More Repairs Needed After Palisades Nuclear Plant Inspection

Submitted by Interclassmy on Tue, 11/20/2018 - 17:13

COVERT, MI -- Another issue was discovered during an inspection at Palisades nuclear plant that will require a repair, according to a Nuclear Regulatory Commission (NRC) document. 

On Saturday, Nov. 10, with the plant in a refueling outage, during an NRC required bare metal visual inspection of the reactor head, a through-wall leak was identified on a reactor vessel head control rod drive nozzle, a NRC preliminary notification document dated Nov. 14 states. 

There was no safety impact on the plant or the public and the leak was small enough that radioactive levels were not detected above normal within a containment area of the plant, NRC Spokeswoman Viktoria Mitlyng said.

Control rods inside the reactor vessel control the nuclear reaction, and control rod drive mechanisms sit above the reactor vessel and move the control rods in and out of the reactor core, Mitlyng said. 

The nozzles are tubes that penetrate through the reactor head that provide for the connection between the control rod drive mechanisms and the control rods, she said. 

"Over time the nozzles can develop small cracks which can allow a very small amount of borated reactor water to leak onto the vessel head. This is why the NRC has established examination requirements to ensure licensees identify cracks or leaks at an early stage to ensure repairs are made," she said. 

The borated reactor water is radiated water that contains boron, she said, which is used in the reactor. 

An NRC metallurgical specialist was onsite inspecting the licensee's reactor vessel assessment activities when the issue was identified. Resident inspectors onsite were notified of the issue, NRC said. 

While assessing the condition of other control rod drive nozzles, plant personnel identified similar ultrasonic test characteristics in another nozzle, the NRC document states. This nozzle did not exhibit evidence of through-wall leakage, NRC said. 

"The tests Palisades performed per NRC requirements involved visual and ultrasonic tests of the nozzles with the intention of identifying flaws or cracks that could result in leakage," Mitlyng said. 

The tests are not destructive in nature, she said, and do not have any impact on the tested material. 

"The plant performed such examinations of all the nozzles on the reactor vessel head. Through those tests, they saw a similar ultrasonic pattern on the nozzle that had the crack and this other nozzle. Both nozzles will be repaired," Mitlyng said.

Entergy Spokeswoman Val Gent said hundreds of tests are performed at Palisades during planned refueling and maintenance outages to make sure equipment is working as designed, confirm safety margins, and correct any identified issues before returning the plant to service.

"During the current outage, which began October 28, engineers inspected the reactor vessel head, including all 54 tubes that penetrate the reactor head. During these scheduled inspections, we identified two tube penetrations where repairs will be made before the plant is returned to service. The tube penetrations contain mechanical controls that position control rods in the reactor vessel," Gent said. 

"All inspections are rigorously performed, using industry best practices to ensure even the slightest variation in equipment is identified, analyzed, and if necessary, repaired. We informed the NRC of the issue. At no time did this impact the health and safety of the plant's workers or the public, and all equipment remained operational," Gent said.

She said safety is the top priority.

"We adhere to rigorous safety standards, act conservatively, and correct any identified issues," Gent said.

The licensee's extent of condition assessment is ongoing, NRC said. 

The plant remains shut down as of Nov. 16, and has initiated repairs that will be completed prior to the plant restarting from the current refueling outage, NRC said. 

The plant was shut down Saturday, Oct. 13, after radioactive water leaked through a control rod seal, Palisades' Resident Inspector Julie Beottcher said. 

Palisades remained offline and began a scheduled $62 million refueling and maintenance outage following the completion of the maintenance outage. 

The latest issue was discovered during an inspection that occurred during the shut down. 

NRC inspectors will continue to be onsite to monitor the licensee's assessment, actions, and repairs to ensure they are conducted in accordance with safety regulations, according to the NRC, and an inspection report will be publicly available after the inspection activities are finished.