SMiRT 11 Conference
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Challenges to the Enhancement of LWRs in Japan
Currently, forty (40) units of nuclear power plants (NPPs) with a capacity of 32 GWe are under operation, and a further, ten (10) units with a capacity of 10 GWe are under construction in this country. In 1987, Japanese nuclear power plants supplied approximaely 30% of the total national electricity demand.
Most of the NPPs in Japan are light water reactors (LWRs) which were introduced on the basis of a license agreement with US reactor manufactures more than twenty years ago. Since that time, Japanese manufacturers have experienced various problems and have overcome them by improving the technology through concentrated endeavors jointly made by the regulatory and industry fields.
As a result, domestic NPPs are showing a considerably good performance and are playing an important role in Japanese electricity production.
As the LWRs may continue to be the main stream in Japanese nuclear power generation for a long time in the future, further development and improvement of its technology must be promoted to respond to increasing needs.
1. Improving with LWRs Technology
In early 1975, NPPs in this country met with various failures (such as leakage of steam generator tubes, stress corrosion in the primary piping, fuel rod failure and leakage, etc.) which reduced the average capacity factor down to an order of 40%. These initial failures served as a warning to us as to the vulnerability of the technical basis of nuclear power, and consequently we recognized need to enhance our technological level by promoting research and development.
As a result, the domestic industry made every effort to develop its own technology and to cooperate among each other in research projects, thus promoting the consolidation of its R&D basis and the improvement of its technological capability. This resulted in the enhancement of technologies not only as countermeasures for initial failures but also for improved plant operating performance and for the reduced radiation does of workers.
The Government has strived for the perfection of the safety research at the Japan Atomic Energy Research Institute (JAERI), and further started the “Committee for LWR Improvement and Standardiation” in June, 1975 to promote the improvement and standardization of the LWR design.
In order to validate the importance against initial failures and promote the further improvement of the technology, the “NUCLEAR POWER ENGINEERING CENTER” (NUPEC) was established in March 1976.
The “LWR Improvement and Standardization Program” was conducted during the period of 1975 through 1985. At the last stage of the program, overseas manufactures (GE, WH, ASEA-ATOM, AMN) were involved in the development of the advanced LWR.
Technologies developed by this program have been applied to actual plants and have greatly contributed to the enhancement of the reliability of domestic LWRs and to the reduction in the radiation dose of the workers (Unplanned plant shutdown rate: 0.3~0.6 times/year/unit. Capacity factor in 1990: 72.7%. Annual average radiation does of all workers in 1989: 1.6mSv).
During that period, countermeasures, such as instituting the qualification systemof a responsible operator (shift supervisor), establishent of the operator and maintenance training centers and further fulfilment of the inspection system of the regulatory side were taken, which resulted in the enhancement of reliability of LWRs in Japan.
2. Future Problems
It is important that the Government and industry together address themselves to the study of further safety and reliability of the nuclear power plants. Especially, the development of various technologies, including life extension of aged plants, management of severe accidents, bold improvement of future LWR design, etc., should be pursued.
The TMI and Chernobyl accidents had a large influence on the public. In order to dissipate such public anxieties, public acceptance (PA) activities on the safety and necessity of NPPs should be made more frequently and effectively.
Furthermore, the safety problem of NPPs is not only associated with Japan, but it must be solved internationally. In Japan, we have so far committed ourselves to enhancement activities of the safety and reliability of domestic NPPs.
We should now make positive efforts to contribute to world wide nuclear industries.
Tsutomu Inoue
Nuclear Power Engineering Center
President