Quality Management- Customization for Qualification,  Inspection and Testing During Automated Braze Welding of Austenitic Stainless Steel to Electrolytic Tough Pitch Copper for PFBR Sodium Purification Circuit Cold Traps

R.G. Rangasamy¹, Prabhat Kumar¹ and N. Manoharan³

¹Department of Atomic Energy, Bharatiya Nabhikiya Vidyut Nigam Limited, Kalpakkam- 603102, India. ³Director – Research and Development Division, AMET University, Kanathur - 603112, India.

DOI : http://dx.doi.org/10.13005/bbra/1388

ABSTRACT: Prototype Fast Breeder Reactor (PFBR) is sodium cooled, pool type, 500 MWe reactor which is at advanced stage of construction at Kalpakkam, Tamilnadu, India. The heat generated in the reactor core is removed by circulating sodium through the core. This sodium is called primary sodium and becomes radioactive as it passes through the core. The primary sodium then transfers its heat to secondary sodium in IHX which is non radioactive. Besides the primary and secondary circuit, safety grade decay heat removal (SGDHR) circuit also exists for removing the decay heat from the core. All these sodium circuits have cold traps for purifying the sodium. Cold traps works on the principle of temperature dependent solubility and by reducing the temperature of sodium, the main impurities in sodium i.e. Oxygen and hydrogen are removed as oxides and hydrides. All the cold traps are skirt supported (vertical) austenitic stainless steel vessels and consists of an inner shell and outer jacket. Between the inner shell and outer jacket air/nitrogen is used as the cooling medium for reducing the temperature of sodium. Copper fins are provided on the inner shell segment of cold traps for increasing the heat transfer area. These copper fins are distributed over the inner shell segment with very close pitch. Due to certain constraints in fabrication, braze welding of copper fins to stainless steel inner shell segment was adopted in place of brazing. The cold traps are thin walled components. These cold traps were manufactured as per stringent PFBR specification with SS 304 LN stainless steel as material of construction. Materials, Welding, Inspection and Testing of these vessels are more stringent than ASME. Since ASME doesn’t provide exact details of braze welding qualifications, based on the functional requirements of cold traps, tensile test, bend test, IGC practice E, macro test and fracture test were stipulated in the Braze welding procedure specification. This paper brings out the Quality management methodologies adopted and customized during dissimilar welding i.e. braze welding of Sodium purification circuit cold traps for PFBR.

KEYWORDS: Sodium purification; Copper fins; Stainless steel; Braze welding; Quality management

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