Sources from NR

Question 1

What types of fuel are used in Nuclear Reactors?

Answer 1

U-235 and Plutonium-239

These are ceramic fuel pellets due to corrosion resistance and thermal conductivity issues.

Question 2

What type of fuel is used by NNPP?

Answer 2

NNPP uses highly enriched U-235. Commercial sources use 3-5% U-235, but we use much higher in Navy NP.

Question 3

Name the types of radiation emitted during the fission process.

Answer 3

Answer: Fission fragments, Beta, Gamma, Fast neutrons. Fragments and Beta are held in the metal reactor by the fuel cladding, and neutrons and gamma are able to escape and pass through.

Question 4

Overall what are the products of the fission process?

Answer 4

Overall, U-235 + thermal neutron = U-236*
U-236* undergoes fission with approximate daughter nuclei of 90 AMU and 130AMU. It also releases Beta, gamma, 2-3 fast neutrons per fission, and ~200MeV energy.

Question 5

What do the neutrons do that are produced by fission.

Answer 5

1. Cause neutron activation
2. Escape to the atmosphere and interact with components external to the reactor.
3. Be captured by U-235 and result in U-236 with no fission.
4. Survive to cause fission in another U-235 atom.

Question 6

Explain a chain reaction as it relates to fission.

Answer 6

Neutrons from one fission event survive to cause further fissions. Since they are born fast, they must be slowed down to thermal energies to efficiently cause fission to occur.

Question 7

Describe criticality.

Answer 7

Condition such that for each fission, at least 1 neutron survives to produce fission. Geometry and sufficient fissile material are required.

Question 8

What is subcritical fission?

Answer 8

Neutron losses > production

This is during one generation of neutron creation/utilization.

Question 9

What is supercritical fission?

Answer 9

Neutron losses < production. This is during one generation of neutron creation/utilization.

Question 10

What is critical fission?

Answer 10

Neutron losses = production. This is during one generation of neutron creation/utilization.

Question 11

Where can neutron losses occur?

Answer 11

Neutron losses caused by absorption of neutrons by core structures. (Don’t need to know these, but these include U238, Mn55, Co59)

Question 12

Describe the purpose of control rods in a nuclear reactor?

Answer 12

To control the rate of the fission chain reaction by absorbing neutrons causing les neutrons to continue the chain reaction.

Question 13

What does Navy Nuclear power use for control rods?

Answer 13

Hafnium (Hf)

Question 14

Which direction should control rods move to increase or decrease the criticality of a NNPP reactor?

Answer 14

Control rods inward (down) decreases fuel exposure and decreases criticality.
Control rods outward (up) exposes more of the fuel and increases criticality.

Question 15

What is a SCRAM?

Answer 15

Rapid inward movement of all of the control rods to rapidly shut down a reactor.

Question 16

What are the four purposes of the water in the Reactor Vessel. HINT HINT.

Answer 16

1. Reflector - keeps neutrons in the core.
2. Coolant - Removes heat from fission and radioactive decay.
3. Moderator - thermalizes neutrons to promote fission.
4. Shielding - attenuates radiation emitted from fission and radioactive decay.

Question 17

What is the major nuclide that causes radiation exposure during reactor operations. Note secondary sources.

Answer 17

80% is N-16 gamma radiation.
10% is from fast neutrons from fission.
10% is from capture gammas from neutron-activated components inside the reactor compartment.

Question 18

What is the major nuclide that causes radiation exposure during reactor maintenance?

Answer 18

Cobalt-60. Reasons why…

• Long Half Life; 5.27
• Decays in pipes outside the primary shield
• It can be inhaled or ingested during maintainence.

Question 19

What is the purpose of the Primary shield, what is it composed of, and where is it?

Answer 19

• Reduces gamma, neutron radiation from the reactor core.
• Liits neutron activation of other materials inside the reactor compartment.
• Limits gamma radiation in the reactor compartment after shutdowns so that personnel can enter if necessary.
  Surrounds the reactor vessel, composed of steel, lead, and water.

Question 20

What is the purpose of the Secondary Shield, what is it composed of, and where is it?

Answer 20

It limits personnel exposure to both gamma and neutron radiation coming from the reactor and its coolant system during operation.
It is located in the reactor compartment bulkheads/ surrounds the primary shield, piping, and steam generators. It is composed of steel, lead, borated poly, and virgin poly. Forward portion includes the Normal Fuel Oil Tank.