Complex sentence: The RBMK reactor also has an Accident Localization System, which serves as a containment but this system can only handle minor pipe breaks, the Accident Localization System's ineffectiveness was shown in Chernobyl accident.
Split into simpler sentences: The RBMK reactor also has an Accident Localization System which serves as a containment but this system can only handle minor pipe breaks. The Accident Localization System's ineffectiveness was shown in the Chernobyl accident.