En la gestión de la planificación institucional y curricular

S.N. BOGDAN

Scientific and Engineering Centre for Nuclear and Radiation Safety (SEC NRS) Moscow, Russia

Email: [email protected] D.A. MISTRYUGOV

Scientific and Engineering Centre for Nuclear and Radiation Safety (SEC NRS) Moscow, Russia

Abstract

The Working Group on new VVER designs (VVERWG) within the Multinational Design Evaluation Programme (MDEP) comprises the members from the nuclear regulatory authorities of China, Finland, Hungary, India, Russia and Turkey.

VVERWG as well as the other five MDEP design specific working groups (EPR, AP1000, APR1400, ABWR and HPR1000) is successful in sharing information and experience on the regulatory safety reviews of new reactor designs with the purposes of enhancing the safety and enabling regulators to make timely licensing decisions.

Since 2013 up to mid-2018 VVERWG had been chaired and managed by SEC NRS (TSO of the Russian Regulatory Authority) in arrangement of the group activity providing support to the regulators and reporting to the MDEP Steering Technical Committee and Policy Group on the benefits. Since mid-2018 VVERWG has been chaired by STUK (Finnish Regulatory Authority).

VVERWG includes four technical expert subgroups: Severe Accidents Management, Fukushima Lessons Learned Covered by Design Solutions, Reactor Pressure Vessel & Primary Circuit Components and Accident and Transient Analysis.

The group activities include exchange of information on national legal framework related to new designs, regulatory safety requirements, safety assessment approaches, safety review results and experience.

SEC NRS supports the interactions between the VVERWG members and the Russian design, vendor and operating organizations to get additional information about new VVERs design solutions related to safety during joint meetings and technical visits to new VVER units under construction and commissioning in the Russian Federation and abroad.

1. INTRODUCTION

The working group on new VVERs (VVERWG) is one among other design-specific working groups (EPR, AP1000, APR1400, ABWR and HPR1000) within the framework of Multinational Design Evaluation Programme (MDEP).

VVERWG comprises the members from regulators of China, Finland, Hungary, India, Russia and Turkey. The VVERWG (as well as the other five MDEP design specific working groups) is a good platform for sharing information and experience on the regulatory safety reviews of new designs, and on construction and commissioning of new reactors.

Since 2013 up to mid-2018 VVERWG had been, on behalf of Rostechnadzor (Russian Regulatory Authority), chaired and managed by the Scientific and Engineering Centre for Nuclear and Radiation Safety (SEC NRS), being the TSO of Rostechnadzor (according to the [1]) in arrangement of VVERWG activities providing support to the VVERWG regulators and reporting to the MDEP Steering Technical Committee and Policy Group on the benefits. There is a common understanding of regulators [2] to use the efforts of technical support organisations (as additional resource with experts of special high-level skills) for regulatory review and assessment during the process on new reactors commissioning. Since mid-2018, VVERWG has been chaired by STUK (Finnish Regulatory Authority).

2. VVER TECHNOLOGY EVOLUTION

Peculiar design features of water-water reactors (VVER), as compared with the pressurized water reactors (PWR), are the following:

— increased coolant volume above the reactor core level;

— increased coolant volume in the primary circuit, as compared with the nuclear fuel mass and the reactor core thermal output;

— increased volume of pressurizer vessel;

— significant volume of coolant inventory in steam generators of horizontal type;

— absence of tie-ins and holes beneath main coolant nozzles at reactor vessel and, accordingly, below the top elevation mark of the core.

Due to large coolant inventory in the primary and secondary circuits, the behaviour of VVER unit during transients and emergency situations is characterized by higher thermal inertia of the processes. This provides longer retention of safe operation conditions, keeping the reactor core drained, and absence of the operator intervention. Besides, another particular feature of VVER is the compactness of the reactor core that is actually void of xenon density oscillations and provides smooth distribution of neutron flux.

Of course, new VVER-1200 designs [3] took into account both the experience of VVERs operation during the long-term history and the lessons learned from accident at Fukushima NPP (2011). Certainly, new technical solutions are subjects for regulatory safety review and assessment.

3. GOALS AND DIRECTIONS OF VVERWG ACTIVITIES

One of the main goals of VVERWG is to leverage national regulatory resources by sharing information and experience on the regulatory safety design reviews of new VVERs, including exchange of experience on licensing process and design safety reviews, lessons learned, and design-related construction, as well on commissioning of a new VVER unit operation during the initial two years and understanding the differences in regulatory safety review approaches in each country to support potential use of other regulators while design safety evaluations.

Another goal of VVERWG is to provide inputs to other MDEP working groups on potential topics of regulators’ significant interest regarding the safety.

The next goal of VVERWG is to enhance the safety of new designs through regulators’ cooperation and by harmonization of regulatory practices including elaboration of regulators’ technical reports and common positions on design safety review on common assessments results; sharing the regulators’ common positions to vendor and operators regarding the safety; usage of the experience gained in learning similarities and differences in regulatory approaches and requirements to identify potential paths forward to a safety benefit for new VVER designs.

Additionally, the VVERWG activity covers the experience and information exchange on regulators’

approaches and safety review related to new VVER designs in member-countries. VVERWG holds regular meetings of the main group and technical experts’ sub-groups on common assessment of safety issues related to new VVER designs. The comparison table of differences in new VVER designs has been developed and updated by VVERWG members.

4. VVER WORKING GROUP STRUCTURE AND ACTIVITIES RESULTS

VVERWG includes four technical expert sub-groups: Fukushima Lessons Learned Covered by Design Solutions, Severe Accidents Management, Reactor Pressure Vessel and Primary Circuit Components, and Transient and Accident Analysis.

VVERWG ensures the effective cooperation among members on evaluation of new VVER designs, convergence (harmonisation) of safety requirements and regulatory practices, information exchange on national legal framework related to new designs, regulatory safety requirements, safety assessment approaches, safety review results and experience in construction and commissioning of new VVERs.

SEC NRS supports the interactions between the VVERWG members and the Russian design, vendor and operating organizations to get additional information on the design solutions related to safety during joint meetings. Technical visits of VVERWG members to new VVER units being under construction and commissioning in the Russian Federation and abroad are arranged.

4.1 Technical expert subgroup on Fukushima-related issues

Technical expert subgroup ‘Fukushima Lessons Learned Covered by Design Solutions’ (lead by TAEK, Turkey) had the initial task to develop the Common Position [4] addressing Fukushima-related issues. The developed Common Position covers 4 topics: accounting for external events in the design; reliability of safety functions implementation; design solutions to cover specific BDBA’s (SBO and loss of UHS); emergency preparedness and response.

The Common Position [4] was approved by MDEP Steering Technical Committee (STC) in 2017. But, there is a new assignment given by MDEP STC to elaborate an additional section addressing the Vienna Declaration on Nuclear Safety (dated 09.02.2015) in order to pay attention on Principle 1 mentioned in the declaration on avoiding early radioactive releases or large radioactive releases.

SEC NRS was requested to address the Russian design organisations with respect to provide some

4.2 Technical expert subgroup on severe accidents management

Technical expert subgroup ‘Severe Accidents Management’ (lead by SEC NRS, Russia) has objectives to identify commonalities and differences in regulators’ approaches used in VVERWG member countries and develop technical reports and common positions on regulatory approaches and criteria related to severe accident assessment and management.

One Technical Report [5] (covering regulators’ requirements to general and legal issues, procedures, guidelines, equipment and severe accidents analyses) was developed by the group, approved by the MDEP STC and published in 2017.

It is planned to develop a technical report (fall 2019) that will reflect the ex-vessel melt retention and assessment criteria of core catcher efficiency for melt stabilization (technical report will be a basis for further development of the common position).

SEC NRS was requested to address the Russian design organisations with respect to provide the presentations on how new reactor designs touch upon the issue of ex-vessel melt retention in core catcher.

4.3 Technical expert subgroup on reactor pressure vessel and primary circuit components

Technical expert subgroup ‘Reactor Pressure Vessel and Primary Circuit Components’ (lead by HAEA, Hungary) has objectives to identify commonalities and differences in regulatory approaches used in VVERWG member countries, and develop technical reports and elaborate Common Positions related to

— application of leak-before-break concept,

— manufacturing of primary circuit components,

— radiation embrittlement of reactor pressure vessel regarding use of new base metal,

— pre- and in-service inspection of primary circuit components,

— design basis loadings and their combinations for primary circuit components,

— cladding of primary circuit,

— protection against overpressure of primary circuit,

— qualification of a ‘first-only-a-kind’ components (FOAK components), etc.

One Technical Report [6] (covering seven first topics mentioned above) was developed by the group, approved by the MDEP STC and published in 2017. It is planned to develop next Technical Report (fall 2018) and a Common Position (beginning of 2019) on reactor pressure vessel and primary components reliability and submit to MDEP STC for review and approval.

4.4 Technical expert subgroup on transient and accident analysis

Technical expert subgroup ‘Transient and Accident Analysis’ (lead by STUK, Finland) has objectives to identify commonalities and differences in regulators’ approaches used in VVERWG member countries and develop technical reports and common positions on regulatory approaches and criteria related to regulatory requirements and criteria for transients and accidents assessment that could be applied for new reactor designs.

The subgroup started its activity in 2017 on the following topics agreed for joint considerations:

— regulatory requirements for accident and transient analyses, including acceptance criteria, expectation for analyses documentation (lead by STUK, Finland),

— regulatory assessment of tools (computer programs) used for transients and accidents analysis (lead by SEC NRS, Russia),

— performance and analysis of passive systems (lead by STUK, Finland),

— cooling in spent fuel pool with internal and external hazards (lead by TAEK, Turkey),

— regulatory procedures for safety review and licensing (lead by HAEA, Hungary).

It is planned to develop a technical report (mid 2019) on regulators practices for the review and assessment of accidents and transients analysis and send to MDEP STC for review and approval.

4.5 Activities in construction and commissioning experience

VVERWG (as other MDEP design-specific working groups) is an effective platform to share the significant lessons related to construction and commissioning of new reactors. VVERWG members from China, India and Russia provide information both on construction experience as well as on commissioning and operation experience during the first period related to new VVERs.

SEC NRS in close cooperation with Rosenergoatom (the Operator of Russian NNPs) provides actual information on commissioning and trial operation of Novovoronezh NPP-II Unit 1, including operational

events, root causes of the events as well as the technical solutions and regulatory decisions to solve the events.

Moreover, SEC NRS provides actual information on construction experience at Novovoronezh NPP-II Unit 2, and Lenigrad NPP-II Units 1&2 (all of VVER-1200 design).

On the regular basis SEC NRS organizes the meetings with designs organizations to get additional information and data on technical solutions, which are significant to safety of new VVERs.

VVERWG members arrange the technical visits to NPP sites with new VVERs being under construction or at commissioning stage (Leningrad NPP-2 and Novovoronezh NPP-2 in Russia, Tianwan NPP in China).

5. CONCLUSIONS

MDEP is a good regulators’ forum for information exchange on approaches to safety issues and systematic evaluations of new reactor designs.

The achieved results of MDEP activities show its high effectiveness at the practically past phase on common regulators’ design review. Now, the focus of MDEP activity is more and more on the experiences of commissioning and initial operation of new reactors during first years after commissioning.

It is necessary to find some mechanisms to transfer the knowledge of the MDEP regulators (accumulated in many technical reports and common positions at the MDEP library) to regulators of newcomer countries in order to support their activities.

Experience of Rostechnazor shows that it is effective to involve a technical and scientific support organisation for regulatory review and assessment during the process on new reactors commissioning.

Moreover, Rostechnazor used and will continue to use the MDEP technical materials to be applied to the national regulatory practice in Russia.

REFERENCES

[1] Federal Low ‘On Atomic Energy Use’, No.170-FZ. Russian Federation.

[2] International Atomic Energy Agency / Safety assessment for facilities and activities / Vienna:

[3] International Atomic Energy Agency, 2016. | Series: IAEA safety standards series, ISSN 1020–525X; no.

GSR part 4 (Rev. 1).

[4] ‘The VVER today’ / ROSATOM. Retrieved 31 May 2018 / www.rosatom.ru.

[5] Multinational Design Evaluation Programme / Design-Specific Common Position CP-VVERWG-01.

Common Position addressing Fukushima-related issues. VVER Working Group. 2017 / www.oecd-nea.org/mdep/working-groups/vverwg.html.

[6] Multinational Design Evaluation Programme / Technical Report TR-VVERWG-01. Regulatory approaches and criteria used in severe accident analyses and severe accident management / VVER Working Group. 2017 / www.oecd-nea.org/mdep/working-groups/vverwg.html.

[7] Multinational Design Evaluation Programme / Technical Report TR-VVERWG-02. Regulatory approaches and oversight practices related to reactor pressure vessel and primary components / VVER Working Group. 2017 / www.oecd-nea.org/mdep/working-groups/vverwg.html