Integral modelling of the ITER cooling water systems radiation source for applications outside of the Bio-shield

During the plasma pulses, the neutron-induced activation of the cooling water will produce an important contribution to the radiation levels in the ITER Tokamak Complex. The resulting radiation field has a complex spatial distribution due to the combination of decay and production of radioisotopes in the intricate cooling lines that feed the numerous systems inside and outside the bio-shield. An accurate estimation of the cooling water radiation field is necessary to ensure that the radiological zoning is respected. As of today, this issue has been studied using simple, manually defined geometries with limited representation of the tens of thousands of components that constitutes the cooling circuits. This work describes the first production of a realistic and up-to-date integral neutronics modelling of all the cooling systems containing activated water beyond the bio-shield. The work was enabled by the development of computerized geometry modelling techniques to automatically simplify and dimension the system components. An independent review of the method ensured the validity of the simplified model. Moreover, automated scripts produced the activated water radiation source associated with the geometry model. The latter was obtained by linking thousands of cylinders, representing the coolant volumes, in chains of MCNP cells that reproduced the paths of the water lines inside the Tokamak Complex and, eventually, by calculating the radioisotopes activity in each cell. This methodology greatly speeds up the modelling time, reduces the risk of human error and enables the representation of the Tokamak Cooling Water System radiation source with an unprecedented degree of realism.