ERMSAR Results and Progress of Fundamental Research on FP Chemistry. Japan Atomic Energy Agency. May16-18, 2017 Warsaw, Poland

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1 8 TH CONFERENCE ON SEVERE ACCIDENT RESEARCH ERMSAR 2017 Results and Progress of Fundamental Research on FP Chemistry M.Osaka, K.Nakajima, S. Miwa, F.G.Di Lemma, N.Miyahara, C.Suzuki, E.Suzuki, T.Okane, M.Kobata Japan Atomic Energy Agency May16-18, 2017 Warsaw, Poland

2 Introduction Recalled the importance of fission product (FP) behavior under LWR-SA Severe accident (SA) of Fukushima Dai-ichi Power Station (1F) Enhancement of LWR safety after 1F-SA Importance of FP chemistry, in particular fundamental aspects Vulnerable of fundamental (material) basis for FP chemistry in Japan Focal points for the fundamental research on FP chemistry: Re-construction of fundamental (material) basis High temperature region: Boron effects, Cs chemisorption and revaporization Low temperature region: impacts on pool water property, chemical state of FP in the aerosol/particle 2

3 Research framework output and outcome - Output CEA, IRSN, etc. VERDON program Fundamental Research on FP Chemistry Output: Fundamental database for FP chemistry chemical models for SA analysis codes R&D for NRA* 1 R&D for IRID* 2 Output: Improved SA Output: Improved SA analysis code analysis code (THALES-2) (SAMPSON, MAAP) R&D for Manufacturer Output: Knowledge on FP retention and re-suspention/vaporization CEA, VTT Osaka Univ. Fukui Univ. Tokyo Institute of Technology Hokkaido Univ. Tohoku Univ. Outcome Improved regulation criteria Knowledge on Cs localization at top-peak part of the reactor for debris removal Improved methodology for evaluation of rational environmental release of FP *1 Nuclear Regulation Authority *2 Internal Research Institute for Nuclear Decommissioning

Basic approach Sorption Desorption Hot-Cell apparatus Important phenomena V&V Chemical reaction analysis FP Chemistry

Boron effects FP, B Analysis of deposit Filter, Liq.

trap Aerosol formation and growth Release from fuel Release at MCCI Dissolution Revaporization Elemental tests for FP

4 Basic approach Sorption Desorption Hot-Cell apparatus Important phenomena V&V Chemical reaction analysis FP Chemistry database, model Integral test: TeRRa (Test bench for FP Relase and transport) facility Steam injection SIMFuel, B 4 C Boron effects FP, B Analysis of deposit Filter, Liq. trap Cs-chemisorption Temperature distribusiton Core RPV RCS, PCV Analysis of gas/vapor Filter, Liq. trap Aerosol formation and growth Release from fuel Release at MCCI Dissolution Revaporization Elemental tests for FP release and transport FP/boron release kinetics Chemical form Release kinetics Interaction/deposition with structural material in RCS and PCV Chemical reaction Deposited compound Thermodynamic / physical property database 4

Cs-chemisorption behavior objective- Cs-chemisorption onto structural material surface Formation of insoluble Cs-compounds, becoming fixed source (about ~10kg by a rough estimation) Occurring at

5 Cs-chemisorption behavior objective- Cs-chemisorption onto structural material surface Formation of insoluble Cs-compounds, becoming fixed source (about ~10kg by a rough estimation) Occurring at relatively high-temperature (~1000K) Empirical model for SA-analysis code Insufficient knowledge for 1F issues Water-filling option for debris-removal Radiation-dose Cs-fixation or loose adhesion? Fundamental study on the basic mechanism of Cs-chemisorption Speculated model for Cs-chemisorption Cooling water Cs dissolution and migration to the water? Preliminary study Reproduction of Cs chemisorption phenomena Acquisition of basic knowledge Cs chemisorption amount, chemical composition/distribution Si contents, atmosphere

Cs-chemisorption behavior experimental- 6 Parameters for Cs chemisorption tests Sample Si content Temp. Flow rate Gas comp. SS304L, 10mm 10mm 2mm t 0.2, 1.0, 4.9 wt.

9 wt% sample to make the behavior more clear Microstructure Post -Analyses Identification of Reaction product Amount of Cs deposit SEM/EDX XRD, EDX ICP-MS/AES, XRD

6 Cs-chemisorption behavior experimental- 6 Parameters for Cs chemisorption tests Sample Si content Temp. Flow rate Gas comp. SS304L, 10mm 10mm 2mm t 0.2, 1.0, 4.9 wt.%* 800, 1000 ⁰C (3hr) 200 cc/min Reducing : Ar-5%H 2 Oxidizing : Ar-5%H 2-5%H 2 O *Si impurity level in SS304 : wt.% 4.9 wt% sample to make the behavior more clear Microstructure Post -Analyses Identification of Reaction product Amount of Cs deposit SEM/EDX XRD, EDX ICP-MS/AES, XRD Sample furnace Front side Crucible furnace Ni tube CsOH (Ni crucible) 1000⁰C Gas outlet Gas inlet Ar-5%H 2-5%H 2 O Back side Sample holder Gas flow guide Ar-5%H 2 Thermostat (33⁰C) Schematic of apparatus for chemisorption test

distributions were observed for the samples

Formation of CsFeSiO 4 Area 1: adherent,

Cr Area 2: base material, absence of Cs and

7 Cs-chemisorption behavior formation of Cs-Si-Fe-O- 7 SS surface SEM image Si Area 2 Area 1 Fe Area 2 Area 1 Sample N % Si 1000 Steam Area 2 Area 1 Similar distributions were observed for the samples with 1% Si Cs Area 2 Area 1 Cr Area 2 Area 1 Formation of CsFeSiO 4 Area 1: adherent, co-existence of Cs and Si, absence of Fe and Cr Area 2: base material, absence of Cs and Si, co-existence of Fe and Cr F.G.Fidelma, et. al., Nucl. Eng. Des., 305 (2016) 411.

Cs-chemisorption behavior dependence on atmosphere

6-3 on the samples mean Si contents of 0.2, 1.

%, respectively Weight changes of SS samples before

increase with Si contents be different according to

samples*(back side) before and after the test at

Cs-chemisorption atmosphere (not indicated in the

8 Cs-chemisorption behavior dependence on atmosphere and Si content- Before After *Marks of 6-1, 6-2, and 6-3 on the samples mean Si contents of 0.2, 1.0, and 4.9wt.%, respectively Weight changes of SS samples before and after the test Deposition amounts seem to: increase with Si contents be different according to the Ar-5%H 2 Ar-5%H 2-5%H 2 O Appearance of SS samples*(back side) before and after the test at 1073K The colors of the samples get darker by the Cs-chemisorption atmosphere (not indicated in the graph) Cs deposition amounts are influenced by atmosphere and Si content F.G.Fidelma, et. al., J. Nucl. Mater., 484 (2017) 174.

Boron effects under a reductive atmosphere

-30% Low B release kinetics: stable Fe-B

CsI CsOH I Cs CsBO 2 HI FeB As prepared Fe

(left) and 1,373 K (right) Variation of B

9 Boron effects under a reductive atmosphere Cs speciation- Previous B release kinetics case Temp. Cs CsI CsOH CsBO 2 I HI CsBO 2-97% HI/I -30% Low B release kinetics: stable Fe-B formation Temp. CsI CsOH I Cs CsBO 2 HI FeB As prepared Fe 2 B After the test in Ar-H 2 O at 1,173 K (left) and 1,373 K (right) Variation of B release kinetics in Fe-B at 1373 K Ref. S. Miwa, et al., Prog. Nucl. Energ. 92 (2016) 254. Possible impact of B release kinetics on Cs speciation S. Miwa, et. al., Prog. Nucl. Energy, 92 (2016) 254.

Boron effects under a reductive atmosphere revaporization- Basic experiment by a small

interaction with CsI deposit 423 K 1023 K Furnace Sample Thermal Gradient Tube (TGT)

$Iodine fraction in CsI-deposit Before After Iodine fraction in CsI-deposit I. Sato, et.$

10 Boron effects under a reductive atmosphere revaporization- Basic experiment by a small TGTequipped apparatus CsI vaporization and deposition onto TGT B-vapor/aerosol interaction with CsI deposit 423 K 1023 K Furnace Sample Thermal Gradient Tube (TGT) High-frequency oscillator Control panel TGT Induction furnace I vapor? B-vapor CsI-deposit Water-cooled chiller Several tens of deposits are revaporized Iodine fraction in CsI-deposit Before After Iodine fraction in CsI-deposit I. Sato, et. al., J. Nucl. Mater., 461 (2015) 22.

11 Thermodynamic data preparation for Cs-B-O system Cs-B-O sample preparation Vapor pressure measurement Knudsen cell Phase state investigation by TG-DTA and XRD K. Nakajima, et. al., J. Nucl. Mater., 491 (2017) 183.

12 Development of experimental facility Temperature gradient tube ( K) 1000K 900K 800K 700K 600K 500K 400K High frequency induction furnace (~2500 K) FP Flow Representative FP release and transport behavior (Aerosol generation / growth) Aerosol spectrometer - 20,000 particle/cc μm Appearance of heating up to 2500 K Cascade impactor μm (7 stages) TeRRa (Test bench for FP Release and transport) N. Miyahara, et. al., to be presented in WRFPM

13 Summary Results and progress of fundamental study on FP chemistry in JAEA was presented. The study has been conducted after the SA of Fukushima Daiichi NPS (1F), aimed at contributing to improvement of nuclear regulation, 1F decommissioning work and enhanced safety of LWR Fundamental knowledge such as Cs-chemisorption phenome and Boron effects have been obtained. A dedicated methodology for FP chemistry research has been developed. 13

Results and Progress of Fundamental Research on FP Chemistry

Results and Progress of Fundamental Research on FP Chemistry M.Osaka a,*, K.Nakajima a, S. Miwa a, F.G.Di Lemma a, N.Miyahara a, C.Suzuki a, E.Suzuki a, T.Okane a, M.Kobata a a Japan Atomic Energy Agency,