Novel Approach Of Shutdown Dose Rate Analysis And Its Application On Fusion Device

Analysis of activation problems such as radionuclide activity,decay heat and photon dose rate are indispensable research in the shielding design of fusion reactor.At present,the three-dimensional coupling method of particle transport and radiation transport is usually adopted for the calculation of activation problems,and the technical route is relatively mature.However,the calculation of photon dose rate after device shutdown is difficult in practice.So far,there are two main interface code for calculation of the shutdown dose rate,one is the rigorous two-step method(R2S)and another is the direct one-step method(D1S).The R2S method is accurate but time-consuming;the D1S is fast,but the result error is larger.Therefore,this paper developed a new method for fast and accurate calculation of shutdown dose rate.In the new method,the complex irradiation scenario of fusion device and the background of neutron irradiation was fully considered.An approximate linear relationship between the monoenergetic neutron flux and the activation problem was established.By modifying the MCNP source code and introducing the coupling of neutron and decay photon transport,a novel approach NASCA has been developed for fast and accurate calculation of shutdown dose rate.The program has been verified on the JET benchmark by comparison with JET experimental results and the calculating results of R2S and D1S.Results shows the feasibility,high accuracy and efficiency of NASCA for the calculation of shutdown dose rate in the fusion device.At the same time,the new program has also been applied to the activation and dose rate calculations of the helium cooled pebble bed(HCPB)blanket of the European DEMO reactor.In the paper,the effects of impurity nuclides of structural materials in DEMO reactor on the activation level and the influence of geometric structure on the calculation accuracy were explained in detail.The radioactive activity and decay heat level of HCPB were analyzed.The inventory of plutonium produced by neutron uranium reaction and decay was calculated.The NASCA program was used to calculate the global shutdown dose rate of DEMO.The accuracy and efficiency of new approach was verified once again when compared with the R2S method.Based on the linear relationship between the monoenergetic neutron flux and activation,the activation analysis of helium cooled ceramic pebble(HECLIC)blanket in China Fusion Engineering Test Reactor(CFETR)was carried out.The results of the analysis can provide reliable support for the development of HECLIC waste management scheme and the design of the decay heat removal system.Finally,this thesis summarizes the development of new program,verification at JET,and application analysis on DEMO and CFETR.The new program can provide reliable and effective analysis tools for the shielding design of fusion reactor.