Spent Fuel Degradation Eyed at Nuke

Monday, August 15, 2011 @ 04:08 PM gHale

Spent fuel pools at Peach Bottom Atomic Power Station are under watch to see if plant officials can maintain safety guidelines despite the degradation of a material used to control the radioactive waste.

The problem is with Boraflex, the material that absorbs neutrons from fuel burned in a reactor, said officials at the Nuclear Regulatory Commission (NRC). The spent fuel is still highly radioactive when it goes in the cooling pool, said Neil Sheehan, NRC spokesman.

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Tough the temperature of the radioactive waste drops dramatically within a few months, conditions must remain under control to make sure it doesn’t start fission, he said. To this end, Boraflex panels attach to racks where the spent fuel remain stored, 40 feet underwater at the bottom of the spent fuel pool, he said.

But gamma rays, the strongest form of radiation, have caused shrinkage in the Boraflex, so NRC inspectors will examine whether the existing material is safe for use until 2014, when owner Exelon Nuclear plans to replace it, he said.

Failure of the system could cause boiling of water in the pool or the release of radioactivity, he said.

He said there are 19 reactors nationwide that use Boraflex, and other plants noted similar problems.

The Boraflex system first gained approval at Peach Bottom, PA, in 1986, Sheehan said, and Exelon has known since 1996 that there was “minimal degradation” to the material.

“This material has been in there since the mid-’80s and had not held up the way they envisioned,” he said.

The company submitted information to demonstrate the existing Boraflex will continue to “do what it’s supposed to do,” but it was unable to provide sufficient information to answer the NRC’s technical questions, he said.

“They want to say that even with the degradation, there’s still a sufficient safety margin,” he said. “We’re saying our comfort level is not enough that we would agree with that assessment at this point.”

The results of the NRC’s assessment will determine whether some other mitigation measures need to go in place to ensure safety before 2014, he said.

The degradation affects only Unit 2 and Unit 3 at the power station. Spent fuel from Unit 1 remains stored using a dry cask system.

Exelon has moved the spent fuel assemblies in both spent fuel pools to locations where the Boraflex has been holding up better, according to an NRC report.

There were 201 assemblies relocated in Unit 2, and 83 assemblies relocated in Unit 3.

Workers monitor the degradation closely and routinely relocate spent rods to make sure the pools are safe and stable, said Peach Bottom spokesman David Tillman.

Last year, Exelon completed an analysis of the degradation and sent it to the NRC for approval. The two are currently working through areas where they can make improvements, he said.

The atomic station will soon be addressing the concerns by installing the improved neutron-absorbing inserts, Tillman said.

“We’re in full compliance with NRC regulations … and will continue to make sure that our pools are safe and that they’re properly configured,” he said.



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