Severe Accident Management Guidelines for Angra 2 NPP (BR1.01/09T1), Brazil

The project purpose is to reach a situation in which:

• Eletronuclear has established an improved strategy for beyond design basis and severe accident management for Angra 2 during at power conditions

• Eletronuclear will be able to further develop and maintain Severe Accident Management Strategies and Guidelines for Angra 2 in accordance with international practice

• Eletronuclear staff will be trained in developing and implementing the new guidelines with respect to Eletronuclear practices related to safe operation of nuclear power plants.

The Federative Republic of Brazil has a medium-sized civilian nuclear sector. At the time of the project, Angra-1 (650 MW, Westinghouse 2 loop PWR, commissioned in 1982) and Angra-2 (1350 MW, Siemens/KWU, 4 loop PWR, commissioned in 2000), were generating 70% of the electricity of the Rio de Janeiro Region. The licensee was working on the preparatory measures to apply for lifetime extension of Angra-1 up to 2045 (60 years).

Brazil's declared strategic goals are to increase nuclear power generation to produce up to 5.5% of the electricity needs and to provide 100% of the fuel cycle. As specific goals it is intended to finalize Angra-3 and build 4 to 8 new reactors of 1,000 MWe on 2 or 3 sites.

This increase in the proportion of nuclear energy involves the continuous development of technology, and the design, construction and operation of nuclear industrial facilities related to the nuclear fuel cycle. This includes also the technological and industrial capability to design, construct and operate nuclear power plants, to provide electrical energy to the Brazilian grid in a safe, ecologically sound and economic way. Moreover, this also requires the development of necessary human resources for the establishment and continuity of the activities in all these fields.

The nuclear operator Eletronuclear has been suffering from a lack of investment over the last 20 years. Many modernisation activities, in particular in the field of nuclear safety, have become urgent. The need to improve safety requires collaboration with other operators and it is one of the major incentives to start cooperation with the EU under the INSC programme.

At Angra 1 the operator has been completing with Westinghouse the development of Severe Accident Management Guidelines (SAMG) based on the Pressurized Water Reactor's Owner Group concept. At Angra 2, the existing emergency documents were developed in accordance with the German practice. These documents include Symptom Oriented procedures for Design Basis Accidents (DBA) and Anticipated Transient Without Scram (ATWS) conditions as well as procedures for monitoring Critical Safety Functions (CSF) for DBA and BDBA (Beyond DBA) conditions, but not including Severe Accidents. This means that SAMG in accordance with international practice were lacking at Angra 2 NPP.

In order to increase the level of safety of NPP operation in Brazil the European Commission decided to participate in an intervention by Eletronuclear to develop SAMG as appropriate for Angra 2 NPP, in accordance with current international practice.

The overall objective of this intervention was complementing and consolidating the formal arrangements at the Eletronuclear’s Angra 2 NPP with the development of an up-to-date set of Severe Accidents Management Guidelines (SAMG), in accordance with international practice, in order for Eletronuclear to be more aware and better prepared to prevent and mitigate such Severe Accidents.

The specific objectives of the project were:

• Transfer of the best international practice and EU operators’ experience in NPP safety assurance during Design Basis, Beyond Design Basis and Severe Accidents to Eletronuclear;
• Reduction of the probability of human errors during diagnostics and decision making while responding to severe accidents which could occur during at power condition of the reactor;
• Integration of the Severe Accidents Management Guidelines into the emergency documentation system of Angra 2 NPP in order to improve the effectiveness of the Electronuclear accident management strategies and, ultimately strengthen the third and fourth levels of Defence in Depth.

In addition to task 1 on project management and task 4 on finalisation of the project, the project had two technical tasks:
Task 2: Review of the best international practices and situation in Brazil
Task 3: Development of severe accident management guidelines, consisting of 10 sub-tasks:

3.1: Development of Plant Specific Computerized Model necessary to support SAMG development
3.2: Identification of the main phases of the severe accident progression for Angra 2
3.3: Identification of Angra 2 Plant Capabilities
3.4: Identification of Severe Accident Management Strategies for Angra 2 NPP
3.5: Establishment of SAMG Set-points and Computational Aids
3.6: Development of a Writer’s Guide and a User’s Guide for SAMG
3.7: Development of SAM Guidelines
3.8: SAMG verification, validation and workshop
3.9: SAMG training material development, TSC and MRC Pilot Training
3.10: Permanent consolidation of project results throughout the project
The results of the technical tasks are briefly described below.

TASK 2: REVIEW OF THE BEST INTERNATIONAL PRACTICES AND SITUATION IN BRAZIL

The review of the best international practices with respect to the severe accident management guidelines (SAMG) development outlined the various international approaches of SAMG development. The reviewed approaches were: 1) EPRI guidelines for the management of severe accident scenarios; 2) Combustion Engineering Owners Group (CEOG); 3) Westinghouse Owners Group (WOG); B&W Owners Group (B&WOG); Electricité de France (EDF); and OSSA – SAMG for EPR reactor. A more detailed description of the AREVA GmbH concept applied to Angra 2 was presented separately in more detail, as Angra 2 is of identical design as German Pre-Konvoi plants and thus the concept is applicable to the plant. The review was supplemented by a comparison of the SAMG approaches for Angra 1 and Angra 2.

TASK 3: DEVELOPMENT OF SEVERE ACCIDENT MANAGEMENT GUIDELINES

Within this task, the severe accident management strategies for Angra 2 NPP for at power conditions were identified and developed. A plant specific computerized model of Angra 2 NPP for performing severe accident analyses was developed with the MELCOR code. The availability, applicability and adequacy of structures, systems and components at the Angra 2 NPP for SAM were assessed, and the necessity of plant modifications to implement the SAM program was evaluated. SAM strategies applicable to the Angra 2 NPP for severe accidents occurring at power operation were identified. SAMG packages (procedures, guidelines, computational aids…) were written and validated for Angra 2 NPP for at power conditions. Interfaces between Emergency Operating Procedure (EOP) and Severe Accident Management Guidelines (SAMG) and between SAMG and Emergency Planning were defined.

The Angra 2 SAMGs contains a complete set of written guidelines for the Angra 2 NPP. SAMG training material was also developed, and training was delivered to Emergency Response Team (ERT) and Main Control Room (MCR) operators, including Practical exercises on SAM usage.

The End User's personnel have gained the theoretical knowledge and practical skills of drafting, follow-up and application of the whole set of the SAMG at Angra 2 NPP, and of performing severe accident analyses using computer codes in support to severe accident management strategies development and validation.