As stated in the terms of reference of the TACIS contract the primary objective of the project was to provide support to the regulator GOSATOMNADZOR-RF and its TSOs (SEC NRS and others) in:
- Global review of the status of safety assessments of Russian NPPs taking into account the VVER and RBMK validation matrices and the analyses already performed. Definition of further analyses needed and provision of analytical assistance to an accident center being established by GOSATOMNADZOR-RF
- Performance of safety related calculations and analyses for nuclear reactor systems in Russia
- Further adaptation and validation of the transferred codes based on VVER and RBMK specific needs and experiments
- Generation of qualified data bases of VVER-type reactors to create appropriate input data decks for the codes
- Review and assessment of safety related analytical and experimental results
TASK 1: Global review of the status of safety assessment of Russian NPPs
The objective of this task was to review the status of the validation, especially the adequacy of this validation in the specific cases of Russian NPPs i.e.VVERs and RBMKs.
A state of the art report to which can be referred for information on validation was generated for the following codes:
- thermalhydraulic codes ATHLET (German) and CATHARE (French),
- core degradation codes ATHLET-CD (German) and ICARE/ CATHARE(French),
- severe accident integrated code ASTEC (French/German)
- containment codes for severe accident RALOC (German) and DRASYS (German).
Lists of areas (sufficient validation, additional validation necessary and experimental data required) which represent the basic outcome of this review were prepared with specifics for all codes, describing areas for VVER and RBMK which were sufficiently validated, areas where code validation was necessary and areas where experimental validation was necessary.
TASK 2: Further adaptation and validation of transferred codes based on VVER and RBMK specific needs and experiments
For the VVERs validation calculations were made with ATHLET and CATHARE using one test in the PSB facility.
For the part of this task related to RBMKs, there was a review of the needs for adaptation of ATHLET for RBMK applications. The technical outcome was that, in addition to the fields identified in task 1 for code validation, there is a strong need for qualified RBMK NPP input data decks.
TASK 3: Performance of safety related calculations for nuclear reactor systems in Russia
Safety related calculations for Russian NPPs were performed with each of the codes after the last versions had been installed by the French and German experts on SEC NRS workstations and PCs. The aim of these accident analyses was to show the abilities of the different codes to calculate practical cases on Russian NPPs and to investigate the sequences of events occurring during the chosen accidents.
The scenarios which have been calculated are the following:
- Analysis of large break LOCA for VVER•1000/320 with ATHLET code
- Analysis of small break LOCA DN25 with HPIS failure for VVER 1000/320 with CATHARE code
- Analysis of TMLB sequence forVVER-1000/320 with ATHLET CD
- Analysis of small break LOCA DN25 with HPIS failure for VVER 1000-320 with ICARE/CATHARE
- Analysis of TMLB severe accident sequence for VVER 1000-320 with ASTEC code
- Analysis of large break LOCA for VVER 1000/320 with RALOC code
TASK 4: Generation of qualified data bases of VVER reactor systems as basis for input decks
Detailed data for a VVER 440/213 system has been collected. These data have been carefully checked and verified in order to reach the required quality.
TASK 5: Support to operating and developing the LAN and WAN, installed in SECNRS.
This support task included Y2K issues.
TASK 6: Review and assessment of safety related analytical and experimental results.
The review resulted in Issues for future investigation:
- Automated Transient Without Scram (ATWS) scenarios,
- Accidents at low power or shut down reactor conditions,
- Accidents leading to the thermal shock on the reactor pressure vessel (RPV),
- Hydrogen release and control under loss of coolant accident (LOCA) conditions.
The technical objectives, which have been assigned to this TACIS project were considered as globally reached. The obtained results were following a logical strategy in the code transfer and support to SEC NRS and its TSOs.