Guidelines for Site Investigation and Analysis of Nuclear Facilities – A Consultants Perspective

Godwin, William 1, Secanell, Ramon 2; Martin, Christophe 2

1 Fugro Consultants, Inc. 1777 Botelho Drive, Suite 262, Walnut Creek, 94596 California USA

2 GEOTER-SAS, Fugro Group. 3 Rue Jean Monnet, 34830 Clapiers, FRANCE

Abstract: Planning site investigations for siting, licensing, or constructing nuclear power plants require implementation of appropriate technical guidelines. Guideline documents have been developed in the USA and internationally to provide standards for how geologic, geotechnical, hydrologic and seismic data are col-lected, analyzed and presented in safety analysis reports. The authors discuss how guidelines established by both the U.S. Nuclear Regulatory Commission (USNRC) and the International Atomic Energy Agency (IAEA) are used in the regulatory framework of nuclear power plants in France, the United Arab Emirates, Japan and the United States. The importance of the choice of meth-odologies engineering geologists use to successfully perform nuclear safety-related site characterization studies and analysis is also discussed. Lastly, new guidelines and approaches developed to address seismic and flooding risks in response to the 2011 Fukishima Daiichi Power Plant incident in Japan are pre-sented. Keywords: Guidelines, USNRC, IAEA, Nuclear, Safety

1. Introduction

Over the last few years, many new nuclear plant sites have been character-ized using regulatory established procedures. The most commonly used proce-dures are those defined in the USA by the U.S. Nuclear Regulatory Commis-sion (USNRC), described in Regulatory Guides, and the methodology described by the International Atomic Energy Agency (IAEA) in their Safety Guides. The recommendations described by the IAEA have been accepted by almost 200 members of the IAEA. It implies that recommendations of the

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IAEA guides are accepted by USA regulators. However, sometimes, the proce-dures and methodologies imposed by NRC are stricter than the IAEA recom-mendations (and they are not accepted by all IAEA members).

Some countries have adopted all or part of the USA regulations. Other coun-tries and mainly the “newcomers” (countries desiring to become nuclear opera-tor) adopt some IAEA requirements and safety guides as national regulatory documents. France and Japan, with established nuclear regulatory bodies, have their own regulations. A recent shift has been to adopt (and to respect) the gen-eral procedures recommended by the IAEA.

In this article, we describe the methodologies and procedures generally fol-lowed by USA, France and other countries (mainly the “newcomers”) for seis-mic site characterization.

2. Regulatory Framework

2.1 USA, France and other experienced nuclear countries

The USNRC has prepared a series of guidelines used extensively by con-sultants and utilities to collect and analyze of geologic, geotechnical and seis-mological data (Table 1). The most recently used guideline for seismic hazard studies is RG.1.208. The Senior Seismic Hazard Analysis Committee (SSHAC) methodology developed in USA in the last decade is the most accepted meth-odology to reduce uncertainty in seismic hazard analysis (USNRC 1997). The probabilistic approach is the preferred one used for seismic design purposes for describing response spectra and associated time histories.

In France, the reference law for seismic hazard studies is the RFS 2001-01. It provides the details describing the methodology specifically for seismic haz-ard analysis. The RFS 2001-01 is based on the deterministic approach, the most commonly used methodology in the seventies and eighties. The rule is based on a definition of the characteristics of "Maximum Historically Probable Earth-quakes" considered to be the most penalizing earthquakes liable to occur over a period comparable to the historical period, or about 1000 years. Secondly, it defines the "Safe Shutdown Earthquakes". In the last few years the probabilis-tic approach has been used and accepted for the reevaluations of the seismic hazard of existing sites.

Japan is another country with an established regulatory body, the Nuclear Regulation Authority, (NRA) that produces its own regulations. Following the Kashiwazaki-Kariwa event in 2007 and Tohoku earthquake in 2011, Japan has allowed some recommendations given by IAEA.

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Table 1 – Key USNRC Guidelines for Seismic and Geologic Hazards

Regulatory Guides (1,2)

NUREG/CR 6372 Uncertainty & Use of Experts (“SSHAC”, 1997)

NUREG/CR 5503 Techniques Identifying Faults & Origins (1999)

NUREG/CR 5562 Dating & Earthquakes, Geochronology (1998)

RG.1.132 Site Investigations for Foundations (1979)

RG.1.138 Laboratory Investigations of Soils and Rocks (2003)

RG.1.198 Procedures and Criteria for Assessing Seismic Soil Liquefaction (2003)

RG.1.208 Performance-Based Approach Earthquake Motions (2006)

Notes: (1) NUREG references URL: http://www.nrc.gov/reading-rm/doc-collections/nuregs/ (2) RG references URL:http://www.nrc.gov/reading-rm/doc-collections/reg-guides/power-reactors/rg/

2.2 IAEA guidelines

Originally, the IAEA published documents that were used by countries as a basis for national regulations and seismic studies. The NS-R-3 (IAEA, 2003) contains global requirements for site evaluation. They are intended to ensure adequate protection of site personnel, the public and the environment from the effects of ionizing radiation arising from nuclear installations.

The Safety Guides on site evaluation listed in Table 2 provide recommenda-tions on how to meet the requirements established in the Safety Requirements publication NS-R-3. The Safety Guide associated to seismic hazard is the SSG-9. This Safety Guide allows the use of probabilistic and deterministic ap-proaches. Nevertheless, the probabilistic approach is preferred and the deter-ministic case could be used as a deterministic control. The reference safety guide for geotechnical aspects is the NS-G-3.6 (the geotechnical conditions are needed for site response analysis)

In the siting process, the reference guide is the DS433 which now super-sedes IAEA Safety Guide 50-SG-S9 Site Survey for Nuclear Power Plants. It will take account of the Safety Requirements on Site Evaluation for Nuclear In-stallations NS-R-3, especially, in relation to exclusion criteria for the site selec-tion of nuclear power plants.

Table 2 – Main IAEA Guidelines related to Seismic and Geologic Hazards

IAEA Safety Guides NS-G-1.6 Seismic Design & Qualification (2003) (1)

NS-G-2.13 Seismic Safety Existing Installations (2009) (2)

NS-G-3.6 Geotechnical Site Evaluation (2005) (3)

IAEA Specific Safety Guides SSG-9 Seismic Hazards in Site Evaluation for Nuclear Installations

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IAEA Guides Under Development DS433/DPP423 Safety Aspects in Siting

Notes: (1) http://www-pub.iaea.org/MTCD/publications/PDF/Pub1158_web.pdf (2) http://www-pub.iaea.org/MTCD/publications/PDF/Pub1379_web.pdf (3) http://www-pub.iaea.org/mtcd/publications/pdf/pub1195_web.pdf

3. Contents and methodologies used to perform a Site Evaluation Report

The procedures recommended by IAEA Safety Guides and the procedures imposed by NRC Regulatory Guides are similar in many aspects. However, in some aspects, the NRC methodology is more strict and detailed. In this chapter we will briefly describe the main steps that consultants follow to complete site characterization.

3.1 IAEA procedure described in SSG-9

Currently, many countries are in the process of selection and/or characteri-zation of sites for a new nuclear power plants (Jordan, Turkey, Indonesia, Vi-etnam, Lithuania, Poland, etc.). In the majority of these countries, the basic procedures, recommendations and methodologies used to perform seismic haz-ard studies are those published by IAEA. Following the recommendations of the SSG-9 (IAEA, 2010), a Probabilistic Seismic Hazard Assessment (PSHA) follows the following work elements: • Compilation of a geological, geophysical, geotechnical and seismological

database using 4 scales: regional, near regional, site vicinity and site area. The database should be introduced and structured in a GIS. • Development of a Seismic Source model that includes the description and justification of the geometry of the seismogenic sources and its seismic characterization as well as a selection of a set of appropriate Ground Mo-tion Prediction Equations (GMPEs) • Seismic hazard calculation to obtain the seismic hazard curves (at free field conditions). Two seismic levels SL-1 and SL-2 should be defined by the Regulator (usually 475 and 10,000 year return periods). They are character-ized by response spectra and appropriate time histories. • The Uniform Hazard Response Spectra is derived from the seismic hazard curves. Depending on soil conditions, a specific site response analysis may be required. The site characterization is performed at four different scales: 1-Regional scale: takes into account the geological information contained within a radius of 300 km. 2-Near regional: typically a radius of 25-40 km. In this region some new detailed data should be generated with emphasis to geohazards. 3-Site vicinity: evaluation of date contained in a radius of 5 km. At this scale, it is very important to assure the absence of capable faults in this region. 4-Site area: the typical radius is 1 km. It covers the ar-

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ea of the NPP. The generation of new data at this scale corresponds basi-cally to the geotechnical information.

Typically, for these types of studies, the selection and approval of a new nucle-ar site has 2 phases: • Site selection. In this phase only limited studies are performed (Probabilis-

tic Seismic Hazard Analysis [PSHA], geohazards studies, etc.). They are based on existing data. The main references to define the seismic charac-teristics of the site are DS433 and SSG-9. • Site characterization. This phase starts when the site is selected. New geo-logical, geophysical and geotechnical data are generated in this phase. The new data are used to refine the preliminary studies performed in the previ-ous phase. The main references to define the seismic characteristics of the site are SSG-9 and NS-G-3.6 for geotechnical aspects (site area scale).

3.2 NRC procedure for Safety Analysis Report in USA

Site investigations, analysis and preparation of Safety Analysis Reports in the USA follows a process using USNRC guidelines presented in Table 1.

3.2.1 Guidelines for Phases of New NPP Choosing a site suitable for a new nuclear power plant in the US generally

begins with siting study. The study follows a 4-step methodology as described in of the Electric Power Research Institute (EPRI) Siting Guide (2002).

The phase of determining the suitability of a site, even before a technology is chosen is termed by a screening/feasibility study. It typically will include a field and lab testing program, ground motion model and site response calcula-tion following RG 1.208. This analysis is input towards preparation of Safety Analysis Report (SAR) to support an Early Site Permit (ESP).

Following a selection of a particular plant technology, a much more de-tailed site investigation is conducted to either update the ESP SAR or prepare a new SAR for a Combined Operating License Application (COLA).

Upon receipt of a construction license, the owner will proceed with con-struction, implementing additional field and laboratory analysis.

3.2.2 SSHAC Process for PSHA

Two basic principles underlie the SSHAC approach to PSHAs: (a) all the inputs should represent the composite distribution of the informed technical community (ITC) and (b) the analyst must establish ownership of these inputs.

The goal of the SSHAC process is to “represent the center, the body, and the range of technical interpretations that the larger informed technical com-munity would have if they were to conduct the study” (USNRC, 1997). The SSHAC process also identifies a clear definition of “ownership” of the input parameters into the PSHA, and hence ownership of the PSHA results.

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Ownership means “intellectual responsibility” such that the regulator will know the individuals who are responsible for developing the PSHA. Four lev-els of effort (1 to 4) are defined for capturing the range of uncertainty by the ITC. With each increasing level, there is increasing direct involvement of the ITC and, thus, increasing confidence and documentation that the center, body, and range of uncertainty in the ITC have been captured.

4. Impact of the Tohoku earthquake

New guidelines have been developed to address seismic and flooding risks in response to the 2011 Fukishima Daiichi Power Plant incident in Japan. In re-sponse Japanese regulators have their own documents (NRA, 2013)

Samaddar (2013) reports on actions undertaken at IAEA’s International Seismic Safety Centre (ISSC) to develop necessary technical guidance on is-sues relating to the safety assessment of a site hosting multiple units under the impact of single or multiple hazards as highlighted by the impact of the Great East Japan Earthquake and Tsunami.

The USNRC recently has taken many actions to ensure the continued safe operation of U.S. nuclear power plants (Miller, 2013). These actions include: (1) the performance of inspection activities at all U.S. nuclear power plants to evaluate licensee implementation of procedures and equipment which could mitigate beyond design basis events; (2) the establishment of a Task Force which identified lessons learned which could be implemented to further en-hance the safety of U.S. nuclear power plants; and (3) the commencement of a program to identify and take specific near-term and long-term regulatory ac-tions related to these lessons learned.

In France, after the Fukushima event, and as per the L'Autorité de sûreté nu-cléaire (ASN) or the French Nuclear Safety Authority requirement, Electricité de France (EDF) carried out a complementary safety assessment of its 58 units (Ilie Petre-Lazar, 2013).

5. References

Electric Power Research Institute. 2002. Siting Guide: Site Selection and Eval-uation Criteria for an Early Site Permit Application, EPRI, Palo Alto, CA: 1006878. 23-28

Ilie Petre-Lazar, H. Jadot & F. Turpin, S. Guisard, J. Chantron, and P. Labbé, 2013. French Response to Fukushima Event –Seismic Safety Issues. Pro-ceedings of the 8th Symposium Nuclear Plants Current Issues: Challenges & Opportunities, III -4/1 – 4/8

International Atomic Energy Agency, 2011. Seismic Hazards in Site Evalua-tion for Nuclear Installations. Specific Safety Guide No. SSG-9. Vienna, IAEA. 26-28

International Atomic Energy Agency. 2003. Site Evaluation for Nuclear Installations, Safety Standards Series No. NS-R-3. Vienna, IAEA. 1-26

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Miller, Barry W. 2013. United States Nuclear Regulatory Commission Actions Following the Fukushima Dai-Ichi Accident. Proceedings of the 8th Sympo-sium Nuclear Plants Current Issues: Challenges & Opportunities. III -1/1 – 1/11

Nuclear Regulation Authority. 2013. Nuclear Regulation Authority: NRA Li-brary, Regulatory guide, Outline of New Regulatory Requirements (Earthquakes and Tsunamis) http://www.nsr.go.jp/english/data/new_regulatory_requirements2.pdf 1-31

Samaddar, Sujit K. 2013 –ISSC Activities Highlighted by Fukushima Event. Proceedings of the 8th Symposium Nuclear Plants Current Issues: Chal-lenges & Opportunities. 111-3/1-3/8

U.S. Nuclear Regulatory Commission. 1997. Recommendations for probabilis-tic seismic hazard analysis—Guidance on uncertainty and use of experts: Washington, D.C. NUREG/CR-6372. 171pp with Appendices

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