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Provisional Safety Standards Series No. 1

Volcanoes and associated topics in relation to nuclear power plant siting

July 1997

INTERNATIONAL ATOMIC ENERGY AGENCY

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The originating Section of this publication in the IAEA was:

Engineering Safety Section International Atomic Energy Agency Wagramerstrasse 5 P.O. Box 100 A-1400 Vienna, Austria

VOLCANOES AND ASSOCIATED TOPICS IN RELATION TO NUCLEAR POWER PLANT SITING IAEA,VIENNA,1997 IAEA-PSSS-01

 IAEA, 1997

Printed by the IAEA in Austria July 1997

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FOREWORD

This report is intended to provide information and draft guidance on a subject which is still undergoing development at both the international and national levels, namely the siting of nuclear power plants in volcanic areas. Users of the report are encouraged to provide feedback on the text in order to assist the IAEA in the compilation of a future Safety Standards Series publication.

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EDITORIAL NOTE

In preparing this publication for press, staff of the IAEA have made up the pages from the original manuscript(s). The views expressed do not necessarily reflect those of the governments of the nominating Member States or of the nominating organizations. Throughout the text names of Member States are retained as they were when the text was compiled. The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimination of their boundaries. The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part by the IAEA.

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VOLCANOES AND ASSOCIATED TOPICS IN RELATION TO NUCLEAR POWER PLANT SITING

CONTENTS

1. INTRODUCTION ...... 1 BACKGROUND ...... 1 OBJECTIVE ...... 1 SCOPE ...... 1 STRUCTURE ...... 1 2. TYPES OF VOLCANIC PHENOMENA ...... 3 3. GENERAL REQUIREMENTS ...... 10 4. NECESSARY INFORMATION AND INVESTIGATIONS (DATABASE) ...... 13 5. DETERMINATION OF CAPABILITY OF VOLCANOES ...... 17 6. VOLCANIC HAZARD EVALUATION ...... 18 7. DESIGN CONSIDERATIONS ...... 22 8. MONITORING SYSTEM ...... 25 ANNEX I - MAJOR DIVISIONS OF GEOLOGICAL TIME ..... 28 ANNEX II - CLASSIFICATION OF VOLCANOES FOR CAPABILITY ASSESSMENT ...... 29 REFERENCES ...... 31 GLOSSARY OF VOLCANOLOGICAL TERMS ...... 34 CONTRIBUTORS TO DRAFTING AND REVIEW ...... 40 LIST OF RELEVANT IAEA PUBLICATIONS IN THE NUSS SERIES ...... 41

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1. INTRODUCTION

BACKGROUND

101. This report provides guidelines and recommends procedures to adopt in the consideration of volcanoes and associated topics for nuclear power plant siting. The Code on the Safety of Nuclear Power Plants: Siting (50-C-S (Rev. 1)) indicates that historical data concerning phenomena that have potential to produce adverse effects on the safety of the nuclear power plant, such as volcanism, shall be collected and evaluated. If the potential is confirmed, design bases shall be derived (see para. 440 of the Code).

102. Engineering solutions are available to mitigate some potential effects of external events through design. However, when such solutions either are not practicable or cannot be demonstrated as being adequate for mitigation of the effects of volcanic phenomena, it may be prudent to select an alternative site.

103. In the various phases of site survey leading to the selection of a site, particular attention should be paid to two categories of features related to volcanoes:

(1) Features that can have direct influence on the acceptability of the site. (2) Features that can influence the severity of the effects of the volcanic activity on the plant, i.e. the design basis parameters.

Information related to investigations during a site survey may be found in Safety Series No. 50- SG-S9, a Safety Guide.

OBJECTIVE

104. The main purpose of this report is to provide draft guidance on the criteria and methods for the evaluation of a site for a nuclear power plant with respect to the potential effects of volcanic activity which may jeopardize its safety and to elicit feedback from Member States. Different types of phenomena associated with volcanism are discussed in terms of their influence on site acceptability and on derivation of design basis parameters.

SCOPE

105. This report was developed for application to new nuclear power plant sites. It does not address the issue of the re-evaluation of existing nuclear power sites to the potential effects of volcanic activity, although it contains general information and criteria useful for this purpose.

106. The guidelines and procedures discussed in this report can appropriately be used as the basis for the safe siting and design of nuclear power plants in different volcanic environments.

STRUCTURE

107. In this report, the description of the phenomena associated with volcanism and the collection of required data and information are separated from the criteria for hazard assessment. Thus Section 2 gives the non-specialist a general description of the different types of volcanic phenomena and Section 4 provides indication on the acquisition of the database. Section 3

1 This publication is no longer valid Please see http://www-ns.iaea.org/standards/ outlines the general requirements to be fulfilled during site selection and evaluation. Sections 5, 6 and 7 provide guidance to perform the hazard assessment and to derive the design basis parameters. Finally, Section 8 deals with monitoring systems. As general information for the non-specialist, Annex I provides the major divisions of geological time. Annex II provides an example of a classification of volcanoes that may be used for capability assessment, as required in Section 5. Finally, with the same spirit, and recognizing that a complete consensus has not been reached in the scientific community on the use and meaning of some terms, a glossary of volcanological definitions is included, applicable only to the use of this report.

108. Guidance related to some of the subjects covered in this report can be found in Safety Guides 50-SG-S1 (Rev. 1), 50-SG-S5, 50-SG-S8 and 50-SG-S10A.

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2. TYPES OF VOLCANIC PHENOMENA

201. This section briefly describes the main types of volcanic phenomena that may affect a site. It provides an indication of the order of magnitude of critical parameters for each phenomenon such as density, velocity, temperature and areal distribution. The quantification of these parameters requires detailed study of the area as described in Section 4. The manifestations of volcanic activity that may affect the site can be listed as follows [1-3]:

(1) ballistic projectiles (2) fallout of pyroclastic material (ash, , scoria, etc.) (3) pyroclastic flows and pyroclastic surges (4) air shocks and lightning (5) lava flows (6) debris avalanches, landslides and slope failures (7) debris flows, lahars and floods (8) volcanic gases (9) ground deformation (10) earthquakes (11) tsunamis (12) geothermal anomalies (13) ground water anomalies (14) opening of new vents

Ballistic projectiles

202. Ejection of ballistic projectiles such as blocks, bombs and other solid fragments is caused by explosions occurring within craters, domes, or vents. The solid objects are propelled by high-pressure gas and follow ballistic trajectories. The speeds of the projectiles can be more than 300 m/s and the maximum horizontal distances they may travel to the impact point can exceed 5 km from the origin. When the size of projectiles is sufficiently small, the friction of air decelerates them enough to affect the trajectory. Typically, projectiles larger than 1 m in diameter would not be significantly affected by the drag forces.

203. This phenomenon is common to all eruptions but is most frequently observed in explosions from domes, vulcanian eruptions, phreatic or phreatomagmatic explosions. The impact energy of a single projectile may reach 1 Joule. If projectiles at high temperatures fall on vegetation, houses or other flammable structures, they may start fires.

204. Hazard zones associated with ballistic projectiles are normally mapped as concentric circles around existing vents. Radii of hazard zones are determined from the distribution of ballistic projectiles deposited during past eruptive episodes and using probabilistic estimates of eruption energies [4].

Fallout of pyroclastic material

205. The fall and deposition of pyroclastic material such as ash, pumice and scoria occur when these particles are propelled by an to an altitude at which they can be carried by wind. On falling they normally reach a constant velocity (so-called terminal velocity), which is determined by the size, shape and density of the falling particle. Their distribution is governed

3 This publication is no longer valid Please see http://www-ns.iaea.org/standards/ by the direction and strength of prevailing winds and height of the ash column.

206. If the ashfall is thick, it may cause serious damage to transportation, agriculture, forests and other social and economic activities. By loading the roofs of buildings, ash accumulation may cause collapse, particularly when the ash becomes soaked by rain. Ash particles drifting in the air sometimes obstruct air traffic by sandblasting the exterior of aircraft and damaging and even stalling jet engines [5].

207. The most voluminous pyroclastic falls are produced by Plinian type eruptions in which large amounts of high-temperature pyroclastic material is thrust upward from the crater by a high-velocity gas jet [6-8]. At a certain height, admixture and heating of air creates a column of rapidly expanding and ascending gas and suspended solid particles which may reach the stratosphere. Such activity usually forms a mushroom shaped eruption column that may be carried by atmospheric currents at high altitude. A significant fall deposit from a typical can extend several hundred kilometers or more from the source and may be tens of meters thick near the vent. A Plinian3 eruption normally lasts only hours or days but it produces a very large amount (up to 100 km ) of deposits [9].

208. Hazards due to pyroclastic falls are usually determined by mapping past fall deposits, consideration of current wind patterns, and often by computer simulation [10-15]. In some areas seasonal wind direction diagrams can be developed.

Pyroclastic flows and pyroclastic surges

209. Pyroclastic flows are high-temperature mixtures of rock fragments, volcanic gases and air that flow down the slope at high speeds [16-18]. Flow velocities reach 10 to 100 m/s making evacuation impossible once a pyroclastico flow has begun. The temperature can be close to that of the original (around 1000 C in many cases) or near ambient temperatures depending on the degree of mixing with air. Downslope movement of the is driven primarily by gravity. The high mobility of the flow indicates that internal friction is very small. Pyroclastic flows may have sufficient momentum to deviate from drainage lines and to pass over topographic obstacles.

210. Many pyroclastic flows consist of two different parts, although the transition between the two may be gradual. The majority of the moving solid material is concentrated at the bottom part of the flow and the top is a more dilute mixture of ash and gas that rises like a thick dust3 cloud. The lower, dense part of the pyroclastic flow may have3 a bulk density of 0.1 - 0.5 t/m ; the upper dilute cloud has a bulk density close to 0.001 t/m . This dilute part often separates from the denser part and travels considerable distances downwind.

211.5 The3 volume of solid11 materials3 transported by a pyroclastic flow may range from less than 10 m to more than 10 m , depending on the mode of generation and emplacement. Most large scale pyroclastic flows are generated by wholesale vesiculation of felsic magma stored in a shallow . Large amounts of magma are progressively fragmented and ejected from the vent because of the rapid formation and expansion of the bubbles in the ascending magma. Such eruptions may lead to the collapse of . Thick,4 hot2 deposits may extend more than 200 km from the vent and cover an area of more than 10 km . Smaller pyroclastic flows may be formed by the partial collapse of growing lava domes or thick, blocky lava flows. Explosions of gas from domes cause vertical ejections of pyroclastic material, part of which may

4 This publication is no longer valid Please see http://www-ns.iaea.org/standards/ generate pyroclastic flows when it falls back to the surface. Small scale pyroclastic flows have been witnessed on the slopes of large volcanoes but there are no historical accounts of very large flows of the kind that have erupted and produced calderas in the past. Owing to their great mass, high temperatures, velocity, and great mobility, pyroclastic flows present serious hazards, including burial, incineration, asphyxiation and impact. Secondary hazards derive from large amounts of melt water from snow capped volcanoes generating lahars and floods.

212. Pyroclastic surges are turbulent, dilute gas-solid suspensions that flow over the ground surface at high velocities with less regard to topography than pyroclastic flows. They can be divided into two types, hot and cold. Hot pyroclastic surges, also known as ground surges, are generated by many of the same processes that form pyroclastic flows and often over-ride or precede pyroclastic flows. Cold pyroclastic surges, also known as base surges, originate from hydromagmatic explosions in which shallow ground water or surface water interacts with magma. They typically contain water and/or steam and have temperatures at or below the boiling point of water. Base surges are generally restricted to a radius of 16 km from the vent. Pyroclastic surges pose a variety of hazards including destruction by ash-laden clouds, impact by rock fragments, and burial. Hot pyroclastic surges present several additional hazards including incineration, toxic gases, and asphyxiation.

213. Hazards associated with pyroclastic flows and surges are evaluated by mapping past deposits, study of the physical volcanology of these deposits and estimate of the temperature of emplacement of these deposits. Analysis of topography and drainage patterns and computer simulation are also used to estimate hazards associated with these phenomena [19].

Air shocks and lightning

214. Explosive eruption of a can generate supersonic shock waves powerful enough to break windows at distances of several kilometers. They are accompanied by projection of bombs and blocks as discussed in the previous section but the radius of the shock wave effects may be greater than that of the projected material.

215. Lightning often accompanies volcanic eruptions. Lightning results from charge differences between the erupting column of ash and the atmosphere. In some cases, lightning and high static charges occur up to several kilometers from the erupting volcano.

Lava flows

216. Flows of lava are driven by gravity and follow the drainage lines of the topography [20]. They behave like viscous fluids, usually with a semi-solid crust on the surface. The morphology and velocity of lava flows depend on the eruption rate, temperature, composition, vent geometry and topography. Common morphologic types of lava flows include pahohoe, aa, and block lava flows. These different morphologies indicate different magma viscosities and sometimes different effusion rates. Their length can range from a few meters to tens of kilometers and the thickness from lesso than one meter to more than 100 m. The temperatureso of basaltic lavas may be as high as 1200 C; dacitic and rhyolitic lavas may be 1000 C or less. Unusual lavas, sucho as the carbonates erupted at Oldoinyo Lengai (Tanzania) may have temperatures as low as 400 C.

217. The speed of a lava flow is normally slow, but some silica-poor and/or high-temperature lava flows may reach speeds of more than 10 m/s on steep slopes. The lava flows of Nyiragongo

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(1977, Zaire) and of Oldoinyo Lengai (Tanzania) volcanoes reportedly reached velocities greater than 10 m/s. However, the advance of the front of even the most fluid basaltic lava flows is normally much slower, usually a few m/s or less. More felsic lava flows such as andesitic, dacitic and rhyolitic, advance more slowly, less than 100 m/day on gentle slopes. When the viscosity and yield strength of felsic lava are high, the lava may form a with a height to diameter ratio much larger than that of lava flows. Lava domes may reach heights of more than 100 m and have widths of several hundred meters.

218. Hazards associated with lava flows are usually estimated by mapping of the distribution of past lava flows, mapping current drainage patterns and related topographic features that would control lava flows, and mapping vents from which lava flows could erupt. Computer simulation of lava flows has been used to estimate hazards [21, 22].

Debris avalanches, landslides and slope failures

219. Most volcanic edifices are steep-sided and may therefore become unstable as a result of erosion or deformation. Partial or complete failure of the slopes often produces debris avalanches, which are high-speed turbulent flows of rock fragments and entrapped air [23, 24]. The mode of movement of debris avalanches is therefore similar to that of pyroclastic flows in that both phenomena are downslope flows of mixtures accelerated by gravity. Although not as large as debris avalanches, detachment and collapse of unstable slopes of the volcanic edifice may lead to landslides and other types of sudden slope failures, triggered by an earthquake or heavy rainfall.

220. The temperatures of most debris avalanches are much lower than those of the pyroclastic flows and range between ambient temperature to a few hundred degrees Celsius depending on the original temperature of the rocks. Elevated temperatures of deposition can be determined from the presence of a significant fraction of juvenile material in the deposit, the presence of charred wood or3 using paleomagnetic methods [25, 26]. The volume of collapse may reach more than 10 km and the speed of the resulting flow may exceed 100 m/s.

221. A large collapse may leave a horse shoe-shaped scarp on the upper part of the slope. Deposits may reach thicknesses of several tens of meters and extend tens of kilometers from their origin. The damage caused by a debris avalanche is mainly by physical impact and burial and the devastation in the central part of the flow can be total.

222. Hazards associated with volcanic debris avalanches and