Patent Number: 044329326
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a modular reactor head shielding system embodying the invention is designated generally by the reference numeral 10. The modular reactor head shielding system or reactor shield 10 is shown operatively in place mounted on a reactor head 12. The reactor head 12 includes a top 14 from which extends control rods or a control rod cover 16. The reactor head 12 includes a plurality of vent ports 18 each of which is shown with a cover plate 20 of the reactor shield 10. The reactor head 12 includes a generally cylindrical side 22 from which extends the vent ports 18 and which may have various shapes depending upon the manufacturer of the reactor head and may be tapered from the top 14 down to a bottom flange 24 which forms the bottom of the reactor head cover. The top 14 is typically secured to the side 22 by a plurality of bolts 26. The reactor head 12 is secured to a reactor base 28 by a plurality of studs 30 onto which are mounted nuts 32. The reactor base 28 typically is situated in a well 34 which may include a shoulder 36 as illustrated or may be substantially upstanding around the whole reactor head 12. The nuts 32 can be removed with the shield 10 in place. The reactor shield 10 includes a plurality of pads 38 which are hung by mounting plates 40 from the reactor top 14 such as from the bolts 26. Shorter pads 38' are hung below the vents 20 by chains or straps 39. The pads 38 and 38' interleave with one another such that there are no radiation paths between adjacent pads. The pads are secured to one another by straps 42 which can have a hook or loop of synthetic material which adheres to a mating piece 44 on the adjacent pad 38 when pressed together (such as that sold under the trademark "Velcro"). The interleaving or overlap of the pads 38 and 38' is best illustrated in FIG. 2. Each of the pads 38 or 38' includes a pair of outer covers or sleeves 46 and 48 which are secured together offset from one another at a seam 50. Each sleeve 46 or 48 includes a pair of blankets 52 and 54. The manufacture of the blankets 52 and 54 and pads 38 or 38' is best described with reference to FIGS. 3 and 4. One blanket 52 is illustrated in FIG. 3. The blanket 52 includes a cover 56, such as nylon which can be plastic coated to prevent the lead from oxidizing. The cover 56 is filled with lead wool, as for example with 10 pounds per square foot. The cover 56 is then stitched with a grid type pattern 58 to secure the lead wool so that it does not shift within the blanket 52. The blanket 52 is sealed at its top and bottom ends 59 and 60 such as by sewing. Referring to FIG. 4, the covers or sleeves 46 and 48 of one pad 38 are best illustrated, each with a pair of blankets 52 and 54 inserted therein. Each of the blankets has a lead core interior 62 formed from the stitched lead wool. Each pair of blankets 52 and 54 are secured to one another such as by glueing along a common seam 64 prior to insertion into the sleeves 46 and 48. Each pair of blankets 52 and 54 is then glued to a sleeve wall 66 and 68, respectively, adjacent to the seam 50 to provide a very strong but flexible pad 38. The outer cover or sleeves 46 and 48 can be made from nylon or reinforced polyvinyl chloride (PVC) or other suitable material preferably having a tear strength of at least 300 pounds since the total weight of each pad 38 may be on the order of 300 to 350 pounds. The shorter pads 38' weigh less than the pads 38. The assembly of the hanging plates 40 for the pads 38 and 38' is best illustrated in FIGS. 5 through 7. The plates 40 include a large innerplate 70 with a plurality of bolt holes 72 therethrough. A mating outer plate 74 has a plurality of bolt holes 76 which match with the holes 72 in the innerplate 70. Each of the sleeves 46 and 48 has a top portion 78 and 80, respectively, folded over upon itself above the tops of the inner blankets 52 and 54 to provide a secure mounting pad for the plates 70 and 74. The top portion 78 and 80 are sandwiched between the plates 70 and 74 utilizing a plurality of bolts 82 and nuts 84. As best seen in FIG. 7 the sandwiched portion 78 has an outer end 85 which flares out further ensuring the secure mounting of the pads 38. The bolts or studs 26 on the reactor top 14 include a nut 86 which are removed to secure a mounting arm 88 thereon. The arm 88 includes a plate 90 and a stud hole or aperture 92 which is mounted on the stud 26 and secured by the nut 86. The outer end of the mounting arm 88 includes a retaining post or pin 94. Each of the mounting plates 40 includes a projecting mounting ear 96 at each end, which overlap one another behind the retaining post 94. The plates 40 preferably include a lifting aperture 98 into which can be placed a hook or other mechanical means to lift the pads 38 into position on the reactor head 12 or on a frame if desired. The plates 70 and 74 preferably have a shape to fit the outside of the reactor head 12. The resulting pad assembly 38 provides a flexible shield covering which will not injure the reactor side 22 and provides a reactor head shield 10 which is easily placed around the reactor head 12 while the nuts 32 are being removed and replaced and maybe left on the reactor head throughout the work outage. The pads 38' may have the chains 41 attached to their outer bolts 82 in the plate or clamp 40. The resulting shielding with the quaddruple lead wool blankets saves approximately 25 to 30 man rems per outage which is a reduction in exposure factor of magnitudes less than that otherwise required during a refueling outage. Many modifications and variations of the present invention are possible in light of the above teachings. The vent covers 20 can also be blankets or can be lead plates or lead poured into a frame. The scale and shape of each reactor head 12 of different manufacturers or different models would be somewhat different; however, the shaping of the pads 38 and 38' is easily accomplished within the teachings of the invention. The pads 38 and 38' preferably are tapered to fit the curvature of the reactor head 12, but also could be straight with some filler pads in between. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.