Shutdowns restarting after

Whenever a motor is installed in a humid atmosphere and is switched on after a long shutdown, insulation resistance must be checked before energizing the motor. As a precaution, insulation resistance must be checked before a restart after a long shutdown, even in temperate conditions. If the insulation level is found to be below the recommended level as shown in equation (9.1) it must be made up as noted below. 

Commissioning of prestartup channels of high sensitivity to enable reactor restart after a prolonged shutdown. 

Figure 16.10 Shutdown and restart behavior of SILP WGS catalysts, (a) 2 h shutdown of a RuClj on silica catalyst (Nj flow, heating on), (b) O 20 h shutdown after cooling down of RuClj on silica (stop flow, heating off), and (c) A restart after 12day storage...

Design the E-stop such that to restart after Emergency shutdown it is necessary to pull out the E-STOP button and then press the appropriate buttons to initiate normal operation. 

Check valves are required in the piping system at any point where backflow of gas after a shutdown has the ability to restart the compressor, running it backwards or, for that matter, even in the normal direction. Reverse rotation is totally bad, as many components of the various compressor types are not designed for reverse rotation, and there is some possibility, generally remote, that the compressor could reach a destructive over speed. Forward rotation is bad primarily because the intent was to stop the compressor, and it is now operating out of control. This is a problem, particularly if the shutdown was caused by a compressor failure indication, and the need to stop was to prevent further damage. In this mode, it is unlikely that the compressor can attain an overspeed condition. An application with a high potential for backflow is the parallel operation of two or more compressors. 

As noted for experiment HGR-13, the deactivation rate increased significantly when the fresh feed space velocity was increased from 2000 to 3000/hr. During the period of 841-1058 hrs, the fresh feed space velocity was returned to 2000/hr and the CGR ratio was increased from — 3 1 to 9 1 to give a low deactivation rate of 0.0027%/mscf/lb. When the CGR ratio was returned to 3 1 at 1058-1760 hrs, the rate of catalyst deactivation increased to 0.0187%/mscf/lb. After 1760 hrs, the unit was shut down and put in standby condition under hydrogen. After the unit was restarted, the deactivation rate had increased greatly to 0.0821%/ mscf/lb which indicates that the increase in deactivation rate was associated with this particular shutdown. Since this experiment had previously undergone three unscheduled shutdowns at 215, 798, and 894 hrs with no adverse effect on performance, some unknown factor unique to the shutdown at 1760 hrs was responsible for the subsequent rapid decline in activity. 

Some degree of risk exists with cooling towers previously associated with legionnaires disease, with new cooling towers, and with cooling towers being restarted within 4 weeks after a shutdown. 

The system routine operation is automatic after startup. Should a problem develop causing deviation from established operating limits, the system will automatically shutdown. The system cannot be restarted until the problem causing the shutdown has been corrected. The system should be checked twice a shift. 

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. 

Sometimes normal updating of the process model is done correctly by the controller, but problems arise in initialization at startup and after a temporary shutdown. The process model must reflect the actual process state at initial startup and after a restart. It seems to be common, judging from the number of incidents and accidents that have resulted, for software designers to forget that the world... 

After the declaration to the French National Assembly on 19 June 1997, of the decision to finally shut down the Creys power plant, and after 6 months of alternating hopes and disappointments as to a possible restart in order to complete the use of the 1st core, and perhaps even the 2" core, the first structured strategic reflection for definitive shutdown began in February 1998. One of the main aims of this reflection was to prove the technical feasibility of this dismantling based on the assumption of reasonable costs and time limits. In this context of technical doubt, fuelled by the media, a very determined attitude had to be adopted. 

In restarting the reactor after a short shutdown, the time available is limited by xenon growth hence the rods must be withdrawn as quickly as possible. However, the considerations of the preceding paragraph indicate that the maximum tolerable rod withdrawal is 0.1%Ak/k per second. This, then, has been fixed as the "high" rate of rod withdrawal and permits complete withdrawal of all rods in about 6 min. 

If the reactor is shut down, however, a second aspect occurs. The xenon is now not being removed by neutron interaction but is still being produced, faster than it decays, by the decay of the previously produced iodine. Thus the xenon concentration rises sharply to several times its previous value (depending on the operating power level) before it subsequently decays with the drop in iodine production after such a shutdown. If the reactor is to be restarted in this interval, of 20-40 h, yet further reactivity will be needed. If the reactor is partially shut down, a partial xenon transient can occur, calling for addition and subsequent removal of reactivity to compensate if the reactor is to continue to be operated. 

SD = the average time required to restart the process after a shutdown. 

SD = the time required to restart the process after a shutdown RT = average repair time for a detected failure TI = the inspection time interval... 

In 1996, SUPERPHENIX was characterized by excellent operation throughout the year. The reactor was restarted at the end of 1995 after a number of minor incidents. The reactor power was increased by successive steps 30 % Pn up to February 6, followed by 50 % Pn up to May then 60 % up to October and 90 % Pn during the last months. A programmed shutdown period occurred during May, June and mid-July 1996. The reactor has been shutdown at the end of 1996 for the decenial control of the steam generators. 

After the annual maintenance outage and the neutron test campaign at 180, 250, and 345° C, whose purpose was to check the conformity of the new rods and determine their characteristics with respect to reactivity, the plant was restarted around mid-July, as soon as restart authorization was obtained. This restart was performed with both turbo-generator sets, as the results of the expert assessment of the transformer that had previously been shutdown were satisfactory. 

The control rod calibration problem under study in the present discussion is concerned with a special situation where it is desired to calibrate a control rod during a xenon transient. What is meant by a xenon transient is explained briefly in what follows. When a reactor is in operation, certain nuclei with large neutron absorption cross sections are produced, so that they act as poisons. Of these poisons, xenon-135 is the most troublesome. In a reactor operating at power a balance is eventually achieved between rates of formation and loss of the absorbing nuclei, so that an equilibrium concentration is attained in the reactor. However, when a reactor operating at power is shut down, the xenon continues to increase [1, p. 335] without a sufficient neutron flux available to hum out the xenon, so to speak. Thus, the xenon will eventually disappear by radioactive decay, but not before it builds up to a maximum of substantial proportions. The maximum concentration will occur at about 12 hours after shut-down, the magnitude of the peak concentration depending on the power level before shut-down. This explains why, whenever it is necessary to be able to restart a reactor at any time after shutdown (e.g., a submarine reactor), the reactor must be sufficiently fueled so that it is possible to override maximum xenon at any time. 

In order to give some further illustration of the concept of the target curve, we modify the terminal conditions of the problem also, as shown in Fig. 3. Instead of requiring the reactor to be capable of restart at any time after the control period or final shutdown, we may limit the requirement to one of restart capability at some specified time after shutdown, an interval r after tf say. After such an interval, neglecting trivial cases, the xenon density will be exactly the value permitting restart, X= X,. The solution to the zero flux xenon equation from the values Xf, 7y is easily shown to be... 

The line 1 must certainly meet the target curve 2o (for restart at any time after shutdown) at least at one point, for there is certainly at least one point on 2q which would lead to X, after the interval t. The 2 cannot cross 2(), however, or they would enter a region that could not lead to X, at zero flux. Thus, the 2 are tangential to 2q, or 2q is the envelope of all the particular target curves, 2. ... 

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