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From the US NRC:
What is burnup?

‘Burnup’ is a way to measure the uranium burned in the reactor. It is expressed in gigawatt-days per metric ton of uranium (GWd/MTU). Burnup depends on how long the fuel is in the core and the power level it reaches. The burnup level affects the fuel’s temperature, radioactivity and physical makeup.

In a reactor, uranium fuel fissions—splits apart and releases energy—and the metal cladding that encases the fuel reacts with cooling water. This reaction forms oxide on the outside (similar to rust) and releases hydrogen. These processes begin slowly then start to accelerate as the fuel reaches burnup of 45 GWd/MTU. Anything above this level is considered high burnup.

Over time, burnup has increased, allowing utilities to get more power out of their fuel before replacing it. Average burnup, around 35 GWd/MTU two decades ago, is over 45 GWd/MTU today. How hot and radioactive spent fuel is depends on burnup, the fuel’s initial makeup and conditions in the core. All these factors must be taken into account in designing dry storage and transport systems for spent fuel.”

Why does burnup matter?

Burnup is important to the NRC’s review of spent fuel cask designs because each system has limits on temperature and radioactivity. When the cask is being dried, pressure increases inside and the fuel heats up. This may cause the cladding to become more brittle when it cools. These changes depend on burnup and the type of cladding, and need to be accounted for in high burnup spent fuel systems. A great deal of work has been done to understand the conditions that make different types of fuel cladding more brittle.

Testing continues on high burnup spent fuel and the set of available data is growing. Cask designers use the results to redesign their casks for higher burnups and additional fuel types.

As more data becomes available, the NRC expects to be able to certify more casks. Cask designers also need this data to demonstrate the long-term safety of their systems so they can continue storing spent fuel beyond the initial license term.

Nuclear fuel is removed from a reactor every few years when it can no longer economically sustain a chain reaction. This ‘spent’ fuel remains radioactive and must be managed. Initially, it goes into a pool onsite for cooling and storage. Some utilities are moving their spent fuel after it has cooled for several years in the pool into NRC-certified dry storage casks. These casks are specially designed to contain the radioactivity and allow hot spent fuel to cool further.http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/bg-high-burnup-spent-fuel.html (Emphasis added; we’ve changed the order of some paragraphs.)

Here comes their contradiction and BS. Either they know that dry casks are safe, or they don’t know. If they know, then the ongoing DOE (taxpayer) funded research into the matter is nothing but pork barrel for the EPRI, Areva, etc. Indeed it IS pork barrel, because it is research by the utilities, which should be paid for by them, and not the US taxpayer. But, do they know how to safely store high burnup, or even other nuclear fuel, or not? They can’t have it both ways. It appears that they don’t, and that they are stuck between a radioactive rock and hard place. The fuel pools aren’t that safe, especially in earthquakes, and induce corrosion in the spent fuels rods, which can cause problems for dry storage. They apparently don’t know how to store the spent fuel safely in dry store – or they don’t know if they do. The final phase of the high burnup fuel study, is a study of 10 years in dry cask. Yet, they keep making the nuclear waste, and high burnup at that.

NRC continues:
Is it safe to store and transport high burnup fuel?

To be certified by the NRC, dry cask designs must meet transportation requirements in 10 CFR Part 71 or storage requirements in 10 CFR Part 72. The NRC approves designs only after a full safety review. Based on these reviews, the NRC has certified numerous cask designs for spent fuel storage and transportation. Operating experience since dry storage began in 1986 and short-term tests show both low and high burnup spent fuel can be stored and transported safely.” [Most dry cask sites are more recent.]

More casks are available for low than for high burnup spent fuel. Because it has been used longer, there is a great deal more data on low burnup fuel. There is enough data on high burnup fuel that the NRC has been able to certify some high burnup spent fuel storage casks for an initial term of 20 or 40 years. Some systems have also been approved for transporting high burnup spent fuel.http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/bg-high-burnup-spent-fuel.html

But, the research arm of the utilities, EPRI, hired by the US DOE (taxpayer) to do research on storage of high burnup spent nuclear fuel (SNF) states that “While dry storage of lower burnup SNF [less than 45 gigawatt days per metric ton uranium (GWD/MTU)] has occurred in the United States (U.S.) since 1986, dry storage of high burnup SNF has been more recent. As of December 2012, approximately 200 dry storage casks have been loaded with at least some high burnup SNF. Furthermore, almost all SNF being loaded in the U.S. is now high burnup. Since high burnup SNF has different mechanical properties than lower burnup SNF, industry needs additional data on high burnup SNF under typical conditions.“, in “High Burnup Dry Storage Cask Research and Development Project: Final Test Plan Contract No.: DE-NE-0000593, February 27, 2014, High Burnup Dry Storage Cask Research and Development Project, Final Test Plan , Prepared by: the Electric Power Research Institute, REVISION LOG Rev. Date Affected Pages Revision Description, February 27, 2014 Final Test Plan” The High Burnup Dry Storage Cask Research and Development project is not over until 2018 (DOE-EPRI Contract Ends 15-Apr-18), though mention is made of leaving the test fuel for 10 years, until 2028. http://www.energy.gov/sites/prod/files/2014/03/f8/HBUDry%20StrgeCaskRDfinalDemoTestPlanRev9.PDF More on dry cask problems by the very pro-nuclear US DOE: https://miningawareness.wordpress.com/2015/02/08/high-burnup-nuclear-fuel-dry-storage-cask-problems-us-doe-aug-2014-with-intro-commentary/ Also: https://miningawareness.wordpress.com/2015/02/07/us-taxpayer-pays-for-french-gov-japanese-us-corp-nuclear-research-wolves-guarding-american-sheephenhouse/

The NRC-Holtec, want to give waivers to BWR damaged fuel (and some other exemptions for spent fuel and other safety related things): “updates fuel definitions to allow boiling water reactor fuel affected by certain corrosion mechanisms with specific guidelines to be classified as undamaged fuel.https://www.federalregister.gov/articles/2015/02/05/2015-02310/list-of-approved-spent-fuel-storage-casks-holtec-international-hi-storm-100-cask-system-certificate

Oh, what’s this? Pressurization, Embrittlement, Flammable gas generation in high level nuclear waste, which is corroded. That is a dangerous combination, especially for nuclear waste!
Damaged Spent Nuclear Fuel at U.S. DOE Facilities, Experience and Lessons Learned, by INL (Brett Carlsen, et. al. Dangers of Corrosion, p. 2
Damaged Spent Nuclear Fuel at U.S. DOE Facilities, Experience and Lessons Learned“, by Brett Carlsen, Denzel Fillmore, Roger McCormack, Robert Sindelar, Timothy Spieker, Eric Woolstenhulme, November 2005, Idaho National Lab-USDOE (op by BEA consortium) http://www.inl.gov/technicalpublications/documents/3396549.pdf

Here the NRC specifies, as part of the Holtec waiver, that “The applicant stated that ‘for channeled BWR fuel, inspections to classify the fuel cladding as undamaged in accordance with the currently approved definition may be prohibitive from a cost, ALARA,… if it can be determined that this fuel does not have gross cladding breaches, can be handled by normal means, and has enrichment less than or equal to 3.3 wt%, then it does not require a damaged fuel container nor is it limited to certain basket locations in the MPC-68M… Potential corrosion-induced damage to the cladding, characterized by pitting, but not grossly breached spent fuel rods” ” February 28, 2014, “Application Supplementhttp://pbadupws.nrc.gov/docs/ML1426/ML14262A476.pdf This appears to apply to about 1/3rd of US reactors, which are BWR. Average enrichment is about 3%, for light water reactors, BWR are light water reactors. They give an example of copper induced corrosion, but that is only one possibility or it would not be an example (e.g.). It’s also not the only exemption they are asking for. Some of the requests could impact internal configuration, whereas, “In-canister criticality of degraded SNF is an accident scenario where the SNF degrades into a more reactive configuration. Canister design should incorporate features to maintain configuration if degraded SNF is subject to criticality concerns. Examples of this would be compartmentalized canister inserts or placement of smaller canisters within a larger canister, thereby maintaining the analyzed configuration of the SNF. Maintaining a critically safe geometry is a consideration any where damaged or degraded SNF may accumulate (e.g., beneath storage racks)“”Damaged Spent Nuclear Fuel at U.S. DOE Facilities, Experience and Lessons Learned“, by Brett Carlsen,et. al., November 2005, Idaho National Lab-USDOE http://www.inl.gov/technicalpublications/documents/3396549.pdf

A big problem is ALARA. As low as reasonably achievable sounds good, but it isn’t. It favors the finances of the nuclear industry. A well-known nuclear lackey laughed about “As low as reasonably achievable”, when speaking about Fukushima: “ALARA, As low as reasonably achievable, hah, hah”. We know now what that really means. Fukushima showed us. They let it go in the air and dump it in the ocean. No filtration on the new vents of Fukushima type reactors, in the US, is apparently another case of ALARA. The utilities didn’t want to pay, and they don’t. That, Fukushima, WIPP and Holtec demonstrate what ALARA is about. ALARA has its origins in the UK’s refusal to pay anything to the widow of a coal miner killed in a state-owned coal mine (via Common law, case based). In the UK, it is ALARP.

Dangerous Transuranic ALARA at WIPP
WIPP 22 May 2014
It will cost a fortune to clean-up, of taxpayers’money, because contractors were lazy or didn’t know what they are doing. Or, maybe because it is actually designed to fail, but just did so sooner, or more dramatically, than they thought? It is supposed to collapse at about 2 inches per year. $248 million is set aside to help “repair” WIPP for the 2016 DOE budget: http://www.energy.gov/articles/energy-department-presents-fy16-budget-request

Damaged fuel rods are now stuck in a Holtec Cask in Arkansas and can’t be moved! http://pbadupws.nrc.gov/docs/ML1428/ML14286A037.pdf But, it’s ok says the NRC, because Holtec assures them it is, or that’s how it reads to us: https://www.federalregister.gov/articles/2014/12/31/2014-30718/independent-spent-fuel-storage-installation-entergy-operations-inc-arkansas-nuclear-one-units-1-and Of course, what else can one expect from criminally negligent people at the NRC who STILL have not updated this: https://miningawareness.wordpress.com/2014/09/04/the-dangerous-us-nrc-typo-making-low-level-radioactive-waste-more-radioactive-than-allowed-at-wipp/

NRC blah, blah continues:
How does the NRC make sure it remains safe?

The NRC assures safety by requiring many layers of protection. Casks provide several layers and the fuel cladding itself is an important layer.” [Fuel cladding damaged; casks less than one inch (5/8 inch).] “The regulations are designed to ensure the casks will hold up and the cladding will not break during storage or in a transport accident.” [Then why is there still research? And, why is the NRC allowing Holtec to reduce safety standards?] “The NRC carefully reviews each cask application to see if it meets the requirements. As part of this review, the NRC does its own analysis to confirm information in the application.

The NRC also does inspections before and during loading of dry casks to ensure the correct fuel goes into the right storage systems. Fuel with burnup higher than the NRC certificate allows cannot be loaded. It must remain in pool storage until a cask approved for higher burnup becomes available. The NRC also inspects loaded casks every few years.

What confirmatory research is being done?

Testing has provided a lot of information on how different types of cladding on spent fuel will behave, and this work continues. Planning has begun for an important new study, run jointly by the nuclear industry and the Department of Energy, with regulatory oversight by the NRC.” [Oh, here they admit it!] “In this study, high burnup spent fuel will be loaded into a cask fitted with instruments to provide temperature readings and allow gas sampling. Those readings, combined with tests on the fuel assemblies and inspection of the cask’s interior after years of dry storage, will provide a much better understanding of what happens to high burnup spent fuel in a storage cask as it cools over time.” [The test is for 10 years.]

Work is underway to create better models to determine how much cladding actually may become brittle and the impact of vibration during transport. The NRC is also monitoring work going on internationally.

All this work will help cask designers, users and regulators better understand how to ensure high burnup spent fuel will remain safe in long-term dry storage and during transportation to a centralized storage or disposal facility. December 2013 Page Last Reviewed/Updated Friday, December 12, 2014http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/bg-high-burnup-spent-fuel.html (Emphasis added; our comments in brackets). So, why then is the NRC allowing Holtec to remove safety margins? How is that helping designers?
curie.ornl. gov/content/inspection-vertical-used-fuel-casks
Inspection of some vertical spent fuel casks, ORNL

If you believe that the NRC cares if anyone is safe, we can find you some property to buy in Bayou Corne Louisiana – you know the still imploding-collapsing salt dome storage.
Nearer My God to Thee Titanic
Nearer My God to Thee, Sinking of the Titanic
The sinking of the Titanic may have been caused by embrittlement. It was a personal tragedy. Nuclear accidents can be national and international tragedies, as shown by Windscale, Chernobyl and Fukushima. Norwegian reindeer are still impacted by Chernobyl, as are UK sheep (though they lifted the ban in the UK), and German wild boar. Most of Europe is contaminated in a patchy way. Nuclear accidents have consequences which last almost an eternity. They just like to tell you about the shorter lived radionuclides, so that they can claim improvement. No talk of plutonium, americium, etc.