Protection against internal hazards

Internal hazards are extensively addressed in specific IAEA Safety Series publications that also provide guidance for the safety assessment. Some key issues are summarized in this section. 

The design should take into consideration specific loads and environmental conditions (temperature, pressure, humidity, radiation) imposed on structures or components by internal events such as  

It should be demonstrated that the effects of pipe failures such as jet impingement forces, pipe whip, reaction forces, pressure wave forces, pressure buildup, humidity, temperature and radiation on components, building structures, electrical and instrumentation and control (I C) equipment are sufficiently taken into account. Specifically, it should be shown that  

SSCs important to safety should be located at an elevation higher than the expected maximum flood level or should be sufficiently protected. 

CONFORMITY WITH APPLICABLE CODES, STANDARDS AND GUIDES 

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AR59 Design of reactor containment systems for nuclear power plants. Safety guide, NS-G-1.10, 2004. AR60 Protection against internal hazards other than fires and explosions in the design of nuclear power plants. Safety guide, NS-G-1.11, 2004. 

Protection against Internal Hazards other than Fires and Explosions in the Design of Nuclear Power Plants... 

PROTECTION AGAINST INTERNAL HAZARDS OTHER THAN EIRES AND EXPLOSIONS IN THE DESIGN OE NUCLEAR POWER PLANTS... 

Guidance is provided on how to analyse the consequences of PIEs, including the analysis of secondary and cascading effects as well as the corresponding functional analysis. Means of protection against internal hazards are discussed, as well as methods and means of reducing the aforementioned probabilities. 

In practice, protection against internal hazards will involve a great deal of engineering judgement and use of pragmatic rules. Therefore, as far as practicable, an experimental background should be provided in support of the theoretical analysis. 

Wherever possible the design of SSCs should be a failure tolerant design. That is, should these items fail, their failure would tend to move the plant towards a safe plant condition. This technique has broader application to areas other than protection against internal hazards, but where vaUd it may help in mitigating the effects of postulated internal hazards. 

INTERNATIONAL ATOMIC ENERGY AGENCY, Protection Against Internal Hazards Other than Fire and Explosions, Safety Standards Series, IAEA, Vienna (in preparation). 

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... 

If the safety and support systems are not adequately protected against internal flooding hazards, the safe shutdown of the plant can be impaired or an accident initiated. 

The external hazards considered are seismic events, external floods, extreme weather, lightning, external electromagnetic interference, and aircraft crash analysis demonstrates that the design features of the API000 provide appropriate protection against these hazards (External Hazard Report, Reference 14.30). Therefore, it is demonstrated that external hazards do not present a significant probability of a major accident to the environment. Hence, the risk of acute environmental pollution as a result of external hazards is not considered further in this section. Plant faults and internal hazards are discussed further below. 

Regarding protection against internal events, the entire plant is designed to protect personnel and the external environment against radiological hazard. To summarize, the main technical features to protect the plant are ... 

Burn, S.L. (2006) Assessment of personal protective clothing for protection against fire hazards. 33rd International Pyrotechnics Seminar, Fort Collins, CO, July 16-21, p. 493. 

To provide co-ordination in reaching a greater degree of international consensus on how NPPs should be protected against external hazards. The issue of external hazards is especially important for future NPPs, since the levels of safety being achieved by these plants is improving to such an extent that the relative contribution to risk from external hazards is becoming more relevant. 

Abstract. Carbon disulfide is a well-known occupational hazard in viscose industry. This study was focused on assessment of the external and internal exposure to carbon disulfide of occupationally exposed workers with a view to make a comparative analysis of the results and determine the correlation ratio between amounts of carbon disulfide introduced in human organism and amounts that are kept there. These studies are a basis for further identification of methods to protect the workers against the hazardous effect of carbon disulfide as a chemical factor of the workplace. 

An essential requirement is the definition of the degree of protection of the enclosure for the environment, which may be either outdoor or indoor, and hazardous or non-hazardous. The international standards most often used are IEC60529 and NEMA-ICSl-110 for the degree of protection against liquids and particles. These references are applied for the hazardous area protection. See also Chapter 10. 

The canal contains the equipment for the hand ing of assemblies discharged from the reactor and provides space for the storage of spent operating assemblies, irradiated materials, and intern-al parts of the reactor. Water over these materials protects the operating personnel against the hazards of radiation. 

Moreover, Level 1 offers the initial protection basis against important external or internal hazards (e.g. earthquakes, fires, floods), even if some additional protection may be necessary at higher defence levels. 

Protection against direct jet impingement is similar to protection against missiles (see paras 3.1-3.32). Protective measures can be designed in such a way as to cope with both missiles and jets, or generally with as many internal hazards as possible. 

The objective of the review of hazard analysis is to determine the adequacy of protection of the nuclear power plant against internal and external hazards with account taken of the actual plant design, actual site characteristics, the actual condition of SSCs and their predicted state at the end of the period covered by the PSR, and current analytical methods, safety standards and knowledge. 

The key actions in protecting against the internal hazard are aimed at preventing the radioactive material from contaminating the working environment and individuals and, thus, from entering the body. 

The basic methods of protection against the internal hazard are containment, labeling, monitoring, and safe working practice. 

Data about the ability of equipment to protect against a particular hazard is provided by manufacturers who carry out tests under controlled conditions which are often specified in national or international standards. Performance requirements for face masks, for example, are contained in two British Standards which specify the performance requirements of full-face and half/quarter masks for respiratory protective equipment. The method used to determine the noise attenuation of hearing protectors at different frequencies (octave bands) throughout the audiWe range is specified in a European standard . 

This information is drawn upon in the PCSR to show that the DBA addresses all potential initiating events that could result from internal hazards, and that all claims that demonstrate the APIOOO to be adequately protected against the effects of internal hazards have been... 

The Internal Hazards Topic Report (Reference 7.1) identifies safety functional requirements that represent the design requirements on systems, structures and components (SSCs) that enable the key safety functions to be maintained or their loss to be protected against when challenged by internal hazards. 

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