The PWR used for power [1] is to first order "the same type of reactor used in submarines" in the sense that it is a thermal (in terms of neutron spectrum) reactor which is cooled by pressurized water.

The submarine reactor uses highly enriched uranium and, I believe, burns like a cigarette, which makes it easy to start and stop the reactor without worrying about [2]. It doesn't produce a lot of Plutonium because it doesn't have much U238 in it. I believe the fuel elements are horizontally oriented. It's built tough because it might get knocked around in a war.

The commercial reactor has vertically oriented fuel elements and tries to burn the fuel uniformly along the axis because this minimizes cost, because minimizing cost is a matter of maximizing power for a certain sized reactor core, and maximizing power is a matter of maximizing heat transfer out of the interior of the fuel rod and to the coolant, so you want to be producing and removing heat from the whole volume of the core. Temporal uniformity helps with spatial uniformity so the reactor is not so good at starting and stopping, but it can follow loads [3]

Notably the west (where natural gas is available) quit building coal burning power plants at the same time it quit building nuclear power plants, partially because of pollution [4], partially because a 100% steam turbine powerset as used in coal and nuclear plants can't compete with a gas-fired combined cycle powerplant which combines a very-low capital cost gas turbine with a steam turbine that is about half the size (and cost)

The small LWR is a pipe dream because LWR economics improve as the reactor gets bigger. One reason why we can't build reactors on an N-th of a kind basis is that every time we build one we decide the economics weren't that good and they might get better if we scale the design up. Had NuScale ever built a plant they probably would have tried scaling it up too.

It is claimed small reactors could be easier to build but until somebody actually builds one, this claim is hard to take seriously.

One path that makes sense is to pick an optimized design for a large reactor and "get good" at building it, it could be an advanced Western design like the AP1000 or something like the Chinese Hualong One which is an improved version of the reactors that France built in the glory days. The Russians are really good at building the VVER, their version of the PWR.

The other path is to build a reactor that works at much higher temperatures such as the fast breeder reactor, high temperature gas cooled reactor, or molten salt reactor and couple it to a gas turbine powerset or use the heat to produce hydrogen directly. [5] This is still decades away.

[1] Pressurized Water Reactor, there is also a Boiling Water Reactor in which the water boils in the core but it's not a vast difference: these are both called LWRs (Light Water Reactor)

[2] https://en.wikipedia.org/wiki/Xenon-135

[3] https://www.oecd-nea.org/upload/docs/application/pdf/2021-12...

[4] https://en.wikipedia.org/wiki/Acid_rain (SO2 from coal burning plants, ironically, masked the warming effects of CO2 until we cleaned up coal plants)

[5] https://en.wikipedia.org/wiki/Generation_IV_reactor