question_answer

In a controlled thermal fusion reactor, what is the function of (i) the moderator, (ii) the control rods, (iii) the coolant, and (iv)the heavy water ? \[_{92}^{236}X\to _{a}^{141}\Upsilon +_{36}^{b}Z+3_{0}^{1}n\] What are the values of the numbers a and b? Calculate the total energy released per nuclear fission in \[\mathbf{MeV}\] units when the masses in \[\mathbf{amu}\] units are of neutron \[=\mathbf{1}.\mathbf{009}\] of \[\mathbf{X}\] - nucleus\[=\text{ }\mathbf{235}.\mathbf{891}\] of \[\mathbf{Y}\] -nucleus\[=\text{ }\mathbf{140}.\mathbf{673}\] of \[\mathbf{Z}\] -nucleus = 91.791        

Answer:

                (i) A moderator slows down the fast moving neutrons produced during the fission. (ii) Control rods absorb the excess neutrons and hence control the chain reaction. (iii) The coolant removes the heat produced during fission and transfers it from the core of the reactor to the surroundings. (iv) The heavy water acts both as a moderator and a coolant. Given    \[_{92}^{236}X\to _{a}^{141}\Upsilon +_{36}^{b}Z+3_{0}^{1}n\] By conservation of mass, \[141+b+3\times 1=236\] \[b=\text{ 236 }-\text{ 144 }=\text{ 92}\] By conservation of charge, \[a+36+3\times 0=92\] \[\therefore \]  \[a=92-36=56\] Mass defect \[=m(X)-[m(\Upsilon )+m(Z)+3{{m}_{n}}]\] \[=235.891-[140.673+91.791+3\times 1.009]\] \[=235.891-235.491=0.4\text{amu}\] \[=0.4\times 931\text{MeV = }\mathbf{372}\mathbf{.4MeV}\]