The U.S. Nuclear Regulatory Commission has warned all nuclear plant operators and managers to take more care in evaluating and documenting temporary alterations to plants “except those that have permanently ceased operations and have certified that fuel has been permanently removed from the reactor vessel.”
In a five-page information notice dated March 12, the agency cites “recent operating experience at nuclear power facilities where temporary alterations were installed that either negatively impacted the operability” of the plant or were done without following NRC rules. The safety agency notice discusses events as recent as late last November and going back 10 years.
On Nov. 24, 2018, says the NRC, Tennessee Valley Authority operators at the two Sequoyah units near Soddy Daisy, Tenn., “discovered that a door was blocked open to allow a hose to be routed from an outside vacuum truck to an ice bin inside a Unit 2 building. The Westinghouse units at Sequoyah have an ice condenser containment to help control a large loss of coolant accident. The operators, said the NRC, allowed the condition “without meeting the compensatory measures required by the related breach permit. This condition created a breach of th auxiliary building secondary containment enclosure. The breach rendered both trains of the building’s gas treatment system inoperable “with fuel stored in the spent fuel pool.” TVA reported the breach in a report to the NRC on January 22, 2019.
Earlier at Sequoyah, on March 3, 2017, TVA operators again took both auxiliary building gas treatment systems out of service. This was the result of a door beng left open in order to make “a continuous fire watch” easier. TVA also reported this breach to the NRC.
At Salem Unit 2 in New jersey’s Lower Alloways Creek Township in August and again in September 2015, NRC inspectors at the Exelon plant during walkdowns “noted that the boric acid evaporator room’s interior wall had been removed while two watertight doors were fully open, impairing the differential pressures required. “The licensee determined that one apparent cause was inadequate procedural guidance that resulted in work planners not requesting a [plant barrier impairment], personnel not meeting the intent of the attendant requirement, and departments not requiring proof that the technical specifications would be met prior to opening the doors.”
At both Salem units in Oct. 2013, an NRC resident inspector found that a barrier door to a pump room “was being held open for an extended period by an assigned door attendant.” The condition could have taken down both motor driven auxiliary feedwater pumps. “The cause of this event is attributed to an organizational failure to ensure that guidance provided” in the plant’s high-energy line break program “contained sufficient justification for compensatory actions used for barrier impairments.”
At TVA’s Watts Bar Unit 1 in July 2012, NRC inspectors found that the plant located near Spring City, Tenn., failed “to correctly translate the design basis related to onsite flooding into the instructions for a plant design change temporary alteration.” The inspectors found a series of weaknesses in the instructions. “As a result, the thermal barrier booster pumps flood barrier would have failed during a probable maximum flood event, thereby submerging the [pumps] and rendering the equipment inoperable.”
Between January and September 2009, operators at Exelon’s Peach Bottom Unit 3 outside Philadelphia found a failed neutron monitor “and installed a jumper that bypassed its trip feature instead of using the …bypass switch as is described in their plant’s final safety analysis report.” Because only three of the four neutron monitors “were required by technical specifications, no action statement was entered and installing the jumper was thought to be acceptable.” But the NRC noted that the putting in the jumper was done without the required regulatory review. “This installation involved a facility change that likely would have required a license amendment before its implementation.”
All these events, said the NRC information notice “highlight the need to adequately establish and implement procedural controls for temporary alterations to insure their compliance with the requirements of all NRC regulations….”
— Kennedy Maize