Using of SPT method for estimation of mechanical properties changes of RPV steels after irradiation in the Halden reactor

M Adamech,J Petzová,M Kapusňák,M Březina

doi:10.5334/uproc.2

Abstract

The paper deals with experimentally estimation and comparison of the mechanical properties changes of RPV steels before and after irradiation of samples in Halden reactor in Norway coming from Unit #3 and #4 of NPP Mochovce (still under construction). Altogether 180 SPT and 30 mini-tensile samples in two sets were prepared for irradiation, obtained from weld metal material (Sv10ChMFT) and base material (15Ch2MFA). In general, a good agreement between results obtained by SPT technique and using mini-tensile specimens was found. Both, base and weld metals of RPVs were found to be bainitic. After that, the first set of samples was irradiated in Halden reactor at temperature T irr = 270 - 280°C with intention to use two fluence values: ∼ 1.0 × 10 24 n/m 2 and ∼ 2.0 × 1024 n/m 2 (> 1 MeV), respectively. Specimens after 1st irradiation were successfully tested and preliminary results show small increase of the strength characteristics (R e , R m ) if compare to “zero condition” testing results. FATTs, evaluated by the temperature dependence of the SPT energy, exhibit transition behaviour and shift towards higher temperatures.

Highlights

The reactor pressure vessel (RPV) is the most crucial component of every nuclear power plant (NPP) and continuous evaluation of its mechanical properties is necessary for safe operation
The principle of SPT testing procedure which has been applied in VUJE is the penetration of a disk shape specimen by a hemispheric rod and recording of loads and deflections during the test
Using relatively simple testing system and with one type of specimen only, it is possible to estimate yield stress and ultimate tensile strength, and fracture appearance transition temperature (FATT) based on the results of temperature dependence of small punch energy determined from the area under the load – deflection curve

Summary

Introduction

The reactor pressure vessel (RPV) is the most crucial component of every nuclear power plant (NPP) and continuous evaluation of its mechanical properties is necessary for safe operation. The wall of the RPV around the reactor core is exposed to high doses of neutron flux and the steel becomes brittle [1]. The neutron radiation causes changes of mechanical properties; in the first place, it is the shift of the ductile-brittle transition temperature towards higher values. Standard tests require collection of large-dimension samples coming from the precious materials, usually obtained after exposure to radiation. Since samples for SPT testing are quite small, high activity of irradiated materials is no longer an issue. The SPT technique represents a very useful and effective method applied for characterization of mechanical properties such as ultimate tensile strength (Rm), yield stress (Re) and fracture appearance transition temperature (FATT) [2, 3]

Methods

Results

Conclusion