«Item 7b Severe Accidents Related Issues Preliminary Monitoring Report Report to the Federal Ministry of Agriculture, Forestry, Environment and Water ...»
Two teams under the Technical Project Management of Enconet and IRR-ARCS performed the monitoring work on this project.
The Enconet team addressed the broad general assessment of Temelín SAM and SAMGs based on underlying analyses and principles. This approach provided a broad ‘horizontal’ view of SAMGs and SAM.
32 ETE Road Map - Preliminary Monitoring Report – Item 7b: Severe Accidents Related Issues The IRR-ARCS team addressed one of the possible impairments of the WWER 1000 containment function of the Temelín NPP due to adverse hydrogen combustion behaviour. Investigations in that area, which focuses on in-depth analysis of the specific vulnerability of the Temelín containment, are further called the ‘vertical evaluation’.
The technical work was managed separately and in parallel without interference but with a project Synergy Group providing transfer of information and joint discussion of important issues. The PMR is the joint responsibility of Enconet and IRR-ARCS.
1.4 Assessment Framework
The assessment of the effectiveness of the prevention and mitigation of severe accidents at Temelín has been performed in the context of several activities. In the main, these activities have involved an assessment of the state-of-the-art in severe accident management in Western Europe (and more broadly including the US), an assessment of the performance of a generic WWER 1000 NPP in severe accidents (with consideration of Temelín-specific plant characteristics to the extent possible derived from available information to the extent possible) by means of state-of-the-art code calculations, and a two-day Specialist Workshop held in Prague at which presentations on various aspects of accident management were made by Czech experts and discussed with these experts by an Austrian delegation which included members of the PN7 Technical Project Management Teams.
It should be clear from the outset that the assessment is not based on a review of original Temelín documentation. That is, the on-site and off-site emergency response plans, the Emergency Operating Procedures (EOPs), and the Severe Accident Management Guidelines (SAMGs) themselves were not provided for review. Similarly, although a number of severe accident progression calculations were performed by Czech experts as technical support for the development of SAMGs, the details of these calculations were also not provided for review. Likewise, the updated Probabilistic Safety Assessment (PSA) and Pre-Operational Safety Analysis Report (POSAR) were not available for review. Finally, the plant itself was not available for detailed confirmation of geometric arrangement and other details.
It should also be clear, however, that the PN7 Technical Project Management Teams from ENCONET and IRR-ARCS did not come to project with a blank sheet of paper. Both Teams made use of experienced project personnal and subcontractors with familiarity with EOPs and SAMGs based on the Westinghouse approach, and with experience in severe accident progression calculations. Both Teams have previously reviewed the POSAR and the PSA documentation, and have had the opportunity to discuss severe accident issues with Czech experts over the past three years in which the Melk Protocol and Road Map activities have taken place.
Thus, the PN7 approach is to capitalize on this experience, on accident progression calculations made with state-of-the-art codes, on knowledge of the state-of-the-art in accident management in Western Europe and the United States, and on knowledge gained over the years about the Temelín plant design and its risk profile (as well as broad and in-depth knowledge of severe accident and accident management issues across the industry in Europe and elsewhere), to make an informed judgment about the prevention and mitigation of hypothetical severe accidents which might occur at Temelín.
One basic fact is that rules and regulations applied to Temelín NPP were combined for the design, construction and design verification as well as for the introduction of SAMGs from elements from rules and regulations originating from Russian, Czech and United States licensing authorities.
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1.5 Structure of the report
Sections 2 – 5 provide a comprehensive evaluation of relevant aspects relating to severe accident management (SAM) and SAM Programme at Temelín. The material presented in these sections is arranged into several subsections corresponding to the selected evaluation factors or aspects.
With some exceptions, each of these subsections comprises of three parts: ‘The current state-of-the-art requirements and practices’, ‘Current plant status’ and ‘Evaluation’. The first part provides ‘assessment criteria’ specific to the evaluation area/factor i.e. the basis to be used for the assessment. Typically, the ‘Current plant status’ part includes a brief discussion of the related plant status with references to relevant documents or other sources of information. The ‘Evaluation’ part summarizes the results of the assessment against the ‘specific assessment criteria’. Deficiencies or safety concerns as well as issues for further monitoring are identified.
Section 2 provides overview of the general approach to SAM and SAM Programme at Temelín and interfaces with the emergency response plan.
Section 3 presents a more detailed evaluation of SAM at Temelín. Aspects addressed in this section include the supporting analyses (deterministic and probabilistic), development of SAM strategies, performance of equipment in severe accident conditions, SAM related arrangements for personnel response, contents and structure of SAM Guidelines (SAMGs) and the process for SAMG development and implementation.
Section 4 provides comprehensive discussion of SA phenomenology. The accident analyses conducted within the PN7 project are described with the rationale for their selection and a brief overview of the results. This section provides relevant background information for the evaluation of Temelín plant specific SAM strategies.
Evaluation of SAM strategies adopted for the Temelín plant is provided in Section 5. Various threats to the containment integrity and proposed SAM measures are discussed.
Section 6 presents the main conclusions and recommendations for further monitoring by the Austrian Government.
Annex A summarizes the results of comparison study on general approaches to SAM in Western Europe and the USA.
Annex B provides detailed information on SA calculations that were used to support the evaluation of SAM at Temelín. These include the simulations conducted within the PN project as well as the existing (published) analyses conducted elsewhere.
34 ETE Road Map - Preliminary Monitoring Report – Item 7b: Severe Accidents Related Issues
2 SAM APPROACH VERSUS REQUIREMENTS
AND EMERGENCY RESPONSE INFRASTRUCTURE
2.1 National Requirements VLI No. VLI title / description 1.1.1 Are there any national requirements on the overall plant-specific AMP (Accident Management Program) and SAMP (Severe Accident Management Program)?
1.1.2 Have national requirements been addressed in the plant AMP?
1.1.3 Have national requirements been addressed in the plant SAMP?
State-of-the-art requirements and practices According to the current state-of-the-art safety philosophy [IAEA 2000a], the consideration of severe accidents in NPPs includes the identification of event sequences that lead to severe accidents, consideration of existing plant capabilities to return the plant to a controlled state and to mitigate the consequences of the severe accident, evaluation of potential design changes which could either reduce the likelihood of these events or would mitigate the consequences, and establishing accident management procedures.
A set of actions taken during the evolution of an event sequence towards beyond design basis accident (BDBA), which is known as Accident Management (AM), is intended to prevent the escalation of the event into a severe accident, to mitigate the consequences of a severe accident, and to return the plant to a controllable safe state. The preventive actions are covered by the Emergency Operating Procedures (EOPs). The mitigative actions are addressed within the Severe Accident Management Guidelines (SAMGs).
Accident Management Programmes (AMP) based on this concept were adopted in many nuclear plants starting from early 1980s. AMP comprises plans and actions undertaken to ensure that personnel with responsibilities for AM are adequately prepared to take effective onsite actions to prevent or to mitigate the consequences of a severe accident and, when deemed necessary, to plan and implement plant modifications.
Typically, the Severe Accident Management is considered as part of and incorporated into the on-site Emergency Response Plan (ERP). The requirements concerning the emergency preparedness of the plant are normally part of the national law. However, while many Western-European regulatory authorities required the development and implementation of SAMGs (industry commitments to develop and implement SAMGs are also widespread), in most cases the SAMGs are not formally approved by the regulatory authority. Many Western European utilities addressed SAM issue as a voluntary industry initiative and follow the general recommendations of international organizations.
Regulatory requirements were indeed put forward in Belgium, the Netherlands, Sweden, Finland, Germany (as a binding RSK recommendation), Switzerland, the United Kingdom (implicit in the regulations on tolerable risk), and in France. Of the Western European nations with nuclear power plants, the only exception to this is Spain, which strictly follows the USNRC position which accepted an industry commitment in lieu of development of regulatory requirements or issuance of some regulatory vehicle such as a Generic Letter.
A more detailed discussion of SAM related practices in the EU countries and the USA can be found in Annex A.
ETE Road Map - Preliminary Monitoring Report – Item 7b: Severe Accidents Related Issues 35 The obligations, responsibilities, criteria and requirements for emergency response planning are set up in the IAEA series of international safety standards [IAEA 82, IAEA 2000 a - c, IAEA 94, IAEA 96]. Similar requirements are provided in US NRC guides [NUREG-0654, NUREG -0696, NUREG -0818].
Current plant status The Czech Regulator (SUJB) has initiated in 1994 a systematic programme on Accident Management [Miasnikov 03]. Internationally recognized safety guidelines published in documents prepared by the IAEA [INSAG-10, INSAG-12, IAEA 88] and the US NRC [NRC 88, NRC 90] provided a basic input for the development of this programme. The programme was adopted at the plant and is being implemented on voluntary basis. SUJB provides also a technical support for the TSO in SA related research.
The SUJB approach focuses on the definition of acceptance criteria and providing guidance leaving flexibility on the selection of potential AM actions. This approach is consistent with the existing legal framework in Czech Republic requirements on emergency preparedness [Miasnikov 03].including the Symptom based Emergency Operating Procedures (EOPs) have already been implemented at Temelín based on the generic Westinghouse Emergency Response Guidelines [WEC 83].
These procedures have been prepared in accordance with the current international practice.
They have been subject to extensive verification and validation using the plant specific simulator [Hončarenko 03].
Work on the implementation of Severe Accident Management Guidelines at Temelín is well advanced. Westinghouse has developed the SAMG package in accordance to the WOG SAMG generic guidelines [WOG 94, WOG 01]. Currently this package is being translated into Czech language and subjected to internal review. Work on the preparation of SAMGs validation using the plant specific simulator is underway [Dessars 03, Sỷkora 03 b]. It should be noted that a Technical Support Centre, which is intended to implement the new SAM functions in case of a severe accident, was established earlier as part of the implementation of symptom based EOPs. Its organization structure and staffing will be altered to accommodate the implementation of SAMGs.
Evaluation The approach to SAM being implemented in Czech Republic for the Temelín plant reflects the current state-of-the-art in this area. Legal framework for the Czech National Emergency Preparedness Program was clearly presented by SUJB and Temelín experts during the Prague workshop [Miasnikov 03]. Requirements on the content of off-site emergency plan and emergency rules were discussed also. It was stated that the existing Temelín-specific on-site E-plan covers the classification of emergency situation severity, personnel duties and responsibilities as well as the emergency facilities and responses. These are the most important areas that should be covered in such a document. Specific regulations issued by SUJB on this subject have been mentioned in this context [Miasnikov 03].
As stated in the presentation [Miasnikov 03], the E-plan, which includes SAM-related interfaces, is being reviewed by SUJB. It can be expected that the existing national requirements on the emergency response planning will be fulfilled and the plan will be properly adjusted to accommodate SAM. It should be noted that details of the related emergency response administrative framework at Temelín plant were not presented at the Prague workshop and it is not possible to evaluate its contents and quality. However with regard to the SAM related interfaces the current good practices are followed. Some concerns regarding the required authorization of possible plant intentional release from the containment can be raised (see Section 2.3).
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2.2 On-site ER Infrastructure and its Consistency with the Overall ER Plan
VLI No. VLI title / description 1.2.1 Has the overall organisation for emergency response been clearly defined?
1.2.2 Has the overall emergency preparedness been subject to independent / external review 1.2.3 Are all the parts of the on-site emergency response infrastructure (MCR, TSC, Operation Support, etc.) addressed in the overall emergency plan?