'Ageing nuclear reactors need continuous monitoring'

 Dr Fumio Kojima a leading expert in ‘structured health monitoring in NPPs’, currently professor at the department of computer science and systems engineering, Kobe University, Japan, was recently in Chennai for the 20th annual conference of the Indian Nuclear Society. During his visit, he explored new collaborations with India in this vital R&D area. M R Venkatesh of Deccan Herald spoke to him. Excerpts:

You are working on safety of ageing in NPPs in Japan. How many NPPs are there in your country, of what types and how many have aged?
Japanese Utilities are currently operating 56 nuclear power plants (NPPs). Of them, 50 per cent are ‘pressurized light water reactors (PWR), and the other half are ‘boiled water reactor (BWR) systems. So we have two major types of nuclear power plants. And 30 per cent of the total electricity in Japan is made by nuclear power. As for the ageing plants, now in Japan 18 NPPs are beyond 30 years operation and in the next 10 years we will have more than 50 per cent of our NPPs over 30 years old. So, our government has a plan to extend their life to 60 years. That means, we require some ageing management. In the United States also, they have been working on extending their age to 70 years. So, we are going ahead with a comprehensive technical evaluation and review.
What are the key parameters to be periodically monitored in ageing N-reactors?
‘Janus’ — Japanese information, data, their interpretation, unification and integration and evaluation — a branch of the Japanese government has suggested eight typical ‘degradation phenomena’ in NPPs. They include stress corrosion cracking, neuron irradiation embattlement of the outer vessels, primary water stress corrosion cracking and so on. Straining of the piping is another typical degradation phenomena. These are very hard to characterise. You know we had the Mihama N-plant accident (in August 2004 in which a broken steam pipe killed five workers and injured several others). So we now have a programme to take care of all this.

How effective is Japan’s technical evaluation and new safety procedures?
You see, using inverse analysis, the use of electromagnetic non-destructive evaluation or testing (NDT) techniques, which avoids direct contact with the reactor surface or materials to be tested and which can do very rapid calculations, are becoming very important. For in conventional techniques like ultrasonic testing, we need human experts for inspection. But with increasing inspection areas coming with more N-plants, we are worried about lack of experts in Japan. This reduces the operative effectiveness and is a problem in ageing N-plants. So, we require a new philosophy of distance-monitoring, sometimes on-line monitoring. In PWRs detecting the cracks in the steam generator tubes is most vital. But in BWRs which have only one coolant tube, the stress-induced corrosion cracks in the welding joints on the ‘core shrouds’ of the reactor has to be taken care of. So, the most important thing is maintenance. Hence, we want to move from traditional in-service inspection to in-service maintenance. That means, continuous, on-line monitoring has become much more important now. Systemisation of maintenance is the goal of our new maintenance and inspection cycle rules for NPPs that came into force last year.

Has Japan started decommissioning old nuclear power reactors?
No decommissioning of any N-plant has happened so far. We have thoroughly reviewed 13 NPPs and their life extended to 40 years for each. The Mihama plant was stopped and after a review of all the reactor parts followed by corrective steps, it was restarted.
Any road-map on expertise and knowledge-sharing with India in this area, as the Indo-US nuclear deal has ended India’s international isolation?
I don’t know about (the fallout of) the N-deal. That depends on the political discussions. We are scientists. We have already started a non-political academic consortium to promote international exchange and NPP maintenance studies — with Korea, EU, USA and China. India is not part of the consortium yet, but we are planning academic and research collaborations, to start with the Indira Gandhi Centre for Atomic Research (IGCAR) at Kalpakkam near Chennai. The IGCAR has even proposed to hold the next global workshop on NDT techniques in 2011 in Chennai.

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