Revised: US assessing reported leak at Chinese nuclear power facility

(CNN)  Exclusive: US assessing reported leak at Chinese nuclear power facility contains new information. Quoting,

French utility company Electrictie de France (EDF) said in a statement it has been informed of an increase concentration of “noble gases in the primary circuit” of reactor number one of the Taishan nuclear power plant.

The noble gases produced are radioactive:

  • Xenon-135, which has a short half life, affects reactor operation, but is not a significant health hazard.
  • Krypton-85,  with a half life of 11 years, is a health hazard.

These gases accumulate in fuel rods, where they limit  fuel rod lifetime. The outer structure of a fuel rod is zircaloy, a mechanically tough alloy of zirconium. An inner liner of softer, pure zirconium reduces gas leakage.

Accumulation of these gases in the primary loop implies a problem with the zircaloy cladding , which is usually caused by bad welding. ANT International has published Welding of Zirconium Alloys.The first chapter is a very dense 47 pages. Quoting a couple paragraphs cannot portray the complexity of this exacting metallurgy. I’ll quote a little anyway:

2. Cleaning of weld joints and adjacent areas prior to welding. Contamination can lead to welds with poor strength and or poor corrosion resistance.

3. Atmosphere control during many of the zirconium welding processes must be strictly controlled to keep uptake of especially nitrogen and to a lesser extent oxygen at very low levels. In reactor corrosion resistance can be impaired when these gases enter the weld.

Incidents of bad China metallurgy have come to light more than in the West. Russia and Ukraine have a tradition of good metallurgy,  which has not yet become the norm in China. (Sacramento Bee) Troubled welds on the Bay Bridge: How a Chinese builder’s flaws left structural doubts and cost taxpayers.

Noble gases in the primary loop  indicates corrosion of fuel rods. Framatome assesses imminent containment failure; the U.S. estimate is “not yet.” What accounts for the divergence?

It comes down to the trajectory, and the failure mechanism:

  • Gas escapes from porous welds; not so bad, but auguring worse.
  • Severe corrosion  resulting in pinholes, much worse.
  • Water enters a fuel rod. Fresh fuel,  uranium dioxide, is nonreactive. The decay products, which are much more radioactive than the fuel itself, leach into the primary water loop. This could cause a failure cascade, resulting in containment failure.
  • Fuel rods break apart. Impaired cooling could result in partial melting of the core.

Perhaps Beijing  waking from their little nap is a realistic prerequisite for U.S. assistance.

 

 

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