I'm not sure that question has an answer; the regulators are fairly ad-hoc which is why reviews take multiple years instead of happening quickly and it the flux in requirements seems linked to the cost overruns (otherwise the planners would learn and the cost estimates would have error in line with any infrastructure project). Seems doubtful that there are 'some regulations' static enough to be targeted. I have read a lovely article somewhere describing how the regulators interpret nuclear being cost-effective as evidence that the standards need to be raised but I cannot lay my hands on it. However - amusingly - while considering what a reasonable answer would be I discovered that the current head of the NRC appears to have been trained as a priest:

He has a master's from Yale Divinity School and Yale School of Forestry and Environmental Studies, and a Bachelor of Arts degree in Religious Studies from Valparaiso University. [0]

And previous members have been actively opposed to nuclear power as a concept:

After leaving the NRC, Jaczko called for a global ban on nuclear power. [1]

This is not an environment where reasonable and supportive people are trying to make nuclear power work. The NRC is a high-risk arena where the companies involved have confidence only that their applications may be reviewed by people who range between under-educated about the issues and actively hostile to their success as commercial ventures. There is a reason that the industry is almost alone in the 21st century as a technology that is getting harder to implement. That reason is a cult-like group of anti-nuclear activists who are willing to see people starve and freeze before they will allow a Fukushima to happen every 50 years. This is a significant contributing factor to why it is getting harder and more expensive to build nuclear plants.

[0] https://en.wikipedia.org/wiki/Christopher_T._Hanson [1] https://en.wikipedia.org/wiki/Gregory_Jaczko

Ooh! I know! The vienna convention on nuclear power! :D