Protective barrier measures

I would say there are three main factors - safety, reliability and economic profit for NPP's owner. If the NPP can be operated in a safe and reliable way and the investments the owner must make will be paid off during expected life-time, it's usually a no-brainer.

You must look for in Google for nuclear power plant life management. There are different documents from IAEA, OECD, etc.

Almost all the plants with more than 20 years of operation have developped plant life management programs.

For example, the OECD has the document "Nuclear Power Plant Life Management and Longer-term Operation".

Thanks for your response.