o Chapter 0: Introduction 1/210 Belgian stress tests National report for nuclear power plants This national report is provided by the Belgian regulatory body to the European Commission, as part of the stress tests program applied to European nuclear power plants in response to the Fukushima- Daiichi accident. Review Review date Modification description By 0 2011-12-23 First edition FANC-Bel V Introduction Belgium has always been a pioneering country in the development of nuclear sciences and technologies for peaceful purposes. As such, the country is endowed with seven pressurized water reactors currently in operation on two distinct sites: • The Doel site, located on the Scheldt river close to Antwerp (Flanders), home of four reactors: o Doel 1/2: twin units of 433 MWe each, commissioned in 1975, o Doel 3: single unit of 1 006 MWe, commissioned in 1982, o Doel 4: single unit of 1 039 MWe, commissioned in 1985. • The Tihange site, located on the Meuse river close to Liège (Wallonia), home of three reactors: o Tihange 1: single unit of 962 MWe, commissioned in 1975, o Tihange 2: single unit of 1 008 MWe, commissioned in 1983, o Tihange 3: single unit of 1 054 MWe, commissioned in 1985. Both sites are operated by the same licensee, namely Electrabel, a company of the GDF-SUEZ energy and services Group. For all nuclear safety related matters, the licensee’s activities are under the control of the Belgian regulatory body 1, which is composed of: • the Federal Agency for Nuclear Control (FANC), • and Bel V, its technical subsidiary. The current features of the nuclear power plants operated in Belgium result from: • the design basis of each unit, • the modifications that were implemented subsequently over the life of the facilities. During the design phase, the power plants were dimensioned to fulfil the safety, reliability and availability requirements applicable at that time, and to resist predefined accidents and hazard scenarios. The design rules that were used included safety margins in the process (conservative assumptions in the models, safety coefficients in the calculations, penalizing hypothesis in hazard scenarios…). The design rules in force at a given period take into account the latest scientific knowledge (e.g. evaluation of the seismic hazard at a given location), the available techniques (e.g. pre-stress of the concrete), as well as the best practice usually applied in the considered field (e.g. use of a double containment building). These design rules have evolved over time, and therefore the units currently in operation in Belgium present some differences depending on their date of commissioning. In some cases, specific hazards were not taken into account during the design phase, either because the threat was not considered plausible at that time (e.g. terrorist aircraft crash), or because the annual probability of facing an accident leading to unacceptable consequences was negligible (e.g. tornado). This is particularly true for the earliest units (Doel 1/2 and Tihange 1). In those specific cases, the resistance of the units was evaluated retrospectively in order to determine the maximal admissible sollicitations, and to decide the relevant corrective actions to undertake where necessary. Some modifications have therefore been implemented over the life of the facilities, in order to bring the necessary improvements where appropriate, according to the latest knowledge and available technologies, as well as the current state of the art. These improvements take into account the feedback of the accidents that occurred abroad (Three Mile Island, Tchernobyl), and the evolution of 1 Additional information about the Belgian regulatory body and nuclear facilities is available on the FANC website (http://www.fanc.fgov.be ), specifically in the 2010 report for the Convention on Nuclear Safety Chapter 0: Introduction 3/210 the doctrine at the national level (federal regulation) and at the international level (standards and guides from the International Atomic Energy Agency, rules of the American Nuclear Regulatory Commission…). They are put into effect during the periodic (ten-yearly) safety reviews, or through specific action plans implemented spontaneously by the licensee or at the request of the regulatory body. The basic safety principles, such as defence in depth, redundancy of safety related equipment, physical or geographic separation, and diversification, were applied from the design phase, and upgrades were performed on the earliest units to increase their robustness when facing scenarios that were not considered yet. Some structure reinforcements were also achieved where required. All units now have: • first level safety systems, aimed at facing internal and external hazards that might threaten the facilities; • second level emergency systems, aimed at compensating the loss of the first level equipment, e.g. as a result of hazards that were not considered in the design of the first level; • multiple power supply sources: high voltage lines from the external grid, self-powering during house load operation, back-up diesel generators, battery/inverter sets; • multiple ultimate heat sinks, with several means to draw water: river by the site (Scheldt river at Doel, Meuse river at Tihange), artificial ponds (Doel), and wells in the water table (Tihange); • internal emergency plans in line with the public authorities’ emergency plans: emergency management centres, diagnostic tools, emergency procedures… These resources allow to deal with accident scenarios considered individually. However, the accident that occurred on 11 March 2011 at the Japanese Fukushima-Daiichi nuclear power plant showed that the conjunction of several events (earthquake, tsunami, flooding, hydrogen explosion) could lead to particularly unfavourable conditions for which the facilities and the licensee were not sufficiently prepared: failure of the containment, total loss of power supplies, total loss of cooling means, difficulties in accessing the site… The fact that several units on the same site were affected at the same time also constituted an aggravating factor with respect to the accident management. As a consequence, a wide-scale targeted safety reassessment program was set up among the member states of the European Union operating nuclear power plants on their soil. This “stress tests” program is designed to re-evaluate (based on technical studies, calculations and engineering judgment) the safety margins of the European nuclear power plants when faced with extreme natural events, and to take relevant action wherever needed. The approach is meant to be essentially deterministic, and should focus not only on the preventive measures but also on the mitigative measures. The scope of the Belgian stress tests covers all seven reactor units operated by Electrabel, including the spent fuel pools of each reactor unit and the dedicated spent fuel storage facilities at both sites, namely: • “SCG” building at Doel (dry cask spent fuel storage facility), • “DE” building at Tihange (wet spent fuel storage facility). In accordance with the European methodology, the stress tests of the nuclear power plants are performed in three stages: 1. The licensee carries out the stress tests in its facilities and communicates a final report to the Belgian regulatory body. In this report, the licensee describes the reaction of the facilities when facing the different extreme scenarios, and indicates, where appropriate, the improvements that could be implemented to reinforce safety. Chapter 0: Introduction 4/210 2. The regulatory body examines the licensee’s report and evaluates the approach and the results. Based on these data, the regulatory body writes its own national report. 3. The report of all national regulatory bodies is subject to an international peer review: the national reports are examined by other regulatory bodies representing 27 European independent national Authorities responsible for the nuclear safety in their country. This method increases consistency in the whole process and ensures the sharing of experience between regulatory bodies. From that stage, the European Commission will establish a final report that will be presented to the European Council, so as to provide an overall view of the current situation in the European power plants. The first phase of the Belgian stress tests for nuclear power plants was achieved by the licensee on a short-time period until 28 October 2011 (communication of the licensee’s reports to the regulatory body). This phase mobilized around 40 engineers and experts from Electrabel and its technical subsidiary Tractebel Engineering, as well as a number of third-party resources specialized in selected fields (seismic hazard, flooding…). The second phase of the program was then carried out by the FANC and its technical subsidiary Bel V, whose experts have a thorough knowledge of the facilities. The assessment of the approach and results provided by the licensee included detailed examination of the licensee’s stress tests reports and the supporting documents, technical meetings with the licensee, and on-site inspections to check on the field the reality, relevance and robustness of the key data valued in the licensee’s safety demonstrations. That process led to the publication of the present national report. As required by the ENSREG specifications, the Belgian national report for nuclear power plants covers the following risks: • earthquake, • flooding, • extreme weather conditions, • loss of electrical power and