報告書番号

T88049

タイトル（和文）

高レベル廃棄物地層処分時における人工バリア要素の安全評価手法の開発

タイトル（英文）

ANALYSIS CODES FOR ENGINEERED BARRIER SYSTEMPERFORMANCE OF HIGH-LEVEL RADIOACTIVE WASTE DISPOSAL

概要 （図表や脚注は「報告書全文」に掲載しております）

高レベル放射性廃棄物の地層処分を対象として，ガラス固化体，オーバーパック，緩衝材等の人工バリアに関する安全性を評価することを目的に，人工バリアの構成要素毎に安全評価コードを開発し，それらの基本的性能を確認した。得られた結果は以下の通りである。１）ガラス固化体核種浸出挙動解析コードを，数値解法上より安定したＳＴＲＡＧ２に改良し，ＪＳＳプロジェクトで得られた実放射性ガラス固化体の浸出挙動を再現できる事を確認した。２）オーバーパックの腐食挙動を，地下水の放射線分解の影響を考慮して解析するＣＲＡＮＰを開発した。また炭素鋼を用いて処分時に想定される腐食速度を，安全側の仮定として溶存酸素飽和条件で測定した。実験と解析から千年間の腐食は酸素が無限に存在する仮想的条件で１６ｃｍ程度，より現実的な条件では１ｃｍ程度と推定された。３）公開コードＣＨＥＭＴＲＮを拡

概要 （英文）

THIS REPORT DESCRIBES SIMULATION CODES FOR EVALUATING SYSTEM PERFORMANCE OF REPOSITORY ENGINEERED BARRIERS CONSISTING OF WASTE GLASS,OVERPACK,AND BUFFER MATERIAL. THREE COMPUTER CODES WERE DEVELOPED FOR LONG TERM PREDICTION: STRAG2 CALCULATES WASTE GLASS DISSOLUTION;CRANP CALCULATES OVERPACK CORROSION; AND GESPER CALCULATES MIGRATION IN THE BUFFER MATERIAL. 1)STRAG2 IS A REVISED VERSION OF STRAG,THE PROGRAM CONSISTS OF MODELS FOR HEAT GENERATION,DIFFUSION DUE TO BOTH THERMAL AND CONCENTRATION GRADIENTS,AND GEOCHEMICAL REACTIONS OF RELEASED NUCLIDES. THE CAPABILITY OF STRAG2 WAS CONFIRMED BY COMPARING ITS SIMULATION RESULTS WITH EXPERIMENTAL DATA FROM THE JSS PROJECT. 2)CRANPIS A MODEL FOR GENERAL CORROSION OF IRON STEEL. THE MODEL IS BASED ON DIFFUSION CALCULATIONS OF DISSOLVED OXGEN IN THE BUFFER MATERIAL,AND ALSO TAKES GROUNDWATER RADIOLYSIS INTO ACCOUNT. CRANP CALCULATIONS INDICATE THAT THE GENERAL CORROSION DEPTH OF CARBON STEEL PLACED IN A REPOSITORY CONFIGURATION WOULD BE FROM 1 TO 16CM AFTER 1000 YEARS. THE WORST CASE IS BASED ON THE ASSUMPTION THAT THE SURROUNDING SOLUTION IS ALWAYS SATURATED WITH OXGEN. 3)GESPER IS AN EXTENDED AND MORE FLEXIBLE VERSIONOF CHEMTRN. THE PROGRAM TAKES INTO ACCOUNT THE VARIABLE FLUX WITHIN THE BUFFER MATERIAL,AS WELL AS THE COMPOSITE MEDIA OF THE BUFFER MATERIALAND SURROUNDING ROCK. WE TESTED GESPER S PERFORMANCE BY CALCULATION TWO SIMPLE CASES: THE DIFFUSION OF 134-CS IN COMPACTED BENTONITE,AND THE MIGRATION(BOTH DIFFUSION AND CONVECTION)OF U IN A CRUSHED GRANITE COLUMN. CALCULATIONS WERE IN GOOD AGREEMENT WITH THE EXPERIMENTAL RESULTS. WE ALSO DEVELOPED THE RASCAL CODE,WHICH PROVIDES A ROUGH BUT RAPID ANALYSIS OF AN ENTIRE ENGINEERED BARRIER SYSTEM,AND WHICH PERFORMS ONE-DIMENSIONAL CALCULATION OF GLASS DISSOLUTION KINETICS AND OF DIFFUSION PHENOMENA IN BUFFER MATERIAL. RESULTS WITH RASCAL INDICATE THAT THE SLOW DISSOLUTION OF GLASS,AND THE DIFFUSION WITHIN THE BUFFER MAT

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