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論文

Cesium chemistry in the LWR severe accident and towards the decommissioning of Fukushima Daiichi Nuclear Power Station

逢坂 正彦; Gou$"e$llo, M.*; 中島 邦久

Journal of Nuclear Science and Technology, 59(3), p.292 - 305, 2022/03

 被引用回数:4 パーセンタイル:58.27(Nuclear Science & Technology)

事故時及び長期間の2つの期間のソースタームにおけるセシウム化学について、福島第一原子力発電所(1F)事故後に行われたFP化学研究のレビューを行った。事故時についてはCsのMo, B, Siとの化学反応について、また1F固有の水相を介した長期についてはCsのコンクリートへの浸透及び燃料デブリの浸出挙動について、関連する熱力学データ整備状況とともに調べた。これらのCs化学挙動は近い将来取出し予定の燃料デブリ等1Fサンプルの分析及び評価を通して検証されるべきである。

論文

Revaporization behavior of cesium and iodine compounds from their deposits in the steam-boron atmosphere

Rizaal, M.; 三輪 周平; 鈴木 恵理子; 井元 純平; 逢坂 正彦; Gou$"e$llo, M.*

ACS Omega (Internet), 6(48), p.32695 - 32708, 2021/12

 被引用回数:1 パーセンタイル:7.13(Chemistry, Multidisciplinary)

This paper presents our investigation on cesium and iodine compounds revaporization from cesium iodide (CsI) deposits on the surface of stainless steel type 304L, which were initiated by boron and/or steam flow. A dedicated basic experimental facility with a thermal gradient tube (TGT) was used for simulating the phenomena. The number of deposits, the formed chemical compounds, and elemental distribution were analyzed from samples located at temperature range 1000-400 K. In the absence of boron in the gas flow, it was found that the initial deposited CsI at 850 K could be directly re-vaporized as CsI vapor/aerosol or reacted with the carrier gas and stainless steel (Cr$$_{2}$$O$$_{2}$$ layer) to form Cs$$_{2}$$CrO$$_{4}$$ on the former deposited surface. The latter mechanism consequently gave a release of gaseous iodine that was accumulated downstream. After introducing boron to the steam flow, a severe revaporization of iodine deposit at 850 K occurred (more than 70% initial deposit). This was found as a result of the formation of two kinds of cesium borates (Cs$$_{2}$$B$$_{4}$$O$$_{7}$$$$cdot$$5H$$_{2}$$O and CsB$$_{5}$$O$$_{8}$$$$cdot$$4H$$_{2}$$O) which contributed to a large release of gaseous iodine that was capable of reaching outlet of TGT ($$<$$ 400 K). In the case of nuclear severe accident, our study have demonstrated that gaseous iodine could be expected to increase in the colder region of a reactor after late release of boron or a subsequent steam flow after refloods of the reactor, thus posing its near-term risk once leaked to the environment.

論文

Interaction between caesium iodide particles and gaseous boric acid in a flowing system through a thermal gradient tube (1030 K-450 K) and analysis with ASTEC/SOPHAEROS

Gou$"e$llo, M.*; Hokkinen, M.*; 鈴木 恵理子; 堀口 直樹; Barrachin, M.*; Cousin, F.*

Progress in Nuclear Energy, 138, p.103818_1 - 103818_10, 2021/08

 被引用回数:3 パーセンタイル:58.27(Nuclear Science & Technology)

1023Kから453Kの温度勾配管中のヨウ化セシウム粒子の移行挙動に関するデータを取得した。まず、アルゴン(Ar)と水蒸気(H$$_{2}$$O)で構成される層流条件下にてヨウ化セシウム粒子を温度勾配管中に流し、沈着量を調べた結果、低流速、高蒸気濃度であるほどより多くの粒子が沈着することが分かった。次に、雰囲気の異なる三種類の混合ガス(Ar/H$$_{2}$$O, Ar/H$$_{2}$$, Ar/Air)を流すことで沈着した粒子の再蒸発および/または再浮遊の有無を調べた結果、Ar/H$$_{2}$$OとAr/H$$_{2}$$条件では沈着したものと同等の粒径の粒子が再浮遊する一方で、Ar/Air条件ではより大きな粒子が再浮遊することが分かった。実験結果をASTECコードのSOPHAEROSモジュールを用いて解析した結果、沈着挙動は解析結果と一致するものの、再浮遊挙動は再現できなかった。

口頭

Fundamental research on FP chemistry; Boron effects on cesium and iodine chemistry

三輪 周平; 中島 邦久; 宮原 直哉; 西岡 俊一郎; 鈴木 知史; 鈴木 恵理子; 堀口 直樹; 井元 純平; Liu, J.; Miradji, F.; et al.

no journal, , 

ソースターム評価技術の高度化に向けて、シビアアクシデント(SA)時における核分裂生成物(FP)の放出移動挙動を支配する化学挙動を明らかにし、FP化学データベース・モデルを構築するための基礎研究を進めている。SA時のFPの一連の化学挙動を再現可能な実験装置及び解析ツールの基本形を構築し、これらを用いて特にBWR制御材ホウ素のセシウム及びヨウ素の化学挙動に与える影響に関する基礎知見を得た。

口頭

Study on revaporization of deposited CsI from stainless steel 304 surface in high-temperature steam atmosphere

Rizaal, M.; 三輪 周平; 鈴木 恵理子; 井元 純平; 逢坂 正彦; Gou$"e$llo, M.*

no journal, , 

We experimentally investigated the revaporization behavior of deposited CsI on the surface of structural material such as stainless steel in a subsequent high-temperature steam flow (i.e., reflood of the reactor at severe accident). The experimental results showed that the deposited CsI at 850 K could be vaporized, leaving the formation of Cs$$_{2}$$CrO$$_{4}$$ on that once-deposited surface and consequently giving an increase of iodine release observed below 400 K.

口頭

Investigation of effect by the late-phase release of boron containing atmosphere on CsI deposit formed on reactor structural material SUS304L

Rizaal, M.; 三輪 周平; 鈴木 恵理子; 井元 純平; 逢坂 正彦; Gou$"e$llo, M.*

no journal, , 

The gaseous species interaction with the early FP deposits (mostly Cs and I) on the surface of reactor coolant system (RCS) material is considered as one of the factors of gaseous iodine generation at late phase and could affect the containment atmosphere. In this study, we investigated the reaction of CsI deposit formed on stainless steel type 304 L with steam-boron flow. The experiments for reproducing the RCS temperature gradient in the range of 1000-400 K showed a significant depletion of CsI at 850 K, resulted in formation of low volatile cesium borates on the former surface and simultaneously released gaseous iodine that could reach a range below 400 K.

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