Thursday, March 31, 2011

Post # 35: Fukushima-Like Events In Nuclear Power Plants

Daily we watch the unfolding story at Fukushima and look for signs the progression of the events there have stabilized.  Clearly, recovery, cleanup, and remediation there and throughout the remainder of Japan will continue for a long, long time – even under the best of circumstances, 

This set me to thinking about other Fukushima-like "beyond design basis" event scenarios that could challenge the integrity of our nuclear fleet.  First, I want to define what I mean by "Fukushima-like".

On March 11, Fukushima Dai-Ich Units 1-3 were operating, and the other three units were shutdown for maintenance and refueling.  The "top event" at Fukushima was a Richter 9 earthquake.  The safe shutdown earthquake (SSE) for the Fukushima plant was a Richter 8.2 event.  Thus the Fukushima quake was a "beyond design basis event".  

Within an hour after the quake, a hugh (latest estimate is 14 meters high) tsunami struck the northeastern coast of Japan, visiting death and further devastation on the entire region. I understand from media reports that the Fukushima Dai-Ichi plant was designed for "only" a 6 meter tall tsunami.  Another beyond-design-basis event.  

Fukushima Dai-Ichi was at that moment damaged, and isolated from outside help - on it's own to deal with the impacts of these two "beyond design basis" events.  

It is the combination of the impact of two beyond design basis events, coupled with the utter devastation visited on the entire site and the surrounding region, that defines a "Fukushima-like" event in my mind.  Such an event leaves the reactor damaged, constrained by damage to its sister units on the plant site, and isolated from the surrounding region which is, in any event, unable to render assistance to the plant.   What a nightmare.

Nuclear power plants are remarkably robust facilities, incorporating multiple transmission lines to provide off-site power,  multiple backup station diesel generators in the event all of the transmission lines are severed, and multiple station batteries capable of allowing the plant to remain safely shut down for several hours should the station diesels fail.  But the unique characteristic of nuclear power is that one cannot simply "shut it off".  Decay power levels in nuclear reactors remain at the "few tenths of a percent" level for a few months after the reactor is "scrammed".  Ultimately, long-term accident management depends on the ability of the outside world to provide assistance to recover the decay heat removal function - for both the reactors and any spent fuel stored in fuel pools onsite – before the fuel is significantly damaged.  This didn't happen in Fukushima Dai-Ichi 1-3.

So, forgetting "probabilities of occurrence" for a moment, what are other "Fukushima-like" events?  In addition to earthquakes and tsunamis, I can only think of two events that meet my definition: hurricanes and solar superstorms.  We are all familiar with the impact of hurricanes.  Our coastal nuclear power plants (those subject to hurricanes and tsunamis) typically stage backup equipment many miles inland with arrangements for delivery in the event of a major emergency.  

Fewer people are aware of the potential for natural solar superstorms (such as the 1859 Carrington Event) to wreck havoc on our entire electrical grid - right down to the electrical systems in our cars, cell phones, radios, etc.  According to reliable reports, during the 1859 event, telegraph systems all over North America and Europe failed. Many telegraph operators received harmful shocks.  Telegraph systems burst into flames, and some continued to work when disconnected from their battery-driven power sources (see Wikipedia  Given the nature of our electric grid and our electrified society, it's hard to comprehend how such an event would impact life as we know it today – with or without nuclear power plants.  Probably deserves some thought...

No nice "wrap-up" on this.  Just thinking...

Wednesday, March 30, 2011

Post # 34: Natural Gas and Wind Energy Infrastructure Challenges

Yesterday I had the pleasure of speaking at the Infocast's 2011 Small Modular Reactor Seminar (see in Washington, D.C.  I spoke about the new Small modular Advanced High Temperature Reactor (SmAHTR) reactor concept my colleagues and I at Oak Ridge National Laboratory have been developing (more about this in a future post).

At any rate, the Infocast seminar featured a number of interesting speakers and panelists.  One of the panelists was David Mohre, Executive Director of the Energy and Power Division of the National Rural Electric Cooperative Association (NRECA) – see .  During one of the Q&A sessions, Dave related a rather stunning bit of trivia I thought I would pass along here.

Many folks are touting what I call "silver bullet energy solutions" (or SBES for short) to our nation's energy challenges.  These are single-technology solutions that proponents believe with magically address all our varied energy solution challenges.  Among the most commonly mentioned SBES are natural gas and renewable energy.  Now for the trivia...

First, according to Energy Information Agency, the installed U.S. coal-fired generation capacity in 2009 was 339 GWe (  Dave indicated analysts have estimated the cost of building the natural gas pipeline infrastructure required to replace 300 GWe of coal-fired electrical generation with gas-turbine generators to $70-80 BILLION.  

Next, he related the estimate for the cost of building the transmission lines required to enable wind turbines to provide 15% of the U.S. electrical generation.  Are you sitting down?  $100 BILLION.

Then he noted that there's less public opposition to underground gas pipelines than to above-ground electrical transmission lines.

I should note that Dave did not cite the specific reference for either of these statements, but I will attempt to uncover it and modify the post when I do.

Just two more challenges to achieving a sustainable energy future....

Just thinking...

Sunday, March 20, 2011

Post # 33: Spent Fuel Storage Pool Accidents In Nuclear Power Plants

We all continue to watch the unfolding events at Fukushima and pray for those who are working so hard to terminate the accident progression there, as well as the Japanese people who will be dealing the the aftermath of the historic earthquake and tsunami for a long time.

The events at Fukushima illustrate the fact that Boiling Water Reactor (BWR) nuclear power plants normally have three or four types of used nuclear fuel inventories that must be maintained in a safe state.  These are (1) the reactor core, (2) the spent fuel in the "refueling pool" that sits just beside the reactor, (3) the plant's common spent fuel storage pool, and (4) spent fuel in dry cask storage.

The water level, water chemistry, and water temperature in the refueling and spent fuel pools is carefully monitored and controlled.  The refueling pool is used during plant refueling operations to stage used fuel into and out of the reactor.  Thus fuel in the refueling pool fuel normally has the highest decay heat generation rate of any fuel outside of the reactor.  Separate from the refueling pool is the plant's common spent fuel storage pool, which contains fuel removed from the refueling pools for long-term storage.  The spent fuel pool generally services multiple reactors at multi-reactor sites.  The decay heat level of the fuel in the spent fuel pool is lower than that of the fuel in the refueling pool.  Then finally, there is the spent fuel in dry cask storage that is generally the oldest, coolest spent fuel at the plant.

Any event that threatens the integrity of the refueling pool and spent fuel pool boundaries, leads to leaks, or threatens the pool cooling function, can lead to fuel overheating, hydrogen generation, and fission product release.  Unlike BWR severe accidents, which I spent many years studying, I have not personally analyzed spent fuel pool accidents.  But others have.  So here is a (very) short bibliography of public documents relevant to spent fuel pool accidents – extracted from the cobwebs of my mental attic...

1. NUREG/CR-0649, "Spent Fuel Heatup Following Loss of Water During Storage,"Allan S. Benjamin, David J. McCloskey, Dana A. Powers, Stephen A. Dupree, March 1979.

2. NUREG/CR-4982, "Severe Accidents in Spent Fuel Pools in Support of Generic Safety Issue 82," V. L. Sailer, K. R. Perkins, J. R. Weeks, H. R. Connell, July 1987.  

3. Robvert Alvarez, Jan Beyea, Klaus Janberg, et. al., "Reducing the Hazards from Stored Spent Power-Reactor Fuel in the United States," Science and Gobal Security 11: 1-51, 2003

4. Mihaly Kunstar, Lajos Matus, Nora Ver, et al., "Experimental investigation of the late phase of spent fuel pool accidents," Int. J. Nuclear Energy Science and Technology, Vol. 3, No. 3, 2007, page. 287-301

As one would expect, the NRC as spent a great deal of time on this issue.  The following URL is a good entry point to their analysis:

Just a quick list of relevant and useful background material from the mental archives of S. R. Greene.

Just thinking...

Wednesday, March 16, 2011

Post # 32: Understanding and Comparing Boiling Water Reactors (BWRs)

The situation at Fukushima Dai-Ichi continues to evolve and world attention is focused on the unfolding events.  There web is rampant with misinformation and often confusing information.

In the midst of this unfolding tragedy, I think it's important to pause and clarify the most basic facts about the plants themselves and their potential relevance to our plants in the United States.

First, it's important to understand how rare it is for any two nuclear plants at different sites to be identical – particularly for the vintage of plants we're concerned with here.  So even when reactors have the same "make and model number" (to use automobile language for a moment), they are usually not identical units.

Boiling Water Reactor (BWR) Nuclear Plant Nomenclature

First, some nomenclature that is very important.  BWR nuclear plants have a "make and model".  In terms of organizational roles or "makes", every nuclear plant has a designer, a manufacturer, a constructor, and a licensee, and an operator.  Sometimes the same organization plays multiple roles.  Due to the complexity of modern power plants, there are actually hundreds, if not thousands, of equipment suppliers involved in making these plants a reality.

With regard to the physical configuration of the plants, BWRs are characterized by the reactor "type", and the primary containment "type".  Based on historical General Electric nomenclature, there have been six "vintages" of commercial BWRs (not including the ABWR and ESBWR).  These are referred to as BWR-1, BWR-2, BWR-3, BWR-4, BWR-5, and BWR-6 reactors.  Then, there's the primary containment.  These are referred to as Mk-I ("Mark-One"), Mk-II ("Mark-Two"), and Mk-III ("Mark-Three") designs.

Now let's look at how all of this is relevant to today's events.

Fukushima Dai-Ichi Plant

As indicated on Wikipedia ( ) Fukushima Dai-Ichi consists of six boiling water reactor or "BWRs".  Unit 1 is a BWR-3 / Mk-I system.   Units 2, 3, 4, and 5 are BWR-4 / Mk-I systems, and Unit 6 is a BWR-5 / MK-II system.  Thus there are actually three different operational plant configurations at the Fukushima Dai-ichi site.  In addition, two Advanced Boiling Water Reactors are under construction at the site.


There are 35 operating BWRs in the U.S.  As seen below (based on a sort of plant information taken from the U.S. NRC web site Appendix A @ ).  These thirty five plants can be divided into 6 generic categories based upon their reactor / primary containment combinations.

As can be seen from the table, there are six US plants (yellow) with the same generic configuration as Fukushima Dai-Ichi 1, fifteen plants with the same generic configuration as Fukushima Dai-Ichi Units 2-5 (light blue), and 4 US plants with the same generic configuration as Fukushima Dai-Ichi Unit 6 (green).

Generic Plant Type Is Important But Plant Specific Differences Matter

I've noted there are a plethora of significant design details that differ even between plants of the same generic type.  To illustrate, this, I've noted in the table below some significant design differences between four US BWRs of the same generic type (BWR-4 / MK-I) as Fukushima Units 2-5 (excerpted from Table 1.7-4 of the Browns Ferry FSAR):

A quick look at the last three rows of the table will aptly illustrate my point about plant specific differences.

The Bottom Line

As we discuss the events on-going in Japan, we should not jump to conclusions about applicability of events there to plants here in the US.  Similarities with regard to generic plant types are important and very relevant, but these similarities can be overwhelmed by differences in accident initiators, siting, plant design details, plant operating procedures, and a host of other factors.  The DETAILS MATTER.

Tuesday, March 15, 2011

Post # 31: BWR Station Blackout Severe Accidents - Primer Documents

My heart goes out to the Japanese people who are dealing with an overwhelming natural disaster that has resulted in the death of thousands and the destruction of untold billions of dollars in property and infrastructure.   Like almost everyone else, I've been watching the unfolding events at Japan's Fukushima Dai-ichi plant with a mixture of horror and admiration for the heroic efforts of the plant staff to contain and terminate the accident progression in Units 1-4.

Many of you know I've spent my career at Oak Ridge National Laboratory.  I've been at ORNL since 1978.  From 1980 through the late 1990s, ORNL had a pioneering program in the investigation of severe accidents in boiling water reactors or "BWRs". This work was primarily funded by the U.S. Nuclear Regulatory Commission.   During the almost twenty years of research at ORNL, the Lab produced a large number of reports, journal articles, and professional society presentations on the accident progression and phenomenology of beyond-design-basis severe or "core melt" accidents in BWRs.  During that period, we utilized several U.S. BWR plants as our reference plants for analysis.  These include the Browns Ferry and Peach Bottom (BWR-4/Mk-I) plants, Limerick (BWR-4/Mk-II), and Grand Gulf (BWR-6/Mk-III) plants.

In light of the on-going events at Fukushima, and with an eye toward the inevitable re-examination of such accidents this event will catalyze, I thought I would post here an extremely abbreviated bibliography of ORNL publications relevant to Fukushima's station blackout severe accident and related reactor building hydrogen deflagration/detonation phenomena.

Some critical words of caution regarding applicability of the analyses referenced below to Fukushima:

1. The Fukushima Dai-ichi units were NOT analyzed.  My understanding is that Fukushima Dai-ichi #1 is a BWR-3 / Mark I containment system.  (The alternative nomenclature "MK-I" is often used).  Units 2,3, and 4 are BWR-4 / Mark I plants.  As previously mentioned, the reference plants used in the analyses below were U.S. BWR-4/MK-I plants.

2. The "station blackout" accidents analyzed in these reports began with the assumption that: (1) all off-site AC power was lost, (2) the diesel generators were unavailable to provide backup AC power, and (3) the station batteries were available to provide DC power until the batteries were exhausted.  According to all available accounts, these three head-end events appear to have occurred at Fukushima. HOWEVER, the HUGH difference in the scenarios analyzed below and last week's event is that the historical analyses did not include an earth quake and tsunami as the "top events".  Thus any damage from these two natural events that may have occurred at Fukushima is not accounted for in the analyses reference below.

3. Some of the sequences referenced below assume specific plant operator responses that may or may not be applicable to the Fukushima events.

So, similar reactors and containments, and similar top events BUT caveat, caveat, caveat...

  • NUREG/CR-2182, Vol 1, Station Blackout at Browns Ferry Unit One – Accident Sequence Analysis, D. H. Cook, S. R. Greene, R. M. Harrington, S. A. Hodge, D. D. Yue,  November 1981
  • NUREG/CR-2182, Vol 2, Station Blackout at Browns Ferry Unit One – Iodine and Noble Gas Distribution and Release, R. P. Wichner et al.,  August 1982
  • NUREG/CR-2973, Loss of DHR Sequences at Browns Ferry Unit One – Accident Sequence Analysis, D. H Cook, S. R. Greene, R. M. Harrington, and S. A. Hodge, May 1983
  • NUREG/CR-2940,  Realistic Simulation of Severe Accidents in BWRs – Computer Modeling Requirements, S. R. Greene, April 1984
  • NUREG/CR-3617, Noble Gas, Iodine, and Cesium Transport in a Postulated Loss of Decay Heat Removal Accident at Browns Ferry, R. P. Wichner, et al., August 1984
  • NUREG/CR-5317, Primary Containment Rsponse Calculations for Unmitigated Short-term Station Backout at Peach Bottom, S. A. Hodge, C. R. Hyman, L. J. Ott, 
  • NUREG/CR-5565, The Response of BWR Mark II Containment to Station Blackout Severe Accident Sequences,  S. R. Greene, S. A. Hodge, C. R. Hyman, M. L. Tobias,  May 1991
  • CONF-8310143-11, BWR Severe Accident Sequence Analyses at ORNL – Some Lessons Learned, S. A. Hodge, 11th Water Reactor Safety Information Meeting,  Oct. 25, 1983
  • CONF-8410142--85, Fission Product Transport Analysis In A Loss Of Decay Heat Removal Accident At Browns Ferry, R. P. Wichner et al., 12th Water Reactor Safety Information Meeting, Oct 23, 1984
  • CONF-871011--6, The Impact of BWR MK-I Primary Containment Failure Dynamics on Secondary Containment Integrity,  S. R. Greene, 15th Water Reactor Safety Information Meeting,  Oct 29, 1987
  • CONF-890546--1, Thermalhydraulic Processes In The Reactor Coolant System of A BWR Under Severe Accident Conditions, S. A. Hodge, Jan 1 1989 
  • CONF-9104223--1, Identification and Initial Assessment of Candidate Late-Phase In-Vessel Accident Mitigation Strategies, S. A. Hodge, April 1991
  • Nuclear Engineering and Design, Vol 120, Issue 1, 1 June 1990, Pages 75-86, The Role of BWR Secondary Containments In Severe Accident Mitigation: Issues and Insights From Recent Analyses, S. R. Greene
  •  Nuclear Engineering and Design, Vol 148, Issue 2-3, Pages 185-203, July 1994, Assessment of Two BWR Accident Management Strategies, S. A. Hodge

Some nice accident analysis work was also done at other National Labs during the period.  One particularly-relevant analysis out of Brookhaven National Laboratory:

  • NUREG/CR-5850,  Analysis of Long-Term Station Blackout Without Automatic Depressurization at Peach Bottom Using MELCOR (Version 1.8), I. K. Madni, May 1994

The major  universities also produced some relevant analysis work.  Here's one from the University of Tennessee,

  • Matthew Wesley Francis, Long-Term Station Blackout Sequence and Mitigation MELCOR Model, A Thesis Presented for the Master of Science Degree, May 2006

Finally, I would also recommend as a general primer on light water reactor severe accident phenomena

Over the next several days, I will expand this list and attempt to add URL pointers to the document.  In the mean time, I believe all or almost all of these documents are available through the DOE OSTI Information Bridge @ , or at online journal archive sites such as ScienceDirect @  A diligent google search should turn them up.


Tuesday, March 8, 2011

Post # 30: Oil, the Strategic Petroleum Reserve, and Heads In The Sand

I was listening to radio as I drove home from work this evening.  First was a dialog from Washington regarding the urgent need to open the Strategic Petroleum Reserve (SPR).  The SPR holds 727 million barrels of oil.  (This is only ~ 75 days worth of our average daily petroleum import of 9.7 million barrels.)  The hope among those who are advocates for opening the SPR is that doing so would relieve the upward price pressure on gasoline at the pump.  It's a sad situation when a 30-cent spike in the price of gasoline at the pump sends us into such a panic.

The next discussion I heard had to do with enforcing a "no fly" zone over Libya.  While there a plethora of humanitarian and political reasons for taking such steps, the bottom line is that one of the major factors behind the thinking of many who advocate this step is their hope that stabilization of the Libyan crisis will also stabilize oil prices.  We have and we will again fight wars over oil.

What a price we pay and our children will pay for our "addiction to oil" (to use President Bush's language).

We need a sustainable energy policy... NOW.

Just thinking...

Saturday, March 5, 2011

Post # 29: What is "Sustainable Energy" ?

One of the most significant insights of my life I gained from studying a second language in high school.  The process of learning a second langauge made me aware that one's native tongue frames one's entire thought process and to some extent, one's world view.  The constraints of one's native tongue also constrain one's thoughts.  Words have meaning.  Words can communicate, inform, inspire, enlighten.  Words can hurt, distort, harm.  Words can bring us closer together, or words can separate us.

We hear the word "sustainable" and "sustainability" a lot these days.  Got me to thinking...What, really, is the definition of "sustainable energy"?

One definition I've encountered frequently is quoted in the Wikipedia article on sustainable energy @ .  It reads,
"Sustainable energy is the provision of energy that meets the needs of the present without compromising the ability of future generations to meet their needs."
This definition, which is as useful as any I've encountered, is fascinating if one pauses to really think about it.  It's all about balance.  The key words are   "provision", "energy", "needs", "present", "without compromising", and "future".

  • energy... In all its forms.
  • needs of the present...  Not wants. 
  • without compromising...  That is, without constraining.
  • future generations...  As in forever?
  • their needs ... What will they be?

This definition is deceptively complex.  It witnesses to a plethora of inter-relationships and trade-offs that determine our quality of life and that of the small blue planet we inhabit.  It raises a number of tough questions such as:

  • What am I to assume in my decision making regarding the forward march of science and technology though time?
  • How do we distinguish between "needs" and "wants", and who makes the decision?
  • What is the role of government verses the individual in this grand play?
  • How are present perceived "inequities" in access to energy between nations and peoples addressed?
  • And for the social Darwinists out there, what about "survival of the fittest" ?  

In an event, there's much to ponder in this simple word, "sustainable".  There is an interesting discussion of the various definitions of "sustainability" on the website of the Citizens Network For Sustainable Development at:  I recommend you take a few minutes to read and reflect on the many definitions of sustainability archived there.

Just thinking...