The future Columbia class SSBN(X)'s reactor may be as quiet as SSKs on Battery

How should this diagram be altered to represent a Heat Exchange Reactor with Electric Drive? Diagram courtesy Bright Hub Engineering.

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One of the quieting/stealth features on the future Columbia class SSBN(X) is a possible heat exchanger quiet mode in its proposed S1B reactor. This reactor is also called Columbia Program Element PE0603570N/Project 3219 (see page 32).

Apparently the S8G reactor on the current Ohio SSBN already uses a heat exchanger. I think it logical that the heat exchanger aspect will be carried over to the future Columbia.

Minimising moving parts contributes to quiet mode. Such a quiet mode may ideally be available when future Columbia's are operating at their (about 5 knots?) on station cruising speed. 

The heat exchanger tip comes from Josh in Comments on 29/9/16 12:23 AM: 

"And important attribute of the S8G fitted to Ohios is that it is a natural circulation reactor (at least at low power), relatively revolutionary at the time. The core is placed low and the heat exchanger placed high in the primary coolant loop such that the hot coolant rises to the exchanger then falls back down the other side of the loop once cooled off without the use of a pump. This eliminates an entire type of noise from plant, at the cost of size and weight apparently. The wider hull of a boomer makes this more practical to do in an SSBN than an SSN. Its not clear if the practice carried through to the Seawolf or Virginia's reactors; it might well not have been for size reasons or because more cost effective means of quieting coolant pumps became available (turbopumps, electrical systems that remove the 'snap' noise of pump engagement, etc).

Its also worth noting that any SSBN would spend its patrol at 5knts unless it was fired upon. The pump jet arrangement would only be advantageous getting to station. The Russians likely have much more reason to worry about being tracked during transit than the Americans due to their [Russian] base geography and possibility of USN SSNs off their SSBN bases at any given moment. The USN keeps boats deployed off Russian coasts at much more often than the reverse case, even during the cold war. I suspect its quite the rarity for an Akula [SSN] to appear off Maine [Kings Bay, Georgia SSBN Base] or [Bangor in Washington state] these days."

Other features contributing to the Columbia's quietness/stealth will be electic drive, X-plane rudders and pump jets - on these see this 2013 reference and a major briefing to Congress August 18, 2016 reference. 

If all of these features are in the Columbia's and perhap future US SSN(X)s they may make them quieter than SSKs on battery mode.

Submarine Matters' mentions of Columbia class stealth are at articles dated September 28, 2016

and August 24, 2016.