報告書番号

T88002

タイトル（和文）

高レベル放射性廃棄物地層処分時の人工バリアの予備的安全評価

タイトル（英文）

PRELIMINARY ANALYSIS OF ENGINEERED BARRIEER PERFORMANCES IN GEOLOGICAL DISPOSAL OF HIGH LEVEL WASTE

概要 （図表や脚注は「報告書全文」に掲載しております）

我が国での地層処分実施上の問題点を明らかにするため，公開コードを用いて人工バリアシステムの安全性の概略評価を行い，以下の結果を得た。・処分場内の温度解析：ＯＲＩＧＥＮ２を用いてガラス固化体の発熱量を求め，発熱に伴う処分場の温度分布をＴＲＵＭＰ４によって計算した。その結果処分場の深度が５００ｍのケースでは，周辺岩盤が花こう岩の場合には約５ｍの処分ビット間隔を保てばバックフィル材を１００℃以下に保ち，熱による性能劣下を防止できることが判った。・人工バリア内核種移行解析：ＳＷＩＦＴを用いて，９０Ｓｒ，２４１Ａｍ，２３９Ｐｕ，２３７Ｎｐの４核種を対象とした人工バリア内の核種移行挙動を解析した。その結果，廃棄体内の放射性核種が一定速度で放出され続ける場合，あるいは全量瞬時に放出される場合，何れのケースにおいても，人工バリアから周辺岩盤に放出される最大濃度は，２３７Ｎｐ＞２３９Ｐｕ＞９０Ｓｒ＞２４１

概要 （英文）

THIS REPORT PRESENTS THE PRELIMINARY RESULTSOF A SAFETY ANALYSIS OF THE ENGINEERED BARRIER SYSTEM,WHICH IS DESIGNED TO EFFECT GEOLOGICAL DISPOSAL OF HIGH LEVEL RADIOACTIVE WASTE. ORIGEN2,TRUMP4,AND SWIFR-THREE WELL-KNOWN COMPUTER CODES- WERE USED IN THE SIMULATION. THE MAIN CONCEPTUAL DESIGN OF THE REPOSITORY WAS ALMOST IDENTICAL TO THOSE OF SKB IN SWEDEN AND NAGRA IN SWITZERLAND WITH THE BARRIER CONSISTING OF SOLIDIFIED GLASS WASTE,STEEL OVERPACK,AND COMPACTED BENTONITE.TWO DIFFERENT UNDERGROUND FORMATIONS,BOTH COMMON IN JAPAN,WERE CONSIDERED : GRANITE,AND NEOGENE SEDIMENTARY ROCK. THE REPOSITORY CONFIGURATION,AND PARTICULARLY THE SPACE BETWEEN THE DISPOSAL PITS,WAS DETERMINED FIRST. ORIGEN2 WAS USED TO ESTIMATE THE HEAT GENERATION OF WASTE GLASS REPROCESSED FOUR YEARS AFTER REMOVAL FROM PWR. TEMPERATURE DISTRIBUTION WAS THEN CALCULATED BY TRUMP4. RESULTS OF TWO AND THREE DIMENSIONAL CALCULATION INDICATED THAT THE PIT INTERVAL FOR GRANITE FORMATION AT500M DEPTH, SHOULD BE MORE THAN 5M, BASED ON A TEMPERATURE CRITERIA OF<100 FOR THE BENTONITE LAYER. NUCLIDE MIGRATION BEHAVIOR WAS EVALUATED BY SWIFT CODE. THE BEHAVIOR OF FOUR MAIN NUCLIDES,-90SR,241AM,239PU,AND 237NP- WAS CONSIDERED,USING ONE OR TWO DIMENSIONAL CALCULATIONS. BOTH FOR STEADY RELEASE AND INSTANTANEOUS RELEASE,THE MAXIMUM CONCENTRATION IN PORE WATER AT THE BOUNDARY BETWEEN BENTONITE AND SURROUNDING ROCK WAS IN THE ORDER ; 237NP>239PU>90SR>241AM. SENSITIVITY ANALYSIS IRDICATED THAT THIS ORDER WAS MAINLY DUE TO THE DIFFERENT ADSORPTION CHARACTERISTICS IN THE BENTONITE LAYER.

報告者

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