External hazards

Compression ignition engine Designed, constructed and equipped to protect explosive from external hazards and weather Closed or securely sheeted Trailers to be adequately braked or restrained upon detachment from towing vehicle... 

General Considerations 1 Location of people relative to the unit 2 Location of critical systems 3 Dominant wind direction 4 Climate and weather extremes earthquake, flooding, windstorms 5 Site topography 6 External hazards or threats (fire/explosion/toxic release from nearby process or facility aircraft subsidence sabotage) 7 Traffic flow patterns and clearances from process vessels and lines 8 Security and reliability of all critical feeds and utilities 9 Command center and alternate command center locations 10 Evacuation routes, emergency exits, safe rally spots... 

Radioactivity results when some part of an atom is unstable. The instability exists because the orbital electrons or the nucleus contain too much energy. Radioactive atoms are called radionuclides. They release excess energy by emitting radiation. The type of radiation released (alpha, beta, or gamma particles) may be more or less hazardous to humans, depending on the location of the radioactive materials. Exposure to radioactive materials outside the body poses external hazards. Radioactive materials may also be hazardous when ingested, inhaled, or injected and thus pose internal hazards. The sections below describe the characteristics of radiation particles as external or internal hazards and as they may be encountered after a terrorist attack. Chapter 3 provides additional details and addresses health effects associated with exposure to radiation. 

Radionuclides that do not emit beta particles likely emit alpha particles. An alpha particle is, in effect, a helium atom (two protons and two neutrons) ejected from an unstable nucleus. An alpha particle can only travel a few inches in air and cannot penetrate the outer layers of dead skin cells. Therefore, alpha particles are not external hazards and produce tissue damage only if alpha-emitting radionuclides are ingested, inhaled, or injected. 

The packaging material is a laminate made from layers of paper, plastic (polyethylene) and aluminium foil. The particular composition for a given product is chosen according to its specific requirements. This affords the best protection to each product and keeps it in peak condition until consumed. Polyethylene is laminated to the board to make it impermeable, and an aluminium foil (of 10 p.m or less) is added to increase the barrier properties against external hazards such as sunlight and atmospheric oxygen, which would cause deterioration of product quality. 

External" hazards fire, electricity failure, control failure. 

Alpha (a) particle It is a double positive charge carrying helium nucleus He2+) released spontaneously from a high-atomic mass radioactive element. It has low penetration power and can be stopped by a thin sheet of paper or a layer of air. Has no external hazards has internal hazards. 

X-ray It is a high-energy, highly penetrating radiation. Its origin is the inner orbital electrons in an atom. X-rays are produced by the sudden acceleration of charge particles. It poses high external hazards. 

Safeguarding against external hazards, such as ignition sources if the piping or equipment could contain flammable material, and sealing off drains or other possible sources of noxious liquids, vapors, or gases. 

E. Alpha. Alpha radiation is fully absorbed within the first millimeter of an exposed tissue mass. If the source of the alpha radiation is external to the body, all of the alpha radiation is absorbed in the superficial layers of dead cells. If anything, even tissue paper, is interposed, the alpha particles will be absorbed, and not reach the skin. Because of this, alpha radiation is not an external hazard. If alpha-emitting material is internally deposited, all the radiation energy will be absorbed in a very small volume of tissue immediately surrounding each particle. Internal deposition of alpha particles can cause radiation injury on a long-term basis. 

Because of the penetrating nature of gamma radiation, overexposure of the body to it results in deep-seated organic damage. Of the three types of radiation from radioactive substances, gamma radiation is by far the most serious external hazard and is the one that requires heavy shielding and remotely controlled operations. 

Risk is based on the contrast between reality and possibility (Markowitz, 1990). Only when the future is seen as at least partially influenced by human beings) is it possible to prevent potential hazards or to mitigate their consequences (Ewald, 1993). The prediction of possible hazards depends on the causal relation between the responsible party and the consequences. Becau.se the consequences are unwelcome, risk is always a normative concept. A society should avoid, reduce, or at lea.st control ri.sks. Increasing potentials of technical hazards and the cultural integration of external hazards into ri.sk calculations increase the demand for risk science and risk management (Beck, 1986). 

Approach is founded upon a mechanistic, probabilistic basis, as noted in Section 3.2.3.1 the means for assessing external hazards and their consequences on a purely probabilistic basis are only in the early stages of development. This includes a process for assessing the fragility of structures designed to various codes in response to seismic events of varying intensity. Should validated analytical methodologies consistent with the... 

An experienced outsider will bring a wealth of experience and knowledge from all the other analyses and evaluations in which he or she has participated. This fund of experience provides an invaluable basis for challenging the status quo and coming up with fresh insights. External hazards analysis leaders move from project to project, in the same way that medieval masons moved from cathedral to cathedral, taking their experience and skills with them. 

The third pair of questions relates to the likelihood of damage by external hazards nd the sensitivity of the structure to those hazards. This assessment will depend or. the availability of statistical information which is generally rather sparse in these matters. It is urgently required that general statistics of this nature should be collected and widely published. 

In comparison with Mochovce LPS PSA, Bohunice V-2 LPS PSA has a smaller work scope. It does not consider external hazards. Bohunice V-2 NPP has nearly ten years of operation and therefore plant specific operational experience is used in its LPS PSA. However, it is only used as generic source of information for Mochovce LPS PSA. 

Neighbouring transport installations (roads, rails, waterways) are to be regarded as external hazards, if the increased risk is caused by the trafiic conditions in the vicinity of the establishment (e.g. traffic density, traffic routing, type of transports, weather conditions). Under certain circumstances civil and military air traffic is included. 

Control of the external hazard is based on manipulation of three primary variables, time, distance, and shielding. 

This section describes the hazard identification and evaluation process performed for the SNL HOF and for the HOF associated radioactive material storage areas. The purpose of this information is to present a comprehensive evaluation of potential process-related, natural phenomena and external hazards that could possibly affect the public, workers, collocated workers, and the environment due to single or multiple failures or incidents. Consideration is given to all phases of isotope production operation of the HCF, including the activities, materials, facilities, and equipment of the production process. 

U.S. Nuclear Regulatory Commission (NRC), 1987, Evaluation of External Hazards to Nuclear Power Plants in the United States, NUREG/CR-5042, U.S. Nuclear Regulatory Commission, Washington D.C., December 1987. 

External hazards must not constitute a large part of the residual risk so specific design measures were taken to consider a more appropriate approach on earthquakes, explosion pressure waves and military aeroplane crashes. This requirement had a significant impact on layout requirements. ... 

External hazards play an important role in the safety assessment for nuclear facilities Since they have an impact on the facUity as a whole, they have the potential to cause initiating events (loss-of-coolant accidents or transients) and simultaneously to impair the safety systems necessary to limit the consequences of the initiated events. 

Based on this consideration, the German nuclear power plants have been designed to withstand the impact of external hazards according to the regulations in effect at the time of their construction (BMU 2007). In general, this design was based on deterministic considerations. 

As a part of the (periodic) safety reviews (BMU 1996) of the German nuclear power plants, the protection against external hazards has to be re-assessed. According to the guidance on probabilistic safety reviews (BMU 2005) and following the international state-of-the-art (IAEA 2008) the deterministic assessments have to be supplemented by probabilistic analyses. But up to now, the spectrum of external... 

In nuclear safety there is a clear distinction between internal events (loss-of-coolant accidents and transients) and external events. External events is an umbrella term for internal hazards (e. g. fires) and external hazards. Up to now, most PSAs have focnsed on internal events and internal hazards. With the exception of seismic PSAs, PSAs for external hazards are not yet very common. 

The probabilistic assessment of external hazards represents a relatively new aspect in the German nuclear regulatory process. Only in 2005 a new guideline for probabilistic safety assessments has been issued (BMU 2005) which requires analyses to be performed for the following hazards aircraft crashes, pressure waves due to explosions, flooding, and earthquakes. With the exception of flooding, harsh weather conditions are not within the scope of this guideline. 

The corresponding technical reference docmnent on PSA methods (FAK 2005) provides guidance on the methods to be nsed for these assessments. In general, the extent of the analysis for external hazards is limited to a Level 1 PSA (estimation of the core damage freqnencies, no consideration of release frequencies) and to full power operation states. The depth of the required analyses varies between the individual hazards. But for all external hazards the recommendations have not yet reached the same maturity as for plant internal events. 

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