Effect of steam-exhaust operation of secondary coolant circuit on ship reactor blackout accident

The ship reactor blackout accident can potentially lead to the severe accident and the radioactive fission product release. In the absence of auxiliary electrical source, the effective mitigation of the accident aftereffect is very important. As the exclusive heat trap in the reactor coolant system, the steam-exhaust operation (SEO) in the secondary coolant circuit (SCC) plays an important role in the accident mitigation. In view of the character of ship nuclear power plant (NPP), the ship reactor blackout accident (SRBA) under the typical operating conditions is simulated by the RELAP5/MOD3.2 code, and the mitigation of SEO on the accident is analyzed. It is found that (1) reasonable SEO can obviously mitigate the accident for several hours, the SEO with 1% rated steam flux of secondary coolant circuit provides about 7 h for the mitigation of accident, (2) a less steam flux of SCC during the SEO means a slower pressure drop of steam generation (SG) and a more time we can mitigate the accident, there are 1.5 h between the SEO with 1% rated steam flux and that with 3% rated steam flux, (3) the SEO without the feed water device can hardly mitigate the accident, and (4) during the blackout accident, the SEO with intercurrent steam flux control valve failure will result in the decrease of mitigation time because of the quick decrease of SG pressure, but the mitigation effect is also obvious.