f- /VjtMC- iSS C, &4T UNITED STATES ATOMIC ENERGY COMMISSION NAA-SR-Memo-685 U.P.R. CONTROL ROD LATCH By J. L. Hedgecock April 29, 1953 North American Aviation, Inc. Downey, California Technical Information Service, Oak Ridge, T< Subject Category, PHYSICS. Work performed under Contract No. AT-ll-l-GEN-8. Date Declassified: April 1^, 1955- The Atomic Energy Commission makes no representation or warranty as to the accuracy or usefulness of the Information or statements contained in this report, or that the use of any Information, apparatus, method or process disclosed In this report may not Infringe privately-owned rights. The Commission assumes no liability with respect to the use of, or for damages resulting from the use of, any Information, apparatus, method or process disclosed In this report. This report has been reproduced directly from the best available copy. Reproduction of this information is encouraged by the United States Atomic Energy Commission. Arrangements for your republication of this document in whole or in part should be made with the author and the organization he represents. Issuance of this document does not constitute authority for declassification of classified material of the same or similar content and title by the same authors. AEC, Oak Ridge, Tenn. U.P.R. CONTROL ROD LATCH By J. 0. Hedgecock Several configurations have been considered for the latch on the control and safety rod drive units. The four basic types are shown in sketches on Pages k, 6, 8, and 10, and their performance curves are given on Pages 5> 1> 9> said 11, respectively. Type A was the first considered; it proved to be rela- tively inefficient because friction was not used to best advantage. Type B gave considerable improvement and Type C gave a slight further improve- ment. In Type D the holding links are no longer actuated by toggle links, but by a wedge or cone. In the performance curves, the latch holding load is the load that must be applied upward to the latch mechanism to hold the latch holding links in the spread position shown In the sketches. The negative loads shown indicate that the latch is self -locking because of friction and give the force that must be applied downward to release the latch. The total load that must be held by the electromagnet which controls the release of the latch will be called the total holding load and will exceed the latch holding load by the weight of the latch actuating rod. The weight of the latch actuating rod may tentatively, in the absence of a final design, be estimated at 10 pounds. For a given and constant coefficient of friction, the latch may be designed so that the latch holding load is as small as desired. However, the coefficient of friction may not be known with much precision and may change with time because of pitting, wear, etc. We may expect the friction angle, 0, to be approximately 10° (coefficient of friction f = tan 9 = .176) for chromium plated bearing surfaces, but we wish the electromagnet to hold even if the friction angle should be as low as 5 (f b .087) and we wish the latch to release even if the friction angle should be or become as great as 20° (f = .36U). We may tabulate the following information taken from the performance curves of types C and D, Types A and B being chiefly of historical interest at present: Type C Type D Toggle or wedge angle, /3 or y Latch holding load at 9 = 5 Latch holding load at 9 = 20° Total holding load at 9 = 5° Total holding load at 9 = 20° 81° 2 l^o 56 lbs. 108 lbs 10 lbs. 10 lbs 66 lbs. 118 lbs 20 lbs. 20 lbs Thus we see that the electromagnet for Type D should have nearly twice the holding power as that required for Type C. A way to reduce the size and response time of the holding electromagnets is to adjust the toggle angle /3. The holding power of the electromagnet can be initially calibrated as a function of the current passing through it. Then at each shutdown, the minimum current necessary to hold the control rod load can be determined and the toggle angle /3 adjusted as necessary to compensate for changes in the coef- ficient of friction and insure safe release. Type D cannot be adjusted in a similar manner. Type C also offers a means of forcibly retracting the holding links should there be a tendency for them to stick out and impede re- moval of the control drive rod through the lower shielding. Type D permits the use of three or more holding links, while Type C is limited to two unless ball and socket joints are used. This consideration is felt to be of minor importance though, since the stresses are not excessive in any case. All in all, I believe that Type C is to be preferred for three of the four points mentioned above; 1) Smaller electromagnet required 2) Adjustable after installation 3) Holding links can be forcibly retracted. CONTROL ROD LOAD 750 # LATCH ACTUATING ROD U.P.B. CONTROL ROD LATCH TYPE A. 82° 84° 86° 88' /8, TOGGLE ANGLE, DEGREES U.P.B. CONTROL EOD LATCH PERFORMANCE OF TYPE A. CONTROL ROD LOAD-750# LATCH ACTUATING ROD U.P.R. CONTROL ROD LATCH TYPE B. 120 100 80 60 40 20 -20 -40 -60 -80 -100 NEGATIVE LOADS ARE FRICTIONAL LOADS THAT MUST BE OVERCOME TO RELEASE THE LATCH; THE LATCH IS SELF- LOCKING. 80° 82° 84° 86° 88* & TOGGLE ANGLE, DEGREES 90 e U.P.E. CONTROL ROD IATCH PERFORMANCE OF TYPE B. LATCH ACTUATING ROD U.P.B. CONTROL ROD LATCH TYPE C, 10 100 80 — 60 — (/) Q 2 40 O 0. n 20 < o i o 2 Q _l -?0 O I I O -40 -60 — -80 — -100 6 = FRICTION ANGLE NEGATIVE LOADS ARE FRICTIONAL LOADS THAT MUST BE OVERCOME TO RELEASE THE LATCH; THE LATCH IS SELF -LOCKING. 78° 80° 82° 84° 86° 88° 0, TOGGLE ANGLE, DEGREES 90 e U.P.H. CONTROL ROD TOGGLE TYPE C. 11 CONTROL ROD LEAD-.750* LATCH ACTUATING ROD U.P.R. CONTROL ROD LATCH TYPE D. 12 300 280 - 260 240 h 220 Q 2 2 <80 o" <60|- _i 1 <40 Q _l O x 120 x < 100 80 - 60 40 20 18 0=0 = 5 e = 10° 0=15°" 9 = 20° 22° 24° 26° 28' y, WEDGE ANGLE, DEGREES 32 c U.P.B. CONTROL ROD LATCH TYPE D. UNIVERSITY OF FLORIDA 3 1262 08917 0905