The Nuclear Regulatory Commission's (NRC's) action plans in the aftermath of vessel head penetration cracking have to be upgraded, according to Nils Diaz, chairman of the Advisory Committee on Reactor Safeguards (ACRS).
The action plans, based on the recommendations of a Lessons Learned Task Force, "provide a sound technical basis" for assessing industry efforts to prevent vessel head penetration (VHP) cracking and reactor pressure vessel degradation, but they "need to be augmented in some areas," the ACRS said. It also said that the basis for NRC's determination of reactors' susceptibility to VHP cracking, measured in effective degradation years, is "adequate for prioritising VHP inspections for the near future." However, the ACRS said that because it is based solely on operating time and temperature, it is "incomplete because it does not take into account stress and material parameters." Meanwhile, US operators will now be able to import vessel heads under a general licence rule".
The rule covers reactor pressure vessels, including their major component parts: reactor primary coolant pumps; on-line reactor fuel charging and discharging machines; and complete reactor control rod systems. Those items currently require a specific licence. Under a general licence, NRC provides authorisation to import items that fall into a certain category and thus removes the need for companies to apply for a licence for each individual importation of the item.
The rule change would not cover steam generators.