1 Development of Safety Analysis Tools for WWER Type Reactors Rolf Janke/GRS 7th Anniversary of the independence of State Nuclear Regulatory Committee of Ukraine 5 December, 2007 Hotel Rus, Kyiv, Gospitalna 4

2 Topics 1.Development of Safety Analysis Tools 2.Bringing all Ukrainian NPPs into compliance with internationally recognized safety level and maintaining it. – Early nineties – Today – Prospects and recommendations

3 Second half of nineties – IAEA Safety Issues Books First Safety Missions of WWER type reactors were performed with Western experts in Eastern Germany in (WWER-440 in Greifswald and WWER-1000 in Stendal) Safety Mission at Rovno NPP (first TACIS project in Ukraine) – TOB – Not qualified documentation – Fluctuation of qualified staff – Difficulties in maintaining the equipment status and refinancing – Safety deficiencies IAEA Safety Issues Books (1995) and Safety Review Missions to Rivno 1996, Khmelnitzky 1997, South Ukraine, Zaporozhye 1999.

4 Early nineties В СССР, ГДР, Болгария, Чехословакия и Финляндия все АЭС с реакторами ВВЭР строились по проектам, разработанным в – Курчатовском Институте (Научный Руководитель), – ОКБ «Гидропресс» (Главный Конструктор) и – ВГПИИ «Теплоэлектропроект» (Генеральный Проектировщик). Практически все расчеты были сделаны по программам, разработанным в этих организациях для головных энергоблоков каждого типа, а затем применены для последующих энергоблоков, не всегда учитывая их конструктивные особенности.

5 Early nineties (2) Сами расчеты и их методики ни АЭС, ни «Теплоэлектропроект», которые являлись Генеральными Проектировщиками конкретных АЭС (например: Киевское отделение – АЭС Пакш, Хмельницкая АЭС, энергоблок 4 Ровенской АЭС; Харьковское отделение – Запорожская и Южно-Украинская АЭС) не передавились, в технических обоснованиях безопасности (ТОБ) ставилась только ссылка на инвентарный номер расчета, который хранился в архиве разработчика. Даже результаты расчетов доводились до сведенья в очень ограниченном объеме. Нет верификации и валидации расчетных программ в современном понимании этих процедур. Очень многие расчеты делались по приближенным методикам, или по индивидуально разработанным методикам, правильность которых практически не проверялась.

6 Early nineties - Ядерно-физические расчеты (3) В советское время выполнялись только в Курчатовском Институте и в ОКБ «Гидропресс». После распада СССР и начала широкого международного сотрудничества АЭС, проектные организации и организации технической поддержки получили от западных разработчиков расчетные программы для выполнения ядерно-физических расчетов.

7 Early nineties - Теплогидравлические расчеты (4) Теплогидравлические расчеты собственно реакторной установки были сделаны ОКБ «Гидропресс». Методика и расчетные средства не разглашались. Теплогидравлические расчеты всех систем АЭС за пределами РУ выполнялись вручную. После распада СССР и начала широкого международного сотрудничества АЭС, проектные организации и организации технической поддержки получили от западных разработчиков расчетные программы для выполнения теплогидравлических расчетов.

8 Early nineties - Расчеты прочности (5) Расчеты прочности оборудования и трубопроводов, входящих в границы РУ были сделаны ОКБ «Гидропресс» и разработчиками и изготовителями оборудования. Генеральным Проектировщикам предоставлялся вывод «удовлетворяет условиям прочности» и значения усилий, моментов и перемещений, которые необходимо воспринять на границе РУ. – Расчеты прочности оборудования вне границ РУ делали разработчики оборудования по заданию Генерального Проектировщика. – Расчеты прочности трубопроводов, не входящих в границы РУ, были сделаны Генеральным Проектировщиком большей частью с использованием расчетной программы «Астра». Трубопроводы диаметром менее 100мм расчитывали только в особых случаях. – После распада СССР начали выполнять расчеты всех трубопроводов, важных для безопасности.

9 Early nineties - Расчеты контайнмента (6) Расчет контайнмента на прочность, включая Систему Предварительного Напряжения Защитной Оболочки (СПЗО) был выполнен в ОРГРЭС при разработке контайнмента в годы, скорее всего, вручную. Когда возникла проблема определения минимально допустимого натяжения армоканатов, при котором обеспечивается требуемая герметичность контайнмента, в Украине были разработаны собственные программы расчета (например, «СКАД»). Эти программы проверялись, в том числе, в двустороннем немецко-украинском проекте в гг.

10 Early nineties - Вероятностный и cистемный aнализ (7) Вероятностный Анализ Безопасности не выполнялся. Системный Анализ в современном понимании этого вида анализов не существовал. Только в ТОБ приводилось описание функционирования систем на качественном уровне с немногими количественными данными.

11 Early nineties – Initiation of international support programs At the request of the Ukrainian Nuclear Regulatory Authority, the European Commission invited western Nuclear Regulatory Authorities to provide assistance on regulatory and safety-related issues. An exploratory mission took place in Kiev in August Following that the Tacis assistance program for Ukraine has been initiated. IAEA Additional some bilateral programs have been implemented, the biggest ones were promoted by USA and Germany.

12 Bilateral supports US - Ukraine (DOE, NRC): – Full scope simulators, fire protection equipment – SAR including PSAs (development and review) with code and methodology transfer, training, financing of the work for pilot units. Germany - Ukraine: – Support in safety assessments (codes, training, joint analysis) – Investment program among others: Metal inspection manipulators for RPV and SG, diagnostics (ALÜS), fire protection equipment, unit generator, communication means, data transfer from ZNPP to the crisis centre in Kiev. – Requirements on SAR and updating of OPB and PBYa – Seminars, fellowships

13 Today – implemented tools Safety Analysis Reports including deterministic and probabilistic analysis Periodic Safety Assessments in preparation Full scope simulators at all NPP sites Risk informed decision making

14 Classification of PSA: Level 1–3 PlantEnvironment Core melt progression and interaction Containment behaviour System analysis Preventive AM Event Trees Fault Trees Containment Event Trees Mitigative AM Meteorology Population External AM Consequences risk Release frequ. Source Terms Level 2 Core damage Plant damage System damages Initiators Level 1 Level 3

15 Paths into environment Bypass via SG, and other interfacing systems Leak tightness Containment leak via e.g. ventilation system Containment leak or rupture (structure fails) – upper part with direct releases into environment. – Lower part with releases into reactor building and later on into environment. Modeling of release paths considering retention of releases in the reactor building.

16 Recommendations on Safety Analysis Tools (1) Because Ukraine is (for the time being) either a developer or constructor of NPPs, the development of its own analysis tools, in particular complex ones, is not cost-benefit oriented. Today, Ukrainian organisations have in many areas state-of- the-art analytical tools from Western, Russian and own developers. It is recommended: 1. to focus on a qualified use of international recognized codes in close connection with the code developers. 2. to pay attention on transparent information exchange between (few) experts in Ukraine, may be by user clubs.

17 Recommendations on Safety Analysis Tools (2) 3. to participate in international verifications, if necessary, also with own financial contributions. 4. Effective use of these tools for best estimate plant-specific safety analysis. 5. Involvement of the NPP staff into the analysis. Such participation assure the quality of the performed analysis and facilitates the follow use of their applications for day to day use in the routine NPP operation.

18 Recommendations on Safety Analysis Tools (3) SNRCU should promote and monitor – To provide a cross overview of all technical competence areas and the corresponding organizations equipped with state of the art analysis tools and qualified users. – The purchase of the most verified codes should be considered when the free software tools are outdated. The use of the codes should be free inside Ukraine. – that each NPP has its own updated basic data set for the main safety assessment applications, including PSA. – Sensitivity analysis, because real transients very often differ from calculations performed in advance.

19 Recommendations on Safety Analysis Tools (4) SNRCU should promote and monitor that the development and the review of safety assessments is basically performed by different codes, e.g.: – RELAP – ATHLET, KORSAR – MELCOR – ATHLET-CD, ASTEC, COCOSYS

20 Further trends in the area of Safety Analysis Tools (5) Coupled or integral codes, e.g. thermo hydraulics, reactor physics, component integrity Visualization of results of analysis simulators (аналитического симулятора для ВВЭР-1000/320), e.g. ATLAS (графическая оболочка для интерактивного управления аварийными последователностями и для изображения результатов). This provides an improved Man-Machine-Interface (Взаимодействие человек-машина)

21 Аналитический симулятор для ВВЭР-1000/В-320 Графическая оболочка пользователя во время анализа течи

22 Аналитический симулятор для ВВЭР-1000/В-320 Схема нодализации первого контура (ATHLET)

23 Safety level of NPPs in accordance with internationally recognized own K2/R4 Modernization program is the basis for the Integrated Ukrainian Modernization Program (Svodnaja programma modernizazi) Implementation of the Svodnaja programma modernizazi should be completed as soon as possible to reach at all Ukrainian units the same safety level like K2/R4: – Standardized solutions – Prioritization of measures regarding their impact for further risk reduction, taking into consideration safety benefit - investment cost ratio – Propagation of PSA results among NPPs from the same type – Sustainability of safety assessments results – day to day applications – Systematic room specific fire analysis and following reconstructions – SAMG (Тяжёлые аварии)

24 Operation experience feedback SNRCU should promote and monitor the consequent use of operation experience feedback for identification of modifications, prevention of incidents and updating accident analysis tools. E.g, the NEA Working Group on Operating Experience has noted: Almost all the recent significant events reported at the international meetings have occurred earlier in one form or another. Counteractions are usually well known, but information does not always seem to reach end users or corrective action programs are not always rigorously applied.

25 Applications of risk informed decision making (1) Demonstration of sufficient high safety level by presenting well- balanced safety concept Assessing the adequacy of proposed minor plant modifications and of deviations and changes to operational limits and conditions Making sure that items with greatest risk are included in the inspection programmes Realistically developed and independently reviewed plant specific PSAs Involvement of qualified plant staff Day to day applications

26 Advanced Plant-Specific PSA-Applications (2) Optimization of – component functional testing and in-service inspection intervals – preventive on-line maintenance considering the opposed effects: risk- increase and safety-benefit. – outage schedules (reactor and safety system states - maintenance activities). – operation instructions during shutdown Plant configuration management On-line risk monitoring and active control of plant operational risk Assessing the significance of operational occurrences (precursors)

27 Challenges Plant life time extension (PLEX) – Reassessment of environmental conditions – Confirmation of the equipment qualification by tests – Partly replacement – regulations New plants – Consequent use and consideration of operating experience – Approved solution – regulations

28 Thesis for Safety assessment tools (1) Impressive development during the last 17 years, in particular, during the about last 7 years. – Safety assessment tools were developed from a very low level to an international one. However there is a gap between few high qualified (with Western support) experts and NPPs. Therefore attention should be paid on involvement of NPP's staff focusing on efficient NPP day-to-day applications. It provides the best basis for permanent updating the analysis tools and qualification of NPP users. It should be avoided that safety tools and qualification provided by international support are not submitted to all potential users cost free. User clubs for safety tools may provide a good platform for a transparent information exchange between SNRCU, TSO and NPP experts.

29 Thesis for Safety assessment tools (2) The purchase of state of the art analysis tools and the participate in international verifications should be supported, if necessary, also with own financial contributions. The use of the codes should be free inside Ukraine. Now attention should be paid on best estimate plant-specific safety analysis with corresponding sensitivity and uncertainty assessments. It should be verified whether for all technical competence areas state of the art analysis tools and qualified users are available. It should be ensured that each NPP has its own updated basic data set for the main important safety assessment applications, including PSA. These data sets should be included into the routine documentation updating process. The development and the review of safety assessments should be performed independently and basically by different codes.

30 Thesis for modernization(3) Implementation of the Svodnaja programma modernizazi should be completed as soon as possible to reach at all Ukrainian units the same safety level like K2/R4. Attention should be paid on: – Standardized solutions – Implementation and operational experience feedback from K2/R4 and others (national and international), and if necessary, to modify measures and priorities. – Prioritization of measures regarding their impact for further risk reduction, taking into consideration safety benefit - investment cost ratio. – Propagation of PSA and other safety assessment results among NPPs from the same type. – Sustainability of safety assessments results – day to day applications.

31 Thesis (4) – Systematic room specific fire analysis and following reconstructions – SAMG (Тяжёлые аварии). – Systematic collection and processing of reliability data on the level of NAEK (occurrences, incidents, equipment and human failure). – Implementation of an effective aging management. – Motivation of the staff to recognize and remove also minor deviations in the field. Realistically developed and independently reviewed plant specific PSAs – Some kinds of PSAs could be limited to the NPP type (adaptation) – Involvement of qualified plant staff

32 Thesis (5) – Day to day PSA applications, e.g: demonstration of a well-balanced safety concept including modernization priorities, assessing the adequacy of proposed minor plant modifications and of deviations and changes to operational limits and conditions, making sure that items with greatest risk are included in the inspection program. – Optimization of component functional testing and in-service inspection intervals preventive on-line maintenance considering the opposed effects: risk-increase and safety-benefit. outage schedules (reactor and safety system states - maintenance activities). operation instructions during shutdown.