The Very Spring and Root

An engineer's adventures in education (and other musings).

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Nuclear Power at a Crossroads

By Felix König (Eigenes Werk (own work) – Samsung S750) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons
Building a sustainable energy future is going to take a lot of compromise. Among the sources of energy which I think are often mischaracterized by both proponents and opponents are nuclear power plants.

On one hand, many on the so-called environmental left do have a point in that nuclear power plants can be unstable and lead to dangerous leaks. The recent trouble with the San Onofre plant in California, the news that the nuclear waste units at Hanford are leaking (and actually may be too dangerous to even clean up), as well as the terrible fallout from the Fukushima disaster certainly lend credence to this thinking. Further, it should be no secret that the mining of uranium involves exploitation and environmental destruction of the poor countries in which most of the world’s fissile ore is found.

On the other hand though, I think that many on the environmental left fail to consider the huge positive impact that nuclear power could have on global warming and climate change. Nuclear fission does not produce any direct carbon emissions (the “smoke” rising from the cooling towers is actually steam, water vapor). The positive impact of near-zero airborne pollutants is huge.  For example, a recent paper published by the ACS1 highlights the advantages in clear terms:

Pushker A. Kharecha and James E. Hansen state that nuclear power has the potential to help control both global climate change and illness and death associated with air pollution. That potential exists, they say, despite serious questions about safety, disposal of radioactive waste and diversion of nuclear material for weapons. Concerned that the Fukushima accident in Japan could overshadow the benefits of nuclear energy, they performed an analysis of nuclear power’s benefits in reducing carbon dioxide emissions and air pollution deaths.

The study concluded that nuclear power already has had a major beneficial impact, based upon calculations of prevented mortality and greenhouse gas emissions for the period 1971-2009. Nuclear power could prevent from 420,000 to 7 million additional deaths by mid-century, and prevent emission of 80-240 billion tons of the greenhouse gases linked to global warming, the study found. “By contrast, we assess that large-scale expansion of unconstrained natural gas use would not mitigate the climate problem and would cause far more deaths than the expansion of nuclear power,” it notes.

The positive effects of near-zero emissions has a huge impact, both historically speaking and looking forward. Lifecycle greenhouse-gas emissions for nuclear are far lower than the energy sources we typically use (orders of magnitude lower, in the case of coal and even natural gas), and are actually comparable with photovoltaics2. Another notable advantage to nuclear power include the amount of power produced for near-zero emissions, on the order of 3000 MW (compared to 50 MW for a typical solar farm and about 350 MW for a typical wind farm). This value is generally higher than for even carbon-based natural gas (1000 MW) and coal (2500 MW) power plants as well3.

A standard utilitarian outlook will demand the follow-on question: Are the benefits worth the risks? However, I think this is the wrong question, because it assumes a static, linear type of world. The fact is, an overwhelming majority of the scientific community, and most reasonably-minded people, agree that we need a huge reduction in the amount of greenhouse gases that we currently emit. That said, no one really wants to destroy the environment, exploit poor countries, and create unstable systems. I think better questions might be:

  • How can we reduce the negative impacts of nuclear fission energy through technological and sociopolitical means?
  • Can we require energy companies to make a greater investment in safety technology for reactors?
  • Can we form coherent and sensible strategy for the storage and containment of nuclear waste?
  • Can we regulate the atrocious behavior of multinational energy corporations as it pertains to exploited countries, forcing them to comply with stricter (and therefore more expensive) controls?
  • What feedback-loop impact do the answers to the above have on the original constraints?
  • What percentage of our total energy portfolio should be sourced from fission?

I think that last question also gets at another perspective often missing from the debate — that solutions are seldom either-or. I suspect that neither “no nuclear power” nor “all nuclear power” will ever be a reasonable sustainable solution to our energy problems. As the present generation of reactors reaches design age and the construction of new reactors become mired in political hurdles, these decisions and tradeoffs need to start getting made in a clearheaded and reasonable way soon.

In the near to mid-term, I think nuclear absolutely will have to be on the table as part of the portfolio that gets us to a long term solution. Despite it’s temporary advantages, in the long run we will have to come to terms with the constraint that nuclear fission, just like hydrocarbon energy, relies on a finite resource: uranium and plutonium ore, which are extracted from the ground just like oil and gas. In this sense nuclear fission’s key role may be simply as a bridge to get us by until research and development of photovoltaics, solar/geo thermal, space power, and especially nuclear fusion allow for these much more sustainable energy sources to overcome their present technological hurdles, and eventually take over.

Show 3 footnotes

  1. The full paper is by Pushker A. Kharecha and James E. Hansen (NASA Goddard Institute for Space Studies and Columbia University Earth Institute), Prevented Mortality and Greenhouse Gas Emissions from Historical and Projected Nuclear Power.
  2. See slide 18 of Edenhofer, O., The IPCC Special Report on Renewable Energy Sources: and Climate Change Mitigation“, UN Climate Change Conference June 2011.
  3. I like to link sources, but these didn’t come from one place. Since the variability of power output is very high, depending on the size of the plant, I had to make an eyeballed average of looking up several examples.

Lesson Plan: Predictions With Conservation of Energy

by Nalin A. Ratnayake

Unit: Work and Energy, Component 2: Conservation of Energy
Date: January 15th, 2013
Day/Block: Day 4, Blocks A(3) / E(2) / F(6)
Time Available: E 58 min, A 58 min, F 65 min

Objective: You will be able to predict and analyze motion using the Law of Conservation of Energy.

Criteria for Success:

  1. Can I predict the final mechanical energy of an object in motion using energy conservation?
  2. Can I determine if and how an object’s mechanical energy has changed?
  3. Can I solve a physics problem using energy conservation?

Assessment: Handout and Exit Ticket
The handout will show qualitative understanding of Criteria for Success 1 and 2.
The short worksheet will show quantitative understanding of the Criterion for Success 3.

[10 min] Do Now

Please have a seat and work quietly on the Do Now.

A ball of mass 15.5 kg is released from rest at a point 1.2 m high.

1. If we ignore air resistance, what will be the velocity of the ball at the lowest point of motion?

2. If we assume that air resistance does -20 J of work on the ball as it falls, what will be the velocity at the lowest point of motion?

Share out. Specific questions to ask students: Can you step me through how you found the velocity? How do you know much initial mechanical energy the ball has? How do you know that the total mechanical energy will remain constant? Where does the kinetic energy of the ball come from?  What does the work done by friction do to the mechanical energy of the ball?

[2 min] Framing the Day

The scenario we will be looking at today will be very similar to the Do Now… only more dangerous!

Objective: You will be able to predict and analyze motion using the Law of Conservation of Energy.

Criteria for Success:

  1. Can I predict what will happen to the mechanical energy of an object by using energy conservation?
  2. Can I determine if and how an object’s mechanical energy has changed?
  3. Can I solve a physics problem about the motion of an object using energy conservation?

Can someone please raise his or her hand and explain what we are doing today?
Can someone please raise his or her hand and remind us how we will know if we are successful today?

[35 min] Will Professor Lewin Survive?

Note: The following activity will be outlined on a handout / graphic organizer.

We are handing out a worksheet. These will be collected today at the end of the period. Please take a couple of minutes to read the first two sections, labeled “Video” and “Directions”.

Professor Walter Lewin is going to put his life on the line to prove the law of the conservation of energy. He will release a 15.5 kg pendulum bob from his chin, and wait to see what happens when the ball swings back at his face! Will the ball smash his face in? Or will the laws of physics protect him? We will find out….
Can someone please raise their hand to volunteer to read the first paragraph for us?


  • We will be watching a video that goes along with this handout. Do not move ahead. Some questions we will do as a class, some as a table, and others individually.
  • Write your answers in complete sentences wherever possible. This helps organize your thinking and gives you better study materials later for quizzes and tests.

Can someone please raise their hand and tell us, what is one direction we should follow today? Why should we do that?
Can someone please raise their hand and tell us, what is another direction we should follow today? Why should we do that?

Play the video of Walter Lewin putting his life on the line to prove Conservation of Energy.

Stop the video at 2:54.  (Right after “…this will be my last lecture.”)


Answer question 1 individually on your worksheet now.
1. What kind(s) of mechanical energy does the ball have right now and how do you know?
Quick share, check for agreement or disagreement and why.

Take a couple of minutes to work with your table group on the first column of the table (question 2).
After each column, ask a student to share out what their group answered. Questions to ask: Why do you think that the mechanical energy will increase/decrease? Why will this make the height higher/lower? What does positive/negative work do to the mechanical energy of the pendulum? How will we know if the mechanical energy is higher/lower?

Repeat for questions 3 and 4.

2. Prof. Lewin does not push the ball and we assume no air resistance 3. Prof. Lewin does not push the ball but we include air resistance 4. Prof. Lewin accidentally pushes the ball as he lets go
What kind of work will be done on the ball (positive / negative / none)?
What will happen to the total mechanical energy of the ball (increase / decrease / constant)?
What will be the height of the ball when it swings back to Prof. Lewin (higher / lower / same)?
Will Professor Lewin be safe (yes / no)?

Add this diagram to the slide to be clear about what I mean by “height”:

Answer question 5 on your worksheet individually.
5. Make your prediction: What will happen to the mechanical energy of the ball? How will you know if your prediction is right or wrong?

Play the rest of the video.

Show a side by side of the before (at the time of release) and after (1 cycle):

Ask the class:
I was careful to stop the video exactly when the ball reached its maximum height on the return swing. Is he at the same position or not? What do you notice about the ball’s position?

At this point there should be at least 20 min remaining in the period.

Answer the following question individually:
6. What happened to the mechanical energy of the ball, and how do you know?  What evidence tells you so?

Possible questions:What happened to the mechanical energy of the ball, and what evidence do you have? Was there work done on the ball? If so, by what force and was it positive or negative work? How can we explain what happened using the Law of Conservation of Energy? As students answer, ask for agreement or disagreement and why.

In a couple of minutes, I’m going to ask you to answer question 7 individually. But before we do that. you have 2 minutes to check with your partner and make sure you agree on what happened. This is your only chance to confer before answering question 7 on your own.

Now, answer question 7  on your own.
7. Write out a short story of what happened to Prof. Lewin’s swinging pendulum. You must answer the following questions in your story: Was work done on the ball and by what force?  What did this work do to the mechanical energy of the ball? What did we observe that told us what happened to the mechanical energy of the ball?

[5 min] Exit Ticket

Professor Lewin released a 15.5 kg pendulum from 1.20 m high. We carefully measure the height of the ball when it swings back towards him, and determine that the ball only went 1.05 m high when it came back. How much work was done by air resistance on the ball?

Collect student work. If running out of time, ask co resident to help photograph worksheets and exit tickets of case study students as a worst case fallback option.

52 min total:  ~5 min of buffer
If need be, the CONFER section of the plan can be eliminated without impact to the cognitive demand or student sense-making in the lesson.

Lesson Plan: Conservation of Energy using a Music Video

Lesson 2.2: Exploring Conservation of Energy

Unit: Work and Energy, Component 2 – Conservation of Energy
Date: January 10th, 2013
Day/Block: Day 1 –  A/E/F
Time Available: A 58min / E 48min / F 65min

You will be able to design and analyze a Rube Goldberg Machine using the Law of Conservation of Energy.

Criteria for Success:
Can I design my own machine that transfers mechanical energy between objects through work?

Can I use the Law of Conservation of Energy to explain how my design transfers energy?

Handout with machine design and analysis questions.


[10 min] DoNow:

The complicated chain of events in the music video is called a “Rube Goldberg Machine”. These machines use many transfers of energy between a whole lot of objects in order to do a very simple task.

Invent your own small (2 objects) Rube Goldberg machine. How would you use one object to make another object do something else? Where is there work and energy? How does one object transfer energy to another?


[10 min] Discussion: Music Video

Show OK Go’s music video for “This Too Shall Pass”: (4 min)

Note: Watching the video was assigned as homework the previous night, along with the following guided questions: Where do you see work? Where do you see energy being transferred from one form to another? Write down at least 1 example (note the video time), and make sure to explain what object is doing work on what other object, what kind of energy is being transferred, and how you know.

Talk to a partner next to you and share 1 example of work and energy being transferred from one object to another. I will ask several students to share an observation that their partner noticed, and explain to me what object is having work done on it and what kinds of energy are involved.

Possible questions to ask:
What did you see? Be specific, tell me what happened to the object that makes you think there was work done. What kinds of energy do you think that the object has?  How do you know that the object has that kind of energy?

Record student observations on the whiteboard.

[15 min] In-Depth Analysis: Tire

Show video clip of the tire section twice (7 second clip starting at 1:03). Ask students to write down exactly what they see happening to the tire. Have students share their observations, and assemble a record of the tire’s journey on the board to refer to later.  (Make sure that the bucket hitting the tire is included.)  Hand out the worksheet for scaffolded analysis of the tire scenario.

Refer to your handout. Take 30 seconds to answer the first question by yourself. Ask one student to share what they wrote with the class.
1. At the beginning of the scenario, does the tire already have mechanical energy? If so, what form(s) is it in, and how do you know?

Take two minutes to answer questions 2 and 3 with a partner.  Ask one or two pairs to share, depending on time.
2. During the scenario, is work done on the tire by any other object?  Is this work positive or negative, and how do you know?
3. What happens to the tire’s total mechanical energy when the work is done to it?

Take four minutes to answer questions 4 and 5 with a partner. Ask one or two pairs to share, depending on time.
4. Describe what happens to the tire’s GPE, KE, and total ME as it goes through the scenario.
5.  What happens to the tire’s mechanical energy at the end of the scenario?

[15 min] Creative Activity: Design and Analyze

Turn over your handout. Now you have a chance to design your own Rube Goldberg machine! Draw your machine in the space provided, and use the Tire Analysis as a guide to answer the analysis questions below. The questions are due tomorrow for stamps. If you don’t finish in class, please complete the analysis questions as homework.

6. Draw your own piece of this Rube Goldberg Machine that uses 1 object. You must include at least 1 transfer of energy from one object to another.

7. What is your main object in this scenario? :

8. Describe what happens to your object’s GPE, KE, and total ME as it goes through the scenario beginning to end..

9. Where is work done on your object or by your object? How does this work change your object’s total mechanical energy?

10. Explain how your machine obeys the Law of Conservation of Energy, MEi + W = MEf.

Pilot Plant in the Works for Carbon Dioxide Cleansing –

NYTimes is reporting on recent developments in carbon gas capture technologies.

Now a Canadian company has developed a cleansing technology that may one day capture and remove some of this heat-trapping gas directly from the sky. And it is even possible that the gas could then be sold for industrial use.

Love it.

Should the cost of capturing carbon dioxide fall low enough, the gas would have many customers, he predicted. Chief among them, he said, would be the oil industry, which buys the gas to inject into oil fields to force out extra oil.

Does anyone else find anything ironic about the fact that most of the CO2 cleansed from the air would then be used to extract more hydrocarbons for us to burn, thus filling the air with more CO2? Still, it’s an improvement despite the irony — we’d probably burn that new oil anyway, so scrubbing some of the previous pollution before we do it is a net gain.

Gas capture would be extremely important in developing a rational price for carbon emissions, said Dr. Fox of the British mechanical engineering society. “Whatever it costs to take it out of the air and store it away,” Dr. Fox said, “that’s the price polluters would pay if they want to put carbon into the air.”

Bingo. Large industries would no longer be able to complain the value of carbon is arbitrary in a cap and trade program.

via Pilot Plant in the Works for Carbon Dioxide Cleansing –