Reliability Assessment of Fueling Machine Head Encoders

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Justin M. Julian
N. Fluegel
Mahesh D. Pandey
Pardis Khavari

Abstract

Online fueling at the Darlington Nuclear Generating Station (DNGS) is performed one channel at a time, using a pair of fueling machine heads (FMH). During the fueling operation, motions of the ram and charge tube sub-assemblies are guided by four rotary position encoders. Encoders in- service failures during online fueling can disrupt the operation, ranging from a short stoppage to a long-term unavailability resulting from complex recovery operations. The sequence jump is such a fault in which the encoder output about the position of a component suddenly increases/decreases by a large magnitude in a spurious manner. In a degraded encoder, a high frequency of such errors would seriously disrupt the fueling and require an emergency replacement of the encoder at a higher cost of unavailability. At present, there is no systematic approach available for health monitoring and reliability tracking of FM encoders. This paper aims to tackle these challenges by analyzing the operating experience of the four FM encoders, deriving the reliability function, and looking for the probabilistic pattern of sequence jump errors as a part of a monitoring strategy. The proactive maintenance and monitoring strategies developed in this paper will reduce the unavailability of fueling machine caused by abrupt encoder failures.

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