Saturday, January 20, 2007

MIT drives much pebble bed reactor research

MIT, the Massachusetts Institute of Technology, is a great institution. For example, the MIT Department of Nuclear Science and Engineering has led the study of basic nuclear processes and nuclear engineering for a half century. In light of the fact that the US has not built a nuclear power plant since the 1970s, we are fortunate that the science lives on with in faculty of 28 and senior research staff, 101 graduate and 48 undergraduate students.

Andrew Kadak has the unusual title of Professor of the Practice in this department. He has served the US government looking into issues of nuclear waste and safety. His pre-MIT career within the nuclear power industry included being the CEO of Yankee Atomic Electric. This nuclear power plant in Rowe, Massachusetts was decommissioned in 1992. Click Yankee Rowe to see before and after pictures and learn the fate of the spent fuel.

Much of the current interest in pebble bed reactors sprang from an MIT student summer project in January 1998 advised by faculty advisors Ronald Ballinger and Andrew Kadak. Nuclear Power Plant Design Project involved 6 students and 10 guest lecturers. The students reviewed:
  1. Westinghouse AP600 advanced pressurized light water reactor (LWR)
  2. ABB System 80+ LWR
  3. GE Advanced Boiling Water Reactor (ABWR)
  4. General Atomics high temperature gas reactor (HTGR)
  5. German AVR pilot pebble bed reactor (a HTGR)
  6. Lead bismuth reactor
  7. Thorium breeder reactor
  8. Liquid metal breeder reactor
They evaluation process considered 26 criteria such as safety, economics, construction time, modularity, efficiency, and lifetime. The process selected the small, modular pebble bed high temperature gas reactor. Some of the identified unique features of the PBR are:
  • Inherent safety: no operator actions nor automated systems needed
  • Proliferation resistance: reprocessing spent fuel pebbles is impractical
  • Short, 36 month construction time
  • Modular growth: 100 MW units
  • Refueling: no shutdown
  • Fuel disposal: spent fuel ready for disposal on removal from core
  • High thermal/electric efficiency: no water cooling needed
  • On-site assembly/disassembly: components shipped intact to/from factory
Subsequently a number of research projects were conducted and documented at the MIT Pebble Bed Reactor web site. Marc Berte and Andrew Kadak prepared the interesting Modularity Approach of the Modular Pebble Bed Reactor which contains a physical design for a PBR, including designs for all component parts that permit construction in a factory, shipment by rail and truck to a job site, and on-site assembly with no welding required.

I am pleased that in the recent three-decade dark ages of US nuclear power plant construction the US government has funded and MIT has continued research and development in nuclear engineering. Unfortunately it appears that US-sponsored funding of pebble bed reactor research projects at MIT has dropped off in recent years. China and South Africa are both developing pebble bed reactors, attracting the attention of university scientists and engineers. MIT is cooperating and sharing information with Tshinghua University in China. The university now has an operational pilot PBR. Kadak has traveled to China to observe the plant's fail-safe testing, and he is now consulting with the South African project.


Stewart Peterson said...

Now, the IFR has all the advantages you listed, too:
-It is inherently safe (recall the EBR-II tests and the fact that the sodium fires problem is basically solved);
-It reprocesses onsite without extracting plutonium, so there's no proliferation risk;
-Even an AP-1000 has a 36-month construction schedule--there's no reason an IFR (which is a lot simpler than even an AP-1000) can't do that also;
-An IFR in its PRISM incarnation was also modular--you could choose between 150 and 380 MWe, and an operating plant would have six modules IIRC;
-Online refueling isn't designed into any IFRs that I know of, but you'd only refuel one module at a time, so it's essentially 5/6-power refueling, and I don't see why you couldn't easily design an IFR with tubes, since it operates at atmospheric pressure;
-IFR spent fuel contains no graphite and is shorter-lived (~300 years with no treatment);
-An IFR can be designed with a helium or combined-cycle secondary as well as a steam system;
-Installing an IFR/PRISM module is if anything easier than a PBMR module.

I'm also concerned that while the public is ready to listen about safety, they're not ready to listen about waste, and to design a reactor that produces all the graphite HLW that a PBMR does without the option to reprocess and without breeding capability closes out a lot of options. Out on the ground, talking to people, I get "what do you do with the waste" a lot more often than "isn't it dangerous," and if I were to hold up the PBMR as an example, I couldn't say what I always say, which is that the mine-to-cask efficiency of the open fuel cycle is 1% and we should use up the fuel we've already mined and have stored in underwater racks and in barrels and casks before we start calling it waste. In short, I don't see much of a case for the PBMR as opposed to other reactors. As opposed to heating oil, yes, and I'll never oppose PBMR development--all we need is something better than what we've got--but I just don't see how it's better than all these other concepts, especially things like thorium and plutonium breeders that can extend the conventional uranium supply by a factors of over 1000. And it's not like we're accepting tradeoffs in any other areas by using an IFR. I don't see what's so wrong with the current approach (read: what we would have done since the 50s if the no-nukes-kooks had let us) that we need to abandon everything we've done so far.

I would really like to hear your thoughts on this.

Robert Hargraves said...

I'll learn more about the IFR. I'll write some future posts about other nuclear power plant options. There are many safe, practical designs. The PBR appeals to me because I think the public would accept its demonstrated safety. Waste is definitely a big issue in the public mind, though.

Alessio said...

Mr.Peterson,I found your debate about IFR/reprocissing vs Pbmr very interesting;there is a question about I'd like to deal with.

My own idea is,instead to re-burn them in fast reactors (see integral fast
reactor program) that are costly to buil and difficult to operate with
multiple recycles (I suppose due to low burn-ups achievable),to burn Pu and
minor actinides in very high burn-up (e.g. > 700 MWg/kg HM),good neutron
economy thermal reactors with only one reprocessing (pyroprocessing) cycle.I
think that pebble bed reactors developed in South Africa or generally HTGR
based could have these features

I found a lot of Authors are really developing this point of
thermal actinides transmutation versus fast reactors. (pag.50)

Clearly,an other approach I thought about is to load pebble bed cores with
two different kind of Triso,of course in the right proportions:only thorium
Triso and
only Pu and Ma Triso in order to "consume" all o nearly all Pu/Ma fuel and
to reprocess only thorium Triso,if needed,or simply recirculate them in the
reactor if not needed (low poison or parasitic absorptions?)

Moreover,what is the actual state of the art of "dry" nuclear
waste reprocessing
systems like pyroprocessing,expecially those who can deal with oxide fuel
(for example at Russian RIAR).What are their efficiency in extracting
actinides,for example U or Pu and MA in/out and their typical
decontamination factors? What their typical size/footprint ? What about
their estimated cost?

A big question I know,but I'd appreciate any comments,
suggestions or opinions. Thanks.

Anonymous said...

Congratulations Mr. Hargraves for your very interesting blog.Pebble beds are surly one of the most promising technology in the energy field of our times
I'd like to know more about the features of a pebble bed reactor,to fix ideas let's say the South African version
For example,what's a typical "fuel economy" of a PBMR?AFIK a higher enrichment allow
higher in situ conversion/breeding
So in a pebble bed reactor 9,6% U enrichment, > 90 MWd/tonn burnup in the SA
version,which could be typical
conversion ratios?Is it possible in that case approching 1?
I didn't find any data about uranium enrichment at discharge in a PBMR from
which we could calculate plutonium (and uranium 238....) in situ
fissions contribution,does someone of you know more about?
Best regards

Alessio said...

Sorry,of course "Anonymous" is me!

Charlie Duveen said...

Is anyone aware of studies done for marine applications using the PBMR. My physics students are designing a research submarine power plant that will be safer and lighter than current PWR plants. Any suggestions/sources?

Thanks much,


Robert Hargraves said...

I recommend you contact Rod Adams at
Rod is an ex-submariner who has a company designing a small pebble bed reactor.