Sunday, February 24, 2008
Tech Review - 2
In my reactor analysis course last semester, one group project focused on the effect the presence of U-236 would have on reusing uranium from spent nuclear fuel. It has long been known that U-236 introduces a long-lasting negative reactivity to the fuel. So-called penalty factors have been defined to quantify how many extra units of U-235 are needed to overcome the negative reactivity of one unit of U-236. These factors have been found to be roughly 0.30, or in other words, for every extra gram of U-236 produced, one must have present an additional 0.30 grams of U-235 to maintain the reactivity desired.
J. P. Renier et al. looked at this problem in depth, especially with respect to GNEP and waste disposal. The reuse scheme was to mix a sufficient amount of recovered uranium from an initial cycle with natural uranium to create fresh fuel for consecutive cycles. The first cycle was assigned 33 GWd/t burnup, typical of U.S. operations, and 55 GWd/t for subsequent cycles--why they focused on higher burnup for later cycles remains unclear to me. Perhaps it was merely assumed that future operations would employ such higher burnups.
Their conclusion states an asymptotic weight percentage of U-236 was found (~0.85%). The penalty factors for the cycles were roughly 0.25, which agrees pretty well with historical values.
Perhaps important to state is why U-236 would even be present. Uranium purification usually employs some form of centrifugal separation based on weight. For natural uranium, comprised only of U-235 and U-238, this works well, as the relative mass difference between the isotopes is large (enough). For U-235 and U-236 (produced during the cycle), this is not the case, and over half the U-236 remains with the re-enriched product.
The article is merely a transaction, so much detail is left out. What I'd like to know is how the data uncertainties look after propagation through 7 cycles. To me it seems perturbations in just about any factor could introduce significant changes in the U-236 concentrations (and hence the requisite U-235). Perhaps I'll solicit an opinion from the group who reviewed this work in class.
Sunday, February 17, 2008
The Renaissance: Job Market Impact
Nuclear power had its commercial roots in the 1950’s, touted from its birth as the “answer to humanity’s energy needs.” However, neither was its full promise realized nor did nuclear power continue its ascendancy; the 1979 incident at Three Mile Island effectively stopped commercial growth of nuclear in the U.S. Moreover, the 1986 disaster in Chernobyl induced worldwide fear of nuclear power.
Despite these incidents, nuclear power has remained important both in the U.S. and abroad as an energy source, and more importantly, it has seen greater support in recent years. In the U.S., utilities, investors, and the government are beginning to consider nuclear power again. The rest of this report details in what capacity they are doing so and how this could change the domestic nuclear job market.
Recent Maneuvers: The Industry Revisits Nuclear
2007 was a milestone year for the nuclear industry. Four companies—NRG Energy, NuStart, Dominion, and Duke Energy—submitted full Combined Operating License (COL) applications, the starting point with the Nuclear Regulatory Commission (NRC) for constructing new plants. A fifth company, UniStar Nuclear, has submitted a partial application (expected to be finished in early 2008) .
These applications are of paramount importance to future applications, as they are the first for several new baseline plant designs. In the NRC’s new application process, plant designs are first submitted for approval by vendors, after which the various generation companies adapt these basic designs for their needs and submit separate applications. Currently, two of four proposed reactor designs—the ABWR by General Electric and AP1000 by Westinghouse—have been approved by the NRC; all COL applications based on other designs would be contingent on reactor approval .
Given these submittals and the promise they provide, many within the nuclear industry feel 2008 will be even more flourishing. Another ten companies are expected to submit COL applications. Together with 2007 applications, this would amount to 33 new nuclear reactors in the U.S., roughly a 33 percent increase to the current fleet.
Investors: Money Where their Mouth Is
Certainly, a driving force behind any resurgence in nuclear construction will be support on Wall Street. While much skepticism still exists, there are vocal enthusiasts among financiers for several reasons. The following quotes elucidate some of these viewpoints.
Fitch Ratings Ltd. noted in its March 13, 2006 Wholesale Power Market Update,
High natural gas prices, continuing constraints on rail deliveries of coal, and longer term concerns about carbon dioxide emissions and a new mercury rule have made fuel diversity a more pressing priority on a national and state level. It is no longer a matter of debate whether there will be new nuclear plants…the discussion has shifted to predictions of how many, where and when. 
Financial power Merrill Lynch has reported, “We view large nuclear utilities as beneficiaries of the rising cost profile of coal generation and potential future carbon reduction … [We] believe that nuclear utilities represent a free option on potential future carbon-reduction legislation…” .
That coal costs have continued to rise has caused many to revisit nuclear as an environmentally-friendly tool, and with increased public support for stricter emissions standards, nuclear will continue to be one, if not the only, practical solution for large-scale energy production.
Nuclear Politics – Progress on the Back of an Elephant (or Donkey?)
To quote the recent Nuclear News, “…[The] general belief is that another Republican president would either accept or encourage new reactors, while a Democrat would oppose them…” . This general view has been held widely within the nuclear community, but upon looking at the candidates, is it really clear a Democrat would nullify the near-term future of nuclear? A recent NEI release  offers an answer to this question.
Senator Hillary Clinton is “agnostic” toward nuclear power and is not against it if solutions to waste and financing issues are found. Senator Barack Obama is “open-minded” about the nuclear question and echoes Clinton’s concerns about waste. The only major player against nuclear was former Senator Edwards who has since dropped out of the race. The leading Republican candidate Senator John McCain has said, “The idea that nuclear power should play no role in our future energy mix is an unsustainable position.”
It would seem as long as a candidate is not openly averse toward a nuclear rebirth, than we in the industry should not worry excessively; however, given the Democratic majority in Congress, either Democrat could succumb to party pressures. Only Obama would have personal reasons for remaining at worst a neutral player—his Illinois is a leading nuclear market.
The People: Powering the Renaissance
While the future of nuclear is by no means set in stone, to ensure the industry lands running, the nuclear workforce has to be developed and ready for the challenge. An old adage says the nuclear workforce is comprised of individuals ready to retire; while not entirely true (average age is 48), the Nuclear Energy Institute (NEI) notes 27 percent of personnel could retire by 2011, leaving a gaping void in labor and knowledge .
What exactly are the prospects for new nuclear engineers? If there are to be no new nuclear plants, that exodus of retirees will leave nearly 20,000 jobs to fill (not all engineering) . Additionally, the NRC looks to hire 600 new engineering staff, most likely to accommodate the workload associated with incoming licensee applications . If NRC-approval of recent applications becomes imminent, we can expect utilities also to undertake massive hiring—which would likely tax the outgoing pool of the 29 U.S. nuclear engineering programs (of which there had been 38 some 30 years ago!).
In summary, it is impossible to quantify exactly the effect this nuclear “renaissance” will have on the nuclear job market, but what is clear is that it is already affecting it.
1. Blake, E. M., “Renaissance Now?”, Nuclear News. January 2008
2. Fitch Ratings, Special Report: Wholesale Power Market Update. March 13, 2006
4. Nuclear Energy Insight, publication of the Nuclear Energy Institute. May 2007
5. Howard, Angie, “Achieving Excellence in Human Performance: Nuclear Energy Training and Education,” American Nuclear Society. Conference on Nuclear Training and Education, Jacksonville, Florida. February 5, 2007
6. Washington, E. H., “Workforce issues big challenge for NRC”, Inside N.R.C., 2. November 12, 2007.
Tech Review - 1
In the article, Wagner notes that Monte Carlo methods are widely believed the best tool for solving radiation transport problems, but at the same time, are extremely computationally-intensive for difficult, "deep penetration" problems. The work described aims to provide a way in which to cut down on this computer time via variance reduction.
The method does two key things. First, it produces for the problem a so-called biased source, which is defined essentially as the space- and energy-dependent source, s(x,E) weighted over the entire detector response function via the adjoint flux, A, i.e.
--> s'(x,E) = A(x,E)s(x,E)/R
where R is just the integral of the numerator over all energy space. What this source does is that it gives to us those particles most important to the detector response of interest. If, for example, we had a fission source (think the Chi-spectrum) and detector separated by a thick concrete wall, we imagine our detector response is largely dependent on the fastest of those neutrons; as such, we bias the source to give more of those particles while simultaneously decreasing the per-particle weight to maintain "fair" biasing.
The method uses weight-windows for transport biasing. WW's are essentially a superficial grid placed on the problem geometry. The various superficial regions are assigned a range of particle importance that it will let enter; for those particle outside the range, either Russian roulette or splitting occurs (i.e. if the particle 'weighs' too much, it is split into two or more particles of appropriate weight, and if the particle 'weighs' too little, a game is played to see whether it can enter; if so, its importance is raised a consistent amount; if not, it is destroyed).
The lower bounds of the WW's are inversely proportional to the importance function, A. and proportional to the overall detector response. That is to say
--> wl(x,E) = R/(Ak)
where k is some constant I won't explain here. Suffice it to say, wl(x,E) is defined such that biased-source particle weights are in (wl,wu) to remain consistent; this reduces unnecessary splitting or rouletting straightaway.
The article goes on to apply these methods to difficult problems, namely a nuclear well-logging simulation (which I've done before!). Time is saved by several orders of magnitude, which makes this theory a very valuable one indeed.
In the future, I would like to couple the idea with charged-particle problems, namely with proton beam therapy facility shielding analysis in mind.
Saturday, February 16, 2008
A Statement of Personal Interests
Having spent nearly a year in Finland studying, I must say that Finnish language and culture hold special places in my heart; note my blog's title, nyrtin kotisivu--Finnish for "the nerd's homepage". In fact, for a brief account of my stay and its importance, see my College's latest newsletter (~5mb pdf!).
Moreover, foreign languages in general are a favourite topic of mine. I know Spanish well enough to read most everyday sorts of things. My Finnish is rough despite my stay (see that newsletter), and I know a smattering of Russian (again, see newsletter). I also wish I had time to learn Estonian, German, Swedish, Sami, and perhaps the Classics.
Reading is important, too, and I find it frustrating that my better half does it so much more quickly than me. I did read B. Russell's article "Science and Art under Socialism" yesterday as fast as I could; I should also say it was while, hmm, doing one's business.
Cycling, running, and other forms of exercise make me feel better; and when I can, I try to do them.
Cooking and baking are newfound life loves; without them, I would certainly be yet again a ramen noodle connoisseur.
Writing, an activity I love so much, is, unfortunately, an activity neglected just as much.
E'er I wish to be an expert,
That I may succomb to comfort
In the words of mine own libro
Off'ring all a chance to know!
A Statement of Professional Interests
My professional interests, as a student in nuclear engineering, are wide-ranging. I enjoy the computational aspects of nuclear engineering; simulations or analytical studies of nuclear phenomena are engaging and show how much we know (and do not know) about the physical world.
Specifically, I (think I) like methods of (neutral particle) transport; in other words, I like to know how radiation works in large-scale, real-world problems. I note my skepticism only because I have not myself actually dug deeply into the 'guts' of such methods; rather, I've simply 'used' them a bit.
As for applications of transport, I find reactor physics, shield analysis, and radiotherapy all to be stimulating.
To support this interest, I find also I like numerical methods in mathematics. Pure math has always seemed so abstract to me, and while beautiful, I cannot say it is 'relevant.' Additionally, high performance computing is a necessary companion to applied math and engineering.
During my research experiences, a number of relatively specific sub-genres within nuclear engineering have struck me as particularly engaging. Sensitivity analysis, especially with respect to nuclear data analysis is an important application of applied math and transport theory. Additionally, optimization, a rather broad topic within many science (or even all of life!) has come into play more than once.
Having stated these interests, which are certainly not exhaustive, I feel it is my duty as a good and soon-to-be graduate to keep abreast of the 'latest-and-greatest' within the fields. I will try using this blog as a technical log of those things which seem especially valuable. My goal will be every Sunday morning to browse a recent volume of a related journal for relevant material; upon finding an article of interest, I shall read it over coffee and then recount the very basics of it via this blog. I shall also try finding ways such work could be applied in my own work or expanded to be of further utility.