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[Updated 29, 30 Apr; 1, 2, 3 May, 3-4 May, updated multiple times 4 May UTC, updated 5 May; 8 May]
This NUREG looks like a hoax. It does not live up to its title, nor to its scope. One interesting point made, but not adequately evaluated, is that peak cladding temperature (PCT) increases 14.4F for every 10F ambient temperature. Research-estimates suggest that at 80F the added external temperature in the sun to the Holtec casks would be 68F, leading to 148F. The US government only considers 100 F in the shade. This 100F in the shade would be at least 168F in the sun, probably higher. Thus, the spent fuel would be around 100 F hotter than in the shade (divide 68 by 10 and multiply by 14.4). In most of N. America the NRC’s 100 F is frequently exceeded. A proper calculation should involve the US max temp. of 134 F plus approx. 68F or more added for sun. This would be around 202F. Sun should be measured near summer solstice, not winter solstice. Contingency should be added. Furthermore, they calculated heat load at 34 kW, whereas Holtec, 2014, states that it is 47.05 kW, which is 13.05kW higher, leading to approximately 255 F higher peak fuel cladding temp than they state. This makes their calculations off by around 355 F or more. Their false assumptions regarding humidity cause a further underestimation of peak fuel cladding temperature. The only thing which the NUREG evaluates is low level wind, and it doesn’t do a proper job of that. These two authors are highly paid by taxpayers.
Holtec Dry Casks Grand Gulf Miss
Holtec Dry Casks of spent nuclear fuel sweltering on pavement in the Mississippi sun, on the river, with ultra-high humidity. The US NRC allows Holtec and others to pretend that the temperature is only 100F (38C).

Impact of Variation in Environmental Conditions on the Thermal Performance of Dry Storage Casks”, NUREG, US NRC comment deadline MAY 4th-Nuclear Waste Dry Cask Storage Temperature, etc. http://www.regulations.gov/#!documentDetail;D=NRC-2014-0273-0001 ID: NRC-2014-0273-0001
Holtec casks Diablo Dec. 26 2005 or 2006
Dry Casks at Diablo Canyon in California. NRC visit was 26 December, when the sun is its weakest.

The summary of this NUREG starts off sounding reasonable in spots, before quickly degenerating to the point that it would be fair to wonder if anything in this document can be trusted. It is important to note that at least two very well paid bureaucrats wrote this and probably had months to work on it full time, and maybe years. Maybe it was written by interns as it looks, but it was signed off by 2 bureaucrats, who appear qualified. In short, they don’t have excuses for any errors. It’s hard to know if their faulty assumptions are due to too much central heat and air (climate control) and not enough time outdoors or if the faulty assumptions are intentional or what? Some of the faulty assumptions are based on faulty US NRC rules. But, this was their chance to change that.

In the Executive Summary they correctly point to an important problem: “using average values may not be adequate, because more adverse ambient conditions could exist for prolonged periods of time, allowing a storage system to reach new steady-state conditions that could result in higher spent fuel cladding temperatures as compared to the steady-state conditions analyzed in the cask’s safety analysis report (SAR) for normal conditions of storage. For cases with predicted small thermal margin, these adverse ambient conditions could result in peak cladding temperatures exceeding recommended limits for normal conditions of storage.” In other words, this is critically important.

In the Introduction they tell us:
1.0 INTRODUCTION

The U.S. Nuclear Regulatory Commission (NRC) certifies spent fuel dry storage systems according to Title 10 of the Code of Federal Regulations (10 CFR) Part 72, “Licensing Requirements for the Independent Storage of Spent Nuclear Fuel, High-Level Radioactive Waste, and Reactor-Related Greater Than Class C (GTCC) Waste.” The review guidance documented in “Standard Review Plan [SRP] for Spent Fuel Dry Storage Systems at a General License Facility,” issued July 2010, requires a thermal evaluation for the spent fuel dry storage system to confirm that the spent fuel cladding temperatures will be maintained below recommended limits throughout the storage period, to protect the cladding against degradation that could lead to gross rupture. The thermal evaluation should identify the boundary conditions for normal, loading, off-normal, and accident conditions. The required boundary conditions include the external conditions on the cask. External ambient conditions that have a major effect on the cask’s thermal performance include ambient temperature, solar heating, relative humidity, elevation, and wind speed and direction.

This appears good until you find out what the assumptions are! And, as inadequate as these assumptions are, the new NUREG seems to want to weaken them further by confusing people. Whether they themselves are confused remains an outstanding question.

The 2010 NRC document to which the NUREG draft refers states that the assumed temperature for these highly radioactive spent fuel casks, which are huge and, in the case of Holtec, seem to have only a 1/2 to 5/8ths inch thick metal sealed container, with an external and vented concrete-metal protection, should be the average high and the average low of the years of record. What are the years of record? There are records in many locations going back to the 1700s. Not so far from Grand Gulf Nuclear reactor, in Natchez, the record temperature is considered 105 F. However, in 1799 one temperature in the sun was 120F [1], far exceeding the 100F which Holtec is allowed to use as an assumption for the dry casks at Grand Gulf near Port Gibson. The 120F was probably in March of 1799, as the other records are for March, which is a cool time of year, half-way between both solstices. It was probably on grass. The NRC assumption seems to be for the shade, and excludes consideration of the dry cask location on concrete, as well as daytime highs and lows and the issue of radial cooling (or not). On sultry summer nights with 100% humidity there won’t be much cooling at Grand Gulf Nuclear Reactor, which is sweltering on a sweating concrete slab near the Mississippi River. The same can be said for quite a few US nuclear reactors. Worse, Grand Gulf was given several “exemptions” because fuel which was more high burnup than it was supposed to be and fuel which was more enriched than supposed to be was packed in the casks.
Grand Gulf on the River

Furthermore, the ambient temperature should be the maximum (and minimum) extremes ever at the location, with contingency, and not the average of the maximums, as the NRC says! The temperature should be of the casks in the sun. However, since the dry casks may be moved, it is probably best to use the US extreme for hot air temperature of 134 F, with the heat of the sun added. The minimum would be minus 70 F. http://en.wikipedia.org/wiki/U.S._state_temperature_extremes
NASA Global Temp 1900 to 2000
Shows temperature increases: 1.8 F is 1 C in this context

The maximum temperature added to the casks by the sun might be determined from the difference between ambient temperature in the shade and that of empty casks in the sun at the summer solstice, after days of sun, in the late afternoon, near the equator (if it didn’t rain), added to the US record of 134 F (plus contingency). If, for instance, it were 108 F in the shade and 176 F on the casks in the sun, then the difference would be 68F. This could be added to the 134 F to be 202 F. If it were to stay in place, then it could be the local max with contingency, but since the casks may move throughout the US, then assumed temp should be 134F plus the temperature added to the cask by the sun plus contingency. Concrete can hold heat for days, even where it is cool at night. The cask itself already has a high temperature because of the spent nuclear fuel.

NASA’s “MODIS measures something different: land skin temperature. LST is a measure of heating of the land surface—where solar energy is absorbed and re-emitted and it is often significantly hotter than air temperature. If you’ve ever walked barefoot across hot sand or pavement on a summer day, you know the difference. The surface beneath your feet feels much hotter than the air around your head. Scientists first measured that difference in June 1915. “Around the same time that the Death Valley record air temperature was measured, an analysis of the temperature conditions of air and soil was conducted in the desert near Tucson, Arizona,” Mildrexler explains. In the midday sun, the temperature 0.4 centimeters below the soil surface was 71.5°C (160.7°F). The air temperature, measured four feet above the ground, was 42.5°C (108.5°F).http://earthobservatory.nasa.gov/Features/HottestSpot/page1.php
Note that the above temperature is earth. Pavement or concrete would be hotter. If it’s really hot you won’t be able to walk on concrete or asphalt barefoot! This point could be especially important for the lids of the underground casks.

According to the US NRC:
(1) Normal Conditions
For a given SNF specification, the primary external conditions that affect DSS performance are the ambient temperatures, insolation, and the operational environment experienced by the DSS.

The NRC accepts as the maximum and minimum “normal” temperatures the highest and lowest ambient temperatures recorded in each year, averaged over the years of record. For the SAR, the applicant may select any design-basis temperatures as long as the restrictions they impose are acceptable to both the applicant and the NRC.” WHO DOES THAT MAKE SENSE TO? ANYTHING GOES AS LONG AS IT MAKES THE NRC AND THE UTILITY OR HOLTEC HAPPY? “If the cask is also designed for transportation, the temperature requirements of 10 CFR Part 71 could determine the design-basis temperatures for storage.

For storage casks, the NRC staff accepts a treatment of insolation similar to that prescribed in 10 CFR Part 71.71 for transportation casks. If the applicant selects another design approach, the alternative approach should be justified in the SAR.

The operational environment experienced by the DSS under normal conditions includes the manner in which the cask is loaded, unloaded, and lifted. Occupational dose rates will, in part, depend on whether the cask is sealed in a wet or a dry environment. Fuel cladding temperatures may also be affected. The manner in which the cask is lifted will determine the load on the trunnions and/or lifting yoke. The orientation of the cask (vertical or horizontal) and its height above ground during transport to the ISFSI will establish initial conditions for the drop accidents discussed below.

Off-Normal Conditions

An applicant’s SAR generally addresses several off-normal conditions. These should include variations in temperatures beyond normal, failure of 10 percent of the fuel rods combined with off-normal temperatures, failure of one of the confinement boundaries, partial blockage of air vents, human error, out-of-tolerance equipment performance, equipment failure, and instrumentation failure or faulty calibration.NUREG-1536 Revision 1Standard Review Plan for Spent Fuel Dry Storage Systems at a General License Facility Final Report Manuscript Completed: July 2010 Date Published: July 2010
Office of Nuclear Material Safety and Safeguards

Thibadeau (2005) found, both experimentally and theoretically, that at 80F, in the sun, concrete was 120F, asphalt 140F, and a dark grey car 152F ; a light bronze car was 144F. http://rack1.ul.cs.cmu.edu/hotcars/ The Holtec overpack is steel-concrete-steel (Holtec 2014, 1-35) covering a steel container and painting seems to be generally gray-military green. Thus, the external temp added might be estimated as around 148F at 80F in the sun, based on the metal. This is 68F hotter than ambient temperature. The US government mentions a hot sidewalk getting up to only 145°F, but fails to discuss the ambient temperature. http://www.loc.gov/rr/scitech/mysteries/friedegg.html

It appears safe to assume that at 105 F, in the sun, that Holtec casks would be exposed to a minimum addition of 173 F (beyond spent fuel temp impact on cask) and probably hotter. For the US record temperature of 134F this would then be 202 F or greater.

In the UK, Armson et. al. 2012 found at air temperatures around 25 C (77 F) that concrete was 40 C (104F) in sun and 28 C (82.4 F) in the shade. It was 17 C (30F) hotter in sun on concrete and 4C (7.2 F) hotter in the shade on concrete. Note that 17 C is apparently an interval, so would be 30F. As a temperature the 17 C would be 62.6F, which is closer to the 60F differential given by Thibadeau. Of related interest: http://www.nhtsa.gov/people/injury/enforce/ChildrenAndCars/pages/Unattend-HotCars.htm

Additionally, Holtec has been trying to reduce cooling circulation within the casks. This was proposed in a recent NRC comment period. This reduced circulation of helium was probably not calculated by this NUREG.

Researchers in the UK found “the surface temperature results for the 4th July 2009 (a), 17th June 2010 (b) and the 3rd July 2010 (c) which were all typical of hot days, being dry and sunny, except for occasional clouds, and with maximum air temperatures between 23.5 ◦C and 25 ◦C. The pattern of surface temperature change was similar on all three days. The concrete surfaces were always hotter than the surrounding air, rising to peaks of around 40 ◦C in the sun, and 28 ◦C in the shade, around 17 ◦C and 4 ◦C higher than peak air temperature. Grass surface temperature was much lower…” (“The effect of tree shade and grass on surface and globe temperatures in an urban area“, by D. Armson , P. Stringer, A.R. Ennos , in Urban Forestry & Urban Greening) The concrete was up to 104 F (40C) in the sun, around 17C [30.6 F as an interval] higher in sun than peak air temp. The max air temp was 77 F (25C). The Natchez temperature record of 105 F plus 30.6 F is 136 F. However, the days which they studied in the UK were dry and sunny, whereas Grand Gulf would be very humid, especially since it’s on the Mississippi River. Note that as an interval the 17C is 30.6 degrees. As an actual temperature it would be 62F, which is closer to what Thibodeau found for concrete, which would give 167F for concrete. We suspect that the difference is time of year and proximity to the equator, and probably concrete type. The UK is far north and simply warmed by the extension to the Gulf Stream. Summer days are long, however.

For metal we can estimate it as a minimum of 173 F. It is important to recall that this would be heat added from the outside. There will be heat coming from the spent fuel, as well.

Wednesday, 29 April 2015, continuation

[Original NRC NUREG proposal for comment in quotes-italics; comments in brackets; additional information is identified and put in quotes-italics where appropriate.]

Proposed NUREG:
2.0 ENVIRONMENTAL VARIABLES
2.1 Introduction
Among the environmental variables that have a major effect on the thermal performance of a spent fuel storage system are ambient temperature, humidity, elevation, and wind magnitude and direction. Solar heating also has some effect and should be considered in the analysis.
” [SOLAR HEATING HAS SOME EFFECT ON THERMAL PERFORMANCE? ONLY SOME EFFECT?!!!!! IT HAS A LOT OF EFFECT ON METAL-CONCRETE FROM WHICH DRY CASKS ARE MADE. These guys are spending too much time in air conditioned offices! Or they are nuts.] “However, solar insolation values are well established and typical values are applied. NUREG-1536 states that, for storage casks, the NRC staff accepts a treatment of insolation similar to that prescribed in Title 10 of the Code of Federal Regulations (10 CFR) Part 71, “Packaging and Transportation of Radioactive Material,” for transportation casks. Since the values specified in 10 CFR Part 71 are considered bounding, solar insolation is not considered in this study, and the investigation focuses only on the other factors (i.e., ambient temperature, humidity, elevation, and wind).” (p. 3)
[The transport rules only consider -29°C (-20°F) and +38°C (+100°F), in the shade, which are not extreme conditions in North America, and are routine temperatures in parts of N. America. They even occur as ambient temperatures in temperate Europe. Temperatures in “Chambres de Bonne” (attic rooms) in Paris are known to have reached at least 106F (measured) and to melt hard plastic (temp unmeasured), when it was around 100F (38 C) outside. One of the US nuclear labs did not even use these limits, but even lower maximums, in their dry cask research study, but that’s another story for another day. There seems to be no insolation for the quasi-permanent dry casks, except to the extent that concrete would help insolate people from the radiation within the casks. Transport, by definition, is temporary and could easily to be shaded, though it may not. In theory, it could even be air-conditioned. It is an inappropriate and inadequate model for casks sitting on concrete in the sun]

Here’s what the NRC rule “Part 71, Subpart F–Package, Special Form, and LSA-III Tests2 § 71.71 Normal conditions of transport” says: “(g) A package must be designed, constructed, and prepared for transport so that in still air at 38°C (100°F) and in the shade, no accessible surface of a package would have a temperature exceeding 50°C (122°F) in a nonexclusive use shipment, or 85°C (185°F) in an exclusive use shipment.

(b) Initial conditions. With respect to the initial conditions for the tests in this section, the demonstration of compliance with the requirements of this part must be based on the ambient temperature preceding and following the tests remaining constant at that value between -29°C (-20°F) and +38°C (+100°F) which is most unfavorable for the feature under consideration. The initial internal pressure within the containment system must be considered to be the maximum normal operating pressure, unless a lower internal pressure consistent with the ambient temperature considered to precede and follow the tests is more unfavorable.
(c) Conditions and tests.
(1) Heat. An ambient temperature of 38°C (100°F) in still air
, and insolation according to the following table:

2) Cold. An ambient temperature of -40°C (-40°F) in still air and shade
“. https://www.law.cornell.edu/cfr/text/10/71.71
http://www.nrc. gov/reading-rm/doc-collections/cfr/part071/full-text.html
[Since the NRC has been known to screw up the laws on its web site, it is best to compare the info to Cornell.

Transport temperatures are inappropriate, because they are only very short-term and could be shaded. What resists for the very short-term, may not be sufficient for short, medium or long term. Apparently insulation, in this context, means concrete, although they do not say. What insulator would help keep dry casks cool on concrete or asphalt, without trees, in sunshine and sweltering heat? Snow? Ice? But, it would quickly melt from the heat of the spent fuel and the sun. They need to put them under an open-sided shed or tent of some type to block the sun. They really should be in a building cooled by solar power air conditioning, with windows for backup.

The 1970s are con0sidered to have been exceptionally cool. Yet, the old USNRC Regulatory Guide from 1977 called for shipping casks designed for more extreme temperatures, even though weather was cooler: “REGULATORY GUIDE 7.8LOAD COMBINATIONS FOR THE STRUCTURAL ANALYSIS OF SHIPPING CASKS, May 1977″:
“Regulatory Position C.1.a of this guide mentions environmental initial conditions. The external thermal environmental limits for which a shipping cask must be designed are stated in Appendix A of 10 CFR Part 71 as being 130°F (540 C) in direct sunlight and -40°F (-40’C) in shade.
http://rampac.energy. gov/docs/nrcinfo/RegGuide_7-5.pdf
NOAA says: “Comparing these decades using our best dataset for climate change analysis, the USHCN, we find that the decade of the 2000s was about 1.5°F warmer than the 1970s. For maximum, minimum, and mean temperature the difference, respectively, was 1.37°F, 1.55°F, and 1.46°F.http://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/climate-normals/1981-2010-normals-data

The proposed NUREG continues with more stupidities]:
However, this definition does not consider seasonal variations that may result in higher maximum and minimum values. In this case, a monthly averaged value may be more appropriate for the hottest months (summer season).” [Huh? This is false. The averages of the maximum of each year would be the highest. Seasonal averages within one year might be higher, depending on which years are included, but overall the highest in any year will be the highest! Whoever wrote this needs to be removed from their job and stripped of their degrees. If it’s not the NRC’s Jorge Solis or Ghani Zigh, both of whom signed off this document, then they are still to responsible.] “Measured monthly temperatures at some sites (ASHRAE, 1997) show that the annual average ambient temperature of 300 Kelvin (K) [80 degree (°) Fahrenheit (F)] could be easily exceeded for about 4 months.” [This is the understatement of the 20th and 21st centuries. Of course it will be exceeded. Firstly it is an average; apparently the mean or arithmetic average. An average will be exceeded, unless every temperature reading is the same. Secondly, because yearly average is irrelevant to the yearly maximum, and the average given for June, July, August runs as high as 85 or more, in places with nuclear reactors. They should not be using the average, anyway, but rather the maximum temperature ever, plus contingency. Then they must add the impacts of sun and humidity and yes, wind. Dew point should be examined, as well.

This is the 30 Day Max Mean 31 Aug. 2014
30 Day Max Mean USA Aug. 2014
90 day Max mean showing that while most Deep South temps were below normal, they were still 85F or even 90 F for last June, July, August.
90 day max mean below normal but still 85, 90 F
Although cooler than normal, the mean (average) of the high and low together for June, July, August 2014 was 80-85F and even 85 -90F in spots.
Mean high and low 90 days still 85 to 90, cooler than norm

Here are the numbers of times that the temp in Vicksburg, fairly close to the Grand Gulf Nuclear Reactor, has exceeded 100 degrees, according to NOAA. Clearly testing for 100F is inadequate and unacceptable. The temperature in the sun would be even greater!
Vicksburg MS temps exceeding 100 F
Holtec Dry Casks are allowed to pretend that the temp is 100F for these Mississippi spent fuel casks, whereas even in the shade this number has been frequently exceeded.
Holtec Dry Casks Grand Gulf Miss
Here is the list of records at Vicksburg:
Vicksburg, MS records NOAA

If these nuclear dry casks were concrete-metal houses with no hot spent fuel and large windows they would be impossible to cool naturally at night, unless the night was very cold, and then only in southern latitudes where the days are shorter. Even then, it would be almost impossible without a fan, unless the windows were left open all night. But these dry casks have no windows. They only have small vents. They need to stop screwing around and put exhaust fans in these things, assuming they are sealed. If not exhaust fans with filters. There is a time-lag for heating and cooling of concrete. Days are shorter but nights not even cool in the southern latitudes where the US has many nuclear reactors-dry casks. They can put solar panels to power the exhaust vents, or even air conditioning-heat for the dry casks.

According to wikipedia: “In warm or humid climates, maintaining thermal comfort solely via natural ventilation may not be possiblehttp://en.wikipedia.org/wiki/HVAC This is somewhat false, depending on construction, but certainly true for the spent fuel casks, even without the hot spent fuel, because they are metal-concrete.

Scotsman, William Dunbar, who took the 1799 Natchez temperature, seems to have been one of the rare people interested in temperature in the sun. Curiosity, education, and logic-common sense have helped make Scots great inventors. http://en.wikipedia.org/wiki/William_Dunbar_(explorer)

From NOAA: “The vast majority of weather stations utilized in the 1981–2010 Climate Normals only routinely report air temperature and precipitation. A smaller set of stations have fairly complete records of additional variables such as dew point temperature, sea level pressure, and wind speed and direction. For 262 first order stations, we provide hourly normals of temperature, dew point temperature, heat index, wind chill, heating and cooling degree hours, sea level pressure, and windhttp://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/climate-normals/1981-2010-normals-data Too ridiculous that they can’t bother to do more testing, in this day and age.

Rather ironically, and unlike the US NRC, and Holtec, who appear hell-bent on killing everyone and everything through stupidity or malicious intent, the 1950s military didn’t want its people to die, so invented (or probably re-invented) a more complex system. At least this level of complex analysis is needed. Instead the NRC delivers exemptions to Holtec and other stupidities too long to name or even recall.
The wet-bulb globe temperature (WBGT) is a composite temperature used to estimate the effect of temperature, humidity, wind speed (wind chill), and visible and infrared radiation (usually sunlight) on humans. It is used by industrial hygienists, athletes, and the military to determine appropriate exposure levels to high temperatures.
http://en.wikipedia.org/wiki/Wet_Bulb_Globe_Temperature
The WetBulb Globe Temperature (WBGT) is a measure of the heat stress in direct sunlight, which takes into account: temperature, humidity, wind speed, sun angle and cloud cover (solar radiation). This differs from the heat index, which takes into consideration temperature and humidity and is calculated for shady areas. If you work or exercise in direct sunlight, this is a good element to monitor. Military agencies, OSHA and many nations use the WBGT as a guide to managing workload in direct sunlight.http://www.srh.noaa.gov/tsa/?n=wbgt Formulas are found here: http://www.hse.gov.uk/temperature/heatstress/measuring/wetbulb.htm

The limitations of the WBGT are low air movement and high humidity which are most certainly problems with the dry casks:
WBGT’s most serious limitation is that environments at a given level of the index are more stressful when the evaporation of sweat is restricted (by high humidity or low air movement) than when evaporation is free“. “J Sci Med Sport. 2008 Jan;11(1):20-32. Epub 2007 Aug 31. Wet-bulb globe temperature (WBGT)–its history and its limitations.” Budd GM.http://www.ncbi.nlm.nih.gov/pubmed/17765661 [For dry casks this low air movement and high humidity is an issue for inadequate heat removal, but also material sweating and corrosion. Many, or even most, of the nuclear reactors are close enough to the ocean to have chloride induced corrosion-degradation issues too. Mold induced degradation is probably an issue at the sites, especially as mold is highly radiation resistant.]
Figure 36:  NADP Deposition Maps of NaCl
Figure 36: NADP Deposition Maps of NaCl
Author U.S. Navy photo by Gary Nichols
English: PENSACOLA, Fla. (May 24, 2010) Cryptologic Technician (Technical) Seaman Antron Johnson-Gray, a student at the Center for Information Dominance (CID) Corry Station, checks the wet bulb globe temperature meter, or WBGT meter, at Corry Station. The WBGT index indicated the base would be flying the black flag for the first time in 2010, indicating vigorous outdoor exercise, regardless of conditioning or heat acclimatization, is not advisable. (U.S. Navy photo by Gary Nichols/Released)

From the proposed NUREG: “An ambient temperature of 300 K (80°F) is typically considered in the thermal evaluation for most of the dry casks certified by the NRC. However, the measured ambient temperatures suggest that, to bound all sites, the SAR thermal evaluation should consider seasonal variations since, during the hot months, the dry cask reaches a new steady state that the SAR has not analyzed.” [We should be very, very scared]. “This study considered variations in the ambient temperature in the range of 300 to 322 K (80 to 120°F), which seems to envelope the natural variation of the ambient temperature during the hot season, according to measured data.” [Well, no they don’t seem to have considered it except for low speed wind. And, the low speed wind issue seems to be a false debate. They need solar powered exhaust fans and open sided sheds to cover the casks from the sun or solar powered air conditioned sheds, would be better. Roof Vent Turbines would be a huge improvement over nothing, though may still be inadequate in some climates: http://wiki.smc.org.in/index.php?title=Roof_Vent_Turbines,_is_it_affordable_? ]

2.3 Humidity
Traditionally, the thermal evaluation for design certification assumes dry air, which is conservative, since humidity will increase the air thermal conductivity and heat capacity.

[Conservative? Conservative is less safe now? Whose stupid “tradition” is this? Since humidity makes it hold more heat then it is important! More on their misunderstanding of the humidity issue further below.]
Therefore, this study considers relative humidity in the range of 0 to 90 percent for ambient temperatures of 300 and 323 K (80 and 120°F).” [Sounds maybe ok except they seem to only be discussing wind as ventilation.] “However, high relative humidity values do not seem to persist for the prolonged periods of time necessary for the dry cask to reach a new steady state.” [THEY ARE STARK RAVING LUNATICS! IT IS HOT AND HIGHLY HUMID (often 100%) FOR MANY OF THESE SITES.]
Therefore, this study assumes that dry air will continue to be an adequate approach, a slightly conservative assumption, as demonstrated in this evaluation.
[IS THIS A SICK JOKE? THE NRC NEEDS TO BE SHUT DOWN. THEY ARE MORE MAD THAN MAD HATTERS.]

Friday, 1 May 2015 update

As noted in the introduction, this NUREG appears a hoax. The name implies that it will be a thorough evaluation, whereas it seems mostly to evaluate low level wind. Zigh and Solis (NRC authors) appear most concerned with the impact of wind on underground dry casks, which seem to be in the minority, if they exist yet at all. Parameters such as the impact of sun on an underground dry cask lid; and impact of soil-rock type and depth on underground temperature and the casks appear ignored. Some were to be stacked underground, which would impact temperature.

But having such a comprehensive title and scope may allow them to pretend that these topics have been addressed. Here is the title and scope:
Impact of Variation in Environmental Conditions on the Thermal Performance of Dry Storage Casks, Draft Report for Comment NUREG-2174
“1.1 Scope
This document evaluates the thermal impact of varying environmental conditions on spent fuel dry storage casks. The primary goal is to examine the natural variation of the major environmental factors (ambient temperature, wind conditions, and elevation, among others) that could lead to higher spent fuel cladding temperatures as compared to the bounding thermal evaluation provided in SARs. The evaluation includes different designs to determine how the parameters considered in the evaluation affect the thermal performance of a specific design. The majority of dry storage casks that have been certified or are currently under review by the NRC include vertical and horizontal casks located aboveground and vertical underground casks (located mostly underground, except for the cask lid). Therefore, to include most of the certified designs, the study considered three casks: vertical aboveground, horizontal aboveground, and vertical underground.
” (p.1)

Here are some heat parameters which do not match up. It seems that the NUREG draft may have taken an average of the 2000 version (Holtec HI STORM 100) and the 2014 version (Holtec HI STORM FW). This would not seem acceptable. The MPCs were supposed to be interchangeable within the various overpacks, from our understanding. Also, how did the kW go up so high within the same model? An exemption? A change in size? More parameters (size, etc.) may be found in these Holtec documents, which are hundreds of pages long. There is also a 2010 version which we just found online.

Table 1.2.2 KEY PARAMETERS FOR HI-STORM 100 MULTI-PURPOSE CANISTERS (MPC)
Total heat load, max. (kW) [PWR] 20.88 kW (MPC-24) [BWR] 21.4 kW (MPC-68)
HI-STORM FSAR Rev. 0 REPORT HI-2002444 1.2-24 FINAL SAFETY ANALYSIS REPORT for the HOLTEC INTERNATIONAL STORAGE AND TRANSFER OPERATION REENFORCED MODULE CASK SYSTEM (HI- STORM 100 CASK SYSTEM) DOCKET 72- 1014 VOLUME I OF II (2000)http://pbadupws.nrc.gov/docs/ML0724/ML072420254.pdf

Tables 1.2.2, 1.2.3, 1.2.4, pp. I 51-53, say PWR max total heat load is 47.05 kW (MPC 37; 37 cells); and BWR (MPC 89; 89 cells) is 46.36 kW. Found in “FINAL SAFETY ANALYSIS REPORT ON THE HI-STORM FW MPC STORAGE SYSTEM, Holtec Project 5018 Holtec Report No. HI-2114830 Safety Category: Safety Significant, Revision 2″, February 18, 2014 http://pbadupws.nrc.gov/docs/ML1405/ML14052A369.pdf

NUREG draft (NRC: Zigh and Solis) (p. 10):
Table 4-3 Decay Heat Values for Analyzed Casks Cask Type Decay Heat (kW):
HI-STORM 100 34 kW (Holtec)
HI-STORM 100U 36.9 kW (Holtec)
Standardized NUHOMS 24 kW(Areva)
Advanced NUHOMS 24 kW(Areva)

Where in this NUREG is discussion of the impact (and causes) of degradation on structural-mechanical integrity of multi-purpose canisters and the overpack? Routine readers know by now: neutron embrittlement; possible hydrogen attack; corrosion, exacerbated by salt in the air, even some distance inland, will all impact the strength and integrity of the dry casks, over time. For dry casks there would also be the issue of dampness, fog, condensate from high humidity levels and their impacts on corrosion and even mold. Mold could damage concrete and is radiation resistant. Dew Point seems important in this context.

Saturday, 2 May 2015

Holtec states that “The MPC external diameters are identical to allow the use of a single overpack design, however the height of the MPC, as well as the overpack and transfer cask, are variable” (p. 1-22) This apparently is how they are putting more fuel rods and more kW heat, but they do not seem to be making the MPC thicker. Rather it seems to remain the flimsy one half inch thin. (see p. 3-39, Holtec 2014).

The MPCs are made of the following steel types:
* Type 316 * Type316LN * Type 304 * Type 304LN (p. 1-37)
http://en.wikipedia.org/wiki/SAE_steel_grades

In physics, thermal conductivity (often denoted k, λ, or κ) is the property of a material to conduct heat… In alloys … thermal conductivity increases with temperature, often proportionally to temperature.http://en.wikipedia.org/wiki/Thermal_conductivity

The Zigh and Solis NUREG draft on p. 26 says that “The rest of the specified boundary conditions to perform the wind analysis are summarized below:” “ambient temperature of 300 K (80°F)” They claim that they assumed “no solar insolation (nonconservative assumption but irrelevant to the temperature differential)“, but do not tell what temperature they assumed for this, nor why it would not be relevant. It would be very relevant.

The most silly assumption of all is that cool air will enter the vents at the bottom of the casks, when the casks are sitting on concrete or asphalt, uncovered. Where was the consideration of this point? Heat from the concrete-asphalt will radiate up, especially after sunset and as ambient temperature drops. While this will probably be cooler than the spent fuel, it won’t be very cool. Plus, any serious ventilation needs to be cross ventilation. Common sense suggests a solar powered fan, as well.

Furthermore, Zigh and Solis (NRC-NUREG) cheat in their model: “The four vents in the bottom and top of the cask, respectively, were represented by one continuous inlet at the bottom and one continuous outlet at the top.” (p. 27)
Cask vents

They can’t change the venting system like that in the model, without changing it in reality! Obviously this will increase air flow. A continuous inlet will let in more air! As noted yesterday, the fuel temperature modeled is not the same as the newer Holtec specifications, either, but is much less.

A most important point remains that heat diffuses toward a new equilibrium and if it is hot outside, the spent fuel won’t cool very much. “Heat transfer always occurs from a region of high temperature to another region of lower temperature.http://en.wikipedia.org/wiki/Heat_transfer
As the second law of thermodynamics shows, in an isolated system internal portions at different temperatures will tend to adjust to a single uniform temperature and thus produce equilibrium.http://en.wikipedia.org/wiki/Entropy#Energy_dispersal

Ventilation or a fan could speed up air exchange and the fan cool the air to some extent, but there won’t be much cooling in hot weather, period. They should really put them inside and cooled with air conditioning generated by solar panels. (The “them” that needs to be in AC are the casks. The NRC workers apparently need to learn what no AC means.)

From the NUREG draft:
3.0 GEOMETRY AND METHOD OF ANALYSIS
3.1 Vertical Aboveground Designs

In a vertical-ventilated aboveground spent fuel storage cask design, a spent fuel canister is typically stored in a concrete overpack, with the canister bottom resting on some type of base normal to the ground. Air vents are located in the bottom and top of the overpack, so air can flow freely through the gap between the canister and the overpack to cool the canister’s outer surface, thus keeping the cladding temperature below Standard Review Plan (SRP)-recommended limits (NUREG-1536, 2010). Since the inlet and outlet air vents are separated by the cask’s height, thermal mixing due to low-speed wind may not have an impact on the cask’s thermal performance because of the physical separation of the air vents. This separation will prevent hot air coming from the outlet vents to mix with the cooler air at the bottom of the cask. Also, hot air coming out of the outlet vents will tend to flow up into the ambient air surrounding the cask. However, low-speed wind could block the air vents, which could have an impact on the cooling effect by reducing the mass flow rate through the annular gap. Therefore, this study includes this cask to determine the effect of other environmental factors and to conclusively determine how low-speed wind affects this design.” (p.5)

[Where is consideration of underground temperature? There won’t be much cooling in hot weather by venting out the top!]
3.2 Vertical Underground Designs

In an underground design, the canister is stored inside some type of enclosure that is buried almost entirely, except for the overpack lid, which is located aboveground and includes the air vents. In this design, air needs to flow downwards into the enclosure container and then upwards in contact with the canister’s outer shell. Decay heat from the spent fuel assemblies stored in the canister is thus dissipated through the canister’s outer wall by a combination of convection, radiation, and conduction to flowing air. Finally, hot air exits through the outlet vent, which is located on top of the cask lid. For this design, the inlet and outlet vents are located in proximity to each other. These design features represent a challenge from the analysis point of view since, in addition to the typical environmental factors used in the thermal evaluation (e.g., ambient temperature, ambient pressure), the analysis must include other factors such as low wind speed. This increases both the complexity and the computational times, since usually three-dimensional (3-D) thermal models are needed to properly capture the heat transfer and flow characteristics of this design.” (p.5)

[peak cladding temperature (PCT)]

[This is interesting and damning, even though they used a kW value far lower than Holtec’s 2014 specs say:]
4.8.4 Aboveground Vertical Cask Axisymmetric Model

The study used an axisymmetric model to investigate the effect of the ambient temperature, using steady-state simulations. Table 4-19 shows the effect of the ambient temperature on the predicted PCT in the dry storage cask. The PCT increases by 8 K (14.4°F) for every 5.6 K (10°F) increase in the ambient temperature.

In the transient analysis, used to study the effect of ambient temperature, the initial condition set the ambient temperature at 300 K (80°F). Then the ambient temperature was suddenly changed to 322 K (120°F). As shown in Tables 4-20 and 4-21, 95 percent of the PCT change between 300 and 322 K (80 and 120°F) was reached after 7 days.

The effect of elevation was investigated using a steady-state analysis based on the axisymmetric model. The analyses varied the elevation from 0 to 1500 m (0 to 4921.5 ft). As the elevation is increased, the air density decreases due to the decrease in the ambient pressure. As a result, the mass flow rate decreased and the PCT increased. As shown in Table 4-22, the PCT increases by about 6 K (11°F) for every 500 m (1640.5 ft) of increased elevation.

To study the effect of heat load, steady-state analyses, based on the axisymmetric model, varied heat loads in the range of 20 to 34 kW. As the decay heat increased, the PCT also increased. As shown in Table 4-23, the PCT increases by about 22 K (40°F) for every 2 kW increase in heat load.” (p.35) [Here we need to calculate the difference in the kW they used and the kW Holtec says, but have no time right now. Maybe tomorrow.]

p.39 Transient scenario NUREG draft
p.39 Transient scenario

Heat transfer always occurs from a region of high temperature to another region of lower temperature“. http://en.wikipedia.org/wiki/Heat_transfer
As the second law of thermodynamics shows, in an isolated system internal portions at different temperatures will tend to adjust to a single uniform temperature and thus produce equilibrium.http://en.wikipedia.org/wiki/Entropy#Energy_dispersal

LEE Boon-ying Hong Kong Gov Weather Education Thermal Conductivity Water Vapour
the [thermal] conductivity of water vapour is actually much less than that of dry air. So, if humidity (i.e. water vapour) has any effect on the conductivity of air, it would make it less conductive, not more.http://www.weather.gov.hk/education/edu06nature/ele_air_e.htm
steam does not transfer heat as well as liquid water,…http://en.wikipedia.org/wiki/Boiling_water_reactor

Thus, this is mostly false: “The effect of ambient air humidity was investigated using a steady-state analysis based on the axisymmetric model. The analyses were performed at ambient temperatures of 300 K (80°F) and 323 K (120°F) with a relative humidity of 0, 50 percent, 70 percent, and 90 percent. As the humidity increases, the ambient air contains more water vapor. As water vapor has larger thermal conductivity” [We just saw that water vapour has less thermal conductivity. In the second half of the sentence they say:] “and heat capacity than dry air, more heat is absorbed from the cask by humid air.” [It has more heat capacity but it’s already full of the heat! So this appears a faulty assumption. See:
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase.html ]

[Thus, these assumptions suggest that the worse case scenario might be worse than what they have presented above:] “As such, the PCT will decrease as the relative humidity is increased for both ambient temperatures considered in this study.” [NOT!] “At an ambient temperature of 300 K (80°F), the PCT decreased by 0.6 K (1°F) for every 20 percent increase in the relative humidity (in the 50 to 90 percent range). At an ambient temperature of 323 K (120°F), the PCT decreased by 2.2 K (4°F) for every 20-percent increase in relative humidity (in the 50 to 90 percent range). The rate of decrease in the predicted PCT is higher for the ambient temperature 323 K (120°F) case than for the ambient temperature 300 K (80°F) case because of the higher moisture content change for every 20 percent change in relative humidity in the latter, as shown in Tables 4-24 and 4-25“. [THIS GOES AGAINST COMMON SENSE PLUS THERMODYNAMICS. They need to reevaluate all for both assumptions and kW imputs.]

Sunday, 3 May 2015

[Temperature intervals: 22 Kelvin [K] is 22 Celsius [C} is 39.6 Fahrenheit [F] http://en.wikipedia.org/wiki/Kelvin%5D

As seen yesterday on Table 4.17, the Zigh-Solis-NRC NUREG draft was based on an assumption of a maximum of 34 kW. However, as already seen, HOLTEC (2014) gives 47.05 kW for PWR and 46.36 kW for BWR as maximums.

According to the NUREG draft PCT (Peak Cladding Temperature) increases by 22 K (Kelvin) or approximately 40 F (actually it is 39.6 F and should not be rounded) for every 2 kW of additional heat load.

Holtec’s 47.05 kW exceeds the NUREG draft max of 34 kW by 13.05 kW, which divided by 2 kWs is 6.25 and multiplied by 22 degrees K [C] gives an underestimate of 143.55 K [C]; multiplied by 39.6 gives 247.5 degrees F underestimate. This is excluding any other underestimates coming from faulty assumptions, such as falsely making humid air a cooling factor.

Table 4.17 has day 21 peak cladding temperature as 886.7 K. Plus the 143.55 K gives a total of 1030.25 K, which minus 273.15 is 757.1 degrees Celsius [C} and 1394.78 degrees F.
Their peak temperature day 21 of 886.7 K was 613.55 C or 1136.39 degrees F. This gives a difference of around 258.39 F. Something was apparently lost in rounding and conversions but the difference is in the range of 248 to 258 F. The maximum service temperature for 316 steel is around 870 C or 1598 F. Were Holtec and the NUREG considering the hotter high burnup fuel? [We were taught to wait to the very end to round and then it should be two digits beyond the decimal. This decreases error. The NRC appears not to have been taught this. Also the unnecessary use of Kelvin introduces error. Also, why even use Celsius in the US? Fahrenheit is more precise. Each conversion introduces error. Except for science class no one uses Celsius in the US.]

Also they state that the PCT increases 14.4 F for every 10 F ambient temp. The max which they seem to have considered was 120 F, and due to faulty assumptions re humidity may be the equivalent of less hot.

Their Peak cladding temp on day 21 is around 1136.39 F plus 258.39 F due to the underestimation in kW is 1394.68. 1598 F is the approximate maximum service temp for 316 steel. The difference is 203 F. There is a minimum of 100 F estimated as solar heat, leaving a margin of 103 F. Due to the 14.4 F increase of cladding temp for each 10 F increase in outside temp, an extra 72 or 73 F from ambient temperature or the sun could result in exceeding the maximum service temperature for new 316 steel.

Unknown margins are lost due to their inverted assumption regarding humidity. Also, altitude may matter.

Late Sunday 3 May -Early Monday 4 May Update

After reading the above, you should see the intro in a new light.
1.0 INTRODUCTION

The U.S. Nuclear Regulatory Commission (NRC) certifies spent fuel dry storage systems according to Title 10 of the Code of Federal Regulations (10 CFR) Part 72, “Licensing Requirements for the Independent Storage of Spent Nuclear Fuel, High-Level Radioactive Waste, and Reactor-Related Greater Than Class C (GTCC) Waste.” The review guidance documented in “Standard Review Plan [SRP] for Spent Fuel Dry Storage Systems at a General License Facility,” issued July 2010, requires a thermal evaluation for the spent fuel dry storage system to confirm that the spent fuel cladding temperatures will be maintained below recommended limits throughout the storage period, to protect the cladding against degradation that could lead to gross rupture. The thermal evaluation should identify the boundary conditions for normal, loading, off-normal, and accident conditions. The required boundary conditions include the external conditions on the cask. External ambient conditions that have a major effect on the cask’s thermal performance include ambient temperature, solar heating, relative humidity, elevation, and wind speed and direction.” [This sounds good but they haven’t done it or not properly.]

The cask’s thermal evaluation generally assumes a set of fixed environmental factors (e.g., average annual ambient temperature, quiescent conditions, sea level) that will bound all sites in the continental United States.” [dangerously wrong approach.] “However, for some sites, using average values may not be adequate, because more adverse ambient conditions could exist for prolonged periods of time (for example, more than a month, as reported by the National Oceanic and Atmospheric Administration (NOAA) (NOAA Web site, http://www.noaa.gov) and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) (ASHRAE, 1997)), allowing a storage system to reach new steady-state conditions that could result in higher spent fuel cladding temperatures as compared to the steady-state conditions analyzed in the applicant’s safety analysis report (SAR) for normal conditions of storage.For cases with small thermal margin, these adverse ambient conditions could result in peak cladding temperatures (PCTs) being higher than the SRP-recommended limits, which could create thermal conditions such that spent fuel could degrade and lead to gross rupture.” [TRUE, but it must be properly evaluated.]
The 10 CFR Part 72 licensing requirements mandate that storage systems be designed to allow ready retrieval of spent fuel, high-level radioactive waste, and reactor-related GTCC waste for further processing or disposal. Therefore, to comply with the applicable regulations for safe storage of spent nuclear fuel, the thermal design of a dry storage cask should demonstrate that temperatures are kept below recommended limits by considering all factors that may have an impact on the cask’s thermal performance.” [The NRC has given permission to the utilities to store broken fuel in Arkansas and almost certainly elsewhere, with Holtec’s Kris Singh’s encouragement. A special facility may have to be built to transfer broken fuel in the future at each location which will be costly. Moving broken fuel is dangerous. The casks are known to have life limits and the life is probably much shorter. ]

Correction-update regarding temperature in sun

Thibadeau (2005) found that at 80F, in the sun, concrete was 120 F, asphalt 140 F, and a dark grey car 152F ; a light bronze car is 144F: http://rack1.ul.cs.cmu.edu/hotcars/ The Holtec overpack is steel-concrete-steel (Holtec 2014, 1-35) covering a steel container and painting seems to be generally gray-military green. Thus, the external temp added might be estimated as around 148F at 80F in the sun, based on the metal. This is 68F hotter than ambient temperature. The US government mentions a hot sidewalk getting up to only 145°F, but fails to discuss the ambient temperature. http://www.loc.gov/rr/scitech/mysteries/friedegg.html
These are rough estimates. While there are formulas given at the edu link, it would also be necessary to take into consideration proximity to equator, time of year (proximity to solstice), time of day, the layering effect of metal, air, metal, concrete, metal, and the temperature of the spent fuel radiating from the inner casks.

It appears safe to assume that at 105 F, in the sun, that Holtec casks would be exposed to a minimum addition of 173 F (beyond spent fuel temp impact on cask) and probably hotter. For the US record temperature of 134F this would then be 202 F. In the UK, Armson et. al. 2012 found at air temperatures around 25 C (77 F) that concrete was 40 C (104F) in sun and (82.4 F) in the shade. It was 17 C (30F) hotter in sun on concrete and 4C (7.2 F) hotter in the shade on concrete. Note that 17 C is apparently an interval, so would be 30F. As a temperature the 17 C would be 62.6F, which is closer to the 60F differential given by Thibadeau. Of related interest: http://www.nhtsa.gov/people/injury/enforce/ChildrenAndCars/pages/Unattend-HotCars.htm

Additionally, Holtec was trying to reduce cooling circulation within the casks which will impact internal temps.

Monday 4 May update Humidity

By inverting their humidity assumptions, they may have further underestimated peak cladding temperature by unknown amounts. The amounts are unknown, in part, due to their other faulty assumptions. They falsely state: “As such, the PCT will decrease as the relative humidity is increased for both ambient temperatures considered in this study. At an ambient temperature of 300 K (80°F), the PCT decreased by 0.6 K (1°F) for every 20 percent increase in the relative humidity (in the 50 to 90 percent range).” [Since this was calculated upside down the opposite is probably true, meaning that at 80F and 100% humidity, the temp would be about 3.5 degrees F or higher. However, more may be lost by temperature conversions which are not carrying out to enough decimal points, and rounding up far too soon. While this seems negligible, the impact of higher temperatures in the sun, or shortly after sunset would need to be examined. The dew point; the metal, all make this rather complicated to figure out if they were not figuring out upside down. Also, they have understated the kW of the spent fuel. When would that 80F and 90 to 100% humidity be in the Deep South? It would be overcast during cooler parts of the year.

According to their inverted calculations, their underestimate could go as high as 8 F with 120 F and 90% humidity. What would be the temperature and humidity in the sun on a hot day on the casks? Who knows? We are too tired and fed up with the lazy fat-salaried incompetent team of Solis and Zigh, authors of this NUREG draft, to even think about it in depth right now and can only think that they need to be fired and sent to clean up WIPP or Fukushima, as penance. We would be nastier if this had not already been re-blogged.]

They falsely state that “At an ambient temperature of 323 K (120°F), the PCT decreased by 2.2 K (4°F) for every 20-percent increase in relative humidity (in the 50 to 90 percent range).” [At higher temperatures the upside down nature of their assumptions could become even more problematic.] “The rate of decrease in the predicted PCT is higher for the ambient temperature 323 K (120°F) case than for the ambient temperature 300 K (80°F) case because of the higher moisture content change for every 20 percent change in relative humidity in the latter, as shown in Tables 4-24 and 4-25“. [WRONG! WRONG! WRONG! THIS GOES AGAINST COMMON SENSE PLUS THERMODYNAMICS. They need to reevaluate all for both assumptions and kW imputs.]

Some Summary Points (8 May)

“Impact of Variation in Environmental Conditions on the Thermal Performance of Dry Storage Casks” http://www.regulations.gov/#!documentDetail;D=NRC-2014-0273-0001 ID: NRC-2014-0273-0001

This important topic, with potentially deadly repercussions, must be redone properly. It does not reflect its title or scope and what it does address is incomplete and often wrong.

It calculates max heat load as 34 kW (p. 10) whereas Holtec, 2014, gives it as 47.05 kW, which is 13.05kW higher, leading to a peak fuel cladding (PFC) temp approximately 258 F higher than stated. This is based on: “To study the effect of heat load, steady-state analyses, based on the axisymmetric model, varied heat loads in the range of 20 to 34 kW. As the decay heat increased, the PCT also increased. As shown in Table 4-23, the PCT increases by about 22 K (40°F) for every 2 kW increase in heat load.” p. 35. Actually 22 K is 39.6F. 13.05 divided by 2 and multiplied by 39.6 is 258 F. They also stated that the PCT increases 14.4 F for every 10 F ambient temp. The US historical max is 134 F in the shade and not 120F. This would thus be an additional 20.16 F PCT, making 278 F. Failure to consider sun means the PFC temp may be 100 F or higher than stated. This would make an underestimation of at least 358 F to 378 F. Table 4.17 day 21 PCT is approx. 1136.39 F plus 378 F is 1514.39 F. The service temp 316 steel is around 1598 F. In reality, the 83.6 degree difference is probably non-existent because the influence of the sun would probably be much greater than 100F at higher temperatures; temperature conversions and rounding too soon have led to inaccuracies. Humidity leads to higher cladding temperatures, not lower, which also eats into the margin. They have also incorrectly modeled the vents, making them larger than they are in reality. This also eats into the margin.

These casks have metal exteriors and sit in the sun on concrete or pavement. 120 F does not consider this. 120 F can be ambient temperature in shade. Low level wind is a bogus concern.

The authors do not model real vent size for the casks. They pretend vents extend across top and bottom, which is false: “The four vents in the bottom and top of the cask, respectively, were represented by one continuous inlet at the bottom and one continuous outlet at the top. (p. 27) The larger vents would mean better cooling than really occurs. For underground casks it fails to consider ground temp and impact of sun on lid and cask stacking. Holtec wants reduced helium circulation and broken fuel. This does not seem modeled. Was high burn-up fuel considered?

Humidity is modeled backwards. Humid air will make the casks more difficult to cool. The humidity has already absorbed heat, which is why it is in vapor form. It is why there are nuclear reactors – to boil water. Lack of common sense and basic thermodynamics by the authors is frightening: “the [thermal] conductivity of water vapour is actually much less than that of dry air. So, if humidity (i.e. water vapour) has any effect on the conductivity of air, it would make it less conductive, not more.http://www.weather.gov.hk/education/edu06nature/ele_air_e.htm
steam does not transfer heat as well as liquid water,…http://en.wikipedia.org/wiki/Boiling_water_reactor

With errors corrected the temperatures may exceed service temperature of new steel casks. With radiation and corrosion induced material degradation the risk of exceeding it increases.

Evaluations for sun need to be near summer solstice and in the hottest month (or modeled in this way).

This is not even as sophisticated as WetBulb Globe Temperature (WBGT), which takes into account: temperature, humidity, wind speed, sun angle and cloud cover (solar radiation). Limitations of WBGT are low air movement and high humidity which are problems with dry casks and their small, poorly place vents and waterfront locations.

The lazy incompetence of this document could result in many deaths and abandonment of large sections of America. It’s not to be played around with like it’s a joke. They need to get competent people to work on this. The Federal government pays well. Even welfare to work people are expected to work.

It says peak cladding temperature (PCT) increases 14.4F per 10F ambient temp. 80F in the sun metal adds approx. 68F, making temp 148 F. 100 F plus sun would add 168F and probably more from outside. Using the 14.4 to 10 ratio the spent fuel would be 100 F hotter (or more) US max of 134 F plus sun plus humidity plus contingency needs to be correctly modeled.

Table 4.17 day 21 PCT is 886.7 K (minus 272.15: 613.55 C / 1136.39 F) plus 258 F fuel temp kW underestimation is 1391.39 F; solar underestimation of 100 F or more is 1491.39 F plus, which is dangerously close to 316 steel max service temp of 1598 F (800 C) and can easily be exceeded by sun. As seen above with fuel temp kW underestimation and 120 F plus sun there is an underestimation of at least approx. 358 F. If calculated as 134 F, would be at least 378 F. 1136.39 F plus 378 F is 1514.39 F. This is 84F under the max service temp if 1598 F which is dangerously close. The impact of the sun’s heat is probably much higher at 120F or 134F as compared to 80F. They have incorrectly calculated the influence of humidity as well. Who knows what else?

The NRC authors are clueless re averages. Averaging the maximum temperatures for each year will be a higher number than averaging within summer months. The all time max in the sun, however, is the right number to use, plus contingency.

In the midday sun, the temperature 0.4 cm below soil surface may be 161°F, when air temp 4 ft above ground was 108.5°F in Arizona. (NASA) http://earthobservatory.nasa.gov/Features/HottestSpot/page1.php This is soil. Concrete is hotter. This has not been considered for the underground cask lids or lower vents of above ground casks.

The transport rules discussed only consider -29°C (-20°F) and +38°C (+100°F), in the shade, which are not extreme conditions in North America, and are routine temperatures in parts of N. America. The record maximum in the US is 134 F and the record minimum is minus 70.

Transport temperatures are inappropriate, because they are only very short-term. The old NRC Reg Guide from May 1977 called for 130°F (54 C) in direct sunlight and -40°F (-40’C) in shade. The decade of the 2000s was about 1.5°F warmer than the 1970s.

This should have been done in Fahrenheit, as it is more precise and is the temperature scale of choice in the US, outside science class. Also, rounding should not be until the end of calculation and numbers should be written at least two to the right of the decimal point. Error enters in from temperature conversion and early rounding. [Some numbers don’t match in this post either due to conversions.]
…………………..
1799 temp reference: [1] HISTORY OF WEATHER OBSERVATIONS Natchez, Mississippi 1795 – 1955, January 2006 Prepared by: Gary K. Grice Information Manufacturing Corporation Rocket Center, West Virginia This report was prepared for the Midwestern Regional Climate Center under the auspices of the Climate Database Modernization Program, NOAA’s National Climatic Data Center, Asheville, North Carolina
Some links which may be useful: http://en.wikipedia.org/wiki/Attic_fan http://en.wikipedia.org/wiki/Thermal_wind http://en.wikipedia.org/wiki/HVAC

We apologize for any mathematical errors which may be found. We do the best that we can with little time, sometimes little sleep (and zero salary). The general points still stand, regardless.