Engineered safety

Fig. 6. Schematic ignition diagram for a hydrocarbon+ O2 mixture, with appHcations. Region A, very rapid combustion, eg, a jet engine region B, low temperature ignition, eg, internal combustion engine, safety ha2ards regions C and D, slow oxidation to useful chemicals, eg, 0-heterocycHc compounds in C and alcohols and peroxides in D. Courtesy of Blackwell Scientific PubHcations, Ltd., Oxford (60).

To apply inherent safety appropriately, research chemists must make an in-depth investigation into the process chemistry and into the entire process that may develop based on that chemistry. An adequate investigation necessitates input from a diverse team of people, including research chemists and business, engineering, safety, environmental personnel. They must consider the impact that the use of a particular process chemistry will have on a wide range of populations. These include the ultimate customer of the product, process operating personnel, the general public, and potentially impacted plant and animal populations. To chose the "inherently safest chemistry, the team needs to take into account ... 

Function event trees include primarily the engineered safety features of the plant, but other systems provide necessary support functions. For example, electric power system failure amid reduce the effectiveness of the RCS heat-removal function after a transient or small UJ( A. Therefore, EP should be included among the systems that perform this safety function. Siipfiort systems such as component-cooling water and electric power do not perform safety functions directly. However, they significantly contribute to the unavailability of a system or group of systems that perform safety functions. It is necessary, therefore, to identify support systems for each frontline ssstcm and include them in the system analysis. 

LESF (Figure 3.4.5-5), exemplified for the large LOCA, is compared with SELF. Event tree headings are the refueling water storage tank (RWST) a passive component, an engineered safety system (SA-1) and four elements of the containment system. Other examples of the LESF method show human error in the event tree while the criteria for system success is usually in the tan It tree analysis. 

Accident defenses may be regarded as a series of barriers (engineered safety systems, safety procedures, emergency training, etc.). As barriers fail, incipient failures become real. Inappropriate management policies create inadequate PIFs, which give rise to opportunities foi ermr when initiated by local triggers or unusual conditions. 

Identify critical locations where fires can cause an initiating event that could fail redundant engineered safety functions, or disable redundant and diverse safety-related equipment. 

Manifold barriers confine the radioactivity to the 1) ceramic fuel pellet 2) clad 3) cooling water, as demonstrated by the TMI-2 accident 4) primary cooling loop 5) containment and 6) separation from the public by siting. Further protection is provided by engineered safety systems pressurizers, depressurization, low pressure injection, high pressure injection and residmil heat removal systems. 

Nuclear power plant systems may be classified as "Frontline" and "Support. . iccurding to their. service in an accident. Frontline systems are the engineered safety systems that deal directly with an accident. Support systems support the frontline systems. Accident initiators are broadly grouped as loss of cooling accidents (LOCAs) or transients. In a LOCA, water cooling the reactor is lost by failure of the cooling envelope. These are typically classified as small-small (SSLOCA), smalt (SLOCA), medium (MLOCA) and large (LLOCA). 

The preceding overviewed the operation and engineered safety features of current and advanced LWRs. Before preceding to describe how PSA is performed on nuclear power plants, two accidents are described that have profoundly affected the industiy... 

Ceitain engineered safety features (containment sprays, suppression pools, ice condenscr.s i will effectively remove fission products regardless of form. Other ESF such as filters are less effective. 

The other global dimension of the systems approach is the need for the existence of policies which address human factors issues at senior levels in the company. This implies that senior management realizes that resources spent on programs to reduce error will be as cost-effective as investments in engineered safety systems. 

US Department of Labor, "System Safety Engineering , Safety Manual No. 15, Mine Safety and Healtli Administration, Waslungton, D.C., 1982. 

The safe operation of such processes depends on the design and provision of engineered safety devices, and on good operating practices, to prevent a dangerous situation developing, and to minimise the consequences of any incident that arises from the failure of these safeguards. 

The term engineered safety covers the provision in the design of control systems, alarms, trips, pressure-relief devices, automatic shut-down systems, duplication of key equipment services and fire-fighting equipment, sprinkler systems and blast walls, to contain any fire or explosion. 

In summary, modern DAF units with only 3 min of retention time can treat water and wastewater at an overflow rate of 3.5 gpm/ft2 for a single unit, and up to 10.5 gpm/ft2 for triple stacked units. Of course, the actual retention time used for DAF design will be higher when an engineering safety factor is applied. Figure 27.1 shows a typical DAF clarifier that will be explained in detail later. 

The questions may be divided into specific areas of investigation usually related to consequences of interest, such as electrical safety, fire protection, or personnel safety. Each area is subsequently addressed by a team of one or more knowledgeable individuals. The team answers each question and addresses each concern (or indicates a need for more information) and identifies the hazard, potential consequences, engineered safety levels, and possible solutions. During the process, any new what-if questions that become apparent are added. Sometimes the proposed answers are developed by individuals outside the initial meeting, and then presented to the team for endorsement or modification. 

The Seveso and Duphar accidents could have been avoided if proper containment systems had been used to contain the reactor releases. The proper application of fundamental engineering safety principles would have prevented the two accidents. First, by following proper procedures, the initiation steps would not have occurred. Second, by using proper hazard evaluation procedures, the hazards could have been identified and corrected before the accidents occurred. 

It should be noted that these details indicate wood construction for the NG facilities which is normally not allowed by AMCR 385-100, however, these details have been reviewed and approved for use by the Department of Defense Engineering Safety Board (DDESB). In order to comply with the AMC Safety Manual, approvals may have to be obtained on an individual project basis. 

G-C.Whalen, Chemlnds 54,852-3(1944) "Accident Analysis in Wartime Chemical Plants" 2)H.H.Judson J.M.Brown, "Occupational Accident Prevention",Wiley,NY(1944) 3)C.G.Daubney,Meta llurgia 33,41—4(1945 ) "Accident Investigations 4)US Army, Corps of Engineers Safety and Accident Prevention Div, Safety Requirements,Pamphlet,US Govt... 

Postma, A.K. Pasedag, W.F. (1986) Overview of fission product release and the effectiveness of engineered safety features. In Source Term Evaluation for Accident Conditions, IAEA, Vienna, pp. 621-32. 

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