Zirconium and the Future: Why Research is Important

An Expected Ruling

On Friday, August 6, the Nuclear Regulatory Commission (NRC) turned down a request for enforcement against Vermont Yankee by the New England Coalition (NEC). In June, the NEC had asked that Vermont Yankee be required to operate its core at a much lower temperature. The NEC claimed that zirconium alloy (zircaloy) cladding is a fire hazard at Vermont Yankee's current operating temperatures.

Why all the concern about zirconium cladding? Fuel pellets are made of oxides (mostly uranium oxide) and can't burn. However, the fuel pellets are encased in zircaloy, which is metallic. Metals don't generally burst into flame. However, unlike oxides, metals can burn. So it is reasonable to be concerned about the temperature at which zircaloy will burn.

The NRC regulation for maximum temperature of light water reactor fuel cladding is 2200 F, while Vermont Yankee plant operates at 2060 F or below. However, NEC asked the NRC to rule that Vermont Yankee must operate with fuel cladding temperatures no higher than 1700 F. Naturally, the NRC turned down this request. No reputable regulatory agency is going to tell a plant that is in compliance with regulations: "Sorry. You think you are in compliance, but you aren't in compliance. We have changed the regulations and made them far stricter, just for you."

Besides being unfair, this would be a great way for a regulatory agency to get itself sued. Of course the NRC didn't do this. After several conference calls with people from NEC, the NRC sent NEC a letter basically saying: No. We're not going to tell Vermont Yankee to operate at a lower temperature. Your concerns are more generic than anything specific to Vermont Yankee. Your concerns will be forwarded to our area for general rulemaking.

You can download the letter the NRC sent NEC here, and also read the Brattleboro Reformer article on the ruling.

But Wait, There's More!

The request above was specific to Vermont Yankee. It was filed by NEC in June of this year, and turned down at the beginning of August, as described above.

However, there was an earlier request by Mark Leyse, a nuclear engineer and the son of Robert Leyse, also a nuclear engineer. Mark Leyse lives in New York city. Mark Leyse has made many requests to the NRC for re-evaluation of safety measures. He is particularly concerned with fuel cladding, apparently believing that the NRC has ignored his father's research results on this issue.

Mr. Mark Leyse's November 2009 request for lower temperature operation of all reactors has become an NRC rulemaking docket. Leyse's November 17, 2009 petition to the NRC is the first item in this docket. Leyse claims that oxidation of cladding became a self-sustaining reaction at around 1800 degrees, and that the NRC has ignored this situation for forty years. In the petition asking for rulemaking, Leyse quotes his father's test results from forty years ago. Mark Lesye includes a letter from his father Robert Leyse about tests dated 1970 on pae 116 of his petition. Throughout the petition, Leyse also extensively discusses the test, Flecht Run 9573, reported in 1973. (For simplicity, I am referring to these references as "forty-year old data." Strictly speaking, some of the quoted data is only thirty-seven years old.)

The consequences of all this, as always, are assumed to be dire. Here's a quote from the Rutland Herald article:

The NRC earlier in spring had already agreed to consider the matter raised by Mark Leyse of New York City, but in a review track that will take years, not months. The New England Coalition wants the margin of safety increased immediately.

Leyse and Raymond Shadis, senior technical adviser to the coalition, say Vermont Yankee’s peak cladding temperature of 1,960 degrees Fahrenheit only gives the plant operators 30 seconds to react during a loss-of-coolant incident scenario.

Thirty seconds. Sounds terrible, doesn't it? And "takes years, not months" sounds perfectly awful.

But Wait, There's Less!

I decided to review Mr. Leyse's letter, because I couldn't figure out some of the comments in the press. What does reactor operating temperature have to do with loss-of-cooling accidents (LOCA)? Of course, to some extent, a hotter reactor is slower to cool, but everything about a LOCA analysis is built with huge margins of error. And how could forty-year-old lab data be ignored by everybody, when zircaloy must be one of the most-studied compounds in the world? Zircaloy it has been used for cladding since the very first reactors, and people have been studying it forever. Just Google "Zircaloy" to see the endless lists of papers and references.

And, of course, my major question. If zircaloy bursts into flame in water above 1700 Fahrenheit, and reactors routinely operate at 1900 Fahrenheit, how come they haven't all burned up already?

I reviewed the document to the best of my ability, and I welcome comments that will improve my review. Here's my analysis, with some quotes from Leyse's letter to NRC.

The Leyse request doesn't just refer to the temperature at which zirconium might burn in water. Instead, it also says that the modeling of loss of cooling accidents, the flood rate of water into the core, and the Baker-Just and Cathcart-Pawel equations non-conservative for calculating the temperature at which an autocatalytic (runaway) oxidation reaction of Zircaloy would occur in the event of a LOCA. .....Additionally, it can be extrapolated from experimental data that, in the event a LOCA, a constant core reflood rate of approximately one inch per second or lower (1 in./sec. or lower) would not, with high probability, prevent Zircaloy fuel cladding, that at the onset of reflood had cladding temperatures of approximately 1200F or greater, from exceeding the 10 C.F.R. § 50.46(b)(1) PCT limit of 2200 F.

In other words, this is not just about zircaloy. In this petition. Mark Leyse claims that just about every model used in the nuclear industry is inadequate. Zircaloy properties, LOCA calculations, reflood calculations--all wrong. In 2002, his father, Robert Leyse, said the same thing. The elder Leyse petitioned the NRC for rule-making about the Baker-Just and Cathcart-Pawel equations and LOCAs, and the NRC found his contentions to be not scientifically valid and wrote him to that effect in 2005.

This latest contention by Mark Leyse is a replay of this 2002 petition by Robert Leyse. Unfortunately, the NRC cannot just say: "Hey, we did this before. These contentions were made in a petition in 2002, and we settled these points in a ruling in 2005." No, they have to look at it again. This gives the opponents of nuclear power the opportunity to complain that it takes the NRC three years to look at anything.

Conspiracies Not Research

Robert and Mark Leyse seem to believe that all the research that has been done over the past forty years on LOCA modeling, zircaloy properties, and pretty much everything else....is part of a vast conspiracy to provide just the results the utilities want. The Leyses, and the Leyses alone, have the real facts, the true equations, the correct models. They discovered these "facts" forty years ago and have been ignored ever since.

I call this a conspiracy theory, decked out in scientific trappings.

Of course, once you buy into the idea that everything known about nuclear is wrong, then you can come up with scenarios where the entire core bursts into flame in thirty seconds and there is nothing anybody can do about it and so forth. This plays well with the anti-nuclear groups.

It doesn't play well with me. In science and technology, everything builds on what has gone before. Even the Einstein's famous breakthroughs were built on the past. He reviewed experiments that could not be explained without new ways of thinking about the speed of light. Einstein was attempting to explain the very latest experiments when he wrote his breakthrough papers.

I've done research, supervised research, and I deeply value research. Conspiracy theories that decide to ignore forty years of research should be called exactly what they are. Conspiracy theories.

I prefer science.

Update: NRC review of CORA tests, interim ruling now available here. Simplistic summary of NRC ruling: these results are in line with our other tests, and no rule changes are necessary.

Zirconium rod (not zircaloy) from Wikimedia.