Between 1967 and 1989, 49 French pressurized water reactors went critical. A surveillance program is implemented on each unit with respect to the base metal of the core shell forging, weld, and heat-affected zone of the pressure vessel made of low-alloy steel 16 MND 5 (ASTM Specification for Quenched and Tempered Vacuum-Treated Carbon and Alloy Steel Forgings for Pressure Vessels, A508, Class 3, UNS K12042).
Preirradiation chemical compositions and mechanical properties for 35 units, together with data obtained from 61 surveillance capsules, are presented. The work performed in 1987 and 1988 on the Chooz A unit for the vessel safety reassessment is also presented and results are discussed. Chemical compositions and mechanical properties are homogeneous and scatter is found to be small. The percentages of elements most likely to promote radiation embrittlement, such as copper and phosphorus, are low. Neutronic and dosimetry characteristics for vessel and surveillance capsules are overcome by recent developments, which are taken into account. Brittle-ductile transition temperature shifts are presented for seven capsules removed from Chooz A (neutron dose in the range 1.2 × 1019 n ∙ cm-2 to 1.1 × 1020 n ∙ cm-2) and for 54 capsules removed from thirty-one 900-MW units (neutron dose in the range 0.3 × 1019 n ∙ cm-2 to 5 × 1019 n ∙ cm-2, which is nearly 75% of the design lifetime).
Materials homogeneity in mechanical and chemical properties, equivalent operating conditions of reactors, and surveillance program testing performed by only one laboratory contribute to high quality and reliability of our data bank.
According to the 900-MW unit surveillance program data, transition temperature shifts are below 80°C for 5 × 1019 n ∙ cm-2. This confirms the expected vessel life spans, showing that the initial lifetime could be extended for most vessels.