Patent Number: 
Section: claims

1. A nuclear reactor plant including:a reactor;a coolant in the reactor;a gas system connected to the reactor and adapted to provide a gas supply to and gas removal from space above the coolant;a device for injection of gas into the coolant, the device installed partially in the coolant and partially in the space above the coolant, and the device adapted to supply gas from the space above the coolant to the coolant, the gas system and device configured to carry out steps including:supplying gas to be injected into the coolant from the gas system to the space above the coolant;injecting gas into the coolant by maintaining the gas pressure higher than coolant pressure in the device; andinjecting gas into the gas system from the space above the coolant. 2. The nuclear reactor plant according to claim 1 comprising piping, gas filter and a pump, the piping connected into a loop, the loop having an end adapted to receive gas from the space above the coolant of the reactor and another end adapted to supply gas to the space above the coolant. 3. The nuclear plant of claim 1 further comprisinga controller configured to control a gas supply to the space above the coolant of the reactor and gas removal from the space above the coolant of the reactor; anda controller configured to control the device for injection of gas into the coolant and gas injection into the coolant from the space above the coolant.