Objective

The project shall provide assistance to the Russian Safety Authorities, Gosatomnadsor, to assess the safety improvements to be done at Smolensk.

Result

Due to the fact that the review for the replacement of the main safety valves (MSVs) with impulse safety valves (ISVs) to be performed for the Nuclear Licensing Stages NLS 1, 4 and 5 is nearly in line with the development of the industrial project, an influence of the TSOs’ licensing review is given for the licensing process. Consequently, the whole licensing process is approximately in agreement with Western practice. However, the documentation for NLS 2 should be made available earlier for the preparation of the Technical Specification (NLS 4). Thus, the concept of the 2+2 approach could be partly implemented by performing a licensing practice step by step as requested.

There is a significant lack of information at each of the nuclear licensing stages. Much of the information supplied to the TSOs’ experts considers the valve and its operation "as expected" conditions. Little, if any, information has been supplied to justify the design of the valve and assess its performance in transient and abnormal conditions. Consequently, the review by the TSOs’ experts results in a lot of findings due to the facts that there are missing:

Technical Task for Design (NLS 2);
Design Documentation (NLS 3).
Furthermore, the need to re-route the small-sized control lines of the ISVs and the necessity to upgrade the safety classification of the ISVs from Class 2 to Class 1 according to French Classification were identified by the TSOs’ experts.
However, only after the assessments performed for NLSs 2 and 3, the TSOs would be able to give final conclusions and recommendations to RF Gosatomnadzor for starting the replacement of the MSVs with ISVs. Nevertheless, no essential short-comings were identified by the assessments performed up to now.

Achieved Safety Benefits:

It is claimed that the design of the new ISVs shall prevent rapid cool down and pressure loss in failure of the safety valve to operate in the open position, i.e., cease the uncontrolled steam or steam-water mixture flow and thus will eliminate the different safety deficits of the existing MSV afore-mentioned.

The TSOs' experts estimate that the above mentioned safety benefits envisaged for normal plant operation as well as under emergency accident conditions can be achieved. However, the TSOs’ experts have identified the need for two modification demands (MDs) and some missing information, several Documentation Demands (DDs), needed to demonstrate that the intended replacement of the ISVs does not impact on the safety system protections.

Recommendations Proposed for RF Gosatomnadzor:

It was not possible for the TSOs’ experts to verify that the design criteria for the ISVs replacement have been satisfied in all areas. This resulted in remarks on the submitted licensing related documentation.

The remarks of the RF TSO experts proposed as well as the remarks of the EU TSOs’ experts proposed were commented by and discussed with the NPP. The agreements are summarised. As a result, the identified missing parts of the licensing related documentation will be updated and submitted as summarised. Hence, the TSOs’ experts have no impedimental factors for the implementation of the MSV replacement at Smolensk NPP in the Unit under consideration.

Nevertheless, the TSOs’ experts recommend to RF Gosatomnadzor that, before starting the installation of the impulse safety valves (ISVs), the NPP should fulfil a range of modification demands given in the related documents resulting from the project.