The management of the company Societatea Nationala Nuclearelectrica is closely watching the development of the general emergency situation declared at the Fukushima Daiichi NPP in Japan, following the devastating damage and destruction caused by the earthquake and tsunami of 11 March 2011.
It stands to reason that, in this context, a series of questions may be raised and opinions may occur regarding the safety of other nuclear facilities as well. Information at the present time is constantly evolving, that is why any analysis and conclusions are premature, including comparing this situation with the Chernobyl NPP or wit any other nuclear power plant in Europe.
Our nuclear plant in Cernavoda, supplying 20% of the electricity generated in Romania, is a robust CANDU 6 type nuclear power plant fuelled with unenriched natural uranium, and cooled with heavy water in a closed loop,and has major different technological features as compared to the Fukushima Daiichi NPP in Japan that is fuelled with enriched uranium and is cooled with light water generating radioactive steam right into the reactor.
CANDU technology represents a great advantage over other technologies as the amount of potential energy stored in the reactor is much smaller than in other types of light water cooled reactors because the fuel is loaded on a week basis, while other types of reactors are loaded on an annual basis, and also is provided with high cooling water stored amounts in the reactor vessel (450 tons of heavy water), and the Calandria vault hosting the reactor vessel contains almost 500 tons of light water capable to ensure more than optimum cooling till restoring the normal cooling in case of failure.
In case that, after the radiolysis processes, high amount of hydrogen accumulated under the interior dome of the reactor building, there is a special hydrogen burning system preventing a violent hydrogen ignition, should a controlled hydrogen release into the atmosphere occur.
The Cernavoda NPP is designed to withstand the effects of an earthquake, based on authorized studies performed by the Center for Earth Physics, studies that took into account the history of the entire region, including the closest seismic areas as well: Vrancea area and the Shabla area (Balkan mountains).
The aforementioned studies have shown that, historically, in the two seismic centers situated at a distance longer than 100 km from the plant site there has never occurred an earthquake greater than 7.5 degree and, in this context, the NPP design took into account a maximum possible earthquake of 8 degree at Cernavoda, called the Design Basis Earthquake (DBE).
Last but not least, the side effect that has been a major contributor to Fukushima case, the tsunami, can be completely ruled out in case of the Cernavoda plant because the design took into account the risk of external flooding as a credible risk for the Cernavoda NPP site and studies in conservative hypotheses were performed.
These studies have showed that the Cernavoda NPP is built at a high level of 15.8 compared to the Black Sea level, and 2 m higher than the theoretical maximum Danube water level occurring every 10,000 years.
Considering these hypotheses, the NPP is capable to cope with an earthquake:
1. Design solutions that ensure that:
- All safety structures and security are designed to preserve their integrity and to ensure the safety functions (reactor shutdown and cooling, radioactivity containment) in case of a DBE;
- At the Cernavoda NPP, in the first stage, after the normal cooling sources have failed, the reactor cooling can be achieved without requiring any source of electricity, just by water natural convection (thermalsiphoning) in the (reactor) primary circuit and from the dousing tank in the steam generators from the secondary circuit;
- There is an emergency power supply (EPS), consisting of two diesel generators 2 x100%, especially designed for a DBE.
2. The existence of procedures for responding to abnormal situations (APOP), that the operators are trained to apply in the event of an earthquake. We need to mention that in case of an earthquake event the plant is operated from the secondary control room (SCA), a structure specifically designed and built to cope with such a situation, withstanding a DBE.
3. Ensuring the availability on a continuous basis of the above-mentioned systems by performing periodical test and verification programs approved by CNCAN, the regulatory body, and in case of malfunction, corrective actions are immediately performed to restore their condition provided by the design.
4. The continuous training of the operational personnel at all levels and for all domains and responsibilities within the organization, testing and periodical re-authorization by the regulatory authorities.
Even if the plant is designed to ensure safe shutdown and to resume operation after several design basis events, actions are still provided for public protection under extreme situations, actions stipulated by our laws in force. These measures aim at protecting the population from the consequences of some possible radioactive releases.
Therefore, we may say that, until now, the events at Fukushima in Japan can not lead yet to immediate action to be implemented at the Cernavoda NPP. However, additional preventive verification activities have been initiated.
The Cernavoda NPP branch is still watching the evolution of these events through continuous communication with organizations in the nuclear field, so when the causes and implications of events in Fukushima will be accurately and fully understood, we can learn all the lessons and implement improving actions in order to strengthen the Cernavoda NPP nuclear safety level.
Considering the foregoing, we assure the communities close to the Cernavoda NPP site that there is no reason at all for concerns with respect to the behaviour of the Cernavoda nuclear facilities in case external events might occur, affecting the Cernavoda NPP site.