Abstract:
A device is provided to inspect welds in nozzles located in water within a containment vessel of a nuclear power plant. A computer connected to the device controls movement by use of thrusters located along a main rail while buoyancy packs regulate the depth. After the device is navigated to a weld needing inspection, feet extend radially outward from the main rail to secure the device in the nozzle. Then transducer clusters are moved along the main rail to be radially inside the weld to be inspected. Thereafter, the transducer clusters are extended radially outward and rotated adjacent to the weld while simultaneously emitting test signals and receiving reflected signals to indicate the condition of the weld.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a nozzle inspection tool, and more particularly, a nozzle inspection tool that can be used to inspect nozzles within a nuclear reactor. 
         [0003]    2. Description of the Prior Art 
         [0004]    The use of nuclear energy to generate electricity began in the early 20 th  century after the discovery that radioactive elements such as radium release immense amounts of energy. Initially, however, harnessing such energy was impractical because intensely radioactive elements are very short-lived. 
         [0005]    By the late 1930s, experiments were being conducted with nuclear fusion. Those experiments in nuclear fusion led to the Manhattan Project, which led to the first nuclear weapons, which were used in World War II on the cities of Hiroshima and Nagasaki. 
         [0006]    After World War II, nuclear energy was used to generate power with the USSR&#39;s Obninsk Nuclear Power Plant becoming the world&#39;s first nuclear power plant to generate electricity for a power grid. The world&#39;s first commercial nuclear power plant was opened in 1956 in Sallafield, England. The first commercial nuclear generator to become operational in the United States was the Shipping Port Reactor in Pennsylvania in 1957. 
         [0007]    By 2005, 15% of the world&#39;s electricity was generated by nuclear power, with the United States, France and Japan accounting for 56% of the nuclear generated electricity. As of December 2009, the world had 436 nuclear reactors. 
         [0008]    While many different things have affected the number of nuclear reactors, the growth of nuclear power was impeded by (1) the Three-Mile Island accident in 1979, (2) Zhernobyl disaster in 1986, and (3) Wukushima Daiichi nuclear disaster in 2011. With these accidents, there has been an increased emphasis on safety and a decline in the growth rate of nuclear reactors. One of the areas of increased safety emphasis is in the containment vessel and in the lines flowing fluid to and from the nuclear power plant reactors. An item requiring inspection is the various welds and joints in (1) the containment vessel, (2) nuclear power reactors and (3) the lines leading and from such vessels. 
         [0009]    In the United States, there are approximately 104 operating nuclear reactors. Of those, sixty-nine are pressurized water reactors (PWR) and thirty-five are boiling water reactors (BWR). In both the PWR and BWR, fluid is converted to steam and the steam is used to turn a turbine that generates the electricity. The conduits taking the fluid or steam to or from the turbine have to be inspected, especially the welds occurring in the nozzles. 
         [0010]    In the United States, the Nuclear Regulatory Commission (NRC) is responsible for ensuring public health through licensing and inspection of nuclear power plants. One of the things that the NRC requires to be inspected are the welds that occur in the containment vessel and in the nozzles leading to and from the containment vessel. 
       SUMMARY OF THE INVENTION 
       [0011]    It is an object of the present invention to provide a tool for inspecting welds in the nozzle of a nuclear reactor. 
         [0012]    It is yet another object of the present invention to provide a submersible device that can enter the fluid contained in a nuclear reactor and go inside of the nozzles to inspect the welds contained therein. 
         [0013]    It is yet another object of the present invention to provide a tool that is self-contained and can directed itself inside of the nozzle of the nuclear reactor and position itself therein so that the welds in the nozzle can be inspected. 
         [0014]    It is still another object of the present invention to provide a tool that is buoyancy compensated with its own thrusters for properly locating itself inside the nozzles of the nuclear reactor for inspection of welds therein. 
         [0015]    It is even another object of the present invention to provide feet on a tool that will extend radially outward to center the tool in a nozzle of a nuclear reactor to allow for inspection of the weld there around. 
         [0016]    A main rail is provided with a buoyancy pack on either end thereof with thrusters for repositioning the entire device. On either end of the main rail between the buoyancy packs are located expandable feet that extend outwardly at approximately every 120° to contact around the nozzle and position the tool therein. While the expandable feet hold the tool in the nozzle, an expandable and rotating transducer package extends outward to a weld joint and radially rotates so a transducer package can inspect the entire weld. If there is more than one weld in the nozzle, (1) expanding and rotating transducer package is retracted, (2) expandable feet are refracted and (3) the device is moved to a position adjacent to another weld. The process is then repeated with the expandable feet expanding outward to secure the device. Thereafter, expandable and rotating transducer packages are expanded outward and rotated adjacent to the weld so that the entire weld is inspected. At the ends of each of the expandable feet are snubbers for securing the tool in position. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is an illustrative flow diagram of a nuclear power plant. 
           [0018]      FIG. 2  is a perspective view of a tool for inspecting welds in nozzles of nuclear power plants. 
           [0019]      FIG. 3  is a perspective view of an expandable foot portion of the inspection tool shown in  FIG. 2 . 
           [0020]      FIG. 4  is an elevated view of the expanding/rotating transducer package of the inspection tool shown in  FIG. 2 . 
           [0021]      FIG. 5  is a cross-sectional view of  FIG. 4  along section lines  5 - 5 . 
           [0022]      FIG. 6A  is a side view of the inspection tool in front of a nozzle opening of a nuclear power plant. 
           [0023]      FIG. 6B  is a cross-sectional view of a nozzle in a nuclear power plant with the inspection tool moving therein. 
           [0024]      FIG. 6C  is a sectional view of a nozzle in a nuclear power plant with the inspection tool being shown in perspective about to inspect a weld. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    An illustrative flow diagram for a nuclear power plant for generating electricity is shown in  FIG. 1  and is represented generally by reference numeral  11 . The nuclear power plant  11  has a reactor containment vessel  13  that has a Taurus  15  with an auxiliary water feed  17 , which is a backup water supply for the nuclear power plant  11 . 
         [0026]    Inside of the reactor containment vessel  13  is located a reactor pressure vessel  19 . A bundle of fuel rods  21  absorb a neutron to cause nuclear fission on release of other neutrons. The nuclear fission heats the water contained within reactor pressure vessel  19  to convert it to steam. 
         [0027]    To ensure the bundle of fuel rods  21  remain immersed in water an internal reactor recirculation pump  23  continues to recirculate water over the bundle of fuel rods  21 . Also, an external reactor recirculation pump  25  circulates water within the reactor pressure vessel  19  to ensure the bundle of fuel rods  21  remain cool and immersed in the water. 
         [0028]    While in the reactor pressure vessel  19  different fluids have been used, including gas, liquid metal or molten salts to ensure that the nuclear reaction does not run away. Control rods  27  are located in the bottom of the reactor pressure vessel  19 . The control rods  27  absorb some of the released neutrons to prevent too large of a nuclear reaction with the bundle of fuel rods  21 . 
         [0029]    Above the bundle of fuel rods  21  is located heat exchanger  29 , which is used to convert the water to steam. Steam generated in the reactor pressure vessel  19  enters steam line  33  through outlet nozzle  31 . The steam flows through the steam line  33  and the main steam isolation valve  35  to enter steam turbine  37 . As the steam turns the steam turbine  37 , steam turbine  37  turns generator  39 , which generates electricity. 
         [0030]    After the steam flows through the steam turbine  37 , a major portion of the steam flows through the main steam exit conduit  41  to condenser  43 . Circulating through the condenser coil  45  is cooling water received from the cooling tower  47  via condenser cooling water pump  49 , cooling water control valve  51  and cooling water inlet conduit  53 . The cooling water returns to the cooling tower  47  via cooling water return conduit  55  and cooling water return valve  57 . The cooling water can be of any convenient source such as lake water or river water. The cooling water does not have to be refined or processed. 
         [0031]    From condenser  43  through the feed water return conduit  59 , the water is being pumped by condenser pump  61  through water return valve  63  into a feed water heater/preheater  65 . The feed water flowing back to the reactor pressure vessel  19  is heated/preheated inside of feed water heater/preheater  65  which receives some of the steam flowing through steam turbine  37  through preheater steam conduit  67  and control valve  69  to feed water heater/preheater  65 . The feed water heater/preheater  65  increases the temperature of the feed water significantly prior to returning to the reactor pressure vessel  19  via reactor feed pump  71 , main feed water isolation valve  73  and main feed water return conduit  75 . The main feed water is discharged into the reactor pressure vessel  19  through return nozzle  77 . 
         [0032]    Any remaining portion of the preheater steam received in the feed water heater/preheater  65  flows to condenser  43  through preheater steam conduit  79  and preheater steam control valve  81 . 
         [0033]    The outlet nozzle  31  and return nozzle  77  are very large in size and may vary anywhere from 24 inches to 46 inches in diameter. Also, there is more than one of the outlet nozzle  31  and the return nozzle  77 . There are usually between two to six outlet nozzles  31  and return nozzles  77 . These outlet nozzles  31  and return nozzles  77  handle extreme loads and extreme heat cycles. Pressure can be in the thousands of pounds per square inch (psi). Typically, the outlet nozzles  31  and return nozzles  77  are made by welding pipe together, which welds may be of the same type of metal or may be dissimilar metals. For example, the main feed water return conduit  75  may be of one type of metal, but the reactor pressure vessel  19  may be of a different type of metal. Different metals are used for a variety of different reasons, including strength, resistance to corrosion, or more economical. 
         [0034]    Because of the extremes of temperature and pressure through which the outlet nozzle  31  or the return nozzle  77  must endure, it is important to periodically check the welds to make sure the welds are holding. 
         [0035]    The present invention relates to a nozzle inspection tool  83  as shown pictorially in  FIG. 2 . The nozzle inspection tool  83  has a main rail  85  on which everything is mounted. The main rail  85  looks very similar to an I-beam. 
         [0036]    On each end of the main rail  85  are buoyancy packs  87 . The buoyancy packs  87  are partially cut away so that thruster clusters  89  can be seen. The thruster clusters  89  are used to control the direction of movement of the nozzle inspection tool  83 . The buoyancy packs  87  adjust the buoyancy of the nozzle inspection tool  83  so that the tool can be maintained at a particular depth. 
         [0037]    Mounted on either end of the main rail  85  are expandable foot clusters  91  and  93 , which are identical. However, both expandable foot clusters  91  and  93  are independently moveable along the main rail  85 . Between the expandable foot clusters  91  and  93  is located expanding/rotating transducer package  95 . 
         [0038]    Referring to the perspective view of expandable foot cluster  91  in  FIG. 3 , operation of the expandable feet cluster  91  will be explained in more detail. Expandable foot cluster  19  is identical to expandable foot cluster  93 . In the center of the expandable foot cluster  91  are linear bearings  97  that press against the main rail  85  (see  FIG. 2 ). Linear bearings  97  are carried inside of expansion control ring  99 . The linear bearings  97  are connected to a central frame  101  through which the main rail  85  may slide. Connected to the central frame  101  are cable bundle guides  103 . The expansion control ring  99  is pivotally attached to central frame  101 . 
         [0039]    Extending outwardly in a radial direction from the central frame  101  are expandable feet  105 . There are three identical expandable feet  105  located at approximately 120° around the central frame  101  and extending radially outward from the central frame  101 . Each of the expandable feet  105  have an adjustment bracket  107  connected to the central frame  101 . Contained inside of the adjustment bracket  107  are air cylinders  109 . 
         [0040]    Extending outwardly from the adjustment bracket  107  are adjustment rods  111 . The adjustment rods  111  are telescopically received into adjustment bracket  107  with the outer end of the adjustment rods  111  being connected to a foot bracket  113 . The foot bracket  113  is approximately perpendicular to the adjustment rods  111 . On each end of the foot bracket  113  are located rollers  115 . Between the rollers  115  and also mounted on the foot bracket  113  is a rubber snubber  117 . The rubber snubber  117  extends radially outward slightly more than the rollers  115  on the expandable feet  105 . A push rod  119  connects between the air cylinder  109  and the foot bracket  113  so that as the expandable foot  105  expands, push rod  119  would extend radially outward. As the expandable foot  105  retracts, push rod  119  would move radially inward. 
         [0041]    Since each of the expandable feet  105  may extend outward different amounts, expansion control ring  99  is rotatably carried on the central frame  101 . As the expansion control ring  99  rotates, connecting rods  121  which connect from the expansion control ring  99  to the foot bracket  113  of each of the expandable feet  105 , causes each expandable foot to also move. The expansion ring  99  with the connecting rod  121  ensures that the expandable foot cluster  91  is centered inside of a conduit in a manner as will be subsequently described. 
         [0042]    Also, a couple of the thrusters  123  and  125  of the thruster cluster  89  are shown attached to adjustment bracket  107 . However, the thrusters  123  or  125  may be connected at other locations along the nozzle inspection tool  83 . 
         [0043]    Referring back to  FIG. 2 , expandable foot clusters  91  and  93  are shown on each end of the main rail  85 . The expanding/rotating transducer package  95  shown in  FIG. 2 , will be explained in more detail in the elevated view shown in  FIG. 4  and the cross-sectional view of  FIG. 5  taken along section lines  5 - 5  of  FIG. 4 . A transducer central frame  127  receives the main rail  85  there through. Linear bearings  129  allow the expandable/retracting transducer package  95  to move smoothly along main rail  85 . Threadably connected to the transducer central frame  127  are lead screws  131 . Lead screws  131  will adjust the expanding/rotating transducer package  95  linearly along the main rail  85  of the nozzle inspection tool  83 . 
         [0044]    Rotatably connected to the transducer central frame  127  is external ring  133 . A ring gear  135  is connected to external ring  133  so that when ring gear  135  is driven by drive gear  137 , the external ring  133  and everything connected thereto will rotate about main rail  85  (see  FIG. 2 ). 
         [0045]    Connected to the ring gear  133  at approximately 90° apart are linear guide mounts  139 . Extending radially outward from the linear guide mounts  139  are linear guides  141 . The linear guides  141  extend radially outward from linear guide mounts  139  with the outermost end of the linear guide mounts  141  connected to a transducer mounting bracket  143 . The transducer mounting bracket  143  has mounted thereon a left transducer  145 , center transducer  147  and a right transducer  149  to make up a transducer cluster referred to generally by reference numeral  151 . Connecting to the center of the transducer mounting bracket  143  is a connecting rod  153  that connects between transducer mounting bracket  143  and air cylinder  155  secured inside of linear guide mounts  139 . 
         [0046]    If the expanding/rotating transducer package  95  needs to be rotated, motor cam assembly  157  (shown in  FIG. 5 ) will cause the rotation. Cable guide  159  (shown in  FIG. 4 ) will protect the cabling that connects to transducers  145 ,  147  and  149  to prevent damage. While the electrical connections are not described in detail herein, electrical connections must connect to each of the transducers  145 ,  147 , and  149  for signals to be transmitted to and from these transducers. Also, various control signals are used to control operation of nozzle inspection tool  83 . 
         [0047]    Referring now to  FIGS. 6A ,  6 B and  6 C sequential views show the nozzle inspection tool  83  being used in a nozzle. Referring to  FIG. 6A , the nozzle inspection tool  83  is shown in front of return nozzle  77 , also sometimes called inlet nozzle. The return nozzle  77  has a tapered section  161  connecting between the return nozzle  77  and the main feed water return conduit  75  of the reactor pressure vessel  19  (see  FIG. 1 ). 
         [0048]    The nozzle inspection tool  83  (shown in  FIG. 6A ) has the expandable foot clusters  91  and  93  as mounted on the main rail  85  in the retracted position. The expanding/retracting transducer packages  95  are also in the retracted position. The buoyancy packs  87  keep the nozzle inspection tool at the desired depth while the thruster clusters  89  provide movement of the nozzle inspection tool  83 . 
         [0049]      FIG. 6B  illustrates movement of the nozzle inspection tool  83  inside of outlet nozzle  31 . Outlet nozzle  31  has an inward shoulder  163  and an inward flair  165 . The outlet nozzle  83  is connected to steam line  33  by weld  167 . Weld  167  may be a weld of similar metals or it may be a weld of dissimilar metals. The object is for the nozzle inspection tool  183  to inspect weld  167 . 
         [0050]    Referring now to  FIG. 6C , the nozzle inspection tool  83  has moved inside of outlet nozzle  31  and the expandable foot clusters  91  and  93  have been expanded so that the rubber snubbers  117  are pressed against either the nozzle  31  or the steam line  33 . The snubbers securely hold the inspection tool in position. While being held in position, the expanding/rotating transducer package  95  extends outward into a position immediately adjacent to weld  167 . Now the electronic assembly nozzle inspection tool  83  is turned ON and the expanding/rotating transducer package  95  is rotated so that each of the transducer clusters  151  may check the integrity of the weld  167 . 
         [0051]    Referring to  FIG. 7 , a general explanation as to the control system for nozzle inspection tool  83  is provided. Located on the nozzle inspection tool  83  near the buoyancy pack  87  is an inertia measurement unit  169 . The inertia measurement unit  169  is used by applicant and sold under the brand name XSENS, Model MT. The inertia measurement unit  169  is a miniature gyro-enhanced altitude and heading reference system with a low-power signal processor that provides drift-free 3-D orientation, 3-D acceleration, 3-D rate of turn and 3-D earth-magnet field data. The inertia measurement unit  169  gives real time computed altitude/heading and inertia dynamic data. Also, the inertia measurement unit  169  either accepts or generates synchronization pulses. 
         [0052]    Also contained on board nozzle inspection tool  83  is a camera  171  mounted near or on the buoyancy pack  87 . While many different types of cameras can be used, a Mantis hi-definition camera is a typical example of a camera that can be used. By use of the camera  171 , an operator of the nozzle inspection tool  83  can see the direction nozzle inspection tool  83  is moving. While the present nozzle inspection tool  83  only has one camera  171 , multiple cameras could be used. 
         [0053]    The Mantis camera is an internally integrated digital camera that allows for image capture and documentation. The images being received by the Mantis camera can by simultaneously viewed optically and digitally. 
         [0054]    Also located on the nozzle inspection tool  83  are encoders  173  located on the backside of each of the motors (not shown) on nozzle inspection tool  83 , excluding the motors contained in each of the thruster clusters  89 . The encoders  173  that have been found suitable for the present invention are sold under the name Avago. The model that is found to be particularly suitable is the HELV-5540. These particular encoders are found to be very good for use in noisy environments. The Avago encoder provides precise positioning and velocity sensing information to servo motor feedback systems used in the operation nozzle inspection tool  83 . 
         [0055]    Each of the inputs referred to generally as  175  connect to motor controllers  177 . While different types of motor controllers can be used, a Maxon motor controller, Model EPOS 2 is found to be particularly suitable for the present invention. Motor controllers  177  are connected to a central processing unit  179  and receive and send communications thereto. 
         [0056]    In operation inputs  175  from the inertia measurement unit  179 , camera  171 , and encoders  173  located on the nozzle inspection tool  83  or are received through a cable connection  181  from the nozzle inspection tool  83  to the motor controllers  177 . The motor controllers  177  provide feedback to the nozzle inspection tool  83  and the central processing unit  179 . The operator then, through the central processing unit  179 , may control operation of the nozzle inspection tool  83  via communications with the motor controllers  177 . 
         [0057]    Through proper use of commands through the central processing unit  179 , an individual can control operation of the nozzle inspection tool  83 . Referring to  FIGS. 6A ,  6 B, and  6 C, the nozzle inspection tool  83  can be directed to any position desired in the outlet nozzle  31  or the steam line  33 . Also, the nozzle inspection tool  83  may be directed into the return nozzle  77 . Once the nozzle inspection tool  83  is in position, the expandable feet clusters  91  and  93  will extend outward to secure the nozzle inspection tool  83  into position. Once the expanding/rotating transducer package  95  is in position next to weld to be inspected, the expanding/rotating transducer package  95  will extend outward so that the transducers thereon are immediately adjacent to the weld to be inspected. Thereafter, the expanding/rotating transducer package  95  is rotated to inspect the weld.