FACILITY DESCRIPTION. The AFRRI-TRIGA MARK-F Reactor has a movable core and

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1 1.4. UTILIZATION OF A TV CAMERA FOR UNDERWATER INSPECTION OF FUEL ELEMENTS AT THE AFRRI-TRIGA REACTOR FACILITY,. J. L. McKenzie and R. J. Joseph, (Armed Forces Radiobiology Research Institute) j I. INTRODUCTION The purpose of this paper is to describe an underwater inspection technique used at the AFRRI-TRIGA Reactor Facility to inspect fuel elements and to identify their respective serial numbers. Included in this paper is a brief description of the Reactor Facility/ a discussion of the inspection requirements, a description of the inspection system, and conclusions with regard to the value of the system. II. FACILITY DESCRIPTION The AFRRI-TRIGA MARK-F Reactor has a movable core and capability to operate in steady-state, the square wave, and pulse modes. The reactor can operate in the normal steady-state wave modes up to a maximum power level of one megawatt, in the pulse mode up to a maximum peak power level of 2600MW in a 10 millisecond pulse (FWHM). Since March 1965, the reactor has been operated for a total of 277, 255 kwh and pulsed 5,674 times. The three experimental facilities associated with the Reactor Facility are Exposure Room #1, Exposure Room #2, and the Pneumatic Tube System (Fig. I) 1. Modifications have been made to Exposure Room #1 (20 x 20 x 10 feet high) to limit the thermal neutrons in the radiation field in order to reduce the production of argon-41 and the activation of biological specimens 2. The high energy neutron and gamma corapo- i nents of the radiation field are the components of primary interest for radiobiological research programs. The magnitude of a pulsed dose can be varied up to a maximum of 16,000 rads (tissue kerma, free-in-air) depending upon the position of the 1-19 and 't i

2 CONTROL ROD DRIVES PNEUMATIC TUBE SYSTEM REACTOR TANK POSITION 3 POSITION 2 POSITION 1 REACTOR CORE PLUG DOOR EXPOSURE ROOM 1 EXPOSURE ROOM 2 EAD SHIELDING DOORS PLUG DOOR Figure 1. CUT-AWAY VIEW OF THE AFRRl-TRIGA REACTOR 1-20

3 specimen with respect to the core centerline distance from tank projection, and the desired neutron-to-gamma ratio. The usable neutron-to-gamma kerma ratio (free-in-air) can be varied from 0.4 in the normal field to 10 in a neutron enhanced field by placing a lead shield of various thicknesses (0-6 in.) between the tank projection in Exposure Room #1 and the specimen. The ratio can also be varied from 0.4 in a normal field to 0.1 in a gamma enhanced field by backing the reactor core away from the tank projection and varying the amount of water (0-5 in.) between the periphery of the core shroud and the tank projection. III. INSPECTION REQUIREMENTS The present fuel element inspection requirements are dictated by the AFRRI-TRIGA reactor license (R-84). The reactor license states that "the fuel elements shall be measured for length and bow at intervals separated by not more than 500 pulses of insertion greater than $2.00 or at annual intervals (not to exceed 14 months), whichever comes first. Fuel elements indicating an elongation greater than 1/10 inch, a lateral bending greater than 1/16 inch, or visible damage shall be considered to be damaged and shall not be used in the reactor core". Prior to 1972, AFRRI was required to inspect fuel elements at "... semiannual intervals (not to exceed 8 months)... ". On 5 July 1972, the Atomic Energy Commission authorized a change to the reactor license to extend the inspection interval to 12 months not to exceed 14 months. The justification for this license change can be found in reference 3. IV. INSPECTION SYSTEM The inspection system consists of the fuel element measuring tool, standard fuel element, fuel element handling tool, and closed circuit television system. This discussion will be limited to the use of the closed circuit television system for the visual inspection of the fuel element cladding for physical 1-21

4 damage and for the identification of the serial number for each fuel element. The measurement of fuel elements for elongation and bowing is performed routinely at TRIGA facilities and the techniques used do not vary a great deal, but the techniques used to perform the visual inspection of the fuel element cladding for physical damage can vary significantly from facility to facility. The components of the closed circuit television system used for the inspection consists of a water-tight housing, TV camera, zoom lens, and TV monitor. The water-light housing is an aluminum cylinder approximately 25 inches long and 15 inches in diameter (Fig. 2). Each end of the cylinder is flanged and grooved to hold rubber O-ring seals. An aluminum plate is fastened to the back of the cylinder with 16 screws. The camera and zoom lens mounting bracket is held securely in the housing by two bracket holders. An optically clear plastic cover is fastened over the front of the housing with 16 screws. Thus, this provides a water-tight housing to protect the camera, zoom lens, and the electrical leads. The TV camera is an RCA TK-202 tube type and the zoom lens is a motor driven Wollensak-3M, 30mm-150mm radiation resistant optical unit. The radiation resistant optics can withstand a radiation integrated dose in excess of 10 9 rads. These type cameras and zoom lens are routinely used in the Exposure Rooms to visually monitor all specimens that are irradiated in the rooms. In Figure 3 is shown the inspection system mounted in the Reactor Pool and suspended from an above carriage track by a 15-foot aluminum tube which houses the electrical leads to the camera and zoom lens. The housing is positioned approximately four to five feet horizontally from the fuel element inspection tool, and about ten feet below the surface of the water. The fuel element measuring tool is positioned on a ring attached to the top of the extension tank adapter and the tool is secured to the top of the extension tank. 1-22

5 CAMERA AND ZOOM LENS MOUNTING BRACKET Figure 2. INSPECTION SYSTEM COMPONENTS

6 J} to" c to GO Z GO "0 m n o GO -< GO H m m o 70 m > n -4 o T3 O O I -

7 The routine procedure followed during the fuel element measurements and subsequent visual inspection consists of removing a fuel element from the reactor core, with the fuel element handling tool, and positioning the element in the fuel element measuring tool. The measurements for bowing and elongation of the fuel element are then made. Upon completion of these measurements, the fuel element handling tool is attached to the fuel element in the measuring tool and rotated until the serial number on the tri-flute is facing the TV camera. The zoom lens is then properly positioned and focused until a sharp picture of the serial number can be seen on the TV monitor as shown in Figure 4. A critical parameter in obtaining a sharp clear picture on the TV monitor is the proper positioning of the underwater lights to reduce the light reflection and glare from the fuel element. After the underwater lights and the zoom lens are properly positioned, the identification of the fuel elements by serial number and the visual inspection of the fuel element cladding are relatively simple. The fuel elements are withdrawn from the measuring tool in small increments and then rotated 360 at each increment until the total length of the fuel element cladding has been visually inspected. V. CONCLUSIONS The conclusions that can be drawn, with regards to this visual inspection technique and based upon the experience of the AFRRI Reactor Staff in using the technique, are threefold. First, this inspection technique has proved to be a very useful technique and is used annually for the inspection of the fuel elements at the AFRRI-TRIGA Reactor Facility. Second, the advantages gained in using this technique do not necessarily offset the cost of the required equipment. If a reactor facility presently has a closed circuit television system, and existing equipment can be used, then it would be advantageous to adapt the equipment to this technique. The AFRRI has had a closed circuit television system since 1962 and therefore 1-25

8 Figure 4. PHOTOGRAPH OF FUEL ELEMENT SERIAL NUMBER AS SHOWN ON TV MONITOR

9 the only additional expense in adapting the equipment to this technique was the cost of construction of the water-tight housing. Third, this technique has an additional value in that the identification of the serial numbers and the subsequent visual inspection of the fuel element cladding can be recorded and permanently stored on video tape. This possibility is presently being discussed at AFRRI, but no firm decision has been made to date. 1-27

10 VI. REFERENCES 1. J. L. McKenzie, "Operational Experience at the AFRRI- TRIGA Reactor Facility ( )", ANS Transactions of Conference on Research, Test and Training Reactors, Charlottesville, Virginia, August D. M. Verelli, R. E. Carter, and L. A. Slaback, Jr. "Reduction of 41 Ar Environmental Releases at Research Reactors", AFRRI TN73-9, August J. L. McKenzie, "Operational Experience at the AFRRI-TRIGA Reactor Facility ( )", TRIGA Owner's Conference III, Papers and Abstracts, General Atomic Report TOC-5, February, 1974, pp to