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Date May 2011 Marks available 3 Reference code 11M.2.SL.TZ2.6
Level Standard level Paper Paper 2 Time zone Time zone 2
Command term Determine Question number 6 Adapted from N/A

Question

This question is in two parts. Part 1 is about power production and global warming. Part 2 is about electric charge.

Part 1 Power production and global warming

A nuclear power station uses uranium-235 (U-235) as fuel. Outline the
(i)    processes and energy changes that occur through which thermal energy is produced.

(ii)   role of the heat exchanger of the reactor and the turbine in the generation of electrical energy.

[7]
b.
The Drax power station produces an enormous amount of carbon dioxide, a gas classified as a greenhouse gas. Outline, with reference to the vibrational behaviour of molecules of carbon dioxide, what is meant by a greenhouse gas.
[3]
e.

Markscheme

(i)   U-235 fissions / neutrons are produced;

     nuclei/neutrons have high energy/are fast moving;
     nuclei transfer (kinetic) energy to (reactor) core / neutrons transfer (kinetic) energy to moderator;
     names energy of moving nuclei/neutrons as kinetic;
     core/moderator energy transferred to coolant/named coolant/surroundings;

(ii)  heat exchanger allows transfer of (thermal) energy between reactor and coolant; coolant transfers (thermal) energy to steam/other  

     named fluid;
     steam/fluid allows turbine to drive generator/dynamo;

b.
frequency of vibration is close to that of the frequency of infrared radiation; (atmospheric) carbon dioxide absorbs the infrared radiated by the surface of Earth; the part of the radiation that is re-radiated back to Earth will cause the temperature of the surface to rise / re-radiated at a different frequency / OWTTE;

e.

Examiners report

(i) Outlines of the processes and energy changes in a nuclear power station were very poor. Examiners had to give the benefit of the doubt on many occasions. Some candidates thought that the U-235 is burnt (in the same way as a fossil fuel) to convert the energy for the process. Only rarely were there an attempt to describe the processes consistently and many answers focussed only on the operation of the turbines.

(ii) Equally, the heat exchanger and the turbine roles were poorly described and often simply repeated material from (b)(i).

b.
As in part (d) it was rare to find a well-expressed solution and in the case of incorrect evaluations, examiners found it difficult to understand what the candidate was attempting to do.
e.

Syllabus sections

Core » Topic 8: Energy production » 8.1 – Energy sources
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