Neutrons at W 7-X

The W 7-X deuterium plasma (18 MW NI, 4 keV, 1.5.10"2"0 m"-"3) will produce 6.10"1"6 neutrons during a 10 s pulse. A detailed geometrical model of the W 7-X experiment has been set up for the neutron transport calculations by the MCNP4B code (Monte Carlo neutron particle). The fast neutron flux (2.5 MeV) inside the torus is 100 times higher than inside the hall. The almost homogeneous thermal neutron flux inside the hall is reduced 30 times by doping the concrete walls with 700 ppm of boron. For a pulse scenario of 500 pulses per year the annual dose equivalent rate outside of the hall is down to the legally allowed level of 0.3 mSv/year, mainly by photons, due to the shielding of a 1.8 m thick concrete wall. The skyshine by the flux penetrating the 1.2 m thick concrete roof leads to 0.01 mSv/year at the fence. The structure of the experiment gets activated by the neutrons which for the chosen pulse scenario leads to a total activity varying between 2.6.10"9 and 1.2.10"1"3 Bq. The dominant isotopes are the superconductor compound ("2"8Al, "6"6Cu, "9"4"mNb) on the short timescale (min's) and the steel components ("5"1Cr, "5"4Mn, "6"0Co) on the long timescale (months and years). For the austenitic steel a concentration of 50 ppm of Co has been assumed. After 10 years lifetime of the experiment it takes 4.8 years until the long living "6"0Co (T_1_/_2 = 5.3 years) becomes the dominant radioactive isotope. Having waited for totally 10 years the specific activity has almost come down to 1.10"5 Bq/to at which level a freely use of the material can be allowedSIGLEAvailable from TIB Hannover: RA 71(2/341) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman