EXTREME WINDS

Reference [4] gives guidance for a site specific review of the potential risk of tropical (typhoons and hurricanes) and extra-tropical cyclones, both generated on the ground (tornadoes) and on seas or large water bodies (waterspouts). 

In this section, only wind coupled with abrasive effects by sand and dust or corrosive attack by a salty atmosphere are discussed related effects such as rain and wind induced missiles are dealt with in other sections. 

High winds have been known to cause collapse of cooling towers as a consequence of a group effect , while they were individually designed to withstand an even higher wind speed. 

The group effect from the combination of the influence of neighbouring buildings should always be evaluated [4]. 

Standards and codes developed for the effects of winds on normal buildings should be used for the evaluation of the local effects, with special care taken for the dynamic effects exerted by the wind on the roof, curtain walls and glass openings. The reference values for nominal wind velocity should be consistent with the selected DBEE policy. 

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External Flooding Extreme Winds Extreme Suimner Temperature Fog... 

These scales of extent define the manner in which the ideas of extreme events are applicable to agriculture and forestry. Wind-throw is a small-scale process and the forest manager must grow and manage plantation forests which will survive extreme wind speeds at the spatial scale of his plantation. The question is, how rare must this extreme event be, before it may be discounted. The answer is likely to be dominated by economics and also the longevity of the plants with a 50 year harvesting interval, it seems clear that the return periods of extreme events up to 50 years (at least) are crucial. 

The allowable stress for occasional loads of short duration, such as surge, extreme wind, or earthquake, may be taken as the strength reduction factor times 90% of the yield strength at temperature times Mj for materials with ductile behavior. This yield strength shall be as listed in ASME BPV Code Section II, Part D, Table Y-l (ensure materials are suitable for hydrogen service see API 941), or determined in accordance with para. 

Let us now examine some specific examples using a set of compounds with air-water partition constants, Ku/Vl, between 30 and lxlO-5 (Table 20.5a) and by choosing two extreme wind velocities, uU) = 1 m s 1 and 20 m s 1. From Table 20.4 we get the following reference transfer velocities ... 

Extreme Wind Design Criteria for Nuclear Power Plants. BC-T0P-3A, Revision 3. BPC, San Francisco, CA, August 1974. 

In addition to operational accidents, external accidents also require detailed study. Examples are earthquake, extreme wind, flooding, aircraft crash, external fire, etc. Because of the time limit, the details will not be discussed here. 

Extreme Wind/Tornado Hazard Models for Department of Energy Sites, by D.W. Coats and R.C. Murray. 

Bechtel Co. (1973) Tornado and extreme wind design criteria for nuclear power plants , BC-TOP-3, Bechtel Power Co. 

Lawrence Livermore National Laboratory (LLNL), 1984, Natural Phenomena Hazards Modeling Project Extreme Wind/Tomado Hazard Models for Department of Energy Sites. UCRL-53526, Lawrence Livermore National Laboratory, Livermore, California, February 1984. 

Reinforced concrete road bridges are gradually deteriorating due to various adverse factors that may significantly influence their performance and safety. The main factors include chemical attacks (chlorides, atmospheric CO2, pollutants SO2 and NOj,), physical effects (frost, scouring), overloaded trucks, natural disasters (floods, extreme winds) and vandalism. It is recognised e.g. in COST 345 (2004) or by Rafiq et al. (2004) that deterioration of reinforced concrete... 

D. Walshaw and C. W. Anderson, A model for extreme wind gusts, Appl. Stat. 49, 499-508 (2000). 

External Flooding Aircraft Impact External Explosion Extreme Temperature Drought Extreme Wind External Fire External Missiles Biological Fouling EMI and Lightning Malicious Activities Surrounding Influences... 

The withstand required by plant systems, structures and components against external hazards, such that appropriately safe operation can be maintained, has been addressed comprehensively in the DCD, primarily in Chapter 3 and will be discussed in more detail in the sub-section following. On the basis of the requirements for withstand being directly incorporated into the Design Basis for the plant systems, structures and components, only those postulated hazards with significant requirements on management are taken forward for further assessment in the PRA, to make sure that the requirements to address any potential vulnerabilities are captured. The external hazards taken forward to the PRA for this purpose are external flooding, extreme winds, seismic and transportation accidents (external explosion). 

Extreme winds (including tornadoes) can affect plant stmctures in particular ways ... 

The APIOOO has been designed as such that any hazard caused by extreme wind within the Design Basis would not compromise the control of core reactivity and the removal of heat from the core and would not result in the uncontrolled dispersion of radioactivity or the uncontrolled exposure of plant personnel or the public to radiation. 

Each of the APIOOO principal buildings has been reviewed to identify their specific safety requirements and specify the supporting evidence. It is concluded that the specific claims against extreme wind are satisfied as such that the buildings are designed to withstand extreme wind outside of what is expected in the UK. Where it is required, adequate alarms, systems and controls are in place to inform operators of any action required. These objectives are achieved as follows ... 

APIOOO assessment parameters for extreme wind exceed those associated with the UK Design Basis events. 

Nuclear Island building structures will withstand extreme wind such that KSFs are not compromised. 

Extreme wind-induced damage to SSCs outside the Nuclear Island will not compromise key safety-significant SSCs on the Nuclear Island. 

No other SSC could fail due to extreme wind such that a safety-significant SSC is consequently adversely affected. 

ANS 2.3 Standards for estimating tornadoes, hurricanes and other extreme wind parameters at power reactor sites... 

Tornado missiles (Tm) Tornado-generated missiles carry objects which are accelerated by the forces induced by the extreme wind speeds of the tornado. The parameters specified in the design basis tornado are translated into pressures and forces acting on the structures and its components. The important case is the real analysis that would be necessary to perform on the structure. The analysis is known as tornado structure interaction. In this analysis the load evaluated using a specific path width of the tornado field that experiences wind velocities >75 mph (120 km/h) is generally considered. 

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