From this point of view, even a different in VAT rates are a form of subsidy 🤷 But I would argue that talking of “market levels” doesn’t make sense here until you factor in externalities - such as air pollution or carbon emissions. And taxes like carbon tax are a way to factor in these externalities back into the consumer price of the product. But if you accept that notion, then the subsidy is exactly the same mechanism applied to products with potential to reduce externalities, such as low-carbon energy sources.
construction of a nuclear power plant
No, I don’t limit this to nuclear power plants but to all carbon-removing sources.