Development of Technologies for scaling up
Retrieval of Fuel Debris and Internal Structures(Development for Dust Collection System ofFuel Debris)
Final report for FY 2019 and 2020

Project Main Goals
1

Assessment of dust generation regularity, amount, content and distribution depend on several cutting methods
and conditions






2

Types of generated aerosols, vapor phase, solid particles
Dust amount and particles size strongly depend on cutting methods and cutting conditions
Dust distributes in space irregularly
Particles with different sizes have a different penetrate capability
Particles with different sizes have a different deposit rates

Assessment of separate filtering elements and integrate dust collection system efficiencyFiltering units efficiency depends on types of generated types of aerosols, vapor phase.
Filtering elements efficiency depends on them filtering principle and them position in the system
Different filtering materials could change there properties depend on dose loading

3 Development of initial technical requirements and conceptual design of full scale dust collection system“Dust”
Aerosols (tenths to 10 µm)
LiquidBased onROSATOM
experience






Solid

Solid particles > 10µm
(coarse dust)

Vapor phase(molecule to tenths µm)> 500 μm particles will deposit immediately<50 μm - cloud of long-term floating particles
0.1 – 0.3 μm particles – most dangerous (have the most penetrate capability)< 0.1 μm particles – mostly stick together and generate large conglomerates

2

Russian experience in the field of dust collection
system development and operating review (1/2)
 Report’s content
o real Russian experience in the operation of various gas cleaning systems at the enterprise of
the nuclear industry.
o list of main devices of gas-aerosol cleaning systems used at the enterprises of the nuclear
industry of Russia and MAYAK Plant and them technical description.
o summarizing data on all methods of localizing radioactive gaseous waste, both for normal
operating conditions of equipment and for high-temperature processes.
o overview of methods and equipment for collecting sols (dust) from liquid media and theinfluence of the state of pollution on the choice of cleaning methods.
o Initial recommendations for dust collection system development.
o Explosion and Fire Safety aspects.
Citation:“… The decontamination factors of sequentially installed filters are not equal to each other and theysignificantly decrease along the gas flow. Understanding how the cleaning factor changes with anincrease in the number of filters in the gas cleaning system is of very practical importance and should
be taken into account when developing and creating gas cleaning systems…”

3

Russian experience in the field of dust collection
system development and operating review (2/2)
 Analysis of causes of the formation of explosive and fire hazardous situations in the gas-aerosol treatment
processes
Flammability risk for Zr-Nb alloy (and metallic Zr the same):

Based onROSATOM
experience







Particle size > 600 μm → combustion is impossible
Particle size < 50 μm, concentration >20% → momentary local combustion points is possible
Particle size < 50 μm, concentration >30% → low-flammable environment
Particle size < 50 μm, concentration <20% → low-combustible environment
Dewy particles with moisture mass content 3 – 7% → flammability risk (because of H2 generation)

Flammability risk for Uranium & Plutonium dioxide: Explosion and fire safety materials
Brief conclusions:o All components of fuel contain material (FCM), except for zirconium are non-combustible and do not pose a fire
hazard with any handling in the discussed technological processes.

oWhen the mass content of metallic Zr in the FCM is 10% or less during the cutting of FCM fragments, theformation of finely dispersed Zr with pyrophoric properties is possible. In this case, Zr particles will bephlegmatized by non-combustible components, the formation of combustible dust is excluded. For the same
reason, the accumulation of dust with combustible properties in the units of the gas cleaning system is unlikely.

4Sample types description
Type A
A-1

Type C

A-2

3.73 g/cm3

Components
HfO2
ZrO2
Stainless steel
SiO2
CaO
Al2O3
Fe2O3

press force - 2 t
t°C =1400•••

Type B

10.59 g/cm3

4.1 g/cm3

mass,%
30
16
7
31
6
7
3

•

Unirradiated MOX fuelplaced in a Zr-Nb alloy
U-Pu dioxides
Pu content 2.7-5.3%••[Cutting experiments
implemented using of RIAR
existing vacuum system]

C-1

C-2

D
with Pu

D*
without Pu

10.2-10.4 g/cm3

10.2-10.4 g/cm3

9.4 g/cm3

9.4 g/cm3

SNF WWER placed in a
tube Zr-Nb alloy
235U – 4.4%,
46.31 MW/day×kg
9 years 6 month•••

1F SNF (U1-U2) properties:• 45 MW/day×kg• >10 years• 235U – 3,6 – 3,8%

press force - 2 t
t°C =1000
2 hours exposition[ON AIR]
Diamond bit
Carbide millDisc cutter

•

•
•
•

[ON AIR]
Carbide millLaser cutting[IN WATER]
Carbide mill•••Type D[ON AIR]
Carbide millLaser cutting[IN WATER]
Carbide mill

•
•
•
•

MOX SNF placed insteel tube
235U – 0.6%,
U/Pu=5.68/1
47.39 MW/day×kg
3 years

1F SNF (U3) properties:• 33 MW/day×kg• >10 years•[ON AIR]
Carbide millComp.

mass,%

UO2
ZrO2
FeO
Cr2O3
NiO

50.93
14.0
3.05
0.91
0.47
16.82
3.14
4.24
0.98
0.97
3

SiO2
CaO
Al2O3
Zr
Fe
PuO2
Melting at t°C =1480[ON AIR]
Carbide millLaser cutting[IN WATER]• Carbide mill••[Cutting experiments implemented using of laboratory scale dust collection system inside the hot cell]

The samecomposition,
but without
Pu[ON AIR]
Carbidemill• Laser
cutting•5

Laboratory scale dust collection systemmanufacturing, assembling and testing6

Laboratory scale dust collection system main aims
Due to the fact of many uncertain factors of dust generation during the real fuel debris (FD) retrieval on FukushimaDaiichi (1F) site we provide the number of cutting experiments with laboratory scale dust collection system to study
the following phenomena and aspects which should be taken into account on stage of full-scale system design
development:

1

Types of generated dust and their special properties (solid particles, solid/liquid aerosols, vapor phase).

2

Generated dust particles distribution throughout the cutting point – dust collection system’s filtering units
depending on cutting methods and conditions.

3

Determination of generated dust particles granulometric composition (particles size), mass and dust
particles concentration and specific activity depending on cutting methods and conditions.
Different dust accumulation mechanisms examination as well as different filtering materials examination
depending on cutting methods and conditions.

4
5
6Influence of different types of generated dust (solid particles, aerosols, vapor phase) on filtering
apparatus.
Examination of optimal air-flow rate in a suction unit and in laboratory scale dust collection system toremove as much dust particles from cutting point as possible and collect in Cyclone filter as much dust
particles as possible.

7

How our conservative cutting tests results could be“Conservative” = the worst conditions than on 1F site.
useful on 1F site ?
Samples C cutting => huge dose rate + high α-nuclides concentration + highconcentration of smallest dust particles (carbide mill 1000 rpm)

The number of samples with different properties:

Different cutting methods:

Samples A → imitate the granulometric composition of

Mechanical cutting → provide the high concentration

cutting products of silicate phase of 1F corium
Samples D → imitate the granulometric composition of
cutting products of 1F corium simulants
Samples C → provide the most conservative conditions(e.g. α-nuclides concentration) for dust collection systemof smallest dust particles (carbide mill 1000 rpm)
High temperature cutting→ provide the vapor gas
fraction and smallest dust particles (like a molecule insome cases) (laser 2.4 kW)

On-air/ In-water cutting conditions

Useful Outputs:

Results of comparison the dust particle granulometric composition dependent on samples type and cutting methods allows us topredict the potential 1F dust particles granulometric and specific activity diapasons.



Confirmed the effectiveness of filtering materials and separate filtering units depend on dust particle size, mass and specific activity.
These filtering materials and filtering mechanisms could be recommended for 1F full scale dust collection system. Necessary safetyassessments could be provided to Japanese regulatory bodies.



Recommendations for providing the fire, explosion safety and criticality control of full scale dust collection system operating.



Recommendation for full scale dust collection maintenance and separate filters changing.

8

Laboratory Scale Dust Collection System 3D View
High porosity
cellular filters

Main blower

Block of finefilters (HEPA 1,
HEPA 2)∅25mm

Electromagnetic valves∅10mm

Input fine filter
Aerosol filter

Blower

∅25mm
∅10mm

Samplers

Cyclone filter

Variable air flow
metersCutting box withcarbide mill

Local suction
unit
Cutting box with
laser

9

Dust particles mass and activity balance determination
Input finefilterCutting box

Cyclone filter

mfilter
msurface Cycl

High porosity
cellular filter

Fine filters

mfilter

LegendSampler #3[D12,22,32,42][D13,23,33,43][D441, 442]

[D451, 452]

[D461, 462]

Qsampler#1

Qsampler#2

Qsampler#3

Qsampler#4

Qsampler#5

Qsampler#6•

Vsampler#1
msampler#1

Vsampler#2
msampler#2

Vsampler#3

Vsampler#4

Vsampler#5

Vsampler#6

mtot

mtool

mwall

mwall

msurfacemcut
mcut

Removable bottom

HEPA 2

Sampler #2

Qmain gas

HEPA 1

Sampler #1
Cartridges No. [D11,21,31,41]

•
•
•
•
•
•
•
•
•
•
•

Qmain gasmwall

mcut Cycl
Removable bottom

Measuredparameters

mcut Cycl

Sampler #4 Sampler #5

Sampler #6

msampler#3

Asampler#1

Asampler#2

Asampler#3

Asampler#4

Asampler#5

Asp-sampler#1

Asp-sampler#2
P#2

Asp-sampler#3
P#3

Asp-sampler#4
P#4

Asp-sampler#5

Asampler#6
Asp-sampler#6

P#5

P#6

t, φ#2t, φ#3t, φ#1

mtot (mg or Bq)＝msample-before-cut - msample-after-cut = mtool + mcut+m surface +mwall+mfilter

Transfer fraction in air = mtot / msample-before-cut

•
•
•
•
•
•

Q – air consumption, dm3/min
T – cutting duration, min
V – pumped air volume, dm3
A – activity, Bq
Asp- specific activity, Bq/dm3
D=msampler#/Vsampler# – dustiness, mg/dm3
m – dust mass, mg
P – pressure, kPa
t- temperature, °C
φ – humidity, %msurfaceCycl – mass of the dust accumulated oninternal Cyclone filter surfaces
mcutCycl – mass of the dust accumulated in
Cyclone filter removable bottom
mtot=msample-before-cut-msample-after-cut
mcut=mbottom-befor-cut-mbottom-after-cut
mtool= mtool-before-cut - mtool-after-cut
mfilter= (D#n-D#n-1)˟ Qmain gas ˟ T
msurface - is determined by taking the numberof smears.
m wall = m tot - m cut - m surface - m tool - m filter• Filter’ aerosol effectiveness =Asp-sampler#n/ Asp-sampler#n-1• Integral dust collection system aerosols
effectiveness = Asp-sampler#6 / Asp-sampler#2

10

Laboratory scale dust collection on RIAR site inside theK-10 hot cell
Electromagnetic valves
Samplers
Mechanicalcutting engine

High porosity
cellular filter

Aerosol filter
Laser head
Cyclone filter
Cutting box

Variable air flow
meters11

Cutting Boxes General View
Inside the cutting box

Samples fixator unit
inside the cutting unit

Carbide mill

Carbide mill
SampleLocal suction unit
Cutting box
Laser cutting system 2,4 kW

Chucking
systemVideo
cameraCarbide millCutting box
Removable bottom of
cutting box

12

Cutting experiments results
Samples A cutting

13

Samples A cutting experiments results
Disc cutter, 60 rpm

Experimental cutting scheme
Fluoroplastic
membranemDiamond bit,1000 rpm

Qm

Air flow rate
25 m/sec

Carbide mill,
1000 rpm
Samples A cutting reasons
 to develop initial technicalrequirements for laboratory scale
dust collection systemto select the most conservative
mechanical cutting method

Steel backCutting experiments conditions:On-air, temperature 24-25 °C,
Humidity 26.4-27.3%

A-2 density
4.1 g/cm3

A-1 density
3.73 g/cm3

Fluoroplastic membrane, µm~40 %w~40 %w
A-1[carbidemill]

A-1[diamondbit]

A-2[carbidemill]

A-2[diamond
bit]

A-2
[disc
cutter]Dust particles generation intensity, mg/sec

Steel back, µm

Comparison of results of dust distribution

Dust particles size distribution

14
More details you could find in Appendix 1

Samples A cutting tests conclusions
 Carbide mill 1000 rpm cutting generates the smallest solid dust particles, ~40 wt%. of such generated dust
was collected with existing vacuum system (air flow rate 25 m/sec). Average size of solid dust particles
generated with carbide mill was in diapason 0.34-50 µm.
 Disc cutter 60 rpm generates the biggest solid dust particles, most part of it (~90-95 wt%.) was accumulated
on steel back. Average size of solid dust particles generated with disc cutter was in diapason 1-100 µm.
 Average dust particles size diapason was 0.34 – 800 µm.
 Thus, carbide mill 1000 rpm will be used as conservative mechanical cutting method in laboratory scale dust
collection system for sample B, C, D cutting.

15

Cutting experiments results
Dust behavior phenomena and aspects during samples
B, C, D, D* laser cutting

16

Dust behavior phenomena during laser cutting (1/2)
Laser cutting power was in diapason from 1.2 to 2.4 kW depending on cutting experiment
Splatters

Results of hot vapor phase interaction with cartridges equipped

Splatters

Laser cutting process and general view of sample after laser cutting

Laser cutting method provides:with HEPA material
HEPA material with• Sample’s materials evaporation
accumulated cooledmelted particles• Hot vapor phase of sublimatedmaterials generation• High dust generation intensity• Low efficiency of Cyclone filter
Darkened area
Darkened area
• HEPA material destruction due to theon cartridge afteron cartridge after
direct interaction
1st HEPA
2nd HEPA• Average temperature in cutting box –General view of HEPA material after laser cutting
50 °C during cutting, averagehumidity – 11%

Globule like particles accumulated in
Cutting box and Cyclone filter

Cartridge equipped withmetal grid is covered withfine solid particles

Initial SEM image

U

O

Pu

Cm

Cs

Eu

Ce

Zr

Ultra-fine particles
adhered together
200x

General views of melted dust particles and ultra-fine dust particles

SEM-image of different dust particles types after laser cutting

17

Fig. 1of
SEM
images of fragmentof
industarea 1particle
and elements
distribution
maps
Results
determination
element
composition

Dust behavior phenomena during laser cutting (2/2)
C-1 sample [1,2 kW]
D sample [1,44 kW]

Globuleparticles

Ultra-fineparticles
conglomerates
D* sample [2,4 kW]
B sample [1,24 kW]

Solid dust particles granulometric composition
determination results

•
•
•
•
•

Average filtering units
effectiveness (weight ofaccumulated dust), %Cyclone filter – 20%
HEPA 1 filter – 95,83%
HEPA 2 filter – 71,43%
Cellular filter – x
Total efficiency – 99,05%

Dust particles concentration distribution, mg/dm 3

Dust particles elements composition

•
•
•
•
•

Dust mass generation intensity in cutting point, mg/sec

Average filtering units
effectiveness (sp.activity
accumulated dust), %Cyclone filter – x
HEPA 1 filter – 99 %HEPA 2 filter – 76,1%
Cellular filter – x
Total efficiency – 99,98%

Dust particles β,γ specific activity distribution, Bq/dm3(logarithmic scale)

CONCLUSIONS• Laser cutting provides high dust mass
generation intensity up to 46 mg/sec• Laser cutting provides hot and highly
penetrated vapor phase generation• Cooled and adhered particles average
size → 1-50 µm - 58%, >101 µm – 38%• Melted dust particles contains mostly U
and Zr dioxides• Approx. 40-50 wt% of generated dust
were collected by dust collection system

18Fine filters degradation after B, D, D* samples
New fine filters
Used
HEPA 1
cutting
Before the Samples C cutting wechanged the both fine filters in a maingas duct

All filter’s surface
was darkened dueto the vapor phaseinteraction

Results ofinteraction ofhigh temperaturesmall globule likeparticles withhigh air flow
speed

Used HEPA 2

Local darkened
areas

o

As a result of high temperature laser cutting vapor phase andmelted hot particles were generated and collected with dust
collection system.

oLimited space in K-10 hot cell has restricted the dimensions oflaboratory scale system and as a result hot particles and vapor
phase did not have enough time to cool down before fine filters.

oDue to the hot vapor phase and hot particles influence, the filtering
material was partially damaged, effectiveness of fine filters was
reduced.

o

We recommend to use preliminary enlarging and air cooling stages
in a full-scale dust collection system to enlarge ultra fine solid
particles, aerosols and vapor phase and to protect the following
cleaning stages and safe its efficiency for a long period.

19

Cutting experiments results
Dust behavior phenomena and aspects during samples
B, C, D, D* mechanical cutting on-air

20

Dust behavior phenomena during carbide mill cutting (1/2)

Carbide mill cutting 1000 rpm
Local
combustions

Carbide mill on-air cutting method provides:• Local combustions during the cutting(due to the friction between mill and ZrNb sample’s tube)• Ultra-fine solid aerosols generation• High filtering efficiency of Cyclone filterand HEPA filters

Local
combustions

Dust particles and huge fragments accumulated in removable bottom of
Cutting box

Mechanical cutting on-air process and general view of sample after mechanical cutting on-air
Middle part of cartridge
contains mostly fuelmaterials dust particles

Solid particles
0.1-4 µm

Periphery partcontains mostly ZrNb shavings

Cyclone filter
removable bottom
Zr-Nb
shavings

Zr-Nb
shavings

Nuclear fuelcomposition

Nuclear fuelcomposition

Enlarged view of dust particles collected in Cyclone filter

Enlarged view of dust particles collected in samplers on metal grid

Enlarged view of dust particles collected in samplers on HEPA material

21

Dust behavior phenomena during mechanical cutting (2/2)
C-2 sample[carbide mill]

D sample[carbide mill]

A-2 sample[disc cutter]A-1 sample[diamond bit]
B sample[carbide mill]

•
•
•
•
•

C-1 sample[carbide mill]

A-2 sample[diamond bit]

B sample + loaded filter[carbide mill]

•
•
•
•
•

Average filtering units
effectiveness (sp.activity
accumulated dust), %Cyclone filter – 99 %HEPA 1 filter – 99,2 %HEPA 2 filter – x%
Cellular filter – x
Total efficiency – 99,98%•••

Vapor phase
penetration

Dust particles concentration distribution, mg/dm3(logarithmic scale)D* sample[carbide mill]

Dust mass generation intensity in cutting point, mg/sec

Solid dust particles granulometric composition determination results

Average filtering units
effectiveness (weight ofaccumulated dust), %Cyclone filter – 93%
HEPA 1 filter – 46%
HEPA 2 filter – 85%
Cellular filter – x
Total efficiency – 99,5%

A-1 sample[carbide mill]

A-2 sample[carbide mill]

Dust particles β,γ specific activity distribution, Bq/dm3(logarithmic scale)•

CONCLUSIONS
Mechanical cutting provides dust
mass generation intensity up to 22
mg/sec (twice lower than laser cutting)
85 wt% of dust particles have a size
from 1 to 50 µm, 2.6% - <1 µm
Due to the local short term
combustions vapor phase was
generated as well
Approx. 30-40 wt% of generated
dust were collected by dust
collection system

22

Cutting experiments results
Dust behavior phenomena and aspects during samples
B, C, D carbide mill cutting in-water23

Dust behavior phenomena during cutting in-water (1/2)
Carbide mill in-water cutting method provides:• Generation liquid aerosols• Negative influence on HEPA filters efficiency[mostly due to the changing of fiberglass
properties in wet condition]
Fogging ofcameraMechanical cutting in-water process and general view of sample after mechanical cutting in-water

General view of cutting box for in-water cutting (withbubbling system)

Dust particles and huge fragments accumulated in removable bottom of Cuttingbox

Sifting of the dust particles accumulated in removable bottomof cutting box

Liquid aerosols tracks on cartridges equipped with HEPA material

24

Dust behavior phenomena during cutting in-water (2/2)
C-1 sample[carbide millin water]

D sample[carbide millin water]
B sample[carbide millin water]Solid dust particles granulometric composition determination results

•
•
•
•
•

Average filtering units
effectiveness (weight ofaccumulated dust), %Cyclone filter – 25%
HEPA 1 filter – 60%
HEPA 2 filter – x
Cellular filter – x
Total efficiency – 90%

Dust particles concentration in air distribution, mg/dm 3(logarithmic scale)

•
•
•
•
•

Dust mass generation intensity in cutting point, mg/sec

Average filtering units effectiveness(weight of accumulated dust), %Cyclone filter – 32%
HEPA 1 filter – 96%
HEPA 2 filter – x
Cellular filter – x
Total efficiency – 96,75%

Dust particles β,γ specific activity distribution, Bq/dm3(logarithmic scale)

CONCLUSIONS• Mechanical cutting provides high dust
mass generation intensity up to 22
mg/sec (same as mechanical cutting on air)
• 60 wt% of dust particles have a size
more than 100 µm• Up to 4 wt% of generated dust amount
were collected by dust collection
system• Liquid aerosols were generated and it
was a reason of HEPA filters efficiency
reduction

25

Cutting experiments conclusions

26

Cutting tests summary infographic (1/2)
2.6%
4 %w

8.9%

8.9%

4.5%

20.7%

32 %w

16.1%

Carbide mill
1000 rpm
61.5% In-water 13.4%

38% Laser cutting
1.2-2.4 kW
3.5%

37.8%
<1 µm – 0.02%+ vapor phase

31%

Carbide mill
56.1%
1000 rpm+ vapor phase in
on-aircase of local
combustions in
cutting point<1 µm – 0.05%+ liquid aerosols

Dust particles granulometric composition in cutting point, %w
Laser cutting
on airCarbide millon air

49 %w

Diagram of generated dust mass distribution, %w
1,8E+10 Bq/m3
С-2 mill cutting on air

Carbide mill
In water

99,995% of
these activity
isaccumulated
in fine filters

Dust mass generation intensity in
cutting point, mg/sec

Dust mass generation intensity in cutting
point, dust particle size vs mg/sec

Dust specific activity intensity in local
suction unit of full-scale system system
adopted for 1F*, Bq/sec

7,9E+09 Bq/m3
С-1 laser cutting on air

99% of thisactivity is
accumulated inpreliminary andcentrifugal
cleaning stages

Dust specific activity in a local suction
unit of full-scale system system adopted
for 1F*, Bq/m3*Based on JAEA-Data/Code 2012-018 “Estimation of Fuel Composition in 1F NPP” modeled and calculated average 1F corium
specific activity was up to 6,3E+09 Bq/g and planned air consumption in a full-scale system 350 m3/h

27

Cutting tests summary infographic (2/2)
C-1 laser cutting
1.2 KW

Dust particles concentration in air, mg/dm3

C-2 carbide mill on-air
Vapor
phase

Air specific activity (β,γ) Bq/m3(logarithmic scale)(logarithmic scale)

Vapor phasetransferring

D samplelaser cutting

C-1 sample carbide mill in-water

C-1 laser mill in-water

D carbide mill on-air

In-water cutting
Wet aerosols washed the internal surfaces

C-1 sample carbide mill on-airoMore powerful laser provides higher dust particles concentration in air.

o

Air flow rate higher than 22 m/sec reduces of collected amount of dust
particles from cutting zone and amount of dust particles accumulated in
Cyclone filter.

oOptimal air flow rate (~22 m/sec) and low air flow resistance of fine filters
provide better dust collection process isokineticity.

oLots of cutting operations provide the accumulation of dust particles on finefilters and increase its air flow resistance, thus isokineticity is changed andlow dust amount is collected by dust collection system.

oLaser cutting as a high speed carbide mill cutting provide the generation of28
highly penetrated vapor phase.

Optimal air flow rate – 21-22 m/sec

Diagram of %w dust distribution depending on air flow rate value

Cutting experiments main conclusions (1/3)
Common conclusions
1. Using “hot” samples with nuclear materials and fission products allowed us to detect dust penetration through the filters in case where we wereunable to detect an increase in the dust mass on filters. Also, “hot” samples allowed us to determine the conservative (worst) values of assumed
contaminated air specific activity in cutting point.
2. The particles which penetrated the filters in the largest volume have a size of 0.1-0.3 µm. Russian and worldwide experience review shown thatmost part of gas cleaning systems efficiency are examined with fogs with same particle size.
3. Approx. 40-50% of generated dust particles were successfully collected as contaminated air be the dust collection system in case of laser cutting,30-40% in case of mechanical cutting on air and up to 4-5% in case of mechanical cutting in-water.
4. Approx.70% of accumulated dust particles have a size from 1 to 50 µm, 23% - more than 100 µm and up to 2% - less than 1 µm. It should be notedthat ultra-fine particles as well as particles less than 5 µm mostly stick together during the interaction and form large conglomerates.
5. Dust solid particle’s generation intensity close to the cutting point was up to 46 mg/sec in case of laser cutting and up to 22 mg/sec in case of
carbide mill cutting on air and in-water.
6. Solid dust particles concentration close to cutting point was ~0.3 g/m3 in case of laser cutting, ~0.11 g/m3 in case of carbide mill cutting on-air and~0.014 g/m3 in case of carbide mill cutting in-water.
7. Upper worst contaminated air specific activities close to cutting point are up to (β,γ) 9.91E+09 / (α)8.02E+07 Bq/m3 (for case of Unit 1,2 1F) and up
to (β,γ) 1.8E+10 / (α)2.9E+08 Bq/m3 (for case of Unit 3 1F).* We assume that real 1F contaminated air specific activity during FD cutting will be lessthan mentioned values due to the more than 10 years “storage” period.

29

Cutting experiments main conclusions (2/3)
Common conclusions
8. Results of dust solid particles distribution demonstrate that optimal air flow rate for suction unit and main gas duct should be 21 – 22 m/sec during
the FD cutting operations. Depend on real distance between cutting point and local suction unit it will be necessary to recalculate airflow rate
and/or air consumption in a main gas duct.
9. Cyclone filter (imitation of centrifugal dust collection principle) allows to accumulate up to 60-70% of dust particles with a size of more than 10 µm
collected with the dust collection system. Wherein we determine the effect of abrasive solid particles interaction between each other and the
Cyclone filter internal walls, smallest particles are also generated after it.
10. Our experiments have shown than approx. 2-3% of the mass of collected dust could precipitate on internal walls of the main gas duct, samplingducts and filters. After the accumulation of the significant dust layer on internal walls and the input liquid aerosols, it could be possible to wash ahigh concentration of dust particles onto the following filters instantly.
11. Our experiments have shown that total effectiveness of two consecutive HEPA filters is not equal to the sum of the effectiveness of each separate
filter. It’s reasonable to consider the effectiveness of both filters as 105 in total.
12. Our experiments have shown that HEPA material safes its efficiency even under total alpha activity 5E+07 Gy loading.
13. Our experiments have shown that in case of mostly metal oxides corium phase mechanical cutting on air with high cutting speed there are local
flammable risk in cutting point and risk of accumulation of flammable Zr concentration on filters. Special prevention countermeasures should be
provided.

30

Cutting experiments main conclusions (3/3)
Laser cutting aspects
1. Generation of ultra-fine aerosols (< 1µm) and highly
penetrated vapor phase of sublimated materials.
2. Generation twice higher concentration of 1-50 µm solid
particles concentration in cutting point and before firstcleaning stage than carbide mill cutting on air.
3. Fiberglass/HEPA materials could be partially destructed after
the interaction of hot melted particles of sublimatedmaterials.
4. It should be noted, that the risks of challengeable vapor phaseof Cs and I generation during laser (or any other hightemperature) cutting of FD should be taken into account.
5. Cyclone filter partially could not allow to accumulate the hotvapor phase of sublimated materials.

Mechanical cutting aspects
1. High speed mechanical cutting could provide the local
combustions in cutting point and generation of ultra-fineaerosols and vapor phase as well.
2. Mechanical cutting in water generates liquid aerosols andreduce the efficiency of fiber glass materials on the following
cleaning stages as well as reduce the visibility of video control
system.
3. Wet (in case of in-water cutting) fiberglass/HEPA materials
irreversibly changed its properties such as the distance
between fibers and fiberglass density, such materials
effectiveness is reduced. Such filters should be replaced after
wetting.
4. Cyclone filter partially could not allow to separate of total
amount of generated liquid aerosols from contaminated air.

31

Recommendations for full-scale system basedon cutting experiments results
Based on cutting experiments results we could strongly recommend for full-scale system the following:
1. To use preliminary cleaning stage (cooling and enlarging) for:•cooling of input contaminated air and prevention of the finer filter’s filtering material (fiberglass, fiber mats, HEPA) destruction as
result of hot particles interaction in case of high temperature cutting,•partially reduction of input dust particles, aerosols (and vapor phase in case of high temperature cutting) concentration/specificactivity in contaminated air before the following filtering stages,•

partially reduction of input Zr-contained dust particles concentration and same particles enlarging to prevent the accumulation of
flammable concentrations on the following filters. *Also, we recommend to replace fine filters before the FD retrieval operationsuspension or long works stoppage.

2. To use centrifugal dust accumulation mechanism (Cyclone like filters) for accumulation of most part of enlarged aerosols and solid
particles with size more 10 µm with efficiency up to 60%.* Also, we recommend to use of improved version of centrifugal filter (e.g. SOTAR)
with possibility of forced dust particles and aerosols enlarging within mixing with wet steam to increase the filtering efficiency up to 90%.
3. To use the remotely decontaminated fine filter (e.g. FARTOS) before the HEPA filters to increase the HEPA filters lifetime.
4. To use two consecutive last fine filters to provide guarantee total filtering efficiency in case of unforeseen penetration of ultra-fine dust
particles.

5. To use special vapor Cs, I cleaning stages to prevent of risk of mentioned nuclides discharging in atmosphere.
6. To provide the possibility of first cleaning stages remotely decontamination to prevent of accumulation the significant dust layer inside.

32

Initial technical requirements for full-scale
dust collection system

33

Initial technical requirements for full-scale dust
collection system (1/2)
Current environmental conditions inside the PCV/RPVForecast of dry FD’s surface dust generation

Air conditions
Unit #

Average temperature inside

1

Radioactive concentration inside
the Units
7.1E-01 to1.4 Bq/dm3

2

100 Bq/dm3

3

ND

18.6 °C (inside RPV)
19.5°C (closed to the PCV bottom)
19 °C (inside RPV)
20°C (closed to the PCV bottom)

15.3 °C (inside RPV)
21.7°C (closed to the PCV bottom)

Average humidity
insideUp to 99,9%

Water injection
capacity
3 m3/h
2.8 m3/h
2.9 m3/h

Water conditions
NuclideSpecific
Bq/dm3

activity,

Cs-134
8.5E+04 to
9.1E+04

Cs-137
1.7E+07I-131
4.3E+03 to
6.3E+03

Co-60
9E+03

Mn-54
8E+03 to11E+03

Sb-125
1.3E+04 to
1.8E+04

Ru-106
2.4E+04 to
3.3E+04

Expected environmental conditions inside the PCV/RPV during the FD retrieval operations
Parameter(1) Gas-vapour phase(high temperature cutting, high speed mechanicalcutting)(2) Solid particles (mechanical cutting)Particles size diapason

Molecule size to 0.5 µm.

1-2000 µm.

Particles distribution aspects

Dust collection system mostly accumulate dust particles 75% of dust particles collected by dust collection system havewith size from 0.8 to 300 µm. However approx. 10% of all a size from 10 to 300 µm. However approx. 1% of all particles
particles has a sub-micron size
has a sub-micron size
Vapour phase could easily transfer and penetrate through Up to 50% of generated dust particles amount could be Could provide thethe all filters in case of absence of special treatment collected by dust collection system.
negative influence onstages.
Up to 58-95% of generated dust particles amount sediment fibre-glass filters
close to cutting point.

Dust particles intensity generation in a
cutting point(3) Aerosol particles(underwater cutting,high humidity etc)
Different sizes(4) exfoliationof adherent
dust particles
ND

Up to 46 mg/sec

Dust particles specific activity (β, γ) in
Up to 1.8E+10 Bq/m3 (based on SNF cutting experiments, C-2 sample)
cutting point
Up to 2.69E+09 Bq/m3 (based on assumed 1F corium specific activity)
Other aspects
Vapour phase of Cs is generated. I, Rh gaseous are generated as well.

-

34

Initial technical requirements for full-scale dust
collection system (2/2)
The list of initial technical requirements for full-scale dust collection system#
12

Parameter
Dust particles size diapason before firstcleaning stage
Contaminated air specific activity (β, γ) in
cutting point

Value
Molecule size to 500 µm (vapour phase +solid particles + aerosols)
Up to 1.8E+10 Bq/m3

3

Contaminated air specific activity (β, γ) in a Up to 4E+08 Bq/m3
local suction unit

4

Dust generation intensity in a cutting point

5

Dust specific activity intensity in a local suction Up to 1,63E+08 Bq/sec
unit

Up to 46 mg/sec

RemarkHigh temperature cutting,mechanical cutting
Conservative estimations based on SNF cutting tests
results.
Also, it could be possible to generate Cs vapour phase as
well as Rh and I during the high temperature cutting.
Based on recommended air consumption 350 m3/h
Adopted to 1F conditions (Average sp.activity of corium
is up to 6,3E+09 Bq/g )Up to 99%

Based on recommended air consumption 350 m3/h
Adopted to 1F conditions (Average sp.activity of corium
is up to 6,3E+09 Bq/g )Due to the existing stagnant water and continued FD
cooling with water (up to 3 m3/h)
During the high temperature cutting

Humidity before the first cleaning stage

5

Contaminated air temperature diapason before Up to 100 °C
the first cleaning stage

7

Main gas track diameter

50 – 100 mm

To satisfy optimal air flow rate

8

Air flow rate in full-scale dust collection system

19-22 m/sec

Based on results of experimental cutting tests

9

Air consumption

Up to 400 m3/h

1st cleaning stage

2nd cleaning stage

99% of vapor phasetreatment, aerosols
enlarging, reductionof solid particles
concentration

Accumulation of finesolid particles andaerosols. Should be
self-regenerated

FD retrieval
accesspoint

Full-scale dust
collection from air
system potential
placement
Full-scale dust
collection fromwater system
potential
placement

These clearing stages are required just in case of hightemperature cutting

Required cleaning stages (for all types of cutting methods)
Reduction of solid
dust particle
concentration,
particles enlarging, aircooling

FD retrieval
accesspoint

Conservative estimation based on cutting experiments

4

Preliminary
cleaning stage

Principal of placement of fullscale system

3d cleaningstage

4th cleaning
stage

Adsorption
tower

Ceramic
filter

Accumulationof ultra-finesolid particles
and aerosols

Sanitary
cleaning

I-gas
treatment

Cs gaseous
treatment

35

Full scale dust collection system
Preliminary conceptual design

36Full-scale system conceptual flow-chart (air treatment)
Main equipment
ID on flow-chart
A-01/1,2
A-02
A-03
A-04
A-05
A-06
A-07
A-08
S-01/1,2,3,4,5,6,7,8
H-01
H-02

H-02

2nd a-Zone –sampling/
maintenancearea(~15 m2)
1st a-Zone – aircleaning
equipment
location(~20 m2)

Sampling
bench

A-03

∅20 mm∅10 mmSteam
Samplers 1-8∅10 mm∅10 mm∅10 mmWater∅10 mm∅10 mmAcid
A-06

I gaseoustreatment

Cs vaporphase
treatment∅80 mmH-01

Filtering apparatus
Quantity Parametres
Dephlegmator
2xMulticyclone (SOTAR)
1x
FARTOS filter
1x
FAS fine filter2xAdsorption tower (for I collection)
1
x
High porocity ceramic filter
1xHeat exchanger (heater)
1x
Ejector1x
Sampler8x1
Vacuum pump
Q=280 m3/h
1
Q=60 m3/h
Vacuum pump

Outlet pipe h=15-25 m

Decontamination
solution

Legend:Liquid level detector

A-01/1

A-02

Air flow meter

A-03
A-04

Main gas
duct

A-04

A-01/2
A-07

Valve

A-05

Pressure difference∅80 mmTo preliminary contaminated water
treatment

Access point for FD retrieval

A-08

Accumulation of
90-99% of solid
particles >10µm,
most part ofvapor phase,enlarging andaccumulation ofaerosols

Accumulationof 99.9%
aerosols andremaining solid
particles.
Regenerated.
Allow toincrease of
lifetime offollowing finefilters

Final andsanitary
cleaning
stageswith
efficiency
99.995%Compressed air 5 at, Q=600 m 3/h

Cooling andenlarging stage.
Accumulationof 50% of solid
particles and
5% of vapor
phase amount

Condensate accumulationtank

Reserve system is not shown

Thermocouple
Air flow rate meterContaminated/treated air direction
Vapor phase direction
Liquid phase direction
Quick connection
Decontamination solution37

Conceptual proposals for full-scale local suction unit
We believe that full-scale dust collection system should mainly provide the following aims:
1. To localize the generated dust particles and aerosols close to cutting point to prevent its uncontrolled transfer out of PCV/RPV
2. To reduce dust particles and aerosols concentration around the cutting point to provide the effective video control system operation
Air flow rates in a suction zone of
local suction pipe on a distance x1

Air flow
direction

Percentage ofinitial air flow ratedepend on
distance fromsuction pipe

V0

Based on this diagram we could
assume that providing the optimal
air flow rate on a far distance of
cutting point requires very huge air
consumption, huge gas cleaning
apparatus etc.
Thus we recommend to collect thesurround floating dust particles
cloud mostly than dust particles in
cutting point

I – air flow rates fields in a suction specter without any shields
II – air flow rater fields in a suction specter with flat shield
III – flat shield to localize the dust particles and aerosols

Local suction unit configurationFD
removalfacility

Cloud of long-term
floating particles

50-80% of generated
dust particles (based on
our experiments)

Heavy particles willdeposit close to cutting
point

Preliminarywater
treatment

Dust particles size, µm

2 H.Green, W. Lane “Particulate clouds: Dust, Smokes and Mists”

Full-scale local suction unit design evaluation

Laboratory scale system

VcenterVideo control

Up to 200 µm
30 mm
a
b
Crevice suction
unit configuration

Cuttingpoint

Gas cleaning system

1 V.Pisarenko, M.Roginsky “Ventilation of industrial working place

∅20mm

Vx

Particles deposit rate, cm/sec

V0

Dust collection system access point should be
opposite to FD removal access point

Dust particles deposit rate dependingon size (logarithmic scale)2

Up to 35 m3/h
19-22 m/sec

To provide the same air
flow rate we propose touse ∅80mm main gas ductand 350 m3/h air
consumption.

Cloud of long term
floating particles < 50 µm> 50 µm

Up to
19-22 m/sec 350-400 m3/h

Example∅80 – main gas duct∅200 mm – protective shield (pipe)
Cone like suction unit opening angle 45-60°

Local suction unit should provide the collection of long term
floating particles, aerosols and vapor phase mainly.

In case of increasing the distance to the cutting point to safe the optimal airflow rate, airconsumption should be increased as well.
To provide the optimal design of local suction unit it’s strongly required to know (or tosimulate) the structure of air flows around local suction unit.

38

Full-scale system conceptual flow-chart (water treatment)
Priority proposed preliminary water treatment option
Phlegm from aircleaning 0.3m3/h

Ultrafiltration unit(tangential filters)

Preliminary filtration(coarse discs filter)
Buffer tank

KURION/SARRY/
ALPS
requirements for
input
contaminatedwater :

Existing water
treatment system(KURION/SARRY/ALPS)•Solid particles
concentration
Sludge/slurry

3m3/h

Coarse disc filter~38% of generated
dust particles could
have a size <50µm•Specific activity•Nuclearmaterials
concentration

Hydro-Cyclone filter applicability•

Cutting experiments shown thatapprox. 20-35% of generated solid
dust particles during in-water cutting
Disc filter ishave a size less than 50 µm•

In this case it should be necessary tousehydro-cyclone
filter+microfiltration –> a lot of secondary
waste (spent microfiltration cartridges)

more suitable
Filtration rate: 5-200 µm
Low energy consumption: 0.1-0.3 kW/m3
Fast self washing: 10 sec
Filtration capacity: 3-50 m3/h
Secondary RW amount reduction

39