- Status
- Closed
Objectives
The objective of the project was to analyse the current leak rate of the confinement for VVER-230 reactors and consequently to propose how to decrease it drastically.
Results
Phase I:
The leak paths from the confinement into the environment have been closed as much as possible and increased leak tightness has been verified by tests.
The following work was carried out:
- Comparison of Russian and Western codes and standards;
- Characteristics of the reactor confinement and identification of potential leakage locations;
- Proposal of a leak detection programme and a leak tightness improvement programme;
- Considerations of confinement improvements to cope with larger pipe breaks (up to 200 mm diameter) compared to the Design Basis Accident (DBA) (32 mm diameter pipe break);
- Proposal of improvements of existing equipment.
Four meetings were held in Moscow to co-ordinate the administrative and technical matters.
Phase II:
The following work was carried out:
- For Kola NPP the current leak tightness problems were identified and improvements were proposed on concrete systems/locations:
- Heating, Ventilation and Air Conditioning (HVAC) systems (isolation valves and sealing of fan shafts);
- Electrical penetrations;
- Liner welds;
- Doors and hatches.
- A visit to Unit 4 of NVV NPP and Unit 2 of Kola NPP was made to gather as-built information;
- Specific global and local leak tightness testing procedures were generated for NVV NPP and Kola NPP;
- A global leak tightness test was carried out at Unit 1 of Kola NPP.
The test was conducted in two steps:
- Confinement under pressure test (105 mm wg).
- Confinement overpressure test (90 mm wg and 120 seconds decay time to atmospheric pressure).
The tests were carried out using the ventilation fans (the maximum differential pressure capacity of the fans is estimated to approximately 200 mm wg).
The leakage measured was significantly higher than the target of 400% volume per day.
Phase III:
In a confirmation phase III the gained results were justified and further concrete proposals how to reduce the leak rate were developed.