Effects by Sea Wave on Thermal Hydraulics of Marine Reactor System

TLDR

The study investigates how sea waves affect the thermal hydraulics of the Japanese nuclear ship Mutsu’s reactor system during cruising, and discusses the mechanisms by which wave‑induced motion alters water levels and reactor power. Experiments were conducted by cruising the Mutsu at various wave heights and directions, and the resulting data were analyzed in time‑domain using a modified RETRAN‑02/GRAV code that incorporates ship motion, and in frequency‑domain with the Blackman‑Turkey method to compute spectra and response functions. Vertical acceleration from ship motion directly varied water levels in the steam generators and pressurizer, with the largest changes during head waves and the smallest during following waves; the following wave also produced greater reactor‑power variation when shaft‑speed feedback control was active, and the reactor‑power response to steam‑flow variation during rough seas had a gain or phase shift similar to that without control‑rod work.

Abstract

This paper describes the experiments of the first Japanese nuclear ship 'Mutsu', to investigate the effects of sea wave on the thermal hydraulics of marine reactor system while cruising through various sea conditions. The experimental data were analyzed in time-domain by RETRAN-02/GRAV code. This code was modified so as to simulate the ship motion effect on reactor thermal hydraulics. The data were also analyzed in frequency domain by Blackman Turkey method for the calculation of the spectrum and response function. The experiments involving ship maneuvering were performed by cruising on different wave heights, as well as wave directions in the northern Pacific ocean. From the experiments, vertical acceleration due to ship motion was found to induce direct variation of water levels in the SGs and the pressurizer. The water level variations were largest in the head wave, but smallest in the following wave. On the other hand, the following wave caused greater variation of the reactor power when the feed back control for the shaft revolution speed was used. Mechanism of response of water levels and reactor power with respect to the external forces are discussed. The response function (gain or phase shift) of reactor power to steam flow variation by the wave during cruising at rough sea condition was found to be roughly that without the work of control rod.