12/23/13

Permalink 11:08:00 pm by Steve Schulin, Categories: nuclear plants, Reactor Safety, Accidents, NRC
Dec 23, 2013 (nuclear.com) -- On December 4, 2013, A subcommittee of the Advisory Committee on Reactor Safeguards held a meeting about fuel fragmentation, relocation and dispersal under LOCA conditions. The transcript of the meeting was released today, and it contains much of interest. Here's an excerpt from introductory comments by Kathy Gibson, (NRC/RES Division Director, Division of Systems Analysis):

... our main presenters are Dr. Patrick Raynaud and Michelle Flanagan. They'll talk about the new insights in analysis of the phenomenon of fuel fragmentation, relocation and dispersal under LOCA conditions.

... The work that they'll present is driven by a research plan that we developed in 2011 to investigate this phenomenon.

We put together this research plan as a result of unexpected results that emerged from tests in our LOCA program in Studsvik. The Studsvik tests produced observations of significant fuel dispersal characterized by fine fuel fragments, almost looks like sand.

The fuel lines tested at Studsvik had a right average burnup near 70 gigawatt-days per metric ton of uranium. Halden tests used a very high burnup around 90 gigawatt-days.

Citings had already shown significant fuel dispersal, but the Studsvik tests were closer to the U.S. burnup limits and therefore garnered greater attention.

[MS. FLANAGAN]

... [T]he first observation of fuel dispersal was over ten years ago in the Halden reactor program. This phenomenon was first observed, but it was so unexpected that most of the explanations and discussions were really focused on what was non-typical about those experiments and kind of trying to look at what had happened and why it wasn't normal.

Over the next couple of years, we saw these results again so they were repeatable. But still the data was very limited. Then in the most recent history, around 2010, 2012, we saw that our results at Studsvik repeated significant fuel dispersal.

It started to become something that couldn't be ignored and became a subject of international meetings, and discussions and research program plans that were aimed at resolving them.

However, despite the number of observations that we had by 2012, there still wasn't a unified description of why this was happening or really the ability to identify trends.

And you saw this a little bit in NUREG-1221.

There was a lot of information and there was a lot of scatter in that data, the experimental conditions as well as the observations. So it was really hard to put together a theory at that point.

So as Kathy mentioned, we developed a research plan to identify what was needed to learn more and resolve what was going on in these tests.

And so we collaborated with the Halden Reactor Project and Studsvik to review some of the examinations that they had performed on their past rods which, for whatever reason, weren't presented in the enlarged Halden program. You know, there were supplemental images or discussions that we had with the staff to find out other observations that they had had personally.

And then at Studsvik we ordered a couple service examinations that were based on what we suspected might be going on. So we asked them to look at this specific area, because we thought it could have some insight.

And once we did that work, we came up with five key observations. And I'm going to go into all of these in detail and describe why each of them is significant. So for now I'll just read them.

The first is that extensive fragmentation was not present before the testing. The second was that the extent of relocation and fragmentation was correlated with the local strain of the cladding and the proximity to the rupture location. The third was that there was a significant change quite rapidly somewhere between 60 and 70, some high and very high burnup tests.

We also noticed that pressure transducers in the plenum region, which is where the pressure is measured, sometimes showed slow depressurization which indicates that there are some gas flow restrictions between this plenum region, where the pressure is measured, and the rupture region, where the pressure is released.

And then finally, for high burnup tests, most of the fine fragments that we collected seem to originate from the periphery of the pellet, and I'll explain how we return to this. Whereas for very high burnup rods, the fine fragments that were collected appear to originate from all radii...

The transcript includes copies of presentation slides, including some copyrighted by EPRI. That probably explains why the pdf containing the transcript is considered copyrighted. NRC reports that the pdf is available at http://adamswebsearch2.nrc.gov/webSearch2/main.jsp?AccessionNumber='ML13356A004'. If you have trouble getting it through that link, you'll have to go through NRC's ADAMS system, and search for Accession Number ML13356A004 -- and download the pdf from there.

12/21/13

Dec 21, 2013 (nuclear.com) -- The Dept of Energy is producing a series of "10 things you didn't know about" articles about various sites. The article about Los Alamos National Lab is available at http://links.nuclear.com/W
Dec 21, 2013 (nuclear.com) -- On July 16 the US set off the first atomic bomb ever in Alamogordo, New Mexico. Michael Steinberg, in an article published yesterday in San Diego Free Press, reports that the following account by a Naval officer from July 1945 appeared in the San Francisco Bayview newspaper on August 31, 2009:

'On July 15 we were ordered to go to San Francisco (Hunters Point) to pick up some cargo. We tied up there and two big trucks came alongside. One truck was put in the port hangar. Two Army officers from [the other] truck carried a canister about 3 foot wide by 4 foot tall ... Later on, I found out that this held the nuclear ingredients for the bomb, and the large box in the hanger contained the device for firing the bomb.

'We sailed at 0800 the morning of 16 July. We arrived in Tinian [near Guam Island in the Pacific, from which the B-29 carrying theA-bomb flew off] the morning of 26 July and unloaded the material and bomb which was later dropped over Hiroshima'.

The full article by Mr. Steinberg is freely available at http://links.nuclear.com/V

12/20/13

Dec 20, 2013 (nuclear.com) -- "After considering the environmental aspects of the proposed NRC action, the NRC staff’s recommendation to the Commission is that the COLs [combined construction permits and operating licenses for WS Lee units 1 and 2] be issued as requested." The full report (NUREG-2111, Vol. 1) is freely available at http://links.nuclear.com/U

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