RS-11-100, Dresden, Units 2 and 3, Updated Final Safety Analysis Report (Ufsar), Revision 9, Chapter 4.0, Reactor
| ML11202A180 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 06/29/2011 |
| From: | Exelon Generation Co, Exelon Nuclear |
| To: | NRC/FSME |
| References | |
| RS-11-100 | |
| Download: ML11202A180 (129) | |
Text
DRESDEN- UFSAR Rev. 2 4.5-1 4.5 REACTOR MATERIALS 4.5.1 Control Rod Drive System Materials Control rod drive system materials are discussed in Section 4.6.
4.5.2 Reactor Internals Materials
The major internal components of the reactor include the control rod guide tubes; incore neutron monitors; shroud and other internal core support structures; steam separators; steam dryers; jet pumps; and the feedwater, core spray, and standby liquid control spargers and nozzles. This section does not cover the fuel assemblies, control rods, or incore neutron monitors; these components are discussed in Section 4.2, 4.6, and 7.6, respectively.
The following subsections describe the materials and welding methods used for reactor internals. A further description of reactor internals, including steam separators and steam dryers, is included in Section 3.9.5 and Section 6.1.
4.5.2.1 Structural Components The materials used for the structural members of the reactor internals are listed below:
A. Shroud - Type 304 stainless steel Shroud tie rod with spring stabilizers - 316/316L, XM-19 stainless steel and X-750 nickel base alloy, B. Core top grid -
Type 304 stainless steel, C. Core bottom grid -
Type 304 stainless steel, D. Fuel support piece - Type 304 stainless steel, E. Baffle plate - Inconel, F. Baffle plate supports - Inconel, G. Control rod guide tubes - stainless steel, and H. Incore nuclear instrumentation tubes - stainless steel.
All reactor internal structural members located in high flux regions are constructed of Type 304 stainless steel. The baffle plate and inner rim are made of Inconel to permit welding to the ferritic base metal of the reactor vessel. The welded joints that attach the baffle plate to the vessel wall were made in the vessel fabrication shop in a highly controlled operation. The bottom of the shroud is welded on top of the rim, which provides for the differential expansion between the ferritic, Inconel, and stainless steel DRESDEN - UFSAR Rev. 7 June 2007 4.5-2 components. This welded joint was made in the field and was dye penetrant checked to ensure the weld integrity. Inconel legs welded at intervals around the baffle plate support it from the vessel bottom head.
4.5.2.2 Jet Pump Assemblies The jet pump assemblies are made of Type 304 stainless steel except the following:
A. To accommodate the clamping loads generated in holding the inlet-throat subassembly in place, the beam is fabricated from Inconel X-750. Properly heat-treated, this high-strength, nickel-chromium-iron alloy exhibits good stress corrosion crack resistance in the reactor environment. As discussed in Section 5.4, jet pump parameters are monitored to detect integrity or operability problems which could indicate possible jet
pump beam cracking.
B. The jet pump assembly contains one slip joint which permits removal of the inlet-throat subassembly. Both contacting surfaces utilize Stellite-6 with a minimum Rockwell hardness of RC-30 to prevent wear in the mating parts.
C. The spring used in the restrainer wedge device is Inconel X-750 which has the higher strength properties necessary for desirable spring forces.
D. Some stainless steel members which are threaded or otherwise bear against other stainless steel parts are surface hardened by nitriding to prevent galling. Nitriding, a process whereby nitrogen is diffused into the base material, provides a thin, wear-resistant layer (up to 0.007 inch thick) with a minimum hardness of 90 on the Rockwell 15 N scale.
The diffuser section of each jet pump is attached to the baffle plate by an adapter ring which is welded to the diffuser and to the baffle plate. The latter weld, a field weld, was dye penetrant checked on the first pass, halfway through the weld and on the finish surface weld to ensure its integrity. The seal ring is made of Inconel X.
4.5.2.3 Spargers and Spray Nozzles The following sparger assemblies are part of reactor internals:
A. Core spray sparger The spray sparger, spray nozzles, and the core structure supporti ng the spray spargers are all made of Type 304 stainless steel.
B. Feedwater sparger
Dresden Units 2 and 3 use General Electric triple-sleeve sparger assemblies. The materials are selected to optimize performance, to DRESDEN - UFSAR 4.5-3 minimize the potential for component failure, and to comply with the intent of Regulatory Guide 1.44, "Control of the Use of Sensitized Stainless Steel." The sparger pipe, reduced tee, adapter, elbow, and orifice are all Type 304 stainless steel. The end plates and the extension on the reducing tee are Type 316L stainless steel. The sparger brackets are CF-3 cast stainless steel. Welding was done using 308L welding rod, and the whole assembly was solution-heat-treated after welding. The bracket pin and its stop are Type 304 stainless steel and were solution-heat-treated after machining. The brackets were welded to the end plates in the field to allow matching as-built dimensions. All field welds are made on 316L or CF-3 material.
The thermal sleeve is made of Inconel 600 and Type 316L stainless steel. The upstream portion which contacts the safe end is made of Inconel 600, which was purchased with a carbon limit of 0.1%. This portion of the thermal sleeve contains the mechanical grooves for the two seal rings. The coefficient of thermal expansion of Inconel 600 is close to that of the carbon steel safe end. Therefore, the use of Inconel 600 facilitates maintenance of an interference fit with the safe end and provides good corrosion resistance.
The triple-wall concentric sleeves are 316L stainless steel with a maximum limit of 0.02% carbon. Choice of this low-carbon alloy was made to pr event stress corrosion cracking, since solution-heat treatment was not feasible after assembly by welding.
Welds of Inconel 600 to Inconel 600 and Inconel 600 to Type 316L stainless steel are made with Inconel 82 welding material using the gas tungsten arc welding process. Welding of 316L to 316L components are done with 308L material.
The seal rings are made of Inconel 600, annealed at 2075
+/- 25°F for optimum resistance to stress corrosion. They are machined from forged rings to ensure good dimensional control. The backup springs used to increase the sealing pressure of the rings are made of Inconel X-750. The springs were initia lly stressed at 65,000 psi. This alloy was selected because of its high yield strength at 550°F of approximately 135,000 psi, permitting applied stress to be limited to 0.48 of yield.
C. Standby liqu id control sparger
The standby liquid control sparger is made of stainless steel.
DRESDEN-UFSAR Rev. 9 June 2011
Figures 4.2-1 through 4.2-3a have been deleted intentionally.
DRESDEN-UFSAR Rev. 9 June 2011
Figures 4.3-8 through 4.3-37 have been deleted intentionally.
DRESDEN-UFSAR Rev. 9 June 2011
Figures 4.4-2 through 4.4-5 have been deleted intentionally.