- WELCOME TO NUCLEAR CHEMISTRY PART 6: FISSION VERSUS FUSION.
SO WE WILL EXPLORE THE DIFFERENT REACTIONS.
BUT NOW, LET'S LOOK AT THESE BIGGER PROCESSES
THAT OCCUR IN THE SUN OR HOW WE GENERATE NUCLEAR ENERGY.
LET'S GET STARTED. RIGHT.
SO FUSION QUITE LITERAL, RIGHT?
FUSING NUCLEI TOGETHER.
THESE ARE THE REACTION IN STARS, RIGHT?
SMALL NUCLEI COME TOGETHER TO CREATE LARGER NUCLEI.
AND IN THE PROCESS, RELEASE A BUNCH OF ENERGY.
NOW, FISSION ON THE OTHER HAND, RIGHT,
SO THAT'S GOING TO BE A FISSURE
WHERE THAT'S GOING TO BE THE SPLITTING APART, RIGHT?
SO HERE WE HAVE A LARGE NUCLEI OR NUCLEUS, RIGHT?
AND THEY'RE GOING TO GET SPLIT INTO SMALLER NUCLEI.
EITHER WAY, THERE'S A BIG BOOST OF ENERGY
THAT COMES OUT THE OTHER SIDE.
ALL RIGHTY.
SO HERE, LET'S LOOK BRIEFLY AT FUSION AND SO HERE
WE SEE SOME ISOTOPES OF HYDROGEN, RIGHT.
SO REMEMBER THAT WHEN HYDROGEN HAS A MASS NUMBER OF TWO,
WE DESCRIBE THAT, RIGHT.
IT'D ALSO BE GIVEN THE SYMBOL D FOR DEUTERIUM
AND WHEN THE MASS NUMBER IS THREE,
WE GIVE THAT T FOR TRITIUM.
AND SO WHEN THESE TWO NUCLEI COME TOGETHER IN THE SUN,
THEY ARE GOING TO CREATE A HELIUM ATOM, A NEUTRON,
AND A TON OF ENERGY.
SO HERE WE HAVE--
SO HERE'S THE TYPE OF ENERGY RELEASED
FROM A NUCLEAR REACTION.
LOOK AT THAT. 10 TO THE 8TH KCALS.
LET'S COMPARE THAT WITH THE TYPE
OF ENERGY RELEASED FROM CHEMICAL BONDS, RIGHT?
SO IF WE TAKE METHANE GAS AND DO A COMBUSTION REACTION,
NOTICE THAT WE GET 213 KCALS, RIGHT.
COMPARE. PART, RIGHT?
SO-- AND THIS IS JUST ONE EXAMPLE.
SO THE THING TO KEEP IN MIND IS THAT IF WE REALLY ENJOY
THE ELECTRICITY THAT KEEPS OUR FOOD REFRIGERATED OR HOT SHOWERS
OR ELECTRONICS--
WE LIVE IN A VERY HIGH-ENERGY WORLD
AND WE ENJOY THE BENEFITS OF ALL THAT ENERGY
AND TRADITIONAL FOSSIL FUELS ARE--
WE GET OUR ENERGY FROM CHEMICAL REACTIONS AND WE SEE HERE
LIKE 213 KCALS VERSUS WHEN WE LOOK AT NUCLEAR ENERGY.
THE AMOUNT OF ENERGY HELD INSIDE THE NUCLEUS,
RIGHT, IS 10-- OH,
NO, 10 TO THE 7TH TIMES OR MORE--
HIGHER IN ENERGY.
SO AS WE MOVE TOGETHER ON OUR PLANET, WE--
IF WE WANT TO CONTINUE TO ENJOY A HIGH-ENERGY LIFESTYLE,
WE'RE GOING TO WANT TO BE OPEN
TO THE OPPORTUNITIES PRESENTED BY NUCLEAR ENERGY.
AND THEN TO LOOK HERE,
WE ALSO USE FUSION REACTIONS IN THE LAB.
FOR EXAMPLE AT A CYCLOTRON,
WE COULD TAKE A CALIFORNIUM SAMPLE AND SLAM
A BORON ATOM AND MAKE A NEW HEAVY ELEMENT, RIGHT?
SO ANOTHER EXAMPLE OF FUSION THAT--
THIS WOULD BE MAN-MADE FUSION
AS OPPOSED TO THE FUSION THAT WE SEE IN STARS.
ALL RIGHT.
NOW, LET'S LOOK A LITTLE MORE CLOSELY
AT THE FISSION REACTIONS.
WHAT EXACTLY IS GOING ON THERE?
SO, FOR EXAMPLE, IF WE HAD URANIUM 235
AND IT IS HIT WITH A NEUTRON,
THEN IT PROMPTS THE FISSION INTO BARIUM AND KRYPTON,
THE RELEASE OF THREE ADDITIONAL NEUTRONS LIKE GAMMA RAY
AND A BUNCH OF ENERGY
THAT WE CAN USE FOR OTHER PURPOSES, RIGHT.
SO THE THING TO THINK ABOUT HERE IS, RIGHT,
FOR EACH URANIUM 235, RIGHT,
WE GET MORE THAN ONE NEUTRON PRODUCED.
ALL RIGHT.
SO IF ONE OF THESE NEUTRONS
THEN GOES ON TO COLLIDE WITH ANOTHER URANIUM 235, RIGHT,
WE GET A CHAIN REACTION.
IF MORE THAN ONE OF THESE NEUTRONS GOES ON,
THEN WE GET AN EXPANDING OR BRANCHING REACTION, RIGHT?
SO WE GET MORE AND MORE FISSION PRODUCTS AND THEN
THERE IS THIS CRITICAL RAY
TO WHERE WE GET A CONSTANT CHAIN REACTION,
THAT FOR EACH OF THE NEUTRONS RELEASED,
THERE'S GOING TO BE A SUBSEQUENT--
SO IT'S A SELF-SUSTAINING.
AND WHAT HAPPENS WHEN IT GETS SUPER CRITICAL
IS THE BRANCHING CHAIN REACTION--
IT OCCURS SO QUICKLY THAT IT LEADS TO THE EXPLOSION.
AND THIS IS WHERE WE WOULD BE FOR A BOMB, RIGHT?
BUT FOR NUCLEAR ENERGY WE'RE HERE,
RIGHT, CONTROLLING THE RATE OF THE CHAIN REACTION.
SO WE'VE DESCRIBED THEM IN WORDS
BUT HERE'S A DIAGRAM TO HELP, RIGHT.
SO HERE IS OUR ORIGINAL URANIUM 235
AND THEN HERE IS THE NEUTRON THAT COMES IN AND HITS IT.
AND THAT PROMPTS THE FISSION.
SO NOW WE HAVE THE FISSION PRODUCTS
THAT PRODUCE THREE MORE NEUTRONS.
NOW, IF EACH ONE OF THESE NEUTRONS WAS TO COLLIDE
INTO A URANIUM,
THEN WE WOULD HAVE THREE FISSION PRODUCTS AND WE CAN SEE THE--
WHERE WE GET THE EXPONENTIAL NATURE, RIGHT.
SO IF WE LOOK RIGHT HERE, RIGHT, THIS WOULD--
THIS IS ONE FISSION REACTION.
IT'S DESCRIBED BY THE REACTION AT THE TOP OF THE PAGE.
HOWEVER, THIS ONE REACTION CAN TRIGGER, RIGHT,
ONE FISSION REACTION CAN-- OOPS,
LET ME SLIDE THIS UP, RIGHT--
CAN TRIGGER THREE MORE FISSION REACTIONS, RIGHT?
AND THEN NOW WE'RE LEFT WITH NINE NEUTRONS
AND WE CAN SEE WHERE IT GOES FROM HERE, RIGHT.
AND THAT'S WHERE WE GET TO HAVE THE SUPER CRITICAL STATE.
SO NOW THAT WE UNDERSTAND HOW THE FISSION REACTION WORKS,
LET'S SEE WHAT WE CAN DO TO HAVE IT--
HAVE IT WORK FOR US.
SO WE'LL LOOK AT BOMBS AND THEN WE'LL LOOK AT NUCLEAR ENERGY.
WE'LL START WITH BOMBS
BECAUSE I THINK THEY'RE A LITTLE EASIER TO UNDERSTAND.
ALL RIGHTY.
SO THE RADIOACTIVE MATERIAL IS ON THE INSIDE RIGHT HERE.
OKAY. AND NOTICE IT'S SUBCRITICAL.
SO-- AND IT'S ALL HAS TO DO WITH THE PHYSICAL GEOMETRY.
RIGHT NOW, THE RADIOACTIVE SOURCES ARE
ALL PHYSICALLY FAR APART AND SO THEY'RE RELEASING NEUTRONS
BUT THE ODDS ARE THE NEUTRONS JUST HIT SOMETHING ELSE.
THEY DON'T SPARK THE CHAIN REACTION.
AND SO THEN
WHAT WE HAVE ON THE OUTSIDE OF THE RADIOACTIVE MATERIAL
IS THE CONVENTIONAL EXPLOSIVE.
SO WHAT HAPPENS IN A NUCLEAR BOMB IS WE INITIATE THE EXTERNAL
CONVENTIONAL EXPLOSIVE
AND IT DRIVES ALL OF THE NUCLEAR MATERIAL INTO THE CENTER.
AND NOW, BECAUSE OF THE CLOSE PHYSICAL PROXIMITY,
THE RADIOACTIVE MATERIAL IS NOW SUPER CRITICAL
BECAUSE IT'S SO CLOSE TOGETHER
THAT THE NEUTRONS CAN'T HELP BUT BUMP IN TO OTHER URANIUM ATOMS
OR PLUTONIUM ATOMS AND SO WE GET THE EXPLOSION. BOOM.
SO WE COULD DO THIS IN A SPHERICAL ARRANGEMENT
OR THE SAME IDEA,
WE COULD HAVE IT IN A LINEAR ARRANGEMENT
WITH THE SAME IDEA AND THEN WHEN THE FIRST EXPLOSION GOES,
IT PUSHES THE NUCLEAR MATERIAL
TOGETHER CREATING THE SUPER CRITICAL MASS
AND WE GET THE BOOM.
ALL RIGHTY.
SO NOW WHAT HAPPENS WITH THE NUCLEAR POWER PLANT
IS WE SEE WE CONTROL THE DISTANCE,
THE AMOUNT OF FUEL AND WE PUT UP--
WE CAN CONTROL THE RAY SO THAT IT DOESN'T GO TO AN EXPLOSION.
SO HERE IS A SIMPLE SCHEMATIC, RIGHT?
THAT WE HAVE THE RADIOACTIVE FUEL,
RIGHT, SO THAT'S THE RADIOACTIVE FUEL
AND THEN WHAT WE DO IS WE HAVE CONTROL RODS, RIGHT?
AND THESE TEND TO BE NEUTRON ABSORBERS.
SO, WE CAN CONTROL, RIGHT--
THE CONTROL RODS CAN GO IN AND OUT.
AS THE CONTROL RODS GO IN,
THEY'RE ABSORBING THE NEUTRONS AND THEY SLOW DOWN THE REACTION.
AS THE CONTROL RODS ARE LIFTED UP,
THE REACTION PROCEEDS AT A HIGHER RATE.
IT'S A HIGHLY EXOTHERMIC REACTION
AND SO WE GET A BUNCH OF HEAT.
THAT HEAT IS USED TO BOIL WATER, CREATING STEAM.
THE STEAM THEN TURNS THE TURBINE AND GENERATES ELECTRICITY.
ALL RIGHT.
SO IT'S IMPORTANT TO REMEMBER THAT ALL FORMS
OF ENERGY HAVE NEGATIVE CONSEQUENCES.
WE ARE LOOKING AT HUGE AMOUNTS OF CARBON DIOXIDE
IN OUR ATMOSPHERE RIGHT NOW THAT ARE CAUSING GLOBAL WARMING
AND EXTREME WEATHER CONDITIONS.
COAL MINERS IN DEPTH WITH LUNG DISEASES AND LUNG CANCERS.
AND SO WE JUST WANT TO--
AS WE GO INTO THE FUTURE TOGETHER,
WE WANT TO BE AWARE
OF WHAT THE ENERGY CHOICES ARE AND THAT THERE ARE WAYS
TO WORK WITH NUCLEAR ENERGY IN A SAFE AND RESPONSIBLE WAY.
SO PLEASE TAKE SOME TIME NOW TO WORK A FEW HOMEWORK PROBLEMS
TO REINFORCE YOUR UNDERSTANDING,
AND I'D ALSO LIKE REALLY ENCOURAGE TO TAKE
THIS UNDERSTANDING AND WISDOM
WITH YOU INTO THE FUTURE AS WE DECIDE TOGETHER
WHAT THE BEST ENERGY CHOICES ARE FOR OUR PLANET.