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Research Papers

Iodine Benchmarks in the SARNET Network of Excellence

[+] Author and Article Information
Tim Haste

Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Centre d’Etudes de Cadarache,
BP 3-13115, Saint-Paul-Lez-Durance Cedex, France
e-mail: tim.haste@irsn.fr

Mirco Di Giuli

Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Centre d’Etudes de Cadarache,
BP 3-13115, Saint-Paul-Lez-Durance Cedex, France
e-mail: mirco.digiuli-enea@irsn.fr

Gunter Weber

Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH,
Boltzmannstraße 14, 85748 Garching bei München, Germany
e-mail: gunter.weber@grs.de

Sebastian Weber

Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH,
Boltzmannstraße 14, 85748 Garching bei München, Germany
e-mail: sebastian.weber@grs.de

1Corresponding author.

Manuscript received March 12, 2015; final manuscript received September 11, 2015; published online February 29, 2016. Assoc. Editor: Leon Cizelj.

2Present address: Institute for Applied Energy, Tokyo, Japan, e-mail: mirco@iae.or.jp.

ASME J of Nuclear Rad Sci 2(2), 021022 (Feb 29, 2016) (9 pages) Paper No: NERS-15-1026; doi: 10.1115/1.4031652 History: Received March 12, 2015; Accepted September 11, 2015

Accurate calculation of iodine behavior in the containment is very important in determining the potential radioactive release to the environment in light water reactor severe accidents (SAs). Of particular significance is the behavior of gas phase iodine, particularly organic iodine, which is difficult to remove by filtration, e.g., in containment venting systems. Iodine behavior is closely linked with the containment thermal hydraulics, which have a major influence on the distribution of iodine throughout the containment atmosphere and sump. In the European 7th Framework SARNET project, European Commission (EC) cofunded from 2007 to 2013, SA modeling code capability was assessed through two integral benchmarks. In the first, the basis was the German THAI Iod-11/12 tests, where molecular iodine transport with atmospheric flows and iodine interactions with steel surfaces were emphasized. In the second, data from the international Phébus FPT3 test were used, where all aspects of SAs were studied from core degradation, fission product (FP) release, circuit transport/deposition, and containment behavior using realistic FP sources. Thermal hydraulics in the containment were simpler, being well-mixed, and radiolytic interactions of iodine, e.g., with painted surfaces, were studied. These interactions may be an important source of organic iodine in the containment atmosphere. The two benchmarks are thus complementary. In the FPT3 exercise, the calculations could predict the containment thermal hydraulic conditions fairly well. For the more detailed data from THAI, differences were noted for atmospheric flows and relative humidities, outside experimental uncertainties, affecting iodine behavior. The FPT3 iodine results themselves showed a spread in calculated results outside data uncertainties, indicating the need for model improvements in this area, e.g., for radiolytic interaction of iodine with paint. Experimental programs to generate the necessary data needed for code improvement have been recently completed, e.g., in the OECD/THAI, THAI2, BIP, and BIP2 projects, or are in progress, in OECD/STEM and EC/PASSAM. When model improvements have been made, repeat benchmarks are planned to check progress toward code convergence with experimental data, e.g., under the aegis of the new NUGENIA association of which SARNET now forms a part.

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Figures

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Fig. 3

ASTEC meshing for the Phébus FPT3 containment vessel by IRSN

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Fig. 2

Schematic diagram of the THAI facility

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Fig. 1

Schematic diagram of the experimental circuit in the Phébus bundle tests and its relation with a LWR

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Fig. 4

Examples of Phébus FPT3 benchmark comparison plots of calculated results against data for containment stand-alone cases: (a) mass of iodine deposited on painted surfaces, (b) mass of organic iodine in the gas phase, (c) mass of inorganic iodine moles in the gas phase, and (d) mass of iodine deposited on stainless steel surfaces. Uncertainties given are 1 standard deviation (1σ).

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Fig. 5

MELCOR meshing of the THAI containment vessel by the University of Pisa (UNIPI) [18]

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Fig. 6

Examples of THAI Benchmark comparison plots of calculated results against data for (a) Iod-12 atmospheric temperature in the dome at 8.4 m axial elevation (1σ=0.3°C), (b) Iod-12 RH at 7.7 m axial elevation (1σ=3%), (c) Iod-11 gaseous I2 concentration at 1.8 m axial elevation (1σ=20–30%), and (d) Iod-12 iodine concentration in the condensate of the lower gutter (1σ=5%)

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