TLO 4 Intrinsic And Installed Neutron Sources

Question 1

ELO 1 Describe source neutrons and their importance. Name the two types of source neutrons.

Answer 1

Source neutrons are neutrons that come from anything other than the fission process.
When the Rx is shutdown and there are no neutrons from fission, Source Neutrons allow operators visible indication of Source Range NIs.
The two types of source neutrons are “Intrinsic” and “Installed”.

Question 2

ELO 1 Define Intrinsic Source Neutrons and list their four main sources.

Answer 2

Intrinsic Source Neutrons are source neutrons that result from naturally occurring neutron sources such as:
- Spontaneous Fission
- Photo-neutron reactions
- Alpha-neutron reactions
- Transuranic Elements

Question 3

ELO 1 Define Installed Source Neutrons and list the four main source types.

Answer 3

Neutrons that come from assemblies in the reactor for the sole purpose of producing Source Neutrons.
- Californium-252
- Alpha-neutron Beryllium source
- Photo-neutron Beryllium source
- Antimony-Beryllium source

Question 4

ELO 2 Describe the type of intrinsic neutron source known as spontaneous fission.

Answer 4

Spontaneous fission is a non-induced splitting of the nucleus in some heavy nuclides/Transuranic Elements.
This can occur in heavy nuclides before, during and after power operations.
The four isotopes that contribute the most source neutrons via spontaneous fission:
- U-235
- U-238
- Cm-242
- Cm-244

Question 5

ELO 2 Describe the type of intrinsic neutron source known as photo-neutron reactions.

Answer 5

High-energy gamma rays from fission product decay interact with a deuterium nucleus to produce a hydrogen atom and a neutron (a source neutron).
Deuterium and high-energy gammas abundant at power operations; after shutdown, gamma ray emitters decay off, so photo-neutron reactions decrease.

Question 6

ELO 2 Describe the intrinsic neutron source known as alpha neutron reactions.

Answer 6

Alpha particles from heavy nuclide (including Transuranic nuclides) decay interact with boron-11 and oxygen-18 to produce source neutrons. Oxygen-18 does not produce significant source neutrons.

Question 7

ELO 2 Describe the intrinsic neutron source known as transuranic elements.

Answer 7

The Transuranic elements are beyond uranium (Z >92). They are present in the reactor before, during and after operation and provide source neutrons via spontaneous fission and alpha-neutron reactions.

Question 8

ELO 2 Describe the purpose of type of installed neutron sources.

Answer 8

Californium-252: artificial nuclide emits neutrons via spontaneous fission. Not used much due to high cost and short half-life.
Alpha-neutron Beryllium: uses an alpha-neutron reaction with Beryllium.
Photo-neutron Beryllium: gamma ray causes source neutron to eject.
Antimony-Beryllium: activated Antimony decays emitting gamma rays which interact with Beryllium to produce a source neutron. Most common in PWRs.

Question 9

ELO 4 Primary source of intrinsic source neutrons at BOL immediately following Rx trip.

Answer 9

1. Photo-neutron
2. Spontaneous Fission
3. Alpha-neutron

Question 10

ELO 4 Primary source of intrinsic source neutrons at BOL several weeks after Rx trip.

Answer 10

1. Spontaneous Fission
2. Photo-neutron
3. Alpha-neutron

Question 11

ELO 4 Primary source of intrinsic source neutrons at EOL immediately after Rx trip.

Answer 11

1. Photo-neutron
2. Alpha-neutron
3. Spontaneous Fission

Question 12

ELO 4 Primary source of intrinsic source neutrons at EOL several weeks after Rx trip.

Answer 12

1. Alpha-neutron
2. Spontaneous Fission
3. Photo-neutron