Safety Analysis of PFBR: A Case Study
Prototype fast breeder reactor (PFBR) is a 500 MWe capacity pool-type reactor with two primary loops, two secondary loops, and four steam generators (SGs) per loop. The overall flow diagram comprising primary circuit housed in the reactor assembly, secondary sodium circuit, and balance of plant is shown in Figure 21.1. The nuclear heat generated in the core is removed by circulating sodium from the cold pool at 670 K to the hot pool at 820 K. The sodium from hot pool after transporting its heat to the four intermediate heat exchangers (IHXs) mixes with the cold pool. The circulation of sodium from the cold pool to the hot pool is maintained by two primary sodium pumps (PSPs) and the flow of sodium through IHX is driven by a level difference (1.5 m of sodium) between the hot and cold pools. The heat from IHX is in turn transported to eight SGs by sodium flowing in the secondary circuit. Steam produced in SG is supplied to turbo generator. In the reactor assembly (Figure 21.2), the main vessel houses the entire primary sodium circuit including the core. Sodium is filled in the main vessel with free surfaces blanketed by argon. The inner vessel separates the hot and cold sodium pools. The reactor core consists of about 1757 subassemblies (SAs) including 181 fuel SAs. The control plug, positioned just above the core, houses mainly 12 absorber rod drive mechanisms. The top shield supports the PSPs, IHX, control plug, and fuel handling systems. PFBR uses mixed oxide with depleted uranium and about 25% Pu oxide as fuel. For the core components, 20% cold worked D9 material (15% Cr-15% Ni with Mo and Ti) is used to have better irradiation resistance. Austenitic stainless steel type 316 LN is the main structural material for the out-of-core components.