REACTOR PHYSICS

Posted: Tháng Ba 13, 2010 in Vật lý hạt nhân

VIETNAM NATIONAL UNIVERSITY – HOCHIMINH CITY

UNIVERSITY OF SCIENCE

FACULTY OF PHYSICS

DEPARTMENT OF NUCLEAR PHYSICS

NAME : TRƯƠNG HOÀI ANH

 

 

SOLUTION PROBLEM OF

  NUCLEAR FISSION

 

 

DistributionofFissionEnergy

 

Theaverageenergydistributionfortheenergyreleasedperfissionwithathermalneutronin uranium-235isshowninTables

 

 

 

InstantaneousEnergyfromFission

 

KineticEnergyofFissionProducts

EnergyofFissionNeutrons

InstantaneousGamma-rayEnergy

CaptureGamma-rayEnergy

 

 TotalInstantaneousEnergy

 

167Mev

 

5MeV

 

5MeV

 

10MeV

 

    187MeV

 

 

 

 

 

 


 

 

 

 

DelayedEnergyfromFission

 

BetaParticlesFromFissionProducts Gamma-raysfromFissionProducts

Neutrinos

  TotalDelayedEnergy                     

 

7Mev

 

6MeV

 

10MeV

 

      23MeV

 

 

 

 

 

 

 

 

 

 

Becausethe 10MeV ofneutrino energyshown inTableisnot absorbed inthe reactor, the averagevalueof200MeVperfissionisstillaccurate.   NoteinTable6thatsomefission neutronsundergoradiativecaptureandtheresultantgammarayemissionprovidesanadditional

10MeVo instantaneousenergy,whichcontributestothetotalof187MeVinstantaneous

energy.

 

All oftheenergy released, with the exceptionofthe neutrino energy, isultimately transformed intoheat throughanumber ofprocesses.  The fissionfragments,withtheir highpositivecharge andkineticenergy, causeionizationdirectlyastheyriporbitalelectronsfromthesurrounding atoms.  Inthisionizationprocess,kineticenergy istransferred tothe surroundingatomsofthe fuelmaterial,resultinginanincreaseintemperature.  Thebetaparticlesandgammaraysalso giveup theirenergy throughionization, andthe fissionneutronsinteractand losetheir energy throughelasticscattering.  Ofthe200MeVreleasedperfission,aboutsevenpercent(13MeV) isreleasedatsometimeaftertheinstantoffission.   Whenareactorisshutdown,fissions essentiallycease,butenergyisstillbeing releasedfrom thedecay offissionproducts.  The heat producedbythisdecay energyisreferredtoas”decayheat.”  Although decayenergy represents about seven percent ofreactorheat production during reactoroperation, once the reactor isshut downthedecayheatproductiondropsoffquicklytoasmallfractionofitsvaluewhileoperating. The decay heat produced issignificant, however, and systemsmustbe provided to keep the reactorcoolevenaftershutdown.

Summary

  • Fissionproductshavesomegeneralcharacteristicsincommon.

                                        Theygenerallydecayby emission.

                                        Themostcommonmassnumbersaregroupednear95and140.

 

  • Theenergy releasedbyfissioncanbe calculatedbasedonthedifferencein mass between the massesofthe reactantsbeforefission and the fissionfragmentsand fissionneutronsafterfission.

 

  • Anothermethod to determinethe energy releasedby fission isbased on the change in bindingenergy per nucleonbetween the fissilenuclide and thefission products.

 

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