Abstract: In a nuclear reactor the feedwater control system receives steam generator water level signals, including information to determine signal quality. The signal quality and additional signal validation determine how the water level signals are to be used by the feed-water control system. In the preferred embodiment, each water level signal is compared with a possible range and the difference or differential between all possible pairs of the signals is calculated and compared with an acceptable differential range. While alarms are sounded if any of these checks on the water level signals indicate an invalid signal, the water level signals are used to calculate a median level signal until there is less than two water level signals with good quality within the possible range or all differentials are outside the acceptable differential range.

Abstract: The operating system clocks in each station on a counter rotating ring network of a distributed processing system are synchronized by latching the count in a free running counter in the network interface of each station at the instant a clock message transmitted by a timekeeper station is received. The timekeeper station then calculates from its operating system time-of-day clock and its free running counter, its time of reception of the clock message, and broadcasts this timekeeper time of reception to the other stations. Each other station calculates its own time of reception from its operating system time of day, and the count in its free running counter, and uses the difference between its time of reception and the timekeeper time of reception to correct its operating system time-of-day clock. Repeater and media propagation delays determined from the dynamic topography of the network are taken into account in calculating the correction factor.

Abstract: Real time periodic messages generated by a plurality of stations on a data communication network and having data periods ranging from a shortest to a longest, where the longest data period is an integer multiple of all the others, are assigned by a server station to transmit time slots, equal in duration to the shortest data period, on a global basis to minimize the number of messages transmitted by all stations during each transmit time slot.

Abstract: The guide pin aligning a top nozzle of a nuclear fuel assembly to an upper core plate of a nuclear reactor, is replaced working exclusively from below the upper core plate. The replacement guide pin has a shaft portion engaged with the upper core plate and the clamping nut which held the original guide pin, by threadable connection and/or by an expansion fitting. A shoulder on the pin bears against a lower surface of the upper core plate, and a nose of the pin is received in the top nozzle of the fuel assembly. A preferred expansion fitting has a bushing with ridges on its outer surface and a conical inside surface, and is inserted into the bored out original guide pin shaft. A threaded conical plug is pulled axially with rotation of the replacement pin shaft to expand the bushing. The ridges rigidly lock the replacement pin between the shoulder and the clamping nut.