Working together for safety

Early in the 1990s the US Department of Energy (DOE) initiated programmes to improve safety at Soviet-designed nuclear power plants. The work involved providing equipment upgrades and improving operational practice and training. Other countries contributed to this effort, as did international organisations such as the European Bank for Reconstruction and Development and the IAEA.

The programmes provided hardware – including improved fire protection equipment and safety parameter display systems – developed emergency operating instructions, and sponsored independent safety analyses. However, the work did not focus on safety information and improving plants’ safety technology and analysis

capabilities.

In 1995, Hazel O’Leary, then US secretary of energy, proposed the establishment of the International Nuclear Safety Centres (INSC). They were to co-operate in developing nuclear safety technologies, as well as being international centres for collecting information.

The DOE established the US centre (USINSC) at the Argonne National Laboratory in Illinois in October 1995; Minatom established the Russian centre (RINSC) at the Research and Development Institute of Power Engineering in Moscow in July 1996. In April 1998 the Russian centre established itself as an independent non-commercial organisation. The two centres are collaborating to focus the resources and the talents of the scientists at each centre to develop improved nuclear safety analysis capabilities and safety management techniques at Soviet designed reactors.

The two centres began working together in January 1997. Work focused on four areas: collecting and disseminating nuclear safety information; developing improved safety analysis tools; developing a nuclear safety computing centre at the RINSC; and developing severe accident management guidelines for Russian plants.

So far ten joint safety projects have been established. Some 54 technical working meetings have been held, 13 in the US and 41 in Russia. Russian scientists have spent 323 person-days working in the US and US scientists have had 354 person-days in Russia.

Some of the most significant activities have involved construction of a database in support of joint development. Open exchange of nuclear safety data, in particular the results of generic nuclear safety calculations performed to support in-depth plant safety assessments, has also been an achievement.

Improved coupled neutronic and thermal hydraulic computer codes are being used to better characterise the risks attributable to a wider variety of plant upsets and postulated accidents in the in-depth safety assessments. US computer codes for the transient analysis of design basis accidents are being validated against Russian reactor and experimental data. The codes can then be used in safety assessments with confidence that the results are valid for RBMKs and VVERs.

Modern three-dimensional structural analysis software and computer models for seismic, thermal, external and internal shock waves and loadings are being developed for in-depth safety assessments.

US accident management technology is being used to assist Minatom in developing severe accident management guidelines.

Constructing databases

Databases of reactor and nuclear safety information have been established at both Safety Centres.

These databases are accessible on the Internet at www.insc.ru and www.insc.anl.gov. Both sites have extensive collections of information on reactor characteristics and nuclear safety data.

The database at the RINSC is being developed as a module that could be transferred to sites in other countries that wish to establish nuclear safety centres with compatible websites.

A significant area of nuclear safety information is a material property database that contains critically assessed thermodynamic and transport properties of reactor materials under normal, transient and severe accident conditions. The emphasis is on materials that are unique to Russian reactors, such as Russian steels and Zr–Nb alloys.

Unique Russian measurement techniques have provided data for properties for which there were no previous data and for which existing data was contradictory. Under this programme, new measurements of the liquid density for zirconium and the solid and liquid enthalpy of zirconium from a melting point up to 4000K were made at the United Institute of High Temperature Physics, at the Russian Academy of Sciences.

Thermophysical property data available in Russia and the US for UO2, Zircaloy, and Zr-Nb alloys have been reviewed by a joint USINSC-RINSC group. They have recommended thermophysical properties of Zr-1%Nb and Zr-2.5%Nb, two materials that are unique to Russian reactors.

Cracking the codes

A state-of-the-art computing centre has been established at the RINSC. Minatom has designated it as the centre for foreign computer codes used for nuclear safety analysis and a number of nuclear safety analysis applications are installed. It is also used to train Russian scientists and engineers on the theory and operation of these codes. The codes are accessed remotely from many institutes in Russia.

RINSC is currently managing two ‘outside’ projects. One is the translation of the probabilistic safety analysis code SAPHIRE into Russian, so that Russian scientists can work in their native tongue when they are using this code to analyse plants. The other is a project to develop computer programming and related support activities in the city of Sarov through the Open Computing Centre established by the US Nuclear Cities Initiative programme.

PERSONAL CONTACTS

The joint work of Russian and US specialists to improve the fidelity and efficiency of coupled neutronic and thermal-hydraulic codes used for analysing the dynamic behaviour of water-cooled reactors has led to many technical personnel exchanges to analyse benchmark problems with Russian and US codes. Out of this came several papers to international nuclear conferences.

One summarised results from VVER-1000 and RBMK benchmark analysis using various codes; another evaluated the performance of a Russian parallel code on the ANL IBM-SP super computer; a third discussed code models and results for the OECD Nuclear Energy Agency PWR main steamline break benchmark problem.

Validating RELAP5

RELAP5 is often used in the transient analysis of nuclear reactors. However, the code has not been fully validated for VVERs and RBMKs. A group of US and Russian specialists has been working to identify significant transient phenomena important to RBMK and VVER safety and they have identified existing Russian reactor and experimental data that can be used to validate RELAP5. They have also enhanced the safety culture by establishing a configuration control system for the codes and the analyses. Currently they are analysing standard problems for VVERs and RBMKs. This is another situation where long-term exchange of technical personnel has made significant accomplishments possible.

Specialists from both centres have also been working to adapt the MELCOR code for VVERs. MELCOR is a code being used to develop severe accident sequences and is dependent on reactor design. The VVER version is now running in the RINSC computing centre.

Structural specialists have been developing validated, three dimensional analysis software and models to evaluate Russian and US plant structures. They are participating in the International Round Robin Analysis of Containment Structures. Both sides have generated computer models and made predictive calculations for the response of the containment under internal pressure.

Severe accident management

Severe accident management guidelines are now in place at all US nuclear power plants. They have become a part of the safety culture and Russian regulators require them. The plans are currently at the discussion and formulation stage in Russia and USINSC and RINSC have been working together to provide Russian experts with the benefit of the accident management planning and training processes that have been installed at all US plants. Two week-long meetings have been held in Russia with US experts to foster an understanding of the approach and to transplant the safety culture.

Other activities the RINSC is involved with include the development of a strategic nuclear safety research and development plan for Minatom. The working group included 32 experts from all parts of the Minatom organisation. It should set the direction of Minatom’s future research in nuclear safety. The plan has been reviewed by the Nuclear Energy Agency and this review has been published.

The two centres have done much to transfer nuclear safety technology from the US to Russia and to improve the safety culture in Russia. It is hoped the success can be replicated elsewhere. Similar centres are starting up in Lithuania, Ukraine and Kazakhstan. Similar concepts are under consideration or in development in the Czech Republic and Slovakia. Close co-operation between safety centres in all countries operating nuclear power plants could offer synergistic benefits to the safety of plants worldwide.