DESCRIPTION
During the course of the licensing action for North Anna Units 1 and 2, a number of questions were raised as to the potential for lamellar tearing and low fracture toughness of the steam generator and RCP support materials for these facilities. Two different steel specifications (ASTM A36 and ASTM A572) covered most of the material used for these supports. Toughness tests, not originally specified and not in the relevant ASTM
specifications, were made at various temperatures. The toughness of the A36 steel was found to be adequate, but the toughness of the A572 steel was relatively poor at a temperature of 80F. In the case of North Anna Units 1 and 2, the applicant agreed to raise the temperature of the A572 beams in the steam generator supports to a minimum temperature of 225F, prior to reactor coolant system pressurization to levels above 1,000 psig.
Auxiliary electrical heat was supplied as necessary to supplement the heat derived from the reactor coolant loop to obtain the required operating temperature of the support materials. Concerns regarding the supports at North
Anna were applicable to all PWRs. This item was originally identified in NUREG-0371[1]and was later declared a USI in NUREG-0510.[2]
CONCLUSION
This USI was RESOLVED with the publication of NUREG-0577, [3]Revision 1. The resolution contained no backfit requirements and applied only to new construction after issuance of SRP [4]Section 5.3.4.
[1] NUREG-0371, "Task Action Plans for Generic Activities (Category A)," U.S. Nuclear Regulatory Commission, November 1978.
[2] NUREG-0510, "Identification of Unresolved Safety Issues Relating to Nuclear Power Plants," U.S. Nuclear Regulatory Commission, January 1979.
[3] NUREG-0577, "Potential for Low Fracture Toughness and Lamellar Tearing in PWR Steam Generator and Reactor Coolant Pump Supports," U.S. Nuclear Regulatory Commission, (Rev. 1) October 1983.