Abstract: This paper addresses the availability assessment of key components of pressure transmitters under severe accident conditions in nuclear power plants, with a particular focus on the irradiation damage characteristics of the bipolar operational amplifier LM108 when subjected to coupled high-temperature and high dose rate environments representative of beyond-design-basis events. Based on the NB/T 20149—2012 standard and the severe accident environmental spectrum established for the HPR1000 reactor design, irradiation tests were carefully designed to simulate the transient and harsh conditions that instrumentation may experience during severe accident scenarios. Using a ⁶⁰Co γ-ray source, LM108 samples were irradiated at three elevated temperatures (50, 100, and 150 ℃) and at a high dose rate of 3.3 kGy/h until a cumulative absorbed dose of 36 kGy was reached. Emphasis was placed on monitoring the degradation behavior of the input bias current (I_b), the device parameter identified as most sensitive to ionizing dose in preliminary characterizations, and on recording time-resolved parameter evolution for detailed mechanistic analysis. The experimental results reveal a pronounced and non-monotonic suppression effect of elevated temperature on LM108 irradiation damage. At 50 ℃, taken as the reference operating temperature, I_b increases monotonically with cumulative dose, demonstrating classical damage accumulation due to trapped oxide charge and interface states induced by ionizing radiation. In stark contrast, at 100 ℃ and 150 ℃, I_b exhibits a marked increase at low-to-intermediate doses followed by a decline as the cumulative dose continued to rise. Particularly at 150 ℃, I_b reaches a distinct damage peak at intermediate doses and then partially recovers toward its initial, pre-irradiation value at higher accumulated doses. These behaviors indicate that during the early phase of severe accident conditions the high dose rate accelerates the generation of radiation-induced defects, whereas at elevated temperatures thermally activated annealing processes, especially the annealing of oxide-trapped charge density (N_ot) and recombination of some interface defects, become progressively dominant and effectively counteract further ionizing damage. To quantitatively capture this interplay, a dynamic competition model between trap charge capture and thermally activated annealing was developed. The model incorporates generation terms proportional to dose rate and trapping efficiency, as well as annealing terms governed by Arrhenius-type temperature dependence. Key model parameters were extracted by fitting the measured I_b-versus-dose curves across the three temperature conditions. The resulting model not only reproduces the observed non-monotonic trends and the peak-and-recovery behavior at high-temperature but also predicts continued recovery in the late stage of the severe accident scenario. These findings provide a mechanistic explanation for temperature-dependent irradiation responses and supply a theoretical basis for survivability assessment and reliability prediction of instrumentation and control components in nuclear power plants subjected to beyond-design-basis accident environments.