Collection efficiency and decontamination factor of HEPA filter.

Abstract

It is very important in a nuclear air cleaning system that HEPA (High Efficiency Particulate Air) filter is for reduction of releasing amounts of airborne radioactive particles. HEPA filter, by definition, has a minimum collection efficiency of 99.97% for 0.3 , gym particles. However, DF (Decontamination Factor), which is necessary for safety management, can not be directly derived from the efficiency. And the current standard defined for 0.3 pm particles has no scientific justification, because it has been found that the most penetrating particle size through HEPA filter is not always 0. 3 pm. In the present paper, a numerical experiment was made in order to estimate a relationship between DF and the efficiency. And new standard, in which the minimum DF is able to be easily obtained, was proposed. In the multistage filtration system, it was found that lower values of DF was possible to be experimentally indicated in the second and the third stages, even if the collection performance of the each filter is the same. KEY WORD: decontamination factor, collection efficiency, HEPA filter, DF, the most penetrating particle size, numerical experiment, multistage filtration I ‚Í ‚ ¶ ‚ß ‚É OE´ŽqOE´Žq-Í"-"d •Š ‚ð ‚Í ‚ ¶ ‚ß ‚AE ‚µ ‚Ä, •ú ŽË •« •¨ Ž¿ ‚ðˆµ‚ðˆµ ‚¤ Ž{ •Ý ‚É ‚¨‚¢‚¨‚¢ ‚Ä ‚Í, •ú ŽË •ü ˆÀ 'S ŠÇ-•‚Ì ‚½ ‚ß, ‚» ‚Ì "r ‹C •E"r •…‚É ‚Í •" •X‚Ì •ú ŽË •« •¨ Ž¿ "r •o-h Ž~ •ô ‚ª •Ì ‚ç ‚ê ‚Ä ‚¢ ‚é•B ‚» ‚Ì ‚È ‚© ‚Å, "r ‹C ƒG ƒA ƒt ƒBƒ‹ ƒ^ ‚Í "r ‹C •ˆ-••Ý "õ ‚̈ê‚Ìˆê •" ‚AE ‚µ ‚Ä ‚« ‚í ‚ß ‚Ä •d-v‚È-ð Š" ‚ð ‰Ê‚½ ‚µ ‚Ä ‚¢ ‚é•B ‚» ‚ê ‚É ‚à ŠÖ‚í ‚ç ‚¸, ‚» ‚Ì "r ‹C ƒG ƒA ƒt ƒBƒ‹ ƒ^ ‚Ì •« "\ ‚Ì •] ‰¿‚É ‚ ‚¢ ‚Ä ‚Í •\ •ª ‚É OEŸ"¢ ‚³ ‚ê ‚Ä ‚¢ ‚È ‚¢•B ‚½ ‚¾ ‚µ ‚± ‚± ‚Å ‚¢ ‚¤ ƒt ƒBƒ‹ ƒ^ ‚Ì •« "\ ‚AE‚Í ƒG ƒA ƒ• ƒ] ƒ‹-±Žq ‚É 'Î ‚· ‚é •ß •W•« "\ ‚ð Žw‚·•B OE´ŽqOE´Žq-Í•ª-ì ‚É ‚¨‚¢‚¨‚¢ ‚Ä ‚Í, HEPA (High Efficiency Particulate Air) ƒt ƒBƒ‹ ƒ^ ‚AEOEÄ‚Î ‚ê ‚é •‚ •« "\ ƒG ƒA ƒt ƒBƒ‹ ƒ^ ‚ª •" '½ ‚-Žg-p‚³ ‚ê ‚Ä ‚¢ ‚é•B ‚± ‚ÌHEPAƒt ƒBƒ‹ ƒ^ ‚Ì-±Žq •ß •W•« "\ Šî •€ ‚Í, 0.3 ƒÊmƒT ƒCƒY ‚Ì ƒG ƒA ƒ• ƒ] ƒ‹-±Žq ‚É 'Î ‚µ ‚Ä99•E97%ˆÈ •ã ‚Ì •ß •WOEø-¦ ‚ð-L‚· ‚é ‚± ‚AE‚Å ‚ ‚é1,2)•B ‚± ‚Ì Šî •€ •" 'l Ž©•g ‚Ì •¥ "ñ ‚Í ‚AE ‚à ‚© ‚-, •-‚È ‚-‚AE ‚à-±Žq •ß •W•« "\ ‚É ŠÖ ‚µ ‚Ä ‚Í ‚± ‚ê ‚¾ ‚¯ ‚Ì •] ‰¿Šî •€ ‚Å ‚à ‚Á ‚Ä •¬-§ ‚µ ‚Ä ‚¢ ‚éHEPAƒt ƒBƒ‹ ƒ^ ‚© ‚ç, •ú ŽË •ü ˆÀ 'S ŠÇ-••ã •K-v‚È •oe •õ OEW •"DF‚É ŠÖ‚· ‚é •î •ñ ‚ª "¾ ‚ç ‚ê ‚é ‚Å ‚ ‚ë ‚¤ ‚©•B •ß •WOEø-¦ ‚ª99.97%ˆÈ •ã ‚Å ‚ ‚é ‚© ‚ç, ƒt ƒBƒ‹ ƒ^ ‚ð 'Ê ‰ß‚· ‚é Š" • ‡ ‚Í0.03%ˆÈ ‰º, ‚µ ‚½ ‚ª ‚Á ‚Ä, dF‚Í1/(0.03•~10-2)=3.3•~103ˆÈ •ã ‚AE'Z-• "I ‚É •l ‚¦ ‚Ä ‚Í ‚¢ ‚È ‚¢ ‚©•B ŽÀ‚Í, ‚± ‚Ì ‚ae ‚¤ ‚È •l ‚¦ •û ‚É ‚Í-¾ ‚ç ‚© ‚È OEë ‚è ‚ª ‚ ‚é•B ‚È ‚º ‚È ‚ç, ‚Ü ‚¸'‚¸'ae1‚É, HEPAƒt ƒBƒ‹ ƒ^ ‚Ì •ß •WOEø-¦ ‚ª 99•E97%ˆÈ •ã ‚AE‚¢ ‚¤ ‚Ì ‚Í, 0.3ƒÊmƒT ƒC ƒY ‚Ì-±Žq ‚É 'Î ‚· ‚é OEø-¦ ‚Å ‚ ‚Á ‚Ä, ‚» ‚Ì '¼ ‚Ì ƒT ƒC ƒY ‚Ì-±Žq ‚É 'Î ‚· ‚é OEø-¦ ‚Í •-1•ú ŽË •ü ˆã Šw'• • ‡ OE¤‹ † •Š "à •" "í ‚Û ‚-OE¤‹ † •"; •ç-tŽs OEŠ•ì4-9-1 (• §260) Division of Comparative Radiotoxicology, National Institute of Radiological Sciences; 9-1, Anagawa 4-chome, Chiba 260, Japan.