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Cooperating with students from the National Research Nuclear University MEPhI (Russia), scientists from the Kurchatov Institute (Russia) have used new technology to extend the service life of the VVER-440 reactor up to 45 years, saving the cost of dismantling the old vessels. The results of the research were published in the Journal of Nuclear Materials.
A water-water energetic reactor vessel, the most popular type of reactor in the world, the VVER-440 is one of the most important units in a nuclear power plant. Its safety and operating efficiency largely define the safety level of the nuclear plant.
Operating - Reactor - Vessel - Exposure - Results
When operating, a reactor vessel is subject to fast neutron exposure, which results in radiation hardening (loss of plasticity) in the reactor's base metals due to the formation of nanoscale radiation-induced defects and phases.
Due to reactor vessel exposure to radiation and operating temperature (~ 300оС), segregations of impurity elements are formed on grain boundaries, which results in a reduced strength of these grain boundaries. The formation of harmful impurity segregations in grain boundaries results in reduced crack resistance in the metals.
Life - Cycle - Reactor - Vessel - Probability
This limits the life cycle of the reactor vessel, as the probability of a brittle fracture upon reflooding it with cold water in case of emergencies increases over time. In 1991, in order to extend the service life of the VVER-440 reactor vessel, scientists conducted a recovery annealing process on a number of these vessels, thus extending their service life up to 45 years.
Researchers say that in order to extend reactor service life up to 60 years, they would need to carry out a second recovery annealing process after conducting preliminary studies of the structure and mechanical properties of a reactors' base metals, one that has been in operation for a long time after the first annealing.
Technology - Recovery - Annealing
The technology for recovery annealing was developed and patented...
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