During a meeting in Rockville (MD) in February 2003 [D.1], the Expert Elicitation Panel members defined five Base Cases that are denoted as BWR-1, BWR-2, PWR-1, PWR-2 and PWR-3, respectively. The five Base Cases are:

BWR Base Case (Plant ‘B’)

• BWR-1; Reactor Recirculation (RR) System. This reference case includes one-of-two RR System loops. Each loop consists of one NPS28 recirculation pump loop with a NPS22 manifold with five NPS12 risers; NPS is nominal pipe size in inch. The reference case excludes any small-diameter piping or tubing attached to the main RR piping. With a few exceptions, the selected piping system layout is representative of a BWR/4 reference plant as described in NUREG/CR-6224 [D.2]. The Base Case RR System does not include the NPS4 bypass line, however. The RR piping is fabricated from austenitic Cr-Ni stainless steel of Type A-304 (> 0.035% carbon).

• BWR-2; Feedwater (FW) System. As defined by isometric drawings, this reference case includes Loop B of the Class 1 portion of the FW System (i. e., the part of the FW System that is located in the drywell containment structure). This system of two loops includes NPS12, NPS14 and NPS20 piping. The FW piping is fabricated from carbon steel of Type A-333 Gr. 6.

• Section D.1.3 includes additional information on the BWR Base Case system definitions.

PWR Base Case (Plant ‘A. a/b’)

• PWR-1; Reactor Coolant (RC) System. As defined by an isometric drawing, this reference case includes one of the NPS30 hot leg (HL) in the RCS.

• PWR-2; Pressurizer Surge Line. As defined by an isometric drawing, this reference case includes the NPS14 piping, which connects the pressurizer to the cold leg (CL).

• PWR-3; High Pressure Injection/Normal Makeup (HPI/NMU) System. As defined by an isometric drawing, this reference case includes the 2-/2 inch schedule 160 line between the containment isolation valve and the RCS cold leg (CL).

• The PWR base cases associated with the RC hot leg and pressurizer surge line are typical of a 3-loop Westinghouse PWR (Plant A. a). The PWR base case associated with the HPI/NMU line is typical of a Babcock & Wilcox PWR (Plant A. b).

• Section D.1.4 includes additional information on the PWR Base Case system definitions.