GeoWatch Issue 49

The recent tragic disaster in Japan is a painful reminder that although the timing and magnitude of a disastrous earthquake may be predicted with a certain probability, their direct and secondary effects present unforeseen and serious risks. This catastrophic calamity is making all Nuclear Power Plant (NPP) owners to question every aspect of their safety procedures as well as optimising them further to levels beyond the existing stringent rules and regulations.  
The average share of NPPs in the overall electricity production in countries having NPPs is approximately 20% and in some cases covering more than 75% of some of those countries’ overall energy needs [1]. Such important energy production assets require also lucid and up to date maintenance and operation procedures as well as highly reliable safety mechanisms.
It is estimated that, worldwide, 20% of nuclear reactors are operating in areas of significant seismic activity [2]. Many more are being built or planned to be built in highly active seismic zones.
The 11th March 2011 Honshu Earthquake has demonstrated the importance of the safe emergency shutdown of an NPP in case of detecting a potentially damaging ground motion. Although some ancillary facilities for an emergency shutdown such as power generators or reactor cooling system had failed due to secondary effects of the earthquake, the seismic instrumentation proved to be working satisfactorily to detect the respective ground motion and initiate a safe shutdown.
The basic purpose of the seismic instrumentation in an NPP is to provide the relevant information (recorded data, alerts for Operating Basis Earthquake “OBE” and Safe Shutdown Earthquake “SSE”, event reporting) so that the seismic response of the safety-significant plant features can be evaluated promptly after an earthquake. With the proven modern technology the instrumentation should offer additional benefits to the operators such as background noise supervision and seismic signal checks as well as full testing and event simulation facilities. Depending on the topology of the system valuable information about response differences between installation sites and even the behaviour and state of health of the structural components can be determined. All of these functionalities contribute in to the improved sustainability of these critical assets.

Seismic instrumentation of some of the active NPPs may well be as old as the plants themselves. In the meantime there have been many improvements in the underlying mechanical, electronic and computer technology, the understanding of the seismic risk, the evaluation methods of ground motion, the communication and data transfer methods, the data analysis and interpretation algorithms. Over all these years majority of these improvements have already been tested and verified to yield more reliable results when compared to older components and methods. Therefore utilizing all of these new components and methods a significant improvement in terms of accuracy and reliability with fully automatic operation can be achieved in the seismic monitoring systems in NPPs. It goes without saying that modern and up-to-date seismic monitoring instruments will help in bolstering the first line of defence against earthquakes. GeoSIG over the years have successfully implemented state of the art turn-key systems in more than 65 NPPs in Europe, the USA and Asia. We can draw from our experience over the last 15 years to help with:

We know that the old saying according to a Japanese proverb “shikate ga nai” (there is nothing that can be done) when facing natural disasters is not an option and we know for a fact that the Japanese have achieved huge advances in preparing for such disasters.
In conclusion it is all about learning from such unfortunate disasters by revisiting the existing systems or reviewing the design of new ones to make sure they measure favourably against the latest technology, practices and experiences.