"Cracking, the failure of the pressure vessel, has always been one of the major issues that can limit the life of the plant," Was said. "If you can't demonstrate its integrity, you're dead in the water in terms of life extensions."
In ways not yet understood, the corrosion that eventually accompanies the pristine water used in nuclear reactors interacts with and exacerbates incipient breaks in metal alloys. Such cracks are among the primary concerns of NRC when considering the future of U.S. reactors, according to Scott Burnell, an agency spokesman.
This cracking, which can affect core components down to baffle bolts, has been studied for 30 years and has still defied explanation, scientists say. In the meantime, it has cost the U.S. nuclear industry some $10 billion due to forced outages, increased inspection requirements, component replacements and increased regulatory scrutiny, according to EPRI.
Getting a handle on age-induced cracking will be one of the principal missions of nuclear scientists and engineers over the next decade, as U.S. regulators are expected to become much more stringent for extensions to 80 years, requiring models that will predict when cracks will occur, Gaertner said.
Since it is hardly time-effective to reproduce 60 years of natural neutron exposure, scientists instead use test reactors to expose steel and other alloys -- up to 25 varieties of metals can be found in reactor systems -- to higher energy radiation that simulates the plant's conditions.
Once the simulations are complete, high-powered imaging is applied to the metals. For this reason, France's MAI has one of the world's most powerful electron microscopes. Such imaging and vast increases in computing power now allow scientists to reconstruct the millions of individual atoms boiled off the surface of a metal into something similar to a photograph. The resolutions achieved allow unprecedented insights into cracking metals, Was said.
"We have a better understanding of how they form and why they form," Was said. "Once we know that, we can use that knowledge to predict into future how hardening will occur and what potential risks are."
There are also risks that could be wholly unanticipated, or other materials to investigate, such as the long-term effect of radiation on concrete, which is poorly understood, DOE's Szilard said.
"We'll be looking for mechanisms that have perhaps not manifested itself up to now," he said.
The industry has become skilled at replacing even large, expensive components like reactor heads and steam turbines -- in overhauls that can cost several hundred million dollars. Once flaws are identified, nearly any structural problem can be solved.
"Today, virtually every component in a reactor plant has been replaced at one point," said Tiffany Edwards, a DOE spokeswoman. "The exceptions are the reactor pressure vessel and the concrete [containment] structures. However, even those could be considered."
The pressure vessel remains the largest challenge for scientists as they try to determine which types of vessel might not make it to 80 years. If underlying flaws are found, there is the possibility that a metallurgical technique called annealing, employed in the past on nuclear reactors in Russia but never in the United States, could be used.