The Effect of Hydrogen on the Ductile Properties of Irradiated Pressure Vessel Steels

Abstract

The influence of hydrogen on the mechanical properties (ductility, fracture strength, and tendency towards delayed failure) was investigated for several irradiated pressure vessel steels. Included were ASTM A302B, A542, and HY-80 steel irradiated at fluences from 8×1018 to 4×1020 n/cm2, E > 1 MeV. Specimens from plate sections of these steels which had been quenched and tempered and some from A542 which were given prestrain and heat treatment modifications were prepared and tested. The effects of strength level from irradiation, heat treatment, and microstructure were thus determined. Reductions in ductility and true fracture strength occurred with increasing hydrogen content but were not extensive at strength levels less than 180 ksi in specimens containing 1 to 2 ppm hydrogen. This concentration, however, produced a marked effect on the ductile properties when the strength level was increased by irradiation hardening or heat treatment beyond this threshold range. Irradiation hardening increased the magnitude of the decrease in notched strength resulting from a given hydrogen content in all of the steels and conditions tested. Hydrogen induced delayed failure, however, did not occur to any large extent in HY-80, A302B, and A542 steel in the normal quenched and tempered condition even after irradiation to fluences in excess of 1020 n/cm2, E > 1 MeV, and hydrogen concentrations of up to 4 ppm.

Alloying of Steel and Graphite by Hydrogen in Nuclear Reactor

“…Results of the IPH concentration in steel analysis carried out in the USA are shown in Table 2 [4]. One can see that the greater the fast neutron fluence (FNF) the greater the hydrogen content.…”

“…Particularly reactor pressure vessels (RPV) of the WWER-440/230 project were manufactured without stainless cladding that is were in contact with primary circuit water and accessible for hydrogen as a product of RPV wall corrosion. Analysis of the combined radiation-hydrogenation embrittlement of the 48TS type vessel steel was performed in [3] where at the mention of the American [4] and own data question concerning unknown source of hydrogen in metal that was irradiated in nuclear reactor in hermetic ampoules (was named as "irradiation-produced hydrogen" (IPH) was raised. Hydrogen concentration was determined by thermal degasation method at temperatures up to 1000°C with gas chromatograph (thermal conductivity detector) registration of gas released.…”