Verification of safety is a key activity in designing safety critical systems. The objective of safety verification is to avoid unacceptable risk of damage to public health or property or physical injury by any means. To ensure the goals of safety, these systems must reach a safe state for the occurrence of any failure. There is a need to verify the design of such systems to identify and overcome the probable risks, if any. This paper presents a case for safety verification of the main steam system of a nuclear reactor. The technique shown is based on Petri nets, to model and analyze the safety critical computer-based systems for safety verification. The paper further argues that the proposed technique is beneficial in improving faulty design.