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T H E N U C L E A R N E W S I N T E R V I E W Corbin McNeill:A PBMR in Exelon’s future?Corbin McNeill,chairman and co-chief executive fuel balls,it leaves at the bottom at a temperature of about officer of Exelon Corporation, is guardedly opti- 900 °C. This gas passes through three turbines. The first two mistic about the involvement of the Pebble Bed turbines drive compressors, and the third drives the gener- Modular Reactor (PBMR) in the future of nuclear power in At that stage, the gas is about 530 °C, and it then goes into The PBMR, a new design being pursued by Exelon in as- a recuperator, where it loses excess energy and leaves at sociation with South Africa’s state-owned utility Eskom, is about 140 °C. A water-cooled cooler takes it down further claimed to be safer, cheaper, and faster to build than other to about 30 °C. The gas is then repressurized in a turbo-com- reactor technologies. As such, Exelon is watching careful- pressor before moving back to the regenerator heat-ex- ly its design development, which may lead to a decision to changer, where it picks up the residual energy and goes back go forward with a PBMR demonstration project to be start- ed later this year in South Africa, according to McNeill.
Spent fuel balls are passed pneumatically to large storage The PBMR is a high-temperature, helium-cooled reactor tanks at the base of the plant, where there is enough storage using a direct-cycle gas turbine. It is designed in 110-MWe capacity to hold all spent fuel through the life of the plant.
modules for relatively quick operation in an electricity en- The tanks are also designed to hold the spent fuel for 40 to vironment where 1000-MWe units may be too big and cost- 50 years after shutdown. About 2.5 million fuel balls will ly to compete in a deregulated market.
be required for the 40-year life of a 100- tory built” before assembly at a site.
°C is introduced into the top of the re- conducted by Rick Michal, NN senior McNeill: “[PBMRs] could dramatically boost the prospect of nuclear energy on a global scale.” You have gone on record as predicting that new another LWR would never again be built in It’s too early to tell. Our current investment nuclear power plants will be built in the Unit- commitment is designed to take us through the ed States. When will they start being built, and completion of the design feasibility study. At will they be exclusively of PBMR technology? reads this understands that this is my own that point, we should have a good estimate of I don’t control all of that decision making, personal opinion. The current LWR designs what the construction costs and the feasibili- of course. The demand for electricity is con- require extensive safety systems to assure ty of the operation of the design will be. We tinuing to increase as we move more toward public safety, including large containments.
would then make a separate decision as to an information technology age. We’re seeing That structure of large containments that con- whether to continue to participate in the proj- in Chicago, for instance, load growth rising at tain the energy associated with the steam re- about 4–4 1⁄2 percent per year. That’s substan- lease of a hypothetical LWR accident, plus tially above what we’ve seen earlier. The de- holding all the radioactive products that When is the PBMR’s feasibility study expect- mands on the generating community with that might come out of that, produces a relatively kind of electricity growth continue to be chal- high initial construction cost and long con- The path that we are pursuing in the current lenging. I believe that nuclear can be one of struction period. Much of that construction is development is to conclude the design feasi- the answers to the needs of the country, and done on site, as opposed to in a factory, which bility study sometime early in the third quar- at the same time be one that is environmen- ter of 2001. If that proves that there is eco- Having said that, I don’t know of anybody who has plans to build a new nuclear plant in The PBMR will have the
the next several years. Our interest at Exelon is in a new technology—the PBMR [Pebble thermal efficiency of about
Bed Modular Reactor]—which could produce a new plant maybe in five years in this coun- 40–42 percent, versus a 28–30
try. But that will depend on the completion of our design feasibility study from which we percent efficiency for today’s
will be able to predict what the costs will be and whether a plant of that nature would be light-water reactors.
competitive in the kind of deregulated envi- What are the technical and economic advan- Exelon has invested $7.5 million in a PBMR nomic and technical feasibility for the PBMR project being developed by Eskom, in South design, then we would request approval from Africa. What is Exelon’s financial position the South African government to construct a on this investment—i.e., is it equity in the single demonstration plant of 110-MWe de- that affords a degree of flexibility. In terms of sign in South Africa, which would take rough- construction, a utility would be making what It is an equity position in the intellectual ly 36 months to construct and about a year’s might be a $120-million investment decision property development of the PBMR. For the worth of testing after that. If, at some point in instead of a $2-billion–$3-billion investment $7.5 million, we’ve got about a 12 1⁄2 percent time, we were confident about the design, we decision. PBMRs are faster to construct. We share. If the design feasibility study is fa- might then begin to pursue licensing in the think that they can be built in the neighborhood vorable, it also would allow us to participate United States. We probably would not have a of 18–36 months as opposed to perhaps 5-plus in the construction of the first plant. We have plant completed in this country for five or years for a larger plant. The PBMR will have certain contractual rights to build these and the thermal efficiency of about 40–42 percent, market them in various parts of the world.
versus a 28–30 percent efficiency for today’s How closely do you think other U.S. nuclear light-water reactors [LWRs]. There is a sig- Is Exelon also participating in the Eskom de- utilities are watching what Exelon is doing nificantly higher degree of safety of the PBMR in that during the worst predicted accident, the I think they’re aware of what we’re doing. I temperature that would be achieved in the re- don’t know of any specific effort to do much actor would be well below fuel damage tem- amount of time to perhaps 60 percent of their beyond that. I know that the Nuclear Energy peratures, so no meltdown could occur like in time in South Africa today, not necessarily do- Institute is promoting a broad, general effort to an LWR. The operating costs of a PBMR are ing direct engineering, but reviewing engi- try and promote new nuclear construction in substantially less because of the staffing char- neering, helping to review cost-prediction the country, and this is one possible part of that.
acteristics and the lower fuel costs. There is methodologies, trying to develop the best But I don’t know specifically what anybody’s lower low-level waste production in a PBMR probabalistic risk assessment tools for the de- doing one way or the other in that regard.
as opposed to an LWR. And, finally, PBMRs sign, and things of that nature. We’re provid- maintain the traditional characteristics of nu- ing what I would call a contribution to the de- clear plants in that there won’t be any atmos- sign effort, but we are not the designers.
pheric emissions associated with them.
but there needs to be an understanding of the How dedicated is Exelon to PBMR technolo- rationale behind it. In an LWR, under accident At the ANS/ENS International Meeting last gy? Would the company be willing to invest conditions where the safety system has failed, November in Washington, D.C., you said that more into the South African project? fuel damage can occur very quickly. There-fore, there needs to be in place a containmentmechanism to make sure that it doesn’t escapeduring those potential early minutes of an ac-cident situation.
Eskom, the South African utility that is leading the effort to develop the Pebble Bed developing those accident conditions is hours Modular Reactor, has a Web site that contains information on various aspects of the de- and even up to days. The temperature rise in sign. An overview of the PBMR is included, along with information about its operational a PBMR that undergoes a loss-of-coolant ac- requirements, safety principles, main power system, operating principles, fuel, construc- cident is very slow, as opposed to minutes in tion, and maintenance. The Web site is at <www.pbmr.co.za>.
an LWR. What a PBMR design does is allowfor the release of the helium coolant in a loss- of-coolant accident. It also establishes a con- is the issue. The PBMR advantages that we tainment to make sure that if fission products discussed earlier have a bottom line that says are released within the following several days, that this reactor has to be economically feasi- they are contained within the containment ble. We will make a comparison with other forms of generation and the costs of those The kind of containment that would be re- generations that are available in general. We quired for licensing a PBMR in the United believe that the PBMR will be a very com- States is not yet clear. However, there is an petitive design. Therefore, for the foreseeable future, we should be able to build it if it meets has looked at the need for conventional con- the economic criteria that we are looking for from the design feasibility study. The window of opportunity is really the technology that is tainment design and concludes that conven- being developed, but we have to be confident tional containment is not mandated for a high- about the technical and economic parameters structure itself ends up providing containment.
Could you talk about the long-term storage ofthe PBMR’s spent fuel pebbles? In terms of time limits, is there a window of They are much easier to store than our cur- opportunity for PBMR technology to be in- rent fuel rods, for a couple of reasons. First, the silicon-carbide coating on the fuel parti- That’s one of the issues that we are trying cles will, in fact, isolate the decayed products to resolve in the design feasibility study. Here for hypothetically a million years. And sec- PBMR licensing in the United StatesB EFORE A PEBBLE Bed Modular Re- Combustion Engineering System 80. “The process would be the same,” he said. “It’s would first have to be granted by the Nuclear Regulatory Commission. Tom King, director for design certification, a review by NRC of the NRC’s Division of Risk Analysis and staff and a separate review by the NRC’s Applications within the Office of Nuclear Advisory Committee on Reactor Safeguards, Regulatory Research, is leading the agency’s and the opportunity for public hearings.
effort to set up a review process in the event a PBMR licensing application comes in.
Exelon Corporation, which is currently in- Eskom in South Africa, first approached the years to certify the three newer generation NRC in November to discuss the design’s pos- reactor designs, but, Dricks stressed, that is sible licensing in the U.S. A face-to-face meet- ing was held, followed by a letter from Exelon sources available at the time, project priori- to the NRC in December, putting in writing ty, and demonstration of safety features.
the fact that the utility is involved in the Dricks said the review history of those oth- PBMR project and requesting interaction with er certifications should not be tied to what the agency early on. According to King, Ex- should be expected for the PBMR, and that a elon hopes that by meeting with the NRC be- two- to three-year approval process could be fore an application is filed, the utility will get realistic. “Our expectation is that we’ll be a sense of what requirements lie ahead. That able to accommodate a request for a design knowledge will help Exelon make a decision certification in two to three years by what we on whether a licensing request should proceed.
call a pre-application review,” he said. “That King said preliminary talks have revealed means that we’ll have had discussion with the that Exelon is interested in receiving licens- licensee on various design and engineering ing within two to three years following sub- features of what they’re going to bring to us, mittal of an application. “At this point, I so that we’ll be familiar with the technology can’t say whether [Exelon’s expectations and we’ll have done some advance planning are] reasonable or not, until we know more before an application actually comes in.” about the design and their approach for li- censing it,” King told Nuclear News. attempt to familiarize itself with the PBMR review process by offering regulatory assis- tance to the South African government for three other newer generation designs that its licensing of the Eskom project. So far, have received NRC approval—the Westing- though, that government has not responded.
vanced Boiling Water Reactor, and the ABB application, King has studied the technolo- ond, the carbide ball has characteristics June, concluded that if cost and safety goals around it that allow it to be directly stored for are met, “we can expect to see literally hun- not only the life of the plant, but for the per- dreds of PBMR modules being built around manent storage. We think this is easier to the world in the next decade or two.” Do you store than the current rods, but we still need have any comments on this statement? a location. That’s why any nuclear plant is I’m not going to project any number for PBMRs. I do think that if the promise of the coming up with some solution to the long- design pans out, it could dramatically boost term storage problem. Hopefully, the decision the prospect of nuclear energy on a global scale as a non-pollut-ing power source.
That could bridge us We believe that the PBMR will to a hydrogen econo-
be a very competitive design. tury—I don’t know
on Yucca Mountain, with an affirmative suit- pands and Third World countries develop, the ability determination, will be made this com- demand for electricity is going to increase.
I’m seeing and hearing that international de-mand is almost going to double by 2020. That A member of the NRC’s Advisory Committee clearly presents an opportunity for a nonpol- on Reactor Safeguards, in a memorandum last gy. Because of the design’s inherent safety level,” King explained. “And, vice versa, if characteristics, he said, it requires a smaller they take helium out and lower the pressure, that reduces the heat transfer, the core heats miles, compared with the limit for current up, and the power starts to shut down.” light-water reactors of 10 miles. However, It is helium that drives the turbine, and as King added, “What our position would be in such, no steam generator exists for a PBMR [approving an EPZ], it’s certainly one of the plant. Cool helium is put into the reactor ves- sel where the nuclear chain reaction heats it King talked about the make-up of the fuel up. The hot helium under pressure goes to for the PBMR. “The basic element of the fuel the turbine, driving its blades. During this is about the size of a poppy seed,” he said.
process, the helium’s pressure and tempera- That “poppy seed” is a unit of enriched urani- ture are reduced. It is then funneled to a com- um dioxide that has three coatings covering it.
pressor, where pressure is increased, and it The first is a carbon coating to absorb fission is put back in the reactor to be heated up products, the second is a silicon carbide coat- again. “It’s pretty straightforward in terms ing that is the pressure-retaining boundary, and of a simple heat-transfer cycle,” King said.
the third is another outer coating of carbide to “It’s strictly a closed helium loop with a tur- prevent abrasion and rubbing against other bine in-line in the primary coolant piping.” particles. About 15 000 of these poppy seeds form one fuel pebble, about the size of a ten- nis ball. The pebbles fit in the reactor inside PBMR system is a fraction of what is need- “something like graphite blocks” that are up ed for an LWR. In fact, King commented, it against the steel vessel wall, he added.
is important to keep water out of the prima- Once loaded into the reactor, the pebbles ry system because it reacts with hot graphite are cycled out of the bottom in an on-line re- and degrades the integrity of the fuel parti- fueling scheme. “There is no refueling out- cles, as well as produces hydrogen, carbon age,” King said. “This is on-line refueling.
This process is continuing as the reactor op- erates. [Plant workers] are constantly taking nents that are in the primary cooling system, pebbles out the bottom, checking the burn- up, checking for leakers, and then putting them back in the top or discarding them and to better understand the PBMR design, look- ing at experiences that other countries have had with high-temperature gas reactors (HT- once every several years for maintenance of GRs), particularly pebble beds. Germany op- other mechanical parts of the plant, King said.
compensate for initial heat-up” and “for achieving full cold shutdown.” For normal containment, will likely involve policy judg- operational control while the plant is pro- ducing power, according to King, the tem- cluded. “The sooner we can get [key issues] perature of the core is moderated by raising settled, the better off the staff will be in terms or lowering helium pressure. With more he- of being prepared to review [the PBMR],” lium in the vessel, the pressure goes up and he said, “and the better off Exelon will be in the heat transfer gets better, which cools the terms of knowing what’s coming down the core. “Cooling the core increases the power road that they will have to deal with.”

Source: http://www.uxc.com/smr/Library%5CDesign%20Specific/PBMR/Other%20Documents/2001%20-%20A%20PBMR%20in%20Exelon%E2%80%99s%20Future.pdf

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