This guideline is an illustration and supplement to relevant articles of "Safety Requirements for Selection of Nuclear Power Plant Site" (HAF 101, hereinafter referred to as "Regulation"). This safety guideline is a guidance document. Methods and schemes different from those specified in this guideline may be used in actual work. However, evidence must be given to the National Nuclear Safety Administration to show that the used method(s) and procedure(s) have the same safety level as that in this guideline and will not cause risks to the staff and the public in plant area.
The general characteristics of tropical cyclones are discussed in this guideline, with particular emphasis on their pressure and wind structures in the light of available data.
General methods are given for the evaluation of the relevant parameters of a Probable Maximum Tropical Cyclone (PMTC), which can be used as the Design Basis Tropical Cyclone (DBTC); these parameters then serve as inputs for the derivation of a design basis surge and a design basis wind. A possible method is also given for the evaluation of the PMTC pressure and wind field based on an approach valid primarily for a particular region. This method depends on the results of a theoretical study on the tropical cyclone structure and makes use of a large amount of data, including aircraft reconnaissance observations for 170 most intense tropical cyclones near the coast of Japan, Taiwan and the Philippines for the period 1960-1974, as well as detailed analyses of all the extreme storms along the Gulf of Mexico and the east coast of the USA during 1900-1978, for the determination of the necessary parameters.
The distribution and estimation of heavy rains in tropical cyclones and their effects on flooding are, however, not discussed, since these aspects are considered in guidelines HAD 101/08, HAD 101/09 and HAD 101/10.
Examples of the application of the various methods are given in the Appendixes. Generally, these examples are based on data for the Gulf of Mexico, the east coast of North America and the western North Pacific.
It is possible that the methods based on a particular physical model developed for a certain region cannot be transposed to another one without proper modification. Therefore, these methods should not be used for evaluating the PMTC in other regions prone to tropical cyclones without first checking the validity of the application to such regions by performing meteorological studies of the available data. Because of the rarity of very severe tropical cyclones, coupled with the scarcity of observations in the intense portion of tropical cyclones, the physical characteristics of cyclones in different regions are not completely known.
Although tropical cyclones occur much more rarely than severe extra-tropical cyclones, their impact is sufficiently important to most countries to merit a continual reassessment of their threat to coastal areas. The major damages from most of these storms result from inundations by tide surges accompanying the disturbances and generally occur some distance away from cyclone centers. At open exposed shorelines, destruction normally begins with the erosive scour and battering from large breaking waves, the effects of which may extend inland with a rising tide to attack foundations and to cause structural damage to the lower floors of buildings.
The damaging effects of the winds in a tropical cyclone are produced by a combination of their strength, their gustiness and their persistence. The dynamic forces exerted by the wind may cause roof failures and, at times, the collapse of curtain walls and glass openings.
Most of the tropical cyclone data used for the development of the PMTC is associated with storms over open waters and, strictly speaking, the methods are only applicable to open coastal sites. For inland locations, the effects of topography and ground friction need to be examined or quantified. In addition, it is known that polewards moving storms generally lose their quasi-symmetrical tropical characteristics and assume the structure of extra-tropical depressions with well-marked thermal contrasts. It is therefore clear that, in considering the siting of installations at higher latitudes, modifications of the criteria developed for coastal sites will have to be made. Finally, it may be pointed out that, in spite of the availability of aircraft reconnaissance data accumulated over the past 20 years, the time variations of a few of the pertinent tropical cyclone parameters over a period of a few hours are still little known so that it is necessary to assume the PMTC in a steady state. Substantial changes in the inner core region from hour to hour have been noted in some matured tropical cyclones
