15MnTi steel as a support plate must withstand both the weight of the reactor core of about 100 tons and dynamic loads at 40°C to 50°C. In this study, the steel was embrittled by the neutron irradiation from the reactor core. The ductile-brittle transition temperature was also increased.

The specimens were taken from base plate, weld metal, and weld heat-affected zone. The specimens were irradiated in a swimming pool reactor (SPR).

The test results included impact energy (αk), reference transition temperature (RTNDT), and transition temperature increase (ΔTcv) of 15MnTi steel under the neutron exposure 1 to 2 × 10¹⁸n/cm²(E > 1 MeV). The transition temperature was 6°C and 2°C for base plate and weld metal, respectively, after 1 × 10¹⁸n/cm²(E > 1 MeV) at 50°C. The transition temperature increase was 40°C, 41°C, and 32°C for base plate, weld metal, and weld heat-affected zone, respectively, after about 2 × 10¹⁸n/cm²(E > 1 MeV) at 50°C.

The data of transition temperature increased on 15MnTi steel after 1 to 6 × 10¹⁸n/cm²(E > 1 MeV) at 50°C was summarized. An empirical equation was obtained: T = 32.7 - 1.8 lnϕt + 17.8 ln²ϕt, where ϕt is fast neutron exposure (E > 1 MeV).