Confirmation of appropriate operation condition with blasting device
Yuuki TSUHARA, Hirotaka IZUKA
KANDEN POWER-TECH, Corp.:
3-6-2, Bingomachi, Chuou-ku, Osaka, 541-0051, Japan
Shinro HIRANO, Yuji MATSUNAGA, Yasuhiro SUGAHARATHE KANSAI ELECTRIC POWER CO., INC.NUCLEAR POWER DIVISION:
13-8, Goichi, Mihama-cho, Mikata-gun, Fukui, 919-1141, Japan
Yoji KANAMORIATOX CO., LTD.
4-11-3, Shiba, Minatoku, Tokyo, 108-0014, Japan
Key words; decommissioning, decontamination, radioactive waste, Blasting

Abstract
The decontamination method of metallic waste was considered to reduce the radioactive waste in the nuclear
power plant decommissioning.
Stainless steel occupies most for material of system equipments of pressurized water reactor (PWR). The
radioactive materials are stuck on the surface of the equipments’ internal as metal oxide (e.g. chromium oxide,iron oxide). It is necessary to remove the metal oxides efficiently from the stainless steel.
The blasting method is widely known as one of the decontamination techniques. It is necessary to introduce a
blasting device that depends on the materials and the volume of metallic waste for each plant.
The cold tests were performed using the non-contaminated stainless steel plate and confirmed the abradeconditions of the plate surface. The best performance of combination of the type of abrasives, the blasting
velocity and angle was selected as the appropriate operation conditions from the test results.
Next, the hot tests were performed using the contaminated samples on the appropriate operation conditions
and confirmed the decontamination performance and the influence of cross contamination. The hot test results
showed that to be able to decontaminate the metal to the clearance level and no influence of cross contaminationin the range of the target radioactivity concentration, and abrasives could be used repeatedly.
(Contents)
1. Introduction
Low level radioactive waste (LLW) is generated
with operation or decommissioning of nuclear power
plants. Some metal LLW can apply clearance system
by decontamination. The blasting techniques arewidely known as effective decontamination
technology for simple shape metals. We areconsidering to introduce the dry blasting device that
does not generate liquid waste.
The blasting method had been utilized to thereplaced steam generator of PWR in Japan and thereduction of radiation exposure was achieved. 1) This
record shows that the decontamination by the blasting
method is effective for metal waste. For the actual
decontamination operation, it is important to confirm
and set the appropriate conditions of the blasting
device in advance.

In this paper, various test results and theappropriate condition of the blasting device aredescribed.
2. BACKGROUND AND SUMMARY OF THE
TESTSThe primary cooling water contains the claddingthat is radioactive metal oxide. The claddings arestuck on the surface of equipments’ internal that
contact with the primary cooling water.
The main material of the PWR system equipments
is stainless steel. We estimated that it would benecessary to abrade the stainless steel not only thecladdings on the surface of stainless steel in order tothe decontamination to the clearance level. Therefore,
it was necessary to confirm the operation conditionsof the blasting device to abrade the stainless steel.
Factors that influence the blasting performance are
the type of abrasives (material, shape), the blasting
conditions (angle, velocity), and also cross6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

contamination. The cross contamination might reduce
decontamination performance because the abrasives
are contaminated after blasting and make contaminate
the decontaminated object again when the abrasives
used repeatedly.
3. APPROPRIATE ABRASIVES AND THE
BLASTING CONDITIONS COMFIRMATION
TEST
3.1 THE COLD TEST CONDITIONS AND
PROCEDURES(1) Blasting device
The centrifugal blasting device which is assume tointroduce on actual decontamination operation wasused for the cold test. The centrifugal blasting deviceis shown in Fig.1.

TABLE.1 Test blasting abrasives
Blasting abrasives

Abrasives
size

Steel cut wire pieces(SWRH)

φ1.0mmSteel grits(HHCS)

1.0mm

Stainless-steel
cut wire pieces(SUS304)

φ1.0mmAppearance(3) Test blasting velocities
The blasting velocity was tested at 55 m / s, 50 m /s, 45 m / s from the output of the blasting device.
(4) Test blasting angles
It is known that the blasting angle influence theblasting performance3).
Based on this information, the blasting angles weretested at 30°, 45°, and 60°. Diagram of blasting angle
adjustment is shown in Fig. 2.

Fig.1 Appearance of the centrifugal blasting device(2) Test blasting abrasives
The material of the abrasives is categorized into
metallic type and nonmetallic type, and among themetallic type, steel and stainless steel are widely used.
Therefore, these two materials were selected.
Incidentally, metallic abrasives have advantages suchas high durability, stable quality, low dust, and highabrade efficiency 2).
There are three shapes of abrasives - grit, cut wire,and shot. The shapes of grit and cut wire are angular,
and the shape of shot is sphere. Grit and cut wire
were selected because their angular shape are
effective for the metal abrading.
Steel cut wire (SWRH), steel grit (high hardnesscast steel) and stainless steel cut wire (SUS 304),
were selected from the above studies. The selectedabrasives are shown in TABLE.1.

Fig. 2 Diagram of blasting angle adjustment(5) Test details
The cold test was performed in the following twosteps.
The first step, the abraded weight was checked bychanging the combination of the type of abrasives
and the blasting velocity. SUS 304 flat plates wereplaced on the rotary table inside the blasting device,
and were abraded at three kinds of abrasives andthree kinds of blasting velocities. The abraded weightwas calculated difference of plate weight blasting
before and after. The largest abraded weightcombination of the type of abrasives and the blasting
velocity was selected as the appropriate blastingcondition.
The second step, the abraded weight was checkedby changing the blasting angle. The type of abrasives
and the blasting velocity selected in the first step
were used as the second step conditions. SUS 304 flat
plates were placed on the angle adjustable table

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japaninside the blasting device, and were abraded at threekinds of blasting angles. The abraded weight wascalculated difference of plate weight blasting beforeand after. The largest abraded weight angle wasselected as the appropriate blasting condition. Theinternal condition of the blasting device during thecold test is shown in Fig.3.

Fig.5 Abraded weight of the each blasting velocity

Fig. 3 The internal condition of the device(3) Blasting angle
Fig.6 shows the abraded weight of the each
blasting angle. The abraded weight increased
according to the blasting angle getting larger, and theangle of the 60° showed the largest abraded weight.
From this result, the blasting angle of 60° wasselected as the appropriate blasting angle.

3.2 TEST RESULTS
Fig. 4 and Fig. 5 show the first step test results andFig. 6 shows the second step test results.
(1) Blasting abrasives
Fig.4 shows the abraded weight of the eachabrasives. The abraded weight by the steel cut wirepieces showed the largest on the every blasting
velocities. From this result, the steel cut wire pieces
was selected as the appropriate abrasives.

Fig.6 Abraded weight of the each blasting angle(4) Summary of the cold test
TABLE.2 shows the appropriate blasting
conditions to the stainless steel on the cold test.
TABLE.2 Summary of the cold test
Item

Appropriate Condition

Blasting
Abrasives

Steel cut wire pieces

Blasting
velocity

55 m / sBlasting
angle

60°

Fig.4 Abraded weight of the each abrasives(2) Blasting velocity
Fig.5 shows the abraded weight of the each
blasting velocity. The abraded weight increased
according to the blasting velocity getting faster on theevery abrasives, and the velocity of the 55 m / sshowed the largest abraded weight. From this result,the velocity of 55 m / s was selected as theappropriate blasting velocity.

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan4. DECONTAMINATION EFFECTSCONFIRMATION TEST
4.1 THE HOT TEST CONDITIONS AND
PROCEDURES(1) Blasting device
The air blasting device was used for the hot test
because the centrifugal blasting device could not be
used due to space restrictions in the hot test site. The
air blasting device is shown in Fig. 7.
The air blasting device was different from the cold
test device, however, the hot test result could beapplied to the centrifugal blasting device byevaluating the abraded depth from the abraded weight.
This is because both the blasting device physicallyremove the metal oxide.

(3) Test details
The test conditions specified in TABLE.3. The test
pieces were decontaminated several times by blastingabrasives, and for each blasting, the test pieces’surface contamination count rate and weight weremeasured. After the surface contamination count rate
went down to the same count rate of the background,radioactivity concentration was measured with aGermanium pulse-height analyzer (Ge-PHA).
TABLE.3 Decontamination effect confirmation test
conditions
Item

Condition

Equipment

Air-blasting device

Blasting Abrasives

Steel cut wire pieces

Blasting angle

60°

Air pressure

0.54 MPa

Blasting unit

120 s/time

4.2 TEST RESULTS(1) Appearance of the test pieces
The blackish brown metal oxide on the surface ofthe test piece was removed a couple of blasting,confirmed to remove at the relatively early stage.
After that, the decontamination was continued.
However, the appearance of the test piece surface did
not change significantly. The appearance of the test
pieces’ surface is shown in TABLE.4.
Fig.7 Appearance of the air blasting device(2) Test sample
The contaminated stainless steel piping was used
as a test sample. The piping is expected to berelatively generated as actual metal wastes.
The piping was cut about 5 cm × 2 cm per piece
for the test and the next measured Co-60 radioactivity
concentration and the surface contamination counting
rate of each pieces. The maximum value of bothmeasurements were about 10 Bq / g, and about
21,500 cpm. Appearance of the test sample before
cutting is shown in Fig.8.

TABLE.4 Surface conditions before and after

decontamination
Test piece

Beforedecontamination

Decontamination
one time blastingFig.8 Appearance of the test sample before cutting

Completedecontamination

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan(2) Decontamination effect
The blackish brown metal oxide was removed at a
relatively early stage, however, the surface
contamination count rate was about 1,000 cpm or
more. This means contamination still remain andnecessary to continue the decontamination.
After several blasting, the surface contamination
count rate of the test piece went down to the same
count rate of the background. At that time, themeasurement result of Co - 60 radioactivity
concentration was 0.1 Bq / g or less. From this, it wasconfirmed that the decontamination to below theclearance level by blasting was possible if the Co - 60
radioactivity concentration of decontamination object
was about 10 Bq / g. Decontamination effectconfirmation test results are shown in Fig.9 andTABLE.5.

abrasives, the contamination count rate was measured.
The Contamination condition of each abrasives isshown in TABLE.6.
Moreover, we compared trends ofthecontamination count rate. The test piece is shown inTABLE.7.
TABLE.6 Cross contamination test abrasives
Abrasives
No.

Contamination
condition

Surfacecontamination
count rate [cpm]①

Contaminated150②

Contaminated150③

Contaminated140④

Non-Contaminated―TABLE.7 Cross contamination test piece
Test piece
ABCD

Fig.9 Decontamination effect confirmation testresults
TABLE.5 Decontamination effect confirmation
test results
NumberTest piece (cpm)
BGof(cpm)blasting
021,500 15,500 14,600
100
2
2,800
1,900
2,100
100
4900
550
700
100
6350
300
310
100
8180
180
160
100
10120
120
120
100
12100
100
100100
5. CROSS CONTAMINATIONCONFIRMATION TESTSurface
contamination
count rate [cpm]
1,000
1,200
1,200
1,100

Used
Abrasives No.
①②③④

5.2 TEST RESULTS
The cross contamination test results are shown in
Fig.10 and TABLE.8.
Both number of blasting by two kind of abrasives
were 5 to 6 times to the background contamination
count rate and the trends of contamination count rate
were almost the same.
Fig.10 shows the trend of the contamination countrate. In this figure, result of the test piece D isindicated by solid line, and result of other pieces areindicated by the point only. The test piece D wasdecontaminated by the non-contaminated abrasives
and other pieces were decontaminated bycontaminated abrasives. The result of the test pieces
A to C showed the same trend as the test piece D, andno influence to the decontamination by the crosscontamination was confirmed.
From the above test results, we confirmed thatabrasives can be used repeatedly less than target
range of the radioactive concentration.

5.1 TEST CONDITIONS AND PROCEDURES
The influence of the cross contamination to thedecontamination effect was tested.
Thesameconditions
as"TABLE.3
Decontamination effect confirmation test conditions"were used for this test.
After the blasting to the test pieces by each of
Non-contaminated abrasives and contaminated6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan

Fig.10 Cross contamination test results

TABLE.8 Cross contamination test results
Numberofblasting0123456A
1,000
360
250
140
140100－Test piece (cpm)
BC
1,200
350
200
150
130
120
100

1,200
320
200
170
140
120
100

DBG(cpm)

1,100
300
200
150
130
120
100

100
100
100
100
100
100100

6. CONCLUSIONSIn conclusion, the appropriate operating conditions(abrasives, velocity and angle) of the blasting device
to abrade the stainless steel were confirmed.
Moreover, the metal waste can be decontaminatedto the clearance level or less by the appropriate
operating conditions, and no influence by crosscontamination and possible to use abrasives
repeatedly was confirmed.
These data would be utilized to study thespecification of the blasting device anddecontamination operation.
REFERENCES(In Japanese)
1) The Atomic Energy Society of Japan, "Handbookof Water Chemistry of Nuclear Reactor System",
CORONA PUBLISHING CO., LTD, (2000).
2) Hiroki Kawai, et al, "Handbook of the industrialcoating", TECHNO SYSTEM CO., LTD, p.227 231 (2008).
3) Hideo NAGASAKA, et al, "Blast technology"
COTEC CO., LTD, p.60-p.107 (1985).

6th East Asia Forum on Radwaste Management Conference
November 27-29, 2017, Osaka, Japan