Prohibitively expensive.

"The Nuclear Industry is heavily promoting the idea of building small modular reactors (SMRs), with near-zero prospects for new large power reactors in many countries. These reactors would have a capacity of under 300 megawatts (MW), whereas large reactors typically have a capacity of 1000 MW.

The enthusiasm for SMRs has little to do with climate-friendly environmentalism.

About half of the SMRs under construction (Russia's floating power plant, Russia's RITM-200 icebreaker ships, and China's ACPR50S demonstration reactor) are designed to facilitate access to fossil fuel resources in the Arctic, the South China Sea and elsewhere.

Another example comes from Canada, where one application of SMRs under consideration is providing power and heat for the extraction of hydrocarbons from oil sands.

A second striking feature of the SMR universe is that it is deeply interconnected with militarism:

Argentina's experience and expertise with small reactors derives from its historic weapons program, and its interest in SMRs is interconnected with its interest in small reactors for naval propulsion.
China's interest in SMRs extends beyond fossil fuel mining and includes powering the construction and operation of artificial islands in its attempt to secure claim to a vast area of the South China Sea.
Saudi Arabia's interest in SMRs is likely connected to its interest in developing nuclear weapons or a latent weapons capability.
A subsidiary of Holtec International has actively sought a military role, inviting the US National Nuclear Security Administration to consider the feasibility of using a proposed SMR to produce tritium, used to boost the explosive yield of nuclear weapons.
Proposals are under consideration in the US to build SMRs at military bases and perhaps even to use them to power forward operating bases.
In the UK, Rolls-Royce is promoting SMRs on the grounds that "a civil nuclear UK SMR programme would relieve the Ministry of Defence of the burden of developing and retaining skills and capability".

SMR projects won't be immune from the major cost overruns that have crippled large reactor projects

(such as the AP1000 projects in the US that bankrupted Westinghouse).

Indeed cost overruns have already become the norm for SMR projects. A 2015 report by the International Energy Agency and the OECD Nuclear Energy Agency predicts that electricity costs from SMRs will typically be 50−100 percent higher than for current large reactors, although it holds out some hope that large volume factory production of SMRs could help reduce costs.

A 2016 OECD Nuclear Energy Agency report said that electricity produced by the Russian floating plant is expected to cost about US$200 per megawatt-hour (MWh), with the high cost due to large staffing requirements, high fuel costs, and resources required to maintain the barge and coastal infrastructure.

Thomas Overton, associate editor of POWER magazine, wrote in 2014: "At the graveyard wherein resides the "nuclear renaissance" of the 2000s, a new occupant appears to be moving in: the small modular reactor (SMR)...

"Over the past year, the SMR industry has been bumping up against an uncomfortable and not-entirely-unpredictable problem:

It appears that no one actually wants to buy one."