Session: MF-06-01 Materials and Technologies for Nuclear Power Plants-1

Paper Number: 123229

123229 - Investigation of Fracture Toughness of the High Flux Reactor Vessel Surveillance Test Specimen 2023 

The reactor vessel of the High Flux Reactor (HFR) in Petten has been fabricated from Al 5154 – O alloy grade with a maximum Mg content of 3.5 wt. %.  The vessel experiences high neutron fluences (notably at the hot spot), of the order of 10²⁷ n/m², during its operational life. Substantial damage to the material’s microstructure and deterioration of mechanical properties can occur at these high fluence conditions. To this end, a dedicated surveillance program: SURP (SURveillance Program) is executed to understand, predict, and measure the influence of neutron radiation damage on the mechanical properties of the vessel material. In the SURP program, test specimens fabricated from representative HFR vessel material are continuously irradiated in two specially designed experimental rigs. Periodically a few surveillance specimens are extracted and tested to evaluate the changes in fracture toughness properties of the vessel as a function of thermal neutron fluence (or transmutation Si).

 

The current paper presents fracture toughness and fractography results from the surveillance specimen to be withdrawn in November 2023. Estimated thermal neutron fluence of the specimen to be tested in this campaign is 19.3 x10²⁶ n/m², which is ~2.9 x10²⁶ n/m² more than the thermal fluence received by the specimen tested in SURP 2021 campaign. This is equivalent to an increase of the total silicon content[1] (due to transmutation) to 4.03 wt.%. The fracture toughness results will be compared against the previous SURP data to check if the fracture toughness values would remain unchanged and follow the plateau behavior established in the previous SURP campaigns. SEM fracture surface investigation will be performed to study the nature of the fracture (brittle vs ductile, transgranular vs intergranular) to verify whether the fracture mechanisms are still controlled by the bulk of the grains or by grain boundaries. Additionally, SEM–WDS and TEM microscopy investigations will be performed to measure the transmutation Si content and investigate various inclusions and irradiation induced precipitates in the microstructure. The fracture toughness results will be discussed in correlation with the observed microstructural results.

 

[1] The reported thermal fluence and Si content values for SURP 2023 specimen are obtained from neutronic analysis. Actual Si content measurements are planned in 2024 using SEM-WDS.

Presenting Author: F. H. E. De Haan - De Wilde NRG

Presenting Author Biography: Ciska is working for NRG for more more than 15 years in asset integrity team. She is currently the cluster manager of decommissioning and waste department. She is also project manager of HFR SURP project.

Authors:

M. Kolluri NRG
F. Naziris NRG
m.a.l. Laot NRG
h.h.s.p Bregman NRG
S. P. A. Hageman NRG
F. H. E. De Haan - De Wilde NRG