transient without scram

A "transient without scram" is a nuclear event where a reactor experiences an unplanned increase in reactivity, but the safety systems designed to rapidly shut down the reactor (known as a scram) fail to activate. This scenario poses a significant risk because the reactor could become supercritical, leading to a rapid and uncontrolled release of energy and potentially a severe accident with the release of radioactive materials.12

Nuclear reactors contain large amounts of radioactive isotopes. If these escape, they can cause severe health impacts, including cancer, cellular damage, and even death. Therefore, reactor design prioritizes preventing accidents and mitigating their consequences through safety systems like emergency core-cooling and containment structures. In the event of a transient without scram, proper operator action and the functioning of backup systems are crucial for emergency response.1