Shutdown life cycle

Many factors affect the mechanical design of evaporator systems, particularly of the calandrias. The two most important are the temperatures and pressures to which the equipment will be subjected. Not only are the temperatures and pressure during normal operation important, but upset, startup, shutdown, dryout, cycling, pulsating pressure, and safety relief requirements are equally important. Other considerations include external loadings from supports or piping and vibrations transmitted from external sources. Wind loadings and earthquake loads must also be considered. Anticipated life expectancy and future service should be considered. 

Reliability and availability of the plant are key elements to consistently produce at maximum capacity. A high System Effectiveness reflects a sustainable high production capacity over the plant life cycle. Underlying assumption is that outage of one or more individual units out of several parallel imits will not escalate into shutdown of a process train or worse, the whole complex. A disturbance should effectively be counteracted by the control system in order not to propagate to other parts of the plant. 

Safety instrumented system (SIS) SIS is meant to prevent, control, or mitigate hazardous events and take the process to a safe state when predetermined conditions are violated. An SIS can be one or more SIFs, which is composed of a combination of sensors, logic solvers, and final elements. Other common terms for SISs are safety interlock systems, emergency shutdown (ESD) systems, and safety shutdown systems (SSDs). So, SIS is used as a protection layer between the hazards of the process and the public. SIS or SIF is extremely important when there is no other non-instrumented way of adequately eliminating or mitigating process risks. As per recommendations of standards lEC 61511 2003 (or ANSI/ ISA-84.00.01-2004), a multi-disciplinary team approach following the safety life cycle, conducts hazard analysis, develops layers of protections, and implements an SIS when hazardous events cannot be controlled, prevented, or mitigated adequately by non-instrumented means. 

Proof test interval for SIF This is an important issue. Proof tests are meant to test the function as far as possible (could be dangerous in a shutdown condition). Major issues related to this shall include but not be limited to the following [12] Description of the proof test procedure Precaution and safety to be under taken for proof test Required proof tests in life cycle... 

SIS and SIL for BMS A master fuel trip required by design codes demands multiple actions. The verification results shall confirm that the required risk reduction is achieved. However, the validation can be compromised when an SIF is not defined properly and its functional requirements are poorly specified or when all actions for total shutdown are included in the same functional requirements of the same SIF [8]. From discussions in previous chapters it is clear that the safety life cycle model not only helps with necessary ways and means to avoid systematic failures, but also helps to ensure the required integrity level to prevent random failures. The safety standards (lEC 61508/61511) required to identify a set of parameters and factors for PFDavg calculations are ... 

At some point in the life cycle of a research reactor it may become necessary to shut down the reactor because of some problem. Based on the nature of the problem and other data (technical aspects, manpower availability, delivery schedules, etc.), it may be possible to predict that the shutdown will be for a fixed period of time. During this period, the operating staff will continue to meet the requirements of the operating license by performing the surveillance. 

It lists the main requirements to the work to be carried out after the NPP final shutdown, which Is necessary to make their decommissioning easier, at design stage In particular, as well as the requirements to designing and engineering to facilitate the work at the last stages of an NPP life cycle (Flg.1). 

This mode of failure involves a redundant system reducing to a single or 1002 mode of protection. The level of protection remains high and the shutdown rate is very low. Initial installation costs are likely to be higher but the life cycle cost may be lower. 

Similar to mode 2 in effect but leaving no choices on production losses. All forms of shutdown mean a loss to the business. In addition there are potentially increased costs for wear and tear on the main plant equipment as crash shutdowns occur. There is often an increased risk of hazards due to the disturbances caused by an unscheduled trip followed by the risks of operation under hastily recovered start up conditions. Measures to reduce spurious or nuisance trips are therefore likely to show benefits for the life cycle cost. 

Ease of installation and commissioning is another reason for gas turbine use. A gas turbine unit can be tested and packaged at the factory. Use of a unit should be carefully planned so as to cause as few start cycles as possible. Frequent startups and shutdowns at commissioning greatly reduce the life of a unit. 

The Experimental Breeder Reactor-II (EBR-II) was designed as a 62.5 MWt, metal fueled, pool reactor with a conventional 19 MWe power plant. The productive life of the EBR-II began with first operations in 1964. Demonstration of the fast reactor fuel cycle, serving as an irradiation facility, demonstration of fast reactor passive safety and lastly, was well on its way to close the fast breeder fuel cycle for the second time when the Integral Fast Reactor program was prematurely ended in October 1994 with the shutdown of the EBR-II. 

For the reasons explained in the report presented during the 28 th IWGFR meeting [Ref 1], major decisions were taken in 1994 in order to extend the life time of the reactor another 10 years. A work programme was decided which involves long shutdown periods. Such a period occurred after the 49 th cycle. This cycle was completed on April 1995 without any incident. 

Thin walls increase tube life because secondary stresses are minimized during thermal cycling on startups, shutdowns, and upsets. Accordingly, the tubewall thickness should be minimized consistent with meeting the tensile strength requirement. For many applications, the minimum sound wall (MSW) can be as low as 0.25 inches. 

In a vessel s operating life, there will be shutdowns and startups. During each of these cycles, the base metal and clad will experience different thermal movements, resulting in shear stresses. These stresses vary as to the relative coefficient of thermal expansion of the two metals. This phenomenon can be analyzed through fatigue analysis, which we will not go into here. The only justification for such an analysis is if many shutdown and startup cycles are expected, resulting in cyclic service. The vast majority of time this phenomenon is not a concern in the operating unit. 

Short dwell times. This type of thermocycling is typically experienced in applications such as industrial gas turbines, aero engines, heat treatment facilities, furnaces, etc. The intervals between start and shutdown of the facilities are generally much shorter than in applications described in 1. Also the design life and/or the time until complete overhaul/repair (typically 10,000 - 30,000 h) are much shorter and, depending on the specific practical application, the number of cycles is much higher than in the cases described in 1. 

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