How does a nuclear submarine reactor cooling loop work?

[gmax137]

Do you have to manually pressurize the primary circuit in a PWR or do you rely on the water boiling when it starts up to self pressurize?

In a PWR, the pressurizer begins solid (full of liquid) at ambient pressure & temperature - they first 'draw a bubble' in the pressurizer by operating the heaters to bring the pressurizer fluid to saturation, and then draining some liquid from the primary loop. This flashes some steam, creating the bubble. The pressure is then raised by operating the heaters until there is adequate pressure (around 150 psi) to operate the main reactor coolant pumps (they need pressure for adequate suction, and for their seals). Once a reactor coolant pump is running the primary system heats up due to the pump heat. In a commercial plant each reactor coolant pump is about six thousand horsepower, so they put a lot of heat into the water and it doesn't take too long to bring the system to operating temp & pressure.

After that the pressurizer heaters run to counteract the heat losses from the system to ambient, and to accommodate a small trickle flow through the spray line (this small flow keeps the spray line and its nozzle 'hot' to avoid the thermal shock that would otherwise be seen when the spray was turned on. The control system monitors the pressurize pressure and turns the power to the heaters up and down to maintain pressure within the desired band.

 

[sub sailor]

The pressurizer creates and maintains a very high pressure (about 2000 psi) in the primary loop to prevent boiling in the core.

 

[chayced]

The whole drawing leaves much to be desired. But here is some clarification:

The Turbo generator is actually a Turbine Generator, it supplies AC.

The dark Blue Pump is the Seawater Pump which moves seawater that cools and condenses the steam as goes through the condenser.

The light blue pump represents the condensate pumps and feed pumps. Although theoretically possible to have both be the same pump, it's not practical nor safe.

The motor generator set converts DC stored into the batteries into AC and vice verse. On modern boats these are replaced with solid state alternatives.

The pressurizer as stated before is what maintains primary pressure. Although the plant could be operated solid (with no steam void) it would cause radical pressure changes with the slightest volume or temperature change. The pressurizer allows for changing plant power levels and for the routine addition and removal of primary coolant. It also provides a small volume of water to keep the core filled in the event of a leak.

The thrust block, is better referred to as the thrust bearing. It takes the entire thrust of the propeller and transfers it to the ship.

The Emergency propulsion motor or EPM is DC powered and provides a limited amount of propulsion to the ship. This works in conjunction with the clutch so that the main engine is not rotated with the rest of the propulsion train.

Also please note that this drawing is very basic. It only shows one of each component when many of the components operate in pairs or groups. i.e. there is more than one condensate pump.

I'm more than willing to provide any other basic info assuming it's not classified and I still remember.