This paper describes a simulator which can be used to study the effects on circuit behaviour of two radiation phonomena: Single Event Upset (SEU) and total-dose radiation effects. The core of the device is BERT (BErkeley Reliability Tools), an IC reliability simulator. The SEU simulator uses an established methodology, but a novel choice of sensitive nodes is made, which allows a fast simulation of very large circuits. The total-dose simulator predicts circuit behaviour after a user-specified radiation dose using an ordinary circuit simulator, such as SPICE. Simulation results are compared to actual experimental data.