To my knowledge, there have been no cases of launch escape systems having been designed for and used to protect expensive or hazardous payloads. The Blue Origin New Shepard capsule, which is used for both human and cargo flights, has a launch escape system which is active in all cases. On the NS-23 flight on 2022-09-12 (coverage here, “Blue Origin New Shepard NS-23 Flight”), the booster engine failed and the capsule, which carried no people, escaped and landed safely, with all payloads intact. SpaceX, by comparison, does not install a launch escape system on its Cargo Dragon ships used for International Space Station resupply missions.
High-value payloads tend to be large and heavy, and are designed around the limits of the launch vehicle payload capacity. Launch escape systems are heavy, and payloads other than crewed capsules do not have heat shields or parachute systems to land safely after a launch abort. Adding all that would dramatically decrease the capability of a payload such as a communication satellite and/or its useful lifetime on orbit by reducing the amount of station keeping fuel it could carry. So, they buy insurance and cross their fingers.
For radioactive payloads, the approach is to package them sufficiently ruggedly that they can survive a worst-case launch vehicle explosion and fall to the Earth without releasing the radioactive material. For a fission reactor, the reactor does not go critical until after reaching its operational orbit, so the nuclear fuel is not dangerously radioactive during the launch phase. Radioactive thermal generators (RTGs), which use intensively radioactive material such as plutonium-238, depend on a rugged capsule to contain the heat source. The RTG from Apollo 13’s lunar module science package plunged into the Pacific after the lunar module burned up in the Earth’s atmosphere and no traces of plutonium release were detected. It is almost certainly sitting intact in the Tonga trench today.