One of the adverse consequences of serious reactor accidents involving reactor coolant leaks and core meltdown can be generation of substantial amount of hydrogen due to the water-zircon reaction at high temperatures. Due to disrupted integrity of the reactor coolant system, the hydrogen may leak into the containment. Considering the high explosiveness of the hydrogen-air mixture, this process can seriously endanger containment integrity incurring risk of radioactivity release into the environment. Mitigation of consequences of such an event has been therefore identified as a significant safety issue.
To help to adequately address the issue also at Russian VVER-based nuclear power plants, the EC-funded design safety project R2.01/03 was established in cooperation with the Concern Rosenergoatom and other Russian institutes and organizations.
The project was implemented within two separate contracts: (1) a fee-based contract 76775 with an EU Consultant, and (2) a global price contract 127699 with a Russia-based Director of Experiments (DoE). The overall project management was under the direction of the Consultant.
The general objective of the project was to address the risk of hydrogen explosion in reactor containment following severe (Beyond-Design-Basis) accidents involving core damage.
The specific objective was to transfer the know-how on the hydrogen risk mitigation techniques from the western nuclear power plants to the Beneficiary. The main focus was on design development and testing of the monitoring part of a hydrogen control system which would be capable of working in VVER-1000 reactor containment in Beyond-Design-Basis Accident (BDBA) conditions including high pressure, temperature, moisture and increased radiation.
The Director of Experiments (DoE) for the project was the Institute for Power and Physical Engineering (IPPE) in Obninsk, Russia. The global price contract No. 127699 with the DoE was concluded on 15 January 2007 and was finished on 15 January 2009.
The project was implemented in five tasks: (1) project management, (2) transfer of know-how on hydrogen control at NPP to the Beneficiary, (3) design development of a hydrogen monitoring system (HMS), (4) qualification testing of the HMS and (5) conceptual design of a comprehensive hydrogen control system, including hydrogen removal system (passive catalytic hydrogen recombiners).
The main DoE’s responsibility was to provide the Consultant with relevant technical information on Russian practices and hydrogen safety analysis results, make available a single module of the HMS for improvement by the Consultant and conduct the qualification experiments of the improved HMS single module at its experimental facility.
The experiments were performed at IPPE in Obninsk in three stages from April to June 2008. The tests included verification of operability of the individual analyzers in “laboratory conditions”, verification of the HMS response at normal operating conditions and verification of the HMS response at simulated BDBA conditions. The latter two experiments were performed at the IPPE experimental facility. The experiments were closely supervised and partially also managed by the Consultant. The Consultant’s involvement in the tests, however, was significantly hampered by strict IPPE regulations and limitations concerning Consultant’s access to the Institute and the experimental facility. Moreover, the gas analyzer characteristics under transient BDBA conditions could not be directly verified due to technical problems of the DoE experimental facility. Additional dynamic experiments were thus conducted in October 2010 and the Consultant performed additional benchmark CFD calculations to verify the gas analyzers’ response in transient situations.
The experiments combined with the additional CFD calculations verified proper performance of the hydrogen gas analyzers in BDBA conditions. The proper performance of the oxygen gas analysers, however, could not be verified. The Consultant identified the weaknesses and recommended further development and testing of the oxygen gas analyser.
During the project implementation, the DoE provided the Consultant with good technical and logistic support and considerably contributed to successful completion of the project.
For additional information, see also the related R2.01/03 project summary on the contract No. 76775.