US20070044427A1

US20070044427A1 - Submarine ultrasonic cleaning machine

Info

Publication number: US20070044427A1
Application number: US11/211,528
Authority: US
Inventors: Kuo-Chi Lan; Tien-Chan Chang; Yu-Tang Yang; Chun-Ming Wu
Original assignee: Institute of Nuclear Energy Research
Current assignee: Institute of Nuclear Energy Research
Priority date: 2005-08-26
Filing date: 2005-08-26
Publication date: 2007-03-01

Abstract

A cleaning machine operated under water to clean radioactive particles on surfaces of nuclear wastes of middle-high activity to reduce activity, and to prevent radiation from leaking out when cleaning the nuclear wastes.

Description

FIELD OF THE INVENTION

The present invention relates to a cleaning machine; more particularly, relates to using the cleaning machine under water to clean nuclear wastes of middle-high radiation activity.

DESCRIPTION OF THE RELATED ARTS

According to a statistic, a nuclear power plant of 1000 megawatt would produce 500 pounds of plutonium and 30 tons of nuclear wastes of middle-high activity in a year. Until 1994, nuclear power plants under commercial operation have produced about 29,700 tons of nuclear wastes of middle-high activity, which is quite a lot. Most of the nuclear wastes are stored in water for further processing. If they are soaked in chemicals, are scrubbed by a scrubber or are sluiced with high-pressure water, a problem of secondary wastes or difficulties in operation may occur.
A general ultrasonic cleaning is done through a cavitation effect function. An ultrasonic sound pressure more than one atmospheric pressure will produce cavity when applied to a liquid. When a vapor or a gas dissolved in the liquid enters the cavity, many micro-bubbles appear. These micro-bubbles will strongly grow and strongly close following the ultrasonic wave. When the bubble is being destroyed, a great deal of impact pressure will be produced (about 100 atmospheric pressure). As such a great impact pressure is directly functioned on cleaned parts, dirt will be emulsified and scattered to be departed from the cleaned parts so that the cleaning can be done.
By referring to U.S. patents of U.S. Pat. No. 6,615,852, 2003073391 and 2003022606 and Japanese patent of JP2002177906, a general ultrasonic cleaning machine of prior arts is just a tank having an ultrasonic transducer. When using the ultrasonic cleaning machine, cleaned parts are put in the tank with water or some cleaning solvent. Then the ultrasonic transducer is turned on to produce cavity in the liquid. When a vapor or a gas dissolved in the liquid enters the cavity, many micro-bubbles appear. When the bubble is being destroyed, a great deal of impact pressure is made so that dirt can be emulsified and scattered to be departed from the cleaned part and so the cleaning can be done. But, the cleaning by the ultrasonic cleaning machine is done exposed to the air; so, if the cleaned parts are nuclear wastes of middle-high activity, radiation may leak from the tank during the cleaning. So, the prior arts do not fulfill users' requests on actual use.

SUMMARY OF THE INVENTION

Therefore, the main purpose of the present invention is to clean radioactive particles to reduce activity with an ultrasonic cleaning machine under water.
Another purpose of the present invention is to prevent radiation from leaking when cleaning nuclear wastes of middle-high activity.
To achieve the above purposes, the present invention is a submarine ultrasonic cleaning machine, comprising a cleaning tank, a plurality of transducers deposed in the cleaning tank, more than one basket deposed in the cleaning tank, a water-shielding box deposed in the cleaning tank and at least one shielding cover covered on the water-shielding box, where the cleaning tank comprises a sealing gate at a side; an inlet pipe is connected to the cleaning tank for providing a cleaning medium; the transducer is deposed on a bottom surface and a side surface in the cleaning tank; the basket is deposed over the transducer on the bottom surface of the cleaning tank to be filled with nuclear wastes to be cleaned; the water-shielding box is deposed on the basket; and the shielding cover is covered on the water-shielding box, and where the ultrasonic cleaning machine is operated under water to clean radioactive particles to reduce activity and to prevent from radiation leakage and secondary wastes when cleaning nuclear wastes of middle-high activity. Accordingly, a novel submarine ultrasonic cleaning machine is obtained.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The present invention will be better understood from the following detailed description of the preferred embodiment according to the present invention, taken in con junction with the accompanying drawings, in which
FIG. 1 is a perspective view of a preferred embodiment according to the present invention;
FIG. 2 is a cross-sectional view of the preferred embodiment according to the present invention;
FIG. 3 is a top view of the preferred embodiment according to the present invention;
FIG. 4 is a model view showing a finite-element analysis of a load-hanging truss for the preferred embodiment according to the present invention;
FIG. 5 is a view showing a status of use for the preferred embodiment according to the present invention;
FIG. 6 is a view showing a flow chart for the preferred embodiment according to the present invention;
FIG. 7 is a view showing a stress check of the load-hanging truss for the preferred embodiment according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description of the preferred embodiment is provided to understand the features and the structures of the present invention.
Please refer to FIG. 1 though FIG. 4, which are a perspective view, a cross-sectional view, a top view and a model view showing a finite-element analysis of a load-hanging truss, for a preferred embodiment according to the present invention. As shown in the figures, the present invention is a submarine ultrasonic cleaning machine, comprising a cleaning tank 1, a plurality of transducers 2, 2 a, more than one basket 3, a water-shielding box 4, at least one shielding cover 5 and a load-hanging truss 8. The ultrasonic cleaning machine can be operated under water to wash radioactive particles off for reducing activity and preventing radiation from leaking when cleaning nuclear wastes.
The cleaning tank 1 is filled with a cleaning medium and comprises two layers of inner wall with air in between to prevent ultrasonic wave from leaking when processing cleaning under water. The cleaning tank 1 comprises a sealing gate 11 at a side; an inlet pipe 12; hook parts 13 at the rim of the cleaning tank 1 and an oil-free submerged pump 14 at the bottom to pump waste water to a depositing tank (not shown in the figures) after cleaning, where the oil-free submerged pump 14 is chosen to prevent the water in a spent fuel pool 7 being contaminated by lubricant oil.
The transducers 2,2 a are deposed on an inner bottom surface and an inner side surface of the cleaning tank 1, where the transducers on the bottom surface of the cleaning tank are inclined correspondingly to each other so that uranium powders from nuclear wastes 6 can be easily gathered up at the middle center of the bottom surface. To deal with different kinds of uranium powder particles adhering on nuclear wastes 6, the transducers 2, 2 a are ultrasonic transducers with multiple bandwidths and a continuous sweep-ware (26 KHz±2 KHz, 36 KHz±2 KHz).
The basket 3 is deposed correspondingly upon the transducers 2 on the inner bottom surface to be filled with nuclear wastes for cleaning. And, a partitioning shelf 31 is deposed between the transducer 2 and the basket 3 to prevent each other from touching and to improve the energy efficiency of the transducer 2.
The water-shielding box 4 is deposed upon the basket to solve the radiation shielding problem when cleaning the nuclear wastes 6. And, the water-shielding box 4 has a hook part at the top rim. When hanging a force-bearing board, each hook part bears: F=612/2=306(kg), supposed that two eyebolts bear no force and only two eyebolts left are bearing force.
The shielding cover 5 is covered on the water-shielding box 4 with a narrowing top forming a bell shape. And, the shielding cover 5 comprises an outside surface of stainless steel and is filled with lead inside.
A load-hanging truss 8 is deposed outside of the cleaning tank 1 to support the transducers 2, 2 a, the basket 3, the water-shielding box 4 and the shielding cover 5. The load-hanging truss 8 is designed and analyzed according to AISC regulations, where dead loads are considered together with all possible dynamic loads and seismic loads to figure out loads of stress the material can bear under AISC regulations for ensuring the security of the load-hanging truss 8; and, a finite-element analysis software of ANSYS V8.0 is used for the load-hanging truss 8. The load-hanging truss 8 is mainly comprised of a square steel of 100×100×t6. The square steel can be made of an element of BEAM 188, as shown in FIG. 4. Regarding boundary conditions in FIG. 4, because the load-hanging truss 8 is hung at the pool side, point B is set to be a fixed point; the degree of freedom a long the x-axle direction for point A, E and F are set to be 0; and, the degree of freedom along the y-axle direction for point C, D, F, G, H are set to be 0.
Because the load-hanging truss 8 is operated under room temperature, the design temperature required for the load-hanging truss 8 is set to be 30° C. Besides, the load-hanging truss 8 is manufactured through using SUS 304, where the characteristics of the SUS 304 under 30° C. are: Young's modulus E=200 Gpa, Poisson's ratio v=0.33, yield stress Fy=206 M Pa, ultimate stress Fu=520 MPa and density p=7850 kg/m³.
The load-hanging truss 8 is hung at the pool side when operating, where the frame part is sunk in the pool. On designing, loads are considered according to regulations, described as follows:
A. Dead Loads:
The load-hanging truss 8 is 530 kg of weight.
B. Dynamic Loads:
Because the cleaning tank 1 of the submarine ultrasonic cleaning machine (about 1200 kg), the bell-shaped shielding cover 5, and two basket 2,2 a are deposed on the load-hanging truss 8, the total dynamic loads of the load-hanging truss 8 is 2140 kg.
C. Thermal Loads:
Because the load-hanging truss 8 is operated under room temperature, no special thermal loads happen.
D. Wind Loads:
Because the load-hanging truss 8 is operated in a room, wind loads are not a case.
E. Snow Loads:
Because the load-hanging truss 8 is operated in a room, snow loads are not a case.
F. Seismic Loads:
When designing the load-hanging truss 8, the seismic loads have to be considered for ensuring the structural security. The seismic loads for operating the load-hanging truss 8 are a 0.3 g seismic load at horizontal direction (x-axle and y-axle) and a 0.2 g seismic load (two third of the seismic load at horizontal direction) at vertical direction (z-axle), analyzed by using a quasi static approach.
Although a part of the frame is sunk in the pool when operating the load-hanging truss 8 and so the water buoyancy makes the dead loads and the dynamic loads lighter for the frame to bear, the buoyance effect of the water is not con side red so as to be conservative concerning the dead loads and the dynamic loads.
Regarding the load assembly of the load-hanging truss 8, the present invention uses the following model according to ANSI 57.9:

- LS1: 1.4 D+1.7 L
- LS2: D+L±E

where

- D: stands for dead loads, or corresponding moments and forces, including a net weight of the piping and the equipments;
- L: stands for dynamic loads, or corresponding moments and forces; and
- E: stands for seismic loads, or corresponding moments and forces.

Then, all loads are applied to the load-hanging truss 8. According to the regulations, the values for the stresses of the load-hanging truss 8 aroused by the loads are assembled with the above model; and, the result value should be smaller than the stress allowance stated in the regulations. The stress allowance for the square steel according to the regulations are described as follows:

(1) The Tensile Stress Allowance for the Shape Steel:

Because the load-hanging truss 8 is mainly comprised of the square steel of 100×100×t6, the tensile stress allowance for the link of the square steel are described as follows:
P all=MIN(0.6 FyAg, 0.5 FuAe)
where

- A_g: stands for a total sectional area of the shape steel and the A_gfor the shape steel of 100×100×t6 is 24 cm²;
- A_e: stands for an effective sectional area of the shape steel, and A_e=C_tA_n;
- A_n: stands for a sectional area of the shape steel after deducting the sectional area of the bolt hole;
- C_t: stands for a reduction factor of sectional area and C_t=0.9;
- F_y: stands for a yield stress of the steel; and
- F_u: stands for an ultimate stress of the steel.

The above values are given into the formula P_all=MIN(0.6 F_yA_g, 0.5 F_uA_e) and the tensile force allowance of the shape steel is acquired as P_all=296640N.

(2) The Stress Allowance of the Axial Load and Moment for the Shape Steel:

When the shape steel is bearing the axial pressure tensile stress and the moment, a secondary bending moment has to be considered with the following three conditions:

(A) when f_a/F_a≦0.15 (without considering the secondary bending moment), $\frac{f_{a}}{F_{a}} + \frac{f_{bx}}{F_{bx}} + \frac{f_{by}}{F_{by}} \leq 1.0 .$
(B) when f_a/F_a>0.15 (with the secondary bending moment considered), $\frac{f_{a}}{F_{a}} + \frac{C_{mx} f_{bx}}{(1 - f_{a} / F_{ex}^{'}) F_{bx}} + \frac{C_{mx} f_{bx}}{(1 - f_{a} / F_{ey}^{'}) F_{bx}} \leq 1.0$ $and$ $\frac{f_{a}}{0.6 F_{y}} + \frac{f_{bx}}{F_{bx}} + \frac{f_{by}}{F_{by}} + \frac{f_{by}}{F_{by}} \leq 1.0 .$

Therein,

F_bx, F_by: stand for bending stress allowances (kg/cm²).
F′_ex, F′_ey: stand for Euler stresses (kg/cm²), where $F_{ex}^{'} = \frac{12 π^{2} E}{23 (K_{x} l / r_{x})}, F_{ey}^{'} = \frac{12 π^{2} E}{23 (K_{y} l / r_{y})} .$
C_m: stands for a reduction factor, which limits the value of the secondary bending moment caused by side move; and, whose value has the following regulations:
- 1) With a truss of rigid frame having side slip (a displacement at a node) and no transverse loading between supports, C_m=0.85;
- 2) With an end-constrained truss of rigid frame having no side slip and no transverse loading between supports, C_m=0.6−0.4 M₁M₂and not smaller than 0.4, where M₁is a smaller moment at an end of the truss and M₂is a bigger moment at an end of the truss; and
- 3) With a truss of rigid frame having no side slip yet having transverse loading between supports, C_mis obtained through a rational analysis as follows: a) when the truss has ends constrained, C_m=0.85; and, b) when the truss has no end constrained, C_m=1.0.
f_bx,f_by: stand for bending stresses (kg/cm²), where f_bx=M_x/S_x, f_by=M_y/S_y.
S_x, S_y: stand for sectional modului of the shape steel (cm³), where
S _x=2Ar_x ² /d, S _y=2Ar_y ² /d.
f_a: stands for axial load (kg/cm²), where f_a=P/A_g. And,
F_a: stands for compressive stress allowance of compression link (kg/cm²).

Therein, the formula $\frac{f_{a}}{F_{a}} + \frac{C_{mx} f_{bx}}{(1 - f_{a} / F_{ex}^{'}) F_{bx}} + \frac{C_{my} f_{by}}{(1 - f_{a} / F_{ey}^{'}) F_{bx}} \leq 1.0$
puts emphasis on the stability requirement, which is a formula concerning buckling fracture and F_bx, F_byare the biggest moments between non-supporting points. The formula $\frac{f_{a}}{0.6 F_{y}} + \frac{f_{bx}}{F_{bx}} + \frac{f_{by}}{F_{by}} \leq 1.0$
puts emphasis on the strength requirement, where F_bx, F_byare the bending stresses for the likely buckled point.
And, The formulas $F_{ex}^{'} = \frac{12 π^{2} E}{23 (K_{x} l / r_{x})}, F_{ey}^{'} = \frac{12 π^{2} E}{23 (K_{y} l / r_{y})}$
are related to effective length factors of the compression material in the shape steel, where the values for K_xand K_yare both taken as 1 in the present invention.

(C) When considering the axial tensile force and the moment at the same time, $\frac{f_{a}}{0.6 F_{y}} + \frac{f_{bx}}{F_{bx}} + \frac{f_{by}}{F_{by}} \leq 1.0,$

where 0.6 F_yis the tensile force allowance for the total sectional area deducted with the sectional area of the pivots.
(3) Load Assembly:
After a load assembly to the loads, the stresses for the links are checked with the follow formulas: $LS 1 : 1.4 D + 1.7 L;$ $LS 2 : D + L \pm E;$ $\frac{f_{a}}{F_{a}} + \frac{f_{bx}}{F_{bx}} + \frac{f_{by}}{F_{by}} \leq 1.0;$ $\frac{f_{a}}{F_{a}} + \frac{C_{mx} f_{bx}}{(1 - f_{a} / F_{ex}^{'}) F_{bx}} + \frac{C_{my} f_{by}}{(1 - f_{a} / F_{ey}^{'}) F_{bx}} \leq 1.0;$ $and$ $\frac{f_{a}}{0.6 F_{y}} + \frac{f_{bx}}{F_{bx}} + \frac{f_{by}}{F_{by}} \leq 1.0 .$
And, the results show that the stress values for the links are all fit in with the regulations, which means that the structure strength of the load-hanging truss 8 is safe on bearing the above strict design loads. So, the design strength of the load-hanging truss 8 according to the present invention is fit in with the design requirements of the regulations.

(4) The Result of Stress Analysis:

Concerning the structure strength of the load-hanging truss 8 in the present invention, it is designed and analyzed according to the regulations of AISC ASD89, which considers the stress values for the load-hanging truss 8 under the functions of dead loads, dynamic loads and seismic loads After the analysis, the stress values for the links are all under the stress allowances described in the regulations, as shown in FIG. 7. So, the structure strength of the load-hanging truss 8 according to the present invention is fit in with the design requirements of the AISC regulations.
Please refer to FIG. 5 and FIG. 6, which are views showing a status of use and a flow chart for the preferred embodiment according to the present invention. As shown in the figures, the present invention can be installed at a pool side of a TRR fuel examining pool. A cleaning tank according to the present invention comprises two layers of inner wall and is operated under water together with a water-shielding box. When using the cleaning machine according to the present invention, a main frame of the cleaning machine is put at a position of seventy centimeters under the water level of the spent fuel pool. Because the cleaning tank comprises two layers of inner wall with air in between, the ultrasonic wave can be prevented from lea king when operating the cleaning under the water. Meanwhile, a demineralization water is used as a cleaning medium. A channel is provided for the cleaning tank to put in and move out baskets. Then a sealing gate at a side of the cleaning tank is opened 81. The baskets are each filled with one hundred tube segments of thirty-five centimeters of nuclear waste; and two baskets are to be washed at a time. The baskets filled with nuclear wastes are then transferred to a predestined position in the cleaning tank 82. The sealing gate at the side of the cleaning tank is then closed to isolate the water in the spent fuel pool from the cleaning water. The cleaning medium is filled to liquid level B. The water-shielding box is hung into the cleaning tank 83 with a hook part at the rim of the water-shielding box, which is used as a radiation shield when doing the cleaning. Then the sealing gate of the cleaning tank is closed and the water in the cleaning tank is pumped to liquid level A for best vibrating power efficiency 84. Ultrasonic transducers are turned on for cleaning the nuclear waste in the basket 85. Because the ultrasonic cleaning is done through a cavitation effect function, an ultrasonic sound pressure more than one atmospheric pressure produces cavity when applied to a liquid; and when a vapor or a gas dissolved in the liquid enters the cavity, many micro-bubbles appear. These micro-bubbles strongly grow and strongly close following the ultrasonic wave. When the bubble is being destroyed, a great deal of impact pressure is produced (a bout one hundred atmospheric pressure). As such a great impact pressure is directly functioned on cleaned parts, dirt is emulsified and scattered to be departed from the cleaned parts so that the cleaning is done. Nevertheless, to deal with different kinds of uranium powder particles adhering on nuclear wastes, the transducers are ultrasonic transducers with multiple bandwidths and a continuous sweep-ware (26 KHz±2 KHz, 36 KHz±2 KHz). After thirty minutes of cleaning is done for the first time, ultrasonic transducers are turned off 86. The water is pumped to the last drop brfore the cleaning tank is refill with the de mineralization water to the liquid level A; and the ultrasonic transducers are turned on again for cleaning three times each for one hour 87. Because the cleaning tank is connected to an oil-free submerged pump at the bottom, the waste water after cleaning can be pumped to a depositing tank. Then the cleaning is checked to see if it is finished 88. When the cleaning is not finished, the following process is done again and again: the water is pumped to the last drop; the tank is refill with the demineralization water to the liquid level A; and, then, the ultrasonic transducers are turned on again for cleaning. When the cleaning is finished, the ultrasonic transducers are turned off; and, the tank is fill with the demineralization water to maintain the liquid at the liquid level B while hanging out the water-shielding box 89. Then the bell-shaped shielding cover is hanged out to be put upon the cleaning tank at a predestined position 90. The baskets are then hanged out into the shielding cover to be moved to the next station for drying by heat tog ether with the nuclear wastes inside 91. Hence, a cleaning for nuclear wastes with middle or high activity is done to reduce activity, where it is examined to have a result of α<3700 Bq/g and a radiation dosage lower than 20 mSv/h.
So, the present invention comprises the following advantages of:
1. Wholesome effectiveness with high cleanliness to identically improve quality;
2. Higher cleaning speed while enhancing whole cleaning efficiency;
3. No harm to the surface of the cleaned parts;
4. Less manual handling, simplified working process, and improved working security (for some dissolvent is not proper to be in touch for long);
5. Capabilities in doing special cleanings, such as cleaning things hard to be disassembled; and
6. Saving resources, such as the dissolvent, the energy, the working space, the human resource, etc.
To sum up, the present invention is a submarine ultrasonic cleaning machine, which is operated under water and is half-automatic to greatly reduce the radiation dosage an operator receives during the operation.
The preferred embodiment herein disclosed is not intended to unnecessarily limit the scope of the invention. Therefore, simple modifications or variations belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present invention.

Claims

1. A submarine ultrasonic cleaning machine, comprising:

(a) a cleaning tank filled with a cleaning medium, said cleaning tank having a sealing gate at a side, said cleaning tank having an inlet pipe;

b) a plurality of transducers deposed on an inner bottom surface and an inner side surface of said cleaning tank;

(c) more than one basket deposed correspondingly over said transducers on said inner bottom surface of said cleaning tank, said basket filled with nuclear wastes to be cleaned;

(d) a water-shielding box deposed upon said basket;

(e) at least a shielding cover covering on said water-shielding box; and

(f) a load-hanging truss deposed outside of said cleaning tank.

2. The cleaning machine according to claim 1, wherein said cleaning tank comprises a plurality of hook parts.

3. The cleaning machine according to claim 1, wherein said cleaning tank comprises two layers of inner wall having air between said two layers.

4. The cleaning machine according to claim 1, wherein said cleaning tank is connected to an oil-free submerged pump at bottom of said cleaning tank.

5. The cleaning machine according to claim 1, wherein said transducers on said bottom surface of said cleaning tank are inclined correspondingly to each other.

6. The cleaning machine according to claim 1, wherein said transducer is an ultrasonic transducer comprising multiple bandwidths and a continuous sweep-ware.

7. The cleaning machine according to claim 1, wherein a partitioning shelf is deposed between said transducer and said basket to prevent each other from touching and to maintain an energy efficiency for cleaning.

8. The cleaning machine according to claim 1, wherein said water-shielding box comprises a plurality of hook parts at a rim of said water-shielding box.

9. The cleaning machine according to claim 1, wherein said shielding cover is narrowed at a direction to be bell-shaped.

10. The cleaning machine according to claim 1, wherein said shielding cover comprises an outside surface of stain less steel and is filled with lead inside said shielding cover.

11. The cleaning machine according to claim 1, wherein said load-hanging truss comprises a plurality of square steels of 100×100×t6.

12. The cleaning machine according to claim 1,

wherein said load-hanging truss comprises seismic loads of 0.3 g seismic load at horizontal direction (x-axle and y-axle) and 0.2 g seismic load at vertical direction (z-axle); and

wherein said seismic loads are analyzed by using a quasi static approach.