” (CH Gaseous iodine production through homogeneous and heterogeneous reactions

, neither of these two issues is really new as they have been addressed in some , like PARIS experiments.

related issues containment Ru behaviour, from the potential revaporisation of Ru from deposits to its persistence in the gas phase containment issues are, again, not exempted from concerns related to representativity scale tests or embedded uncertainties in iodine chemistry modelling.

boiling water reactors ( he accident renewed interest in

decided to install FCVS in addition to those where such measures were already in place, a status report on the matter was issued recently [33]

thFramework Program

Dry systems (sand/gravel/metallic filters) capabilities for retaining iodine gas, Performance of acoustic aerosol and high pressure agglomerators to enhance potential for particle filtration in the first filter stages under anticipated venting conditions behaviour of alternative filtration devices, like wet electrostatic precipitators, improved zeolites or metal

filtration issues is the interest to check their efficiency with respect highlighted by recent research as a potential source term “enhancer” (CH

Figure

Gaseous iodine production through homogeneous and heterogeneous reactions , neither of these two issues is

really new as they have been addressed in some , like PARIS related issues containment Ru of Ru from deposits to its persistence in the gas phase containment issues are, again, not exempted from concerns related to representativity scale tests or embedded

boiling water reactors (

he accident renewed interest in-containment venting through ad filtering devices, known as FCVS. As a consequence, some NPPs all over the world have decided to install FCVS in addition to those where such measures were already in place, a

[33] and a closely Framework Programme

entrainment from saturated contaminated water pools i

Dry systems (sand/gravel/metallic filters) capabilities for retaining iodine gas, Performance of acoustic aerosol and high pressure agglomerators to enhance potential for particle filtration in the first filter stages under anticipated venting conditions of alternative filtration devices, like wet electrostatic precipitators, improved zeolites or metal

under prototypical conditions of severe accident conditions (i.e., high temperature, filtration issues is the interest to check their efficiency with respect highlighted by recent research as a potential source term “enhancer” (CH

Figure 3: The in

Gaseous iodine production through homogeneous and heterogeneous reactions

The Fukushima accident highlighted the significance of having effective source term mitigation systems available in case of a severe accident, preferably of a passive type (i.e., no need to supply any power to make them work); containment sprays in most

boiling water reactors (BWRs), are good examples.

containment venting through ad some NPPs all over the world have decided to install FCVS in addition to those where such measures were already in place, a and a closely-related research project,

me of EURATOM

entrainment from saturated contaminated water pools i

Dry systems (sand/gravel/metallic filters) capabilities for retaining iodine gas, Performance of acoustic aerosol and high pressure agglomerators to enhance potential for particle filtration in the first filter stages under anticipated venting conditions of alternative filtration devices, like wet electrostatic precipitators, improved zeolites or metal-organic frameworks (MOF), under prototypical conditions of severe accident conditions (i.e., high temperature, filtration issues is the interest to check their efficiency with respect highlighted by recent research as a potential source term “enhancer” (CH

The in-containment “iodine

The Fukushima accident highlighted the significance of having effective source term mitigation systems available in case of a severe accident, preferably of a passive type (i.e., no ays in most light water reactor

, are good examples.

containment venting through ad some NPPs all over the world have decided to install FCVS in addition to those where such measures were already in place, a related research project, of EURATOM [9].

The PASSAM project addresses both existing source term mitigation technologies (i.e., sand/gravel filters, water ponds) and innovative ones (i.e., acoustic agglomerators, high s, wet electrostatic precipitators, improved zeolites). A literature review of their bases and an identification of the existing knowledge gaps for their suitable application in NPPs were done and the outcomes were used as the basis for the project test matrices [34]

Pool scrubbing investigation under conditions hardly explored so far and relevant during severe accidents. This includes aspects like high inlet gas velocities (i.e., jet injection and churn turbulent flow), presence of surfactants and submerged structures in the aqueous bulk or vapour FP absorption by water. Likewise, the “reverse” process entrainment from saturated contaminated water pools is of interest, in Dry systems (sand/gravel/metallic filters) capabilities for retaining iodine gas, Performance of acoustic aerosol and high pressure agglomerators to enhance potential for particle filtration in the first filter stages under anticipated venting conditions of alternative filtration devices, like wet c frameworks (MOF), under prototypical conditions of severe accident conditions (i.e., high temperature, filtration issues is the interest to check their efficiency with respect highlighted by recent research as a potential source term “enhancer” (CH

containment “iodine

The Fukushima accident highlighted the significance of having effective source term mitigation systems available in case of a severe accident, preferably of a passive type (i.e., no light water reactor , are good examples.

containment venting through ad-hoc some NPPs all over the world have decided to install FCVS in addition to those where such measures were already in place, a related research project,

.

The PASSAM project addresses both existing source term mitigation technologies (i.e., sand/gravel filters, water ponds) and innovative ones (i.e., acoustic agglomerators, high s, wet electrostatic precipitators, improved zeolites). A literature review of their bases and an identification of the existing knowledge gaps for their suitable application in

[34]:

Pool scrubbing investigation under conditions hardly explored so far and relevant velocities (i.e., jet injection and churn turbulent flow), presence of surfactants and submerged structures in the aqueous bulk or vapour FP absorption by water. Likewise, the “reverse” process s of interest, in Dry systems (sand/gravel/metallic filters) capabilities for retaining iodine gas, Performance of acoustic aerosol and high pressure agglomerators to enhance potential for particle filtration in the first filter stages under anticipated venting conditions of alternative filtration devices, like wet c frameworks (MOF), under prototypical conditions of severe accident conditions (i.e., high temperature, filtration issues is the interest to check their efficiency with respect highlighted by recent research as a potential source term “enhancer” (CH3I);

containment “iodine-cycle”

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in case that ongoing research underlined the potential contribution of Ru in source term, this interest should be extended to RuO₄as well. Consideration of time periods much longer than initially considered would be also a cross-cutting factor in the necessary investigation. A national French programme MIRE addresses some of the issues introduced above.

3 SYNTHESIS AND OUTLOOK

As described in the previous sections, a number of specific issues are considered worthy of investigation in the source term area. FP release under oxidising conditions and/or from fuel configurations other than rod-like MOX are highlighted, and particularly for MOX fuel.

Transport through the circuit needs to continue work on high temperature chemistry and on processes leading to a late in-containment source term, like revaporisation. Research needs on containment issues seem to be well addressed in forthcoming projects under the OECD framework (i.e. BIP3, THAI3 and STEM2) and the only open issue left out would be pool scrubbing, which is being partially tackled within the PASSAM project. A similar situation to the containment one exists in the source term mitigation area, in which the PASSAM and MIRE projects are underway. Aside from the specific issues of each topic, there are two common and strong needs that should be addressed in the short term:

 To determine the current codes predictability of source term to the environment when modelling severe accident sequences in NPPs; in other words, to assess the uncertainties around source term estimates. As a consequence, suitable methodologies would be set and the major uncertainty sources would be identified;

 To help keep the existing source term research capability through building an experimental platform (“pan-European experimental virtual laboratory”) to be shared among the major players in the source term area, both in Europe and beyond. This, in turn, would allow optimisation of resources.

These needs are being presently the focus of two incipient initiatives within NUGENIA and will be proposed as H2020 projects in the next call.

ACKNOWLEDGMENTS

The authors are indebted to the NUGENIA Source Term community and, particularly to the invited speakers of the NUGENIA Source Term workshop: G. Ducros (CEA), A. Auvinen (VTT), S. Dickinson (NNL) and T. Albiol (IRSN), and thank P.D.W. Bottomley of (JRC/ITU) and S. Dickinson for providing Figures 2 and 3 respectively. SARNET was part- funded under the EC 7^thFramework Programme (2007-2013) under grant agreement 231747.

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