WASHINGTON (CN) - Operators of nuclear power plants will no longer be required to perform certain costly remediation procedures designed to prevent the metal in pressurized water reactor vessel walls from disintegrating.
The Nuclear Regulatory Commission has admitted that it overestimated the risk of metal fatigue during high pressure changes in the temperature of a nuclear reactor.
Rapid cooling of the inside of a reactor can cause thermal stress resulting in metal fatigue weakening the rebar used to reinforce the walls of the vessel, under pressure this could cause the reactor wall to crack, particularly if there is a preexisting flaw in the metal.
The agency had developed a number of screening criteria, which if exceeded, would require shut down and repair of the power plants. The NRC now says the criteria impose unnecessary financial and operational burdens on plant operators.
None of the currently operating nuclear plants exceed the existing screening criteria but several are close, and several newer plants are expected to exceed the screening criteria within the lifetime of their 40 year operating licenses.
New screening criteria allows smaller flaws found in reactor walls to go unrepaired and allows interior cracks to get closer to the surface of the reactor walls before the crack needs to be repaired.
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