Void transit time calculations by neutron noise of propagating perturbation using complex-valued weight Monte Carlo

This paper focuses on the propagation of neutron noise induced by void formation in coolant/moderator moving upward in a reactor core within the limit of the first order perturbation. A new Monte Carlo method to solve the frequency domain transport equation of neutron noise observed by in-core neutron detectors has been proposed by adopting the complex-valued weight Monte Carlo technique. The technique has already been established by the author of the present paper to implement the B₁ approximation method into the Monte Carlo method. The newly-developed Monte Carlo method is compared with the conventional method based on the diffusion theory for neutron noise analyses. The Monte Carlo method makes a significant difference in neutron noise distribution as compared to the diffusion theory, suggesting that the transport theory should be introduced for accurate estimation of neutron noise in a reactor core. A numerical test is conducted to simulate the measurement of void transit time or void velocity in a reactor core by calculating a cross power spectral density between two in-core detectors. (author)