| Deuterium(D)and tritium(T)have been regarded as the first generation fuels to achieve earlier commercial fusion energy because D and T scenario requires the lowest fusion triple product to achieve energy self-sustaining among various fuel scenarios.Special radioactivity problems are also introduced not only because tritium is a radionuclide,but mobile activated products are produced during the nuclear reaction of neutron and materials.Taking ITER for example,the maximum tritium inventory on the site is 4 kg,and the maximum mobile radioactive materials are 1 kg tritium and 1000 kg dust inside the vacuum vessel.Potential radioactivity release into the environment could threaten public safety.Further,large amounts of radioactive materials release could lead acute public fatality.Thus,the environment impact and public safety due to radioactivity release from fusion reactor will be a constraint factor of fusion energy development.Firstly,considering the property of tritium environmental migration and biological metabolism behavior under normal and accidental conditions of fusion reactor,we developed a tritium environmental migration module including tritium atmosphere dispersion,soil migration and biology metabolism model based on TAS2.0 software developed by FDS Team.Meanwhile,relations of dose and acute morbidity/cancers were introduced and integrated into the module.Based on the tritium environmental migration and dose response model,we developed the TAS3.0.Series of verifications and validations have been performed including verifications with UFOTRI,ACUTRI,HotSpot,and integration verification based on hypothetical scenario in the frame of IAEA-EMRAS working group 7,and validation based on HT atmosphere release experimental results in Canada.The results showed TAS3.0 can be used to assess tritium environment migration behavior and public dose with reasonable accuracy for fusion reactor.Secondly,based on the models above,tritium environment migration property and public individual dose were analyzed under both normal and accidental condition of fusion reactor.Under normal condition,public dose is far below the Chinese and ITER dose limit referred to ITER release limit of 0.6 g/a as HTO,and even below an exemption level.Based on the results,the tritium release limit was discussed,and it is suggested to increase by one order larger than ITER release limit for future fusion reactor from radiation protection consideration.Under accidental conditions,dynamic tritium concentration in the environment and public individual dose were assessed due to unit gram tritium instantaneous release.Further,the maximum tritium release amounts were evaluated under different accidental conditions with different dose limit defined in Chinese and ITER regulation.The detailed results could provide date reference for tritium release source terms of fusion reactor.Finally,considering the serious consequences of historical fission accidents defined as level 7 in INES,we assessed the environmental and public consequences under the reasonable conservative release and environmental condition for the hypothetical accident of fusion reactor.The systematic evaluations were performed mainly on the point of view of accident description,release source terms,public individual dose,acute lethal area and environmental restoration,etc.Meanwhile,considering the Chinese positive nuclear energy policy and high population density,the acute death and cancers in the radius of 80 km around a nuclear power plant coastal site in China were assessed under fusion hypothetical accident.Comparison analysis with Chernobyl and Fukushima accidental consequences under the same conservative environmental condition were performed to further explain the safety characteristic of fusion reactor.The results showed fusion reactor has a safety advantages,but could also cause severe public consequences. |
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