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The Grind > Experimental Nuclear reactor kinetic > Flashcards

Experimental Nuclear reactor kinetic Flashcards

1
Q

Why is Triga inherently safe?

A

Control
* - high and negative reactivity feedback
* - solid fuel mixed with moderator
Thermohydraulics
* - natural circulation
* - pool design
Containment
* - ambient pressure

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2
Q

How is triga fuel composed and why?

A

UZrH
H because it’s a moderator (Be is toxic, graphite is worse than H)
Zr because it’s good for neutron economy, has good thermal conductivity and is chemically stable
50/80% of fuel feedback coefficent is due to ZrH, the other part to doppler effect

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3
Q

what does the prompt fuel temperature feedback depends on?

A

pag.2

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4
Q

T_max fuel in triga?

A

1150°C

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5
Q

if water goes away from triga?

A

natural circulation air

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6
Q

Triga Mark 1 and 2 differences and similarities?

A

both pool type, water moderated, natural circulation, same fuel
triga 1 was below ground while triga 2 is above ground for easier irradiation of samples

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7
Q

What is core excess?

A

the amount of reactivity that I would get if I removed the control rods

I want it below total reactivity of rods over 2 in triga while i wnat it below 1 dollar in commercial to avoid prompt criticality

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8
Q

Triga fuel element composition?

A

8%w is U, enriched at 20%
cladding in Al or SS
graphite as reflector above and below
Now fuel has more H to be more stable

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9
Q

Triga cooling system?

A

pag 7

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10
Q

Triga CR?

A

SHIMis 3-3.5, B4C, for coarse tuning, close to center
REG is 1-1.5, B4C, for fine tuning, outside
TRANS is 2-2.5, borated graphite, for safety, middle

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11
Q

what’s the easiest way to control the multiplication factor?

A

Absorption rather than production and leakage

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12
Q

What are CR used for?

A
  • Reactivity change
  • start up and shut down
  • neutron population control
  • burnup compensation
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13
Q

What are CR made of usually?

A
  • Boron
  • Silver
  • Indium
  • Cadmium
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14
Q

Why in a PWR the reactivity of CR is higher than FR?

A

becuase FR have no temperature effect, no poisons and less burnup

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15
Q

Reactivity unit of measures?

A

pag 10

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16
Q

CR model for reactivity?

A

HP:
- homogeneous reactor
- 1 rod
- weak absorber
- 1 energy group
- no scattering
- flux is a sine

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17
Q

what’s the limit on core excess?

A

Drho_ce < Drho_tot/2

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18
Q

Why in commercial reactor each rod has a reacitivity worth less than a dollar?

A

toavoid prompt criticality

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19
Q

What is shutdown margin?

A

pag 14

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20
Q

what’s the limit on sutdown margin?

A

Drho_sm > 0.5 $

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21
Q

In which condition do you calibrate CR?

A

Criticality
zero power (no T effect)
no poison

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22
Q

write PK !

A

pag 15

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23
Q

Write PK in 1 group approx with solution

A

s1= lambda* rho0 / (beta-rho0)
s2 = -(beta-rho0) / LAMBDA

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24
Q

Reactor period method? passagges and math

A

pag 16 e 17

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25
Q

Uncertainty propagation

A

pag 18

26
Q

Subcritical method passagges?

A

pag 19

27
Q

what is M in subcritical method?

A

pag 20

28
Q

why and how do we use PK in subcritical method?

A

pag 21 e 22

29
Q

Prompt Jump with spurce?

A

pag 23
correla n1 e n0 alle due sources.
Mi sembra accessorio

30
Q

Subcritical method - calculation on data

A

pag 24

31
Q

advantages and disadvantages of subcritical moltiplication method

A
  • PRO
  • simplicity of measure
  • short measuring time
  • always subritical
  • allow shim calibration
  • Poisson distributed values
  • CONTRO
  • low accuracy
  • dependence from source charateristics
  • calibration of alfa * phi_s
32
Q

subcritical method for core loading

A

pag 26

33
Q

Rod drop method

A

A control rod is dropped in the reacotr and we measure the negative prompt jump effect.
A fast acquisition system is needed

34
Q

Inverse method

A

Startingform PK I write the reactivity as a function of the power P. It’s very precise and needs precise instrumentation to measure it. Can be used to describe transient

35
Q

What are FUEL reactivity coefficients due to?

A

Moderatorand Doppler

36
Q

what are reactivty coefficient due to in water?

A
  • Void (less moderator)
  • Temperature (spectral hardening)
37
Q

Why we want the reactivity coefficents to be negative?

A

Safety

38
Q

scheme of neutronics, thermohydraulics and reactivity

A

pag 28

39
Q

reference values for alfaT,f; alfaV,c; alfaT,mod, alfaEXP?

A

pag 29

40
Q

How does triga fuel moderate?

A
  • ZrH is good moderator for E_n > 0.137 rV
  • ZrH makes upscattering for E_n < 0.137 eV
  • ZrH is better than H for E >0.137 eV
  • DUE TO:
  • no H recoil
  • lattice vibration
41
Q

How can we quantify moderation and what are the main charateristics of a moderator?

A

Low mass number and high scattering crossection
mod = ln(E_in/E_out) * sigma_scat/sigma_abs

42
Q

under vs over moderation?

A

pag 32

43
Q

what is coeherent scattering

A

It’s when a neutron interact with the lattice and the scattering crossection increases.

44
Q

what is the doppler effect?

A

pag 34

45
Q

what causes spectral hardening and what are the effects?

A

pag 34

46
Q

How is the temperature coefficent calculated?

A

pag 35

47
Q

which effects does coolant temperature have on neutronics?

A
  • positive due to scatter with H
  • negative due to thermal voiding
    In any case is very small
48
Q

What is the void feedback coefficent?

A

If inside core is negative due to more moderation, if outside core (before reflector) is positive due to less absorption.

With void:
- f increases
- p decreases
- P_nl decreases

49
Q

It’s void coefficent positive or negative?

A

pag 36

50
Q

which parameter of 6 factor formula depends on voiding?

A

pag 37

51
Q

void coefficent measurements steps?

A

pag 37

52
Q

What is montecarlo used for?

A

To solve transport eqaution

53
Q

Difference between MC solution and determinstic solution?

A

Montecarlo is:
* - more accurate
* - continuous energy
* - good for complex geometry
* - slow
* - difficult adjoint calculation
* - statistical uncertainties

Deterministic solution is:
* - faster
* - easy adjoint calculation
* - less accurate
* - multigroup
* - complicated to compute

54
Q

Which are the principles of MC

A

-Transport
- Sampling
- Collection

55
Q

criticality in montecarlo?

A

pag 40

56
Q

What is serpent used for?

A
  • reactor simulation
  • burnup calculation
  • validation
  • full core modelling
  • coupled multiphysics
  • training
57
Q

serpent steps?

A
  • define materials
  • define zones
  • define cell to replicate
  • define neutron population history
  • define detectors
58
Q

analog vs implicit estimation

A

pag 42

59
Q

zerodimensional reactor model for triga

A

pag 45

60
Q

What are the carateristics of 1D and 3D model of triga

A

pag 46

61
Q

heat transfer coefficent?

A
62
Q

Estimating beta_eff with MC?

A

pag 43 e 44\

The Grind (6 decks)

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