ASME STP/NU-035

Description / Abstract: This work was undertaken in support of the ASME/DOE Generation IV Reactor Materials Program [1]. Most of the advanced nuclear reactor concepts being considered in the Generation IV effort will require that the structural materials operate at temperatures where time-dependent allowable stresses control. In the United States, the design and construction rules for the Class 1 nuclear components operating in the time-dependent temperature regime are provided in ASME Section III, Subsection NH (III-NH). Currently, only five materials are permitted in this construction code and one of the materials, namely alloy 800H (UNS N08810), is limited to service temperatures of 1400°F (760°C). To meet the design goals for some reactor concepts that require the use of alloy 800H, it has become desirable to extend the coverage for alloy 800H to higher temperatures and longer times [2]. Among the several tables and figures that need extension in III-NH are the following.

(1) the yield strength, SY1, provided in Table I-14.5,

(2) the ultimate strength, SU, provided in Table NH-3225-1,

(3) the minimum-stress-to-rupture, Sr, provided in Table I-14.6C,

(4) the limiting time-independent strength, Sm, as represented by the lowest of the timeindependent strength quantities defined in Section II, Part D,

(5) the allowable limit of general primary membrane stress intensity, Smt, provided in Table I- 14.3C,

(6) the maximum allowable value of the general primary stress intensity, So, provided in Table I- 14.2, and

(7) the limiting temperature and time-dependent stress intensity, St, provided in Table I-14.4C.

Other data are needed that are identified in a recent review of the requirements of III-NH [3]. However, the activity reported here is restricted to the estimation of the stress intensity values listed above. The goal is to extend time to 500,000 h, if possible, and extend temperature to 1650°F (900°C), if possible.