Southern and SCE&G seek concrete answers

In nearly identical letters, US utilities building AP1000 reactors at Vogtle and Summer have submitted licence amendment requests intended to clarify concrete reinforcement requirements. Timely action is crucial if construction deadlines are to be met.

The Nuclear Regulatory Commission (NRC) issued licences to Southern Company for the construction of two AP1000 reactors (units 3 and 4) at Vogtle in February 2012 and followed this up in April with licences for two AP1000s (units 2 and 3) at South Carolina Electric and Gas Company's (SCE&G's) Summer plant. These were celebrated as the first new US reactor projects to receive construction approval in almost 30 years.

However, the pouring of the reactors' concrete basemats - the recognised event by which construction on a new reactor is deemed to be offically underway - has yet to be performed at either site as problems have persisted.

Southern Company initially had to delay pouring concrete after the NRC found issues with the design and installation of rebar and the way it was anchored into auxilliary and shield buildings.

This was apparently resolved in October 2012 when the NRC amended the licence, allowing the company to use a higher compressive strength concrete - 5000 psi compared to the previously intended 4000 psi mix.

In September 2012, NRC inspectors identified issues with the shear reinforcement for the basemat at Summer which also affected Vogtle. In this case, the inspectors could not verify that the spacing of shear reinforcement bar met the prescribed maximum.

Southern and SCE&G responded to the spacing issue on 15 January by requesting licence amendments which would "clarify" structural criteria details. They proposed changes to text which had already been included in design information for the AP600 - the smaller forerunner to the AP1000 design - which they claim would not affect safety margins, and that from a licensing standpoint would not require a 'Significant Hazards Consideration'.

Both companies have requested the licence amendment to be made by 1 March, warning that delays beyond this date would impact key construction activities. To date, construction work has continued in non-nuclear areas, such as turbine buildings and cooling towers, so that despite these concrete issues project schedules have not been greatly impacted.

The four AP1000s are to be the first Generation III reactors built in the USA. In September last year, Southern subsidiary Gerogia Power gave notice that the completion date for Vogtle units 3 and 4 had been pushed back by six months to November 2016 and November 2017, respetively. Unit 2 and 3 of Summer are expected to begin commercial operation in 2017 and 2019, respectively. The Shaw Group is the main contractor for both projects.

Researched and written
by World Nuclear News