Wednesday, March 26, 2008
This article by a Badger Herald staff writer Sam Clegg supports nuclear in the context of recent state Assembly discussions regarding (lifting) the effective ban on new nuke in Wisconsin. Of course, the Republican majority passed on a bill only to fail to reach the (Democrat led) Senate floor.
In response to the article, a future teacher of America wrote this article. Suffice it to say I would not feel comfortable with the author being my own science, English, or geography teacher.
Finally, our ANS section's Public Information Officer lent his response to our teacher-in-training.
For each article, some pretty good debate has arisen; moreover, much of it has been pro-nuke.
The program agenda can be found here. Video of the event can be found for the morning and afternoon portions.
The day presented a lot of good information, and if I weren't running on fumes, I would expound a bit on what was said...
Tuesday, March 25, 2008
CNN Money has more details here.
I especially like the fund manager's viewpoint,
"Since 2001, nuclear power plants have achieved lower production costs than coal, natural gas and oil ... We believe higher oil prices, rising standards of living, and demand for cleaner sources of energy are favorable trends powering worldwide growth for the nuclear energy industry. The PowerShares Global Nuclear Energy Portfolio provides investors exposure to the performance of the global nuclear energy industry in the benefit-rich ETF format."
Sunday, March 23, 2008
Burnup credit is the process of taking into account the reduction in reactivity due to irradiation of nuclear fuel (i.e. burnup). The reactivity is decreased via a net reduction of fissile isotopes and the introduction of parasitic neutron absorbers (i.e. non-fissile actinides and fission products).
The paper opens with a discussion of burnup credit and the varying degrees to which it has been implemented. For years, regulations called for the "fresh fuel" assumption. That is to say, when doing safety calculations for used fuel, the fuel was assumed to be unirradiated--which is a grossly conservative assumption! More recently, regulatory guidelines state the major actinides (i.e. changes in U and Pu) can be considered.
However, even these new guidelines neglect the roughly one-third of the possible decrease in reactivity produced by fission products (e.g. Sm-151, Rh-103). If a high-capacity, 32-assembly cask were to be used for shipping and containment, neglecting these fission products allows for only about 30% of current used fuel to be put in such containers; however, and the key point, up to 90% of such fuel could be shipped if we could account for all relevant fission products. The financial ramifications are huge: $156 million is a target minimum savings if we could actually move that much fuel around in these casks.
Thus, the goal is to strive toward guidelines allowing full burnup credit (i.e. accounting for ALL the reduction in reactivity).
Two problems exist: 1) we need better data that says exactly how much negative reactivity a given isotope introduces and 2) we need to know better exactly how much of said isotope is present in used fuel.
The first problem deals largely with our nuclear data and the nuclear codes we use for analysis. Essentially, we need to analyze our database of critical experiments that analyze the specific isotopes of interest with respect to their effect on reactivity. However, we can't just use any old critical experiments--they must be similar to our application, namely the cask and used fuel of interest. ORNL currently is evaluating some foreign experiments for this "similarity" or "applicability"; Sandia has performed one such experimental suite to probe Rh-103 specifically.
While this data all looks pretty good right now, we need more! Last summer, I looked at theoretical modifications to a given critical experiment to see how useful it could be in analyzing all the relevant isotopes. I found several setups that could be easy and useful to implement; I won't go in depth, because I hope to have it presented or published in the near term. Moreover, I expect this summer and for my M.S. thesis to expand on this work and design robust experiments that will satisfy the "applicability" requirements for the isotopes needed.
Furthermore, in regard to the second problem, chemical assays are needed of current used fuel. One might think this is easy enough to do, but suffice it to say, it is not easy for anyone--even the Labs--to get their hands on much of this stuff.
* C. V. Parks, J. C. Wagner, and D. E. Mueller, "Full Burnup Credit in Transport and Storage Casks: Benefits and Implementation," Proc. of the International High-Level Radioactive Waste Management Conference, Las Vegas, NV, April 30-May 4, 2006, pp. 1299-1308.
Sunday, March 16, 2008
The article first points out that over 200,000 new cases of prostate cancer are found every year in the U.S., certainly an important factoid for the gents out there. The big ticket treatment options have been brachytherapy, external-beam radiotherapy, chemo, and the more drastic removal of the prostate. Joining the group as of late has been proton radiotherapy.
In general, proton beam radiotherapy offers a good method by which to deposit quite locally a given dose. However, the high energy used leads to production of secondary radiation, most noticeably being neutrons. The paper's main goal is to determine the equivalent dose Hi to the ith sensitive organ and the total effective patient dose E from secondary radiation. (Note, I had to review what exactly these quantities denote: Hi = dose*weightA; E = sum(Hi*weightB)).
In calculating H for given organs, the authors point out an interesting fact. Typical ICRP protocol assumes only an external neutron fluence, whereas in this treatment a significant neutron population is generated in the patient. They argue then that "weightA" is actually a function of the local neutron fluence, not of the fluence incident on the patient. ( I am confused at this point, for "weightA" is defined simply by incident neutron energy, irrespective of where that neutron happens to be. They give little insight as to what exactly changes. I would think that in a given locality (i.e. organ) the neutron energy spectrum is available, and using that, any set of weights could be applied properly.)
To quantify equivalent and effective doses, the article employs the ratios (H/D) and (E/D), read "equivalent dose per therapeutic absorbed dose" and "effective dose per therapeutic absorbed dose", respectively. D is simply the dose deposited by protons in the target region.
Their results indicate a typical treatment yields an (E/D) value of roughly 5.5 mSv/Gy. (H/D) values range from just under 2 mSv/Gy in the esophagus to nearly 13 mSv/Gy in the bladder. As one might imagine, these values are very dependent on proximity; the bladder neighbors the prostate, whereas the throat lays far from it.
These values match seemingly well with the study I performed last term. While I did not model a full patient phantom (I used a simple Lucite spherical phantom), I found the (H/D) value internal to the target to be roughly 50 mSv/Gy. Given this region could be broken into organs and assigned weights (as shown above), it is conceivable that I would have found a value near 5 mSv/Gy as the article presents.
* Fontenot, et al. "Equivalent dose and effective dose from stray radiation during passively scattered proton radiotherapy for prostate cancer", Phys. Med. Biol. 53 (2008).
Monday, March 3, 2008
A recent article details these views.
I especially like his pointing out that Finland's decision to build nuclear gave rise to the forward movement we see today. Now I simply wish I would have tried visiting the site while abroad!
As a final message from the nuclear professional world, NRC executive director Luis Reyes gave students at this year’s ANS national student conference a tool for rethinking how we represent the changes in our field. Essentially, by changing the words used to describe ideas we often take for granted, we can both arrive more rapidly to the point in conversations with the public and convey a more positive image of nuclear.
Reyes noted that we should use “used fuel” in place of “spent fuel” as a means to rid from the concept of nuclear fuel its oft associated stigma; moreover, instead of “reprocessing” such spent fuel, we should “recycle” it.
The idiom shift does two things. First, the ideas of a “used” item and “recycling” are rather familiar for most people; contrarily, trying to understand exactly what “spent” or “reprocessing” means can leave many people befuddled. Second, and worse yet, putting “spent fuel” and “reprocessing” together leaves for some people the bitter taste of proliferation and other concerns, which are often outside the conversation’s context.
With that, we might all follow Reyes’ suggestion. By doing so and by continually looking for other better, more effective ways of communicating our positive message, we can facilitate the exciting future we all know nuclear has to offer.