Evalvacija metod za kalibracijo moči velikih tokamakov

Fusion reactors based on the fusion of deuterium (D) and tritium (T) emit large amounts of 14 MeV neutrons. As exactly one neutron is emitted per such fusion reaction, neutron yield measurements are the most direct way for the determination of the released energy. Accurate measurements of neutron output will be important in fusion power plants for the determination of a reactor’s power output, tritium accountability in the system, the assessment of neutron damage of components, and for the assessments of the dose rates in the humanaccessible parts of the machine. Additionally, reliable information on a reactor’s neutron emission is important for fusion plasma analyses. The dissertation consists of an introduction and three chapters describing the author’s work related to the calibration of neutron yield detectors at Joint European Torus (JET). Whereas most of the work was performed for the DD and DT calibrations of the tokamak JET, the lessons learned are relevant for other machines as well. The focus of the work are thus the calculations performed in support of the absolute calibrations of the neutron detectors in large fusion reactors. The details of the neutron source properties of the neutron generator used in the calibration of JET’s neutron detectors to 14 MeV neutrons were simulated. This neutron source description of the neutron generator was then used in calculations in support of the calibration experiments. Together with measurements, these calculations resulted in the calibration factors for JET’s main neutron detectors. Additionally, the use of a newly released variance reduction tool ADVANTG was tested for the speed-up of the simulations of the fission chamber responses in JET-relevant geometry. These analyses showed that the computational intensity of these simulations can be significantly reduced. The author’s main contributions presented in this dissertation are the detailed reproduction of the neutron emission properties of a neutron generator, computational quantification of corrections applied to the measured calibration factors, and one of the first independent tests of the ADVANTG code on the model of the tokamak.Fuzijski reaktorji, ki delujejo na osnovi zlivanja jeder devterija (D) in tritija (T), sprostijo velike količine nevtronov z energijo 14 MeV. Pri vsaki reakciji zlivanja devterija in tritija se sprosti en nevtron, zato so meritve števila sproščenih nevtronov, oziroma meritve pridelka nevtronov, najbolj neposreden način za merjenje sproščene energije. V bodočih fuzijskih elektrarnah bodo meritve izseva nevtronov pomembne za meritve fuzijske moči med obratovanjem, spremljanje in nadzor količine tritija v sistemu, ocene poškodb komponent kot posledice interakcije z nevtroni ter ocene hitrosti doz v delih naprave, kjer je predviden dostop delavcev. Poleg tega je natančno poznavanje nevtronskega izseva pomembno tudi pri analizi fuzijske plazme. Disertacija vsebuje uvod v problematiko in tri poglavja, ki opisujejo avtorjevo delo povezano s kalibracijo detektorjev nevtronov tokamaka JET. Čeprav je bila večina dela opravljenega v podporo kalibraciji detektorjev nevtronov tokamaka JET na nevtrone sproščene v DD in DT fuzijskih reakcijah, so rezultati in izkušnje relevantne tudi za druge velike fuzijske reaktorje. Delo se tako osredotoča na izračune v podporo kalibracijam detektorjev nevtronov velikih fuzijskih naprav. Predstavljeno je simuliranje produkcije nevtronov v generatorju DT nevtronov, izračuni v podporo kalibracijskim eksperimentom in testiranje relativno novega programa ADVANTG za pospeševanje simulacij Monte Carlo na geometrijah relevantnih za JET, ki lahko bistveno zmanjša računsko zahtevnost simulacij v podporo kalibraciji detektorjev nevtronov. Avtorjevi glavni prispevki, predstavljeni v disertaciji, pa so reprodukcija lastnosti generatorja nevtronov v nevtronskih simulacijah, računska kvantifikacija popravkov izmerjenih kalibracijskih faktorjev in eno od prvih neodvisnih testiranj programa ADVANTG na modelu tokamaka