Shutdown risks

Social - Opportunities for innovation, since plastic applications are not exhausted - Suppliers are subject to global competition migration, shutdowns, risk of job loss... 

Degradation of natural circulation should be accounted for when estimating the shutdown risks in PSA studies. 

Degradation of natural circulation during shutdown conditions, mainly in WWER reactors, should be accounted for adequately when estimating the shutdown risk in PSA studies. Detailed computer analyses of thermal and hydraulic processes should be carried out to show whether and at what time these processes could lead to core damage. 

For the French PWRs, several measures have been taken to monitor and reduce the shutdown risks. 

Risk assessments should Include consideration of alternatives (including plant shutdown), risk mitigation methods, time-at-risk, and effects on overall plant risk ... 

Operational improvements for shutdown operating state discussed here are primarily the operation and emergency procedures and the training of operators and other personnel. Enhanced procedure and improved understanding of the shutdown risks are key elements in enhancing the outage safety at many plants. 

Similarly to administrative barriers, operational guidance for shutdown was generally lacking at many plants. Safety studies and actual operational events in shutdown triggered the development of outage safety plans and training of personnel to understand the shutdown risks. Many utilities introduced a systematic evaluation of outage plans to identify any safety detrimental activities and correct those. 

Shutdown Risk Analysis - Lessons and Views P. Pyy and R. Himanen, SRA Europe, Fourth Conference, Rome, October 1993. 

Approaches and Results for Recent Shutdown Risk Studies in the U.S. Nelson A. Hanan and Alan S. Kuritzky. 

Guidelines for Shutdown Risk Assessment IAEA working material, 1994. 

In plant maintenance, the availability of quantitative and non-invasive screening NDT methods will reduce the time needed for shutdowns and increase the intervals between them. Modem NDT methods will become just as important a tool for Risk Based Inspection approaches and maintenance planning as operational parameters and degradation mechanisms already are. 

Emergency shutdowns often pose risks in themselves, and therefore they should be undertaken only when truly appropriate. The need to avoid extraneous shutdowns is not just to avoid disruption in production operations. 

Hot feed Provide and maintain an automated inerting (increases system—oxygen concentration or pressure fire/explosion risk controlled with flammable. Eliminate leakage sources (ftimes/air) solvents). Use alternative solvents (nonflammable or less flammable) Reduce feed temperature and/or monitor temperature of feed and interlock with feed shutdown NFPA 69... 

The gas quality feeding the dry faee seal should be elean and dry. Due to the possibility of eondensation of the proeess gas in the seal eavity, it was deeided to use a seal gas heater. The heater eontrol was set to provide warm gas at 15°C above the dew point to ensure no eondensate entered the seal eavity. Also, a dual filter in series with 5 and 2 p filtration elements was ehosen to provide an ideal sealing environment and maintain the optimum performanee of the seal. To reduee the risk of seal damage during reverse rotation of the turboexpander, programming logie was set to open the eompressor bypass valve whenever a shutdown impulse was initiated. 

A change in approach is clearly necessary in order that the full benefit of integrated plant condition management and control can be recognized and exploited. Improved control and enhanced performance monitoring will enable shutdown intervals to be extended without increasing the risk of premature or unexpected failure. In turn, this will increase the confidence of operations, inspection and management personnel in the effectiveness of unified plant administration. 

Operation includes nonual start-up, normal and emergency shutdown, and most activities performed by die production team. Whilst inlierently safe plant design limits inventories of hazardous substances, inherently safe operation ensures die number of individuals at risk are minimized. Access to die plant for non-essendal operational people such as maintenance engineers, post staff, administrators, quality control samplers, warehouse staff delivering raw material or plant items or collecting finished product, members of security, visitors etc., must be controlled. 

One person in a unit retrieved a two-year-old shutdown procedure from his locker and tried to use it. The old procedure was significantly different from the updated procedure. If the old procedure were followed exactly, there would be more risk. If the two procedures were intermingled, there would be high temperature and catastrophic corrosion. The unit management team tore up the bootleg procedure and added the updated shutdown procedure to the controlled document system used for ISO 9002 (ISO 9000, 1994). In this document system, only the current procedure is available. Alternate systems may use an expiration date or require periodic reconfirmation. 

Fire Protection FIVE and FRANC support quantitative and qualitative fire risk, assessmeiil. FRANC also supports the analysis of alternative safe shutdown paths during an Appendix R review. System train availability is exhibited on a system status panel, Using this a strategy can be defined to upgrade Thcrnm 1. if identify risk significant areas. 

Safety Monitor is an interactive computer program (Stamm, 1996) that performs real-time assessments of configuration-specific plant accident risk. Originally used at Southern California Edison s San Onofre station in 1994, further development was sponsored by three nuclear utilities and EPRI, to include shutdown operation and expanded user features. It will be enhanced to calculate large early release frequency (a Level 2 risk). 

The plant internal PSA can be used to identify critical equipment that could be damaged by fire. This form of screening was employed in the fire-risk portions of ZIP. At each location considered, the loss of all the equipment in the zone is postulated regardless of the size or position of the fire in the zone. If this does not show the occurrence of an initiating event (LOCA or transient) or if the safety functions are not damage to required for safe shutdown, the location is eliminated from consideration. If the location is found to be critical, it is considered furilier lot-detailed fire growth and fire suppression analyses. 

L If a nuclear power plant loses its connection to the offsite load, it must shutdown because it cannot be cutback sufficiently that its electrical output matches its "hotel" load. Outline a PSA study to determine the risk reduction that might be achieved by switching in a dummy load to avoid shutdown and keep the plant online. 

The Chemical Process Industry (CPI) uses various quantitative and qualitative techniques to assess the reliability and risk of process equipment, process systems, and chemical manufacturing operations. These techniques identify the interactions of equipment, systems, and persons that have potentially undesirable consequences. In the case of reliability analyses, the undesirable consequences (e.g., plant shutdown, excessive downtime, or production of off-specification product) are those incidents which reduce system profitability through loss of production and increased maintenance costs. In the case of risk analyses, the primary concerns are human injuries, environmental impacts, and system damage caused by occurrence of fires, explosions, toxic material releases, and related hazards. Quantification of risk in terms of the severity of the consequences and the likelihood of occurrence provides the manager of the system with an important decisionmaking tool. By using the results of a quantitative risk analysis, we are better able to answer such questions as, Which of several candidate systems poses the least risk Are risk reduction modifications necessary and What modifications would be most effective in reducing risk ... 

In addition to the product, the designer, equipment installer, user, and all others involved in production should all consider performing a risk assessment and target in the direction of perfection. The production is reviewed for hazards created by each part of the line when operating as well as when equipment fails to perform or complete its task. This action includes startups and shutdowns, preventative maintenance, QC/inspection, repair, etc. 

Inspecting and maintaining the interlock system is a vital function. It is required to ensure general safety and to avoid risks of boiler explosion. Interlocks provide for the safe sequence of boiler startup and shutdown procedures. 

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