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Forty Years Later—NRC Extends Construction Permit for Watts Bar Unit 2

Friday 29 November 2013

On 21 November 2013, the U.S. Nuclear Regulatory Commission (NRC) extended the construction permit for the Tennessee Valley Authority (TVA) Watts Bar 2 Pressurized Water Reactor (PWR). Following an earlier request from TVA, the NRC has granted an extension to the planned completion date from March 2013 until 30 September 2016.

The original Construction Permit for the reactor was issued by the Atomic Energy Commission on 23 January, 1973, with a completion date no later than May 1977. Ten years later, in 1987, the NRC staff described the revised construction timetable proposed by the TVA as ’optimistic’. Yet, as reported earlier this month, TVA have now claimed that completion of Watts Bar 2 as being “on schedule and within budget”. At a Board meeting in 2012, a former TVA chair, reflecting on the then 2 billion dollar cost overrun and 39 year construction history of Watts Bar 2 pointed out that he had been told by TVA management that the reactor was 92% complete in 1979.

Watts Bar 2 reactor is a Westinghouse PWR design with so-called ice condenser containment - thin steel shells with only half the volume and failure pressure of large PWR dry containments. To compensate for the reduced strength of the containment, ice condenser designs are equipped with "ice beds", blocks of ice that are supposed to cool and condense steam flowing past them during a core-melt accident, reducing the threat that the containment will become over pressurized and rupture from the rapid generation of steam. The risk of containment failure due to hydrogen generation has not been solved for ice condenser plants. The NRC has identified that the ice condenser design such as at Watts Bar 2 are "are at least two orders of magnitude [one hundred times] more vulnerable to early containment failure than other U.S. PWRs" as a result of hydrogen explosions during core melt accidents, induced by a loss of on site and off side power or Station Blackout (SBO). Despite this major unresolved safety issue it clearly has not prevented the NRC from giving TVA until 2016 to complete Watts Bar 2, forty three years after construction began.

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