Accident protection

Accident protection includes protection from " fire... 

The studies of this period led to a definition of severe accident protection criteria (see Section 1-2 and Chapter 18) similar to those already in force in Italy and to those developed in Sweden. In Italy, it was thought possible to provide a defence against severe accidents by accident management provisions and by some reasonable plant modification, up to the point of limiting iodine and caesium releases to 0.1 per cent with a probability higher than 95 per cent in the case of core melt (conditioned probability). 

Protection from electrical hazards is one way to prevent accidents. Protective methods include insrdation, electrical protective devices, guarding, grovmding, personal protective equipment (PPE), and safe work practices. 

The ABV reactor plant containment is a steel leak-tight shell designed for the ultimate pressure and tempo ature arising in beyond deagn accidents. Protection against external impacts (e g. air crash) is provided by a special protective enclosure compartment in a floating NPP, or by the reactor building structure in a land-based NPP. 

Hazards can arise from improperly designed tools or work areas, improper lifting or reaching, poor visual conditions, and repetitive motion in an awkward position. Excessive fatigue and discomfort will lead to pain and soreness and eventually to accidents. Protective requirements have been set in many OSHA and NIOSH Standards. 

The reactor protection system shall be designed in such a way that necessary automatic actions, once initiated, cannot be impeded or prevented by manual actions and that no manual actions are necessary within a short period of time following an accident. Protective actions, once initiated automatically by the reactor protection system, shall be designed to proceed to completion. Such automatic actions by the reactor protection system shall not be self-resetting and a return to operation shall require dehberate operator action. 

To ensure the function of reactor power control, two independent systems based on diverse drive mechanisms are provided for reactor shutdown. One system acts as an accident protection system, while the actuated second system is designed to provide guaranteed subcriticality for an unlimited period of time and to be able to account for any reactivity effects including those in accidental states. Either system can operate under the failure of a minimum of one rod with maximum worth. In case of loss of power to the reactor control and protection system (RCP), all rods of this system can be inserted in the core under the effect of gravity. 

Safety. A large inventory of radioactive fission products is present in any reactor fuel where the reactor has been operated for times on the order of months. In steady state, radioactive decay heat amounts to about 5% of fission heat, and continues after a reactor is shut down. If cooling is not provided, decay heat can melt fuel rods, causing release of the contents. Protection against a loss-of-coolant accident (LOCA), eg, a primary coolant pipe break, is required. Power reactors have an emergency core cooling system (ECCS) that comes into play upon initiation of a LOCA. 

The accident at the Three Mile Island (TMI) plant in Pennsylvania in 1979 led to many safety and environmental improvements (4—6). No harm from radiation resulted to TMI workers, to the pubHc, or to the environment (7,8), although the accident caused the loss of a 2 x 10 investment. The accident at the Chernobyl plant in the Ukraine in 1986, on the other hand, caused the deaths of 31 workers from high doses of radiation, increased the chance of cancer later in life for thousands of people, and led to radioactive contamination of large areas. This latter accident was unique to Soviet-sponsored nuclear power. The Soviet-designed Chemobyl-type reactors did not have the intrinsic protection against a mnaway power excursion that is requited in the test of the world, not was there a containment building (9—11). 

U.S. Environmental Protection Agency, Eist of Regulated Substances and Thresholdsfor Accidental Release Prevention and Risk Management Programsfor Chemical Accident Release Prevention Tide 40, Part 68, Subpart C, of the Code of Eederal Regulations (40 CER 68), Federal Register h9(fE) 4493 (fan. 

Loss of containment due to mechanical failure or misoperation is a major cause of chemical process accidents. The publication. One Hundred Largest Losses A Thiiiy Year Review of Propeity Damage Losses in the Hydrocarbon Chemical Industry, 9th ed. (M M Protection Consultants, Chicago), cites loss of containment as the leading cause of property loss in the chemical process industries. 

For many years the usual procedure in plant design was to identify the hazards, by one of the systematic techniques described later or by waiting until an accident occurred, and then add on protec tive equipment to control future accidents or protect people from their consequences. This protective equipment is often complex and expensive and requires regular testing and maintenance. It often interferes with the smooth operation of the plant and is sometimes bypassed. Gradually the industry came to resize that, whenever possible, one should design user-friendly plants which can withstand human error and equipment failure without serious effects on safety (and output and emciency). When we handle flammable, explosive, toxic, or corrosive materials we can tolerate only very low failure rates, of people and equipment—rates which it may be impossible or impracticable to achieve consistently for long periods of time. 

Avoid the temptation to overreact after an accident and install an excessive amount of protective equipment or complex procedures which are unhkely to be followed after a few years have elapsed. Sometimes an accident occurs because the protective equipment available was not used nevertheless, the report recommends installation of more protective equipment or an accident occurs because complex procedures were not followed and the report recommends extra procedures. It would be better to find out why the original equipment was not used or the original procedures were not followed. 

Mitigation Reducing the risk of an accident event sequence by taking protective measures to reduce the likelihood of occurrence of the event, and/or reduce the magnitude of the event and/or minimize the exposure of people or property to the event. 

Layer of protection analysis (LOPA) is a simplified form of event tree analysis. Instead of analyzing all accident scenarios, LOPA selects a few specific scenarios as representative, or boundary, cases. LOPA uses order-of-magnitLide estimates, rather than specific data, for the frequency of initiating events and for the probability the various layers of protection will fail on demand. In many cases, the simplified results of a LOPA provide sufficient input for deciding whether additional protection is necessary to reduce the likelihood of a given accident type. LOPAs typically require only a small fraction of the effort required for detailed event tree or fault tree analysis. 

Frequency Phase 3 Use Branch Point Estimates to Develop a Ere-quency Estimate for the Accident Scenarios. The analysis team may choose to assign frequency values for initiating events and probability values for the branch points of the event trees without drawing fault tree models. These estimates are based on discussions with operating personnel, review of industrial equipment failure databases, and review of human reliability studies. This allows the team to provide initial estimates of scenario frequency and avoids the effort of the detailed analysis (Frequency Phase 4). In many cases, characterizing a few dominant accident scenarios in a layer of protection analysis will provide adequate frequency information. 

A simplified form of event tree analysis using selected accident scenarios and order-of-magnitude estimates to determine whether additional protection is needed... 

Cathodic protection of water power turbines is characterized by wide variations in protection current requirements. This is due to the operating conditions (flow velocity, water level) and in the case of the Werra River, the salt content. For this reason potential-controlled rectifiers must be used. This is also necessary to avoid overprotection and thereby damage to the coating (see Sections 5.2.1.4 and 5.2.1.5 as well as Refs. 4 and 5). Safety measures must be addressed for the reasons stated in Section 20.1.5. Notices were fixed to the turbine and the external access to the box headers which warned of the danger of explosion from hydrogen and included the regulations for the avoidance of accidents (see Ref. 4). 

Decision on the Convention on the Transboundary Effects of Industrial Accidents Decision concerning the non-mclusion of DNOC m Annex I of Directive 91/414/EEC on plant protection products... 

HS(G)63 Radiation protection offsite for emergency services m the event of a nuclear accident... 

Anonymous, How to Prevent Runaway Reactions, EPA 550-F99-004, U.S. Environmental Protection Agency Office of Solid Waste and Emergency Response, August 1999. In addition to the accidents mentioned in the reference, a significant number occurred prior to the 1989 time frame. Serious incidents arc recorded as early as 1957. Accident recording before 1957 was incomplete. 

The hazard remains, and some combination of failures of the layers of protection may result in an accident. Since no layer of protection can be perfect, there is always some risk that an incident will occur. 

The process of engaging the required capabilities must be a formal process so that both the organization in need and the contractor/sub-contractor are protected in the event of a failure to perform, an accident, or a difference of opinion as to terms or performance. Adherence to the provisions of this procedure will help attain good contracting practices and minimize the potential liabilities to the host organization in contractual relationships. 

Ensure that the contractor/subcontractor can implement a comprehensive health and safety program in compliance with applicable regulations, including accident prevention programs, medical surveillance, training, work practice controls, use of personal protective equipment, and so on. 

State intervention in man s activities to protect the health of the inhabitants goes back to prehistory. The motivation may not have been altogether altruistic the king acted to protect his subjects because he regarded them as his property. Public health protection began for disease control. With industrialization, came the need for control of even more hazardous forces and substances. This extended protection became technological in accident analysis and response. Present efforts in controlling risk, such as from nuclear power, are a continuation of this development. 

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