The 250-MW boiling water Gundremmingen reactor (KRB-A) in the Federal Republic of Germany has been decommissioned by the utility owners. A joint USA/FRG/UK study, conceived by the U.S. Nuclear Regulatory Commission (NRC), is underway to evaluate archive material and trepanned material removed from the vessel for a critical assessment of power reactor versus test reactor environmental effects.
This report describes the test reactor irradiation assessments of the archive forging material using light-water and heavy-water reactors. The experiments included Charpy V-notch specimens, tension specimens, and hardness tiles. The results are compared to investigate whether neutron spectrum differences are of importance in the accelerated irradiation exposures. The findings are also compared to published observations for the trepan material irradiated at much lower fluence rates in service. The results of electron microscope and small angle neutron scattering experiments are reported giving information on the radiation-induced microstructure, principally of the vessel trepan material.
There was no evidence of neutron spectrum or fluence rate effects on the embrittlement of ASTM L-C oriented material after accelerated irradiation.
The microstructural studies showed clear evidence of the presence of copper-rich and vanadium-rich precipitates in the trepan material. The copper-rich precipitates contained manganese and nickel, and the vanadium-rich precipitates contained copper.
A suggestion is made as to the origin of the orientation dependence of impact properties in the KRB-A reactor pressure vessel.