'Unknown' welds went unchecked at Japanese plant

26 July 2010

Japan Atomic Power Co (Japco) reported that it had never inspected a welded part in a pump within the reactor containment vessel of Tsuruga 1  - the country's oldest operating unit - because it was unaware the weld existed. 


Tsuruga 1 (JAPC) 
Tsuruga 1 (Image: Japco) 
Under Japanese legislation, nuclear power plant operators are required to inspect welded parts periodically to check for signs of damage and degradation.


Japco said that it had found that the recirculation pump at Tsuruga 1 had not been checked since it was installed at the unit. The 357 MWe boiling water reactor (BWR) began operating in March 1970.


The company obtained design charts and other papers for the pump in March from the US manufacturer ahead of the replacement of the recirculation piping system planned for in January 2011. It was only then, Japco said, that it discovered that the pump contained a welded part.


Japco also said that it had found manufacturing welds in nine valves in other areas of the plant that it had not previously been aware of and were therefore not included in inspection schedules. The company said that it will now conduct inspections on all the newly-discovered welds to ensure their integrity.


In September 2009, the Ministry of Economy, Trade and Industry (Meti) gave approval to Japco to continue operating the Tsuruga 1 unit until 2016, six years beyond its originally scheduled shutdown. The extension was due to delays in the construction of two new units at the site.


Researched and written 
by World Nuclear News