Safety requirements within nuclear power plants (NPPs) have encouraged the development of several rigorous methodologies that, in turn, have stimulated excellence in operability, reliability, availability and maintenance (RAM) to the extent that numerous guides and standards now regulate that industry.
Part 1 of this article, which appeared in the May issue of Hydrocarbon Processing, compared the safety requirements for nuclear facilities and the hydrocarbon processing industry (HPI), indicating that the two industries have similar objectives. Part 2 focuses on the results of RAM simulation of the pump/reactor/agitator system and the evolution of a maintenance strategy.
It is known that un-spared components in a system design contribute to unreliability. System design is affected not only by the system's weakest component but also by an aggregate of "unreliabilities" of all the components. In practical situations, multiple failures of redundant components, as well as outlier events or extreme events, may also contribute to unreliability and loss of system function.
Assessing reliability. In the Fukushima Nuclear Accident in Japan, (5) the spared heat transfer pumping system was rendered inoperable by the tsunami. PSA and extreme value analysis afford tools to assess the impact of such scenarios. It is outside the scope of this article to conduct extreme value analysis, but results are presented of simple probabilistic simulations of a pump/reactor/agitator system (FIG. 2) to assess the reliability of the designed system and how proactive maintenance design steps can help meet target reliability/availability. Probabilistic simulations were made for a mission time of 8,760 hr (1 yr) for pessimistic and improved meantime between failures (MTBF) of the as-designed system components. An additional simulation was made with average component MTBFs and the main high-pressure pump out for repair for 5...