... We have nuclear solutions for anything ship-sized.
Maersk etc. cannot afford an aircraft carrier. If someone has an economic design which would compete with a hydrogen fuel cell then there is only the messy problem of certifying it in multiple jurisdictions. Maersk etc. are most unlikely to engage in that task...
The price I'm finding for the Emma Maersk is $145 million.
The prices being bandied about for NuScale are around $5,000/kW. 120 MW would cost about $600 million, so it appears that you're right, at least about capital cost.
Operating cost may be another matter. The Emma Maersk has a total on-board power of roughly 110 MW. It burns 14,000 l/hr with the main engine going full bore at its 25.5 knots max speed, about 6300 l/hr "slow steaming". Its 20.8 MW of diesel generators are stated to burn 6.6 tons or 6600 l/hr at full power (this appears to be high by about a factor of 2 but it's what I've got). I'm unable to find just what its slow-cruising speed is; I found a quote from a Maersk rep claiming that slowing down 20% saves 40% on fuel, but the reduction here is a full 55%. I'm going to guess 19 knots. HFO is about $400/ton worldwide and density is roughly 1.0, so fuel would cost $2520/hr at economy cruise and $5600/hr all-out. The diesel generators running at half power would add another 3300 l/hr or $1320/hr. Assuming the ship is working hard and on the seas 80% of the year, that's 7008 hours or $26.9 million/yr cruising slow, $48.5 million full bore.
A pair of NuScales at 60 MW(e) apiece would boost total system power from ~110 MW to a full 120 MW, and on-board electric loads are likely to run considerably less than 30 MW. If this translates to a boost from 90 MW to 105 MW at the propeller shaft, you'd expect to see speed go from 25.5 to 26.8 knots. That's almost 50% faster than economy cruise on diesel.
Going nuclear looks marginal at $600 million; you'd need over 22 years of fuel savings to pay it off vs. economy cruise, though you'd probably have 40% more revenue. At $300 million it would be a no-brainer. You could pay for the power plant with just 7 years of fuel savings while running at maximum speed between ports and making more money. I suspect that the breakpoint is at about $450 million, maybe more considering that you'd also be replacing the main propulsion engine and maybe a diesel generator too (the pair of reactors are themselves redundant). So, if the price for a NuScale falls to $3750/kW we should be seeing some serious interest.
Per the EPA, bunker fuel burns to make 11.27 kgCO2/gallon. A CO2 tax of $100/ton would add about $1.13/gallon to the fuel price, and nuclear is immediately in the running even at $5000/kW.
If someone has an economic design which would compete with a hydrogen fuel cell then there is only the messy problem of certifying it in multiple jurisdictions. Maersk etc. are most unlikely to engage in that task...
When the first hydrogen-powered ship explodes in harbor, it may be difficult to find ports that will accept them either.
I'm struck by how cheap HFO is. $400/ton is about $1.50/gallon, $63/bbl. That's barely more than crude oil.