THERMAL ANALYSIS OF THE SGR MARK IV CONTROL ROD ABSORBER ASSEMBLY

Technical Report · Wed May 01 04:00:00 EDT 1963

OSTI ID:4701427

Johnson, C G; Burry, G C

A one-dimensional heat transfer parameter study conducted on the Mark IV Dy/sub 2/O/sub 3/ control rod with absorber thicknesses of 1/8, 1/4, and 3/8 inch and an inside Hastelloy-X clad thickness of 1/16 inch revealed that the clad temperature limit of 1800 deg F would be exceeded in the linear heat rate range of interest for this control rod. These conclusions were based upon a constant helium gap thickness of 28 mils and a Dy/sub 2/O/sub 3/ thermal conductivity of 0.6 Btu/hrft- deg F. Although there is some uncertainty associated with the magnitude of Dy/sub 2/O/sub 3/ thermal conductivity, the use of an optimistic value of 1.0 Btu/hr-ft- deg F would only permit a linear heat rate of 6.3 kw/ft for a 1/8-inch absorber thickness and a 1800 deg F clad temperature limit, which is substantially below the expected heat rate for the 525 Mw(e) SGR. By replacing the inner clad with a solid graphite cylinder and making the outer clad the structural support member of the element, the clad temperature limitation is shifted to the much cooler outer clad rather than being set by the inner clad, and higher permissible linear heat rates are possible. This became the basis of the second design. Taking into account radiation, conduction, and the combined effect of differential expansion and temperature dependent conductivities upon the temperature distribution within the Dy/sub 2/O/sub 3/ rod, allowable linear heat rates of 6.3, 10.8, 14.9, and 20.6 kw/ft were determined for the 0.187-inch thick Dy/sub 2/O/sub 3/ rod having initial cold radial helium gaps of 61, 45, 35, and 27.5 mils, respectively. These corresponding gaps under the hot thermal- expanded condition became 55, 37.6, 27.7, and 20.2 mils, respectively. Therefore, assuming uniform heat generation and no axial conduction, a control rod having a local cold gap restriction of 55 mils could dissipate a peak linear heat rate of 14.9 kw/ft. The results of a one-dimensional thermal analysis on the Haynes 25 control rod with absorber thicknesses of 3/8, 3/4, and 1-inch are given. For the Dy/sub 2/O/sub 3/ and Haynes-25 rods there exists a substantial incentive from a heat transfer viewpoint to reduce the initial helium gap as much as possible within practical design limits. The one-dimensional thermal analysis on the Haynes-21 control rod of 3/8-inch thickness indicated that a peak linear heat rate of 20.4 kw/ft as calculated from estimates of neutron and gamma heating would produce a maximum temperature of 1912 deg F for a 35 mil initial cold gap. Under the same conditions, but taking into account axial conduction, the maximum temperature decreased to 1827 deg F. Thus, axial conduction results in an 85 deg F drop in maximum temperature for this heat rate. In general, the basic assumptions of uniform heat generation and no axial conduction are conservative and result in higher calculated temperatures for the onedimensional solutions presented. (auth)

• Research Organization: Atomics International. Div. of North American Aviation, Inc., Canoga Park, Calif.
• DOE Contract Number: AT(11-1)-GEN-8
• NSA Number: NSA-17-029719
• OSTI ID: 4701427
• Report Number(s): NAA-SR-Memo-8529
• Country of Publication: United States
• Language: English

Related Subjects

CHROMIUM ALLOYS
CONTROL ELEMENTS
DYSPROSIUM OXIDES
GAMMA RADIATION
GRAPHITE
HASTELLOY
HEAT TRANSFER
HEATING
HELIUM
MOLYBDENUM ALLOYS
NEUTRONS
NICKEL ALLOYS
PLANNING
POWER
RADIATION EFFECTS
REACTOR TECHNOLOGY
RODS
THERMAL CONDUCTIVITY
THERMAL STRESSES
THICKNESS
ZONES