Seabrook (USA)

Map of Seabrook

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1200 MW PWR unit; constructed by Westinghouse; grid connection in 1990.

Facilities in Seabrook

plantreactor typconstruction startoperation startshut down

Northeast Utilities (NU) is investigating what caused two failed fuel rods to break in half a Seabrook-1 last week. Both rods were part of the same Westinghouse Vantage 5H assembly and had been in the core for just one fuel cycle when the zirkalloy cladding failed.
The breaks occurred May 31 as NU took time during the unit's refueling outage to remove the leaking rods from the assembly so they could be replaced. In both cases, the rods were half way out of the assembly when they broke.
NRC considers the incident a serious problem.
The first sign of trouble surfaced during the last fuel cycle when there were indications that some of the fuel might be leaking. An examination of the assemblies found four with leaks. Three assemblies had one leaking rod each, while the fourth had two. The assemblies with the failed fuel were in a high-power area of the core and had burnups of 25.000 - 30.000 MW-days/metric ton uranium.


During refuelling outage an unattached pump bolt (vane cap screws) had ben detected in the lower part of the RPV. All 92 bolts on the 4 pumps have been replaced. Some fuel assembly bottom nozzles showed degradation. Outage was extended nearly a month over its scheduled time, also cost overrun (30%).


Feedwater check valves failed when screws broke and jammed the valve disc,could allow a loss of steam generator inventory and failure of the AFW system. Condition existed for an indetermined period of time.