Plant trip

An ethylene oxide plant tripped, and a light on the panel told the operator that the oxygen valve had closed. Because the plant was going to be restarted immediately, he did not close the hand-operated isolation valve as well. Before the plant could be restarted, an explosion occurred. The oxygen valve had not closed, and oxygen continued to enter the plant (Figure 14-5). 

The study performed by Burns and Roe (BSR) shows that valve failures constitute the component category most responsible for the shutdown of PWR and BWR plants. This Investigation, contracted with SNL for DOE, identified the principal types and causes of valve failures that led to plant trips for the period from 12/72 to 12/78. The primary sources of data for the report were searches of the data base, the monthly Gray Books, Nuclear Power Experience publications, as well as discussions with utilities, valve manufacturers, and suppliers. 

Event frequency data were developed from a detailed review of plant trip reports and shift supervisor s logbook entries. The first two years of plant experience were discarded as they appear to represent experience typical of early plant operation and tests that are not typical of operation in later years. The plant experience was used to perform a Bayesian update of EPRI NP-2230 reactor trip experience. 

After the development of the steam system dynamic simulation, work was done to investigate the response of steam system following equipment/plant trips. Since the entire complex steam system at the l-P level was simply a number of larger steam generators sullying only 3 steam turbines, the trip of one machine or a plant would lead to severe steam pressure transients. The simulation was used to develop a series of operator procedures following any trip scenario. 

The first problem which was evident during startup was that the steam reformer steam to carbon controls (S/C) were inherently unstable and that minor upsets would lead to plant trips due to low s/c ratio. While the control system is complex, by. modelling using dynamic simulation, it was easy to determine that one of the control loops was unstable due to the discrete sampling nature of the control system and the chosen tuning parameters. (Ref 2)... 

A total of 40 tubes failed, 39 due to overheating in a period of 8 seconds following the plant trip. The remaining tube, which initiated the event, failed due to fretting damage caused by tube vibration. 

This induced a plant trip by rupturing a steam-side bursting disc. Isolating valve closed, causing the steam flow to stop, but the steam pressure fell relatively slowly over a period of about 10 seconds. 

After a plant trip test, Monju restarted operation on 6th December 1995. On 8th December, power was being raised for the next plant trip tests, part of 40% electric power tests. The thermal power had reached 43% when an alarm sounded at 19 47 dueto an off-scale sodium temperature at the outlet of IHX in the secondary circuit loop C. Afire alarm (smoke detector) sounded at the same time. A sodium leak alarm in the secondary circuit followed. The plant conditions of Monju at that time are shown in Fig. 1. The presence of smoke was confirmed when the door of the piping room was opened. The plant operators decided to begin normal shutdown operations becausethey judged it was a small sodium leak had occurred. Reactor power-down operations began at 20 00. 

A monitoring display panel will be installed in the main control room and information from the various sensors and TV cameras will be displayed. The new leakage monitoring system should enable the plant operators to take the necessary actions - such as a plant trip and loop drain - earlier, since they will be able better to understand the condition at the leak site without leaving in the main control room. A schematic of this system is shown in Fig.8. 

After the installation of the system, the whole system was tested to prove the installation integrity. This covered test items as same as the factory tests. In the pre-operation test, the system experienced more than 10 initiation against the transients such as load rejection at 20%, 50%, 75% and 100% power, LOPA at 20% power, plant trip at 50% power and Main Steam Isolation Valve Closure at 100% etc.. 

Questions. Students go on the plant trip, and the first job is to learn what the project is, what has been tried, what critical sources of data and theory exist, and what vendors have been helpfiil in solving related problems. Unfortunately, most student teams have trouble asking cogent questions. We call this a failure of Socrates 101 in recognition of that philosopher s role in teaching the world to ask. 

On Etecember 8, 1995, a leakage of sodium occurred in the piping room (C) of the Secondary Heat Transport System (SHTS) while the output of the reactor was being raised for a plant trip test at 40% output as part of a series of performance tests. The nuclear reactor was shut down manually after the accident, and sodium was drained from the SHTS in which the accident occurred and also from the Loop C of the Primary Heat Transfer System (PHTS). The plant is currently in a low-temperature shutdown state. The plant conditions of Monju at the time of the sodium leak occurrence are shown in Fig. 3.1. 

In addition, diese valves are not actuated during a normal plant trip. 

Reduced likelihood of plant trips caused by instrumentation and control system problems. 

State-point data, including secondary system heat balance measurements, are obtained at various power levels up to full licensed power. This information is used to project plant performance during power escalation, provide calibration data for the various plant control and protection systems and provide the bases for plant trip set-points. 

At prescribed power levels, the dynamic response characteristics of the primary and secondary systems are evaluated. System response characteristics are measured for design step load changes, rapid load reductions and plant trips. 

Paul and 1 had a quick de-brief before several day staff came to the control room to find out what had happened. My sense of shame was made worse when we discovered the shock of the plant trip had caused another steam leak in the steam generator, so the plant foreman and I had to deal with that for a couple of hours. 

The steady generation of hydrogen by formation of magnetite can be accelerated if the magnetite layer becomes cracked or spalled, by a rapid temperature change due to a plant trip for example. This can expose un-oxidised metal to the water, which b ins to oxidise rapidly, generating hydrogen at an increased rate. This may ve the appearance of a leak for a time. 

Overt failures normally lead to a fail-safe response from the safety system often involving a plant trip. Hence the term nuisance trip is used as well as spurious trip . In a redundant channel SIS an overt failure takes out one channel and the system works on a reduced reliability basis until the fault is repaired. Hence the nuisance trip does not occur until perhaps a second overt failure happens. 

A plant trip arising out of an overt or detected equipment failure in the SIS or an erroneous assessment of the situation (e.g. error in the logic functions). A shutdown is initiated, though no real impairment of safety exists. Also referred to as a false trip or a nuisance failure . Spurious trips can contribute to the hazard rate of the plant through the disturbances so caused. 

An operations review committee reviews plant-trip reports in accordance with RDP 2.04 "Reactor Operations Safety Committee (ROSC)." Minutes of all ROSC meetings are sent to the RISRC for review. In addition the ROSC chairman may request assistance from the RISRC. 

The RISRC provides senior management oversight of the reactor safety review system. However, it is not clear that the RISRC is required to review all plant-trip reports. This issue is an open item. 

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