[Federal Register Volume 65, Number 200 (Monday, October 16, 2000)]
[Notices]
[Pages 61200-61202]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-26472]


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NUCLEAR REGULATORY COMMISSION

[Docket Nos. 50-266 and 50-301]


In the Matter of Nuclear Management Company, LLC (Point Beach 
Nuclear Plant, Units 1 and 2); Exemption

I

    The Nuclear Management Company, LLC (the licensee) is the holder of 
Facility Operating License Nos. DPR-24 and DPR-27, which authorize 
operation of the Point Beach Nuclear Plant (PBNP), Units 1 and 2. The 
licenses provide, among other things, that PBNP is subject to all 
rules, regulations, and orders of the U.S. Nuclear Regulatory 
Commission (the Commission) now or hereafter in effect.
    The facility consists of two pressurized-water reactors (Units 1 
and 2) located on the licensee's Point Beach site in Two Rivers, 
Wisconsin. This exemption refers to both units.

II

    Title 10 of the Code of Federal Regulations (10 CFR), Section 
50.60, and 10 CFR Part 50, require that pressure-temperature (P-T) 
limits be established for reactor pressure vessels (RPVs) during normal 
operating and hydrostatic or leak rate testing conditions. 
Specifically, 10 CFR Part 50, Appendix G, states that ``The appropriate 
requirements on both the pressure-temperature limits and the minimum 
permissible temperature must be met for all conditions.'' Appendix G of 
10 CFR Part 50 specifies that the requirements for these limits are the 
American Society of Mechanical Engineers Code (ASME Code), Section XI, 
Appendix G, limits.
    By letter dated July 14, 2000, the licensee submitted a request for 
exemption from the requirements of 10 CFR 50.60 and Appendix G to Part 
50, to allow the use of ASME Code, Section XI, Code Case N-641, for 
PBNP, Units 1 and 2. Code Case N-641 combines former Code Cases N-514, 
N-588, and N-640, and provides guidelines for the

[[Page 61201]]

appropriate use of the three former Code Cases in combination.
    Code Case N-641, similar to former Code Case N-588, permits the 
postulation of a circumferentially oriented flaw (in lieu of an axially 
oriented flaw) for the evaluation of the circumferential welds in RPV 
P-T limit curves. Also, Code Case N-641, similar to former Code Case N-
640, permits the use of an alternate reference fracture toughness 
(K<INF>ia</INF> fracture toughness curve instead of K<INF>la</INF> 
fracture toughness curve) for reactor vessel materials in determining 
the P-T limits. Since the pressure stresses on a circumferentially 
oriented flaw are lower than the pressure stresses on an axially 
oriented flaw by a factor of 2, postulating a circumferentially 
oriented flaw for the evaluation of the circumferential welds (as 
permitted by Code Case N-641) in establishing the P-T limits would be 
less conservative than the methodology currently endorsed by 10 CFR 
Part 50, Appendix G. Further, since the K<INF>IC</INF> fracture 
toughness curve shown in ASME Code, Section XI, Appendix A, Figure A-
2200-1, provides greater allowable fracture toughness than the 
corresponding K<INF>la</INF> fracture toughness curve of ASME Code, 
Section XI, Appendix G, Figure G-2210-1, using the K<INF>IC</INF> 
fracture toughness (as permitted by Code Case N-641) in establishing 
the P-T limits would be less conservative than the methodology 
currently endorsed by 10 CFR Part 50, Appendix G. Considering both, an 
exemption to apply Code Case N-641 would be required by 10 CFR 50.60.

Postulation of Circumferential Flaws in Circumferential Welds (formerly 
Code Case N-588)

    The licensee proposed to revise the P-T limits in the pressure-
temperature limits report (PTLR) for PBNP, Units 1 and 2, using the 
postulation of a circumferentially oriented reference flaw as the 
limiting flaw in an RPV circumferential weld in lieu of an axially 
oriented flaw required by the 1995 edition (1996 addenda) of ASME Code, 
Section XI, Appendix G.
    Postulating the Appendix G reference flaw (an axially oriented 
flaw) in a circumferential weld is physically unrealistic and overly 
conservative because the length of the flaw is 1.5 times the vessel's 
thickness, which is much longer than the width of the reactor vessel 
girth weld. Industry experience with the repair of weld indications 
found during preservice inspections, and data taken from destructive 
examinations of actual vessel welds, confirms that all detected flaws 
are small, laminar in nature, and do not transverse the weld bead 
orientation. Therefore, any potential defects introduced during the 
fabrication process that are not detected during subsequent 
nondestructive examinations would only be expected to be oriented in 
the direction of weld fabrication. For circumferential welds, this 
indicates a postulated defect with a circumferential orientation.
    An analysis provided to the ASME Code's Working Group on Operating 
Plant Criteria (WGOPC) (in which the former Code Case N-588 was 
developed) indicated that if an axial flaw is postulated on a 
circumferential weld, then based on the stress magnification factors 
(M<INF>m</INF>) given in the Code Case for the inside diameter 
circumferential (0.443) and axial (0.926) flaw orientations, it is 
equivalent to applying a safety factor of 4.18 on the pressure loading 
under normal operating conditions. Appendix G requires a safety factor 
of 2 on the contribution of the pressure load in the case of an axially 
oriented flaw in an axial weld, shell plate, or forging. By postulating 
a circumferentially oriented flaw on a circumferential weld and using 
the appropriate stress magnification factor, the margin of 2 is 
maintained for the contribution of the pressure load to the integrity 
calculation of the circumferential weld. Consequently, the staff 
determined that the postulation of an axially oriented flaw on a 
circumferential RPV weld is a level of conservatism that is not 
required to establish P-T limits to protect the RCS pressure boundary 
from failure during hydrostatic testing, heatup, and cooldown.
    The staff also noted that former Code Case N-588 includes a revised 
methodology for determining the thermal stress intensity, 
K<INF>IT</INF>, which was later incorporated into Section XI of the 
1995 edition (1996 addenda) of the ASME Code. The licensee used this 
methodology to calculate K<INF>IT</INF>.
    In summary, the ASME Code, Section XI, Appendix G, procedure was 
developed for axially oriented flaws, which is physically unrealistic 
and overly conservative for postulating flaws of this orientation to 
exist in circumferential welds. Hence, the NRC staff agrees that 
relaxation of the requirements of ASME Code, Section XI, Appendix G, by 
postulating a circumferentially oriented flaw for the evaluation of the 
circumferential welds (as permitted by Code Case N-641) is acceptable 
and would maintain, pursuant to 10 CFR 50.12(a)(2)(ii), the underlying 
purpose of the ASME Code and the NRC regulations to ensure an 
acceptable margin of safety.

Using the K<INF>IC</INF> Fracture Toughness Curve (formerly Case N-640)

    The licensee proposed to revise the P-T limits in the PTLR for 
PBNP, Units 1 and 2, using the K<INF>IC</INF> fracture toughness curve 
in lieu of the K<INF>la</INF> fracture toughness curve as the lower 
bound for fracture toughness.
    Use of the K<INF>IC</INF> curve in determining the lower bound 
fracture toughness in the development of the P-T operating limits curve 
is more technically correct than the K<INF>la</INF> curve since the 
rate of loading during a heatup or cooldown is slow and is more 
representative of a static condition than a dynamic condition. The 
K<INF>IC</INF> curve appropriately implements the use of static 
initiation fracture toughness behavior to evaluate the controlled 
heatup and cooldown process of a reactor vessel. The staff has required 
use of the initial conservatism of the K<INF>la</INF> curve since 1974, 
when the curve was codified. This initial conservatism was necessary 
due to the limited knowledge of RPV materials. Since 1974, additional 
knowledge has been gained about RPV materials, which demonstrates that 
the lower bound on fracture toughness provided by the K<INF>la</INF> 
curve is well beyond the margin of safety required to protect the 
public health and safety from potential RPV failure. In addition, P-T 
curves based on the K<INF>IC</INF> curve will enhance overall plant 
safety by opening the P-T operating window with the greatest safety 
benefit in the region of low temperature operations.
    In summary, the ASME Code, Section XI, Appendix G, procedure was 
conservatively developed based on the level of knowledge existing in 
1974 concerning RPV materials and the estimated effects of operation. 
Since 1974, the level of knowledge about these topics has been greatly 
expanded. The NRC staff agrees that this increased knowledge permits 
relaxation of the requirements of ASME Code, Section XI, Appendix G, by 
applying the K<INF>IC</INF> fracture toughness (as permitted by Code 
Case N-641) while maintaining, pursuant to 10 CFR 50.12(a)(2)(ii), the 
underlying purpose of the ASME Code and the NRC regulations to ensure 
an acceptable margin of safety.

III

    Pursuant to 10 CFR 50.12, the Commission may, upon application by 
any interested person or upon its own initiative, grant exemptions from 
the requirements of 10 CFR Part 50 when (1) the exemptions are 
authorized by law, will not present an undue risk to public health or 
safety, and are consistent with the common defense and security; and

[[Page 61202]]

(2) when special circumstances are present. The staff accepts the 
licensee's determination that an exemption from 10 CFR 50.60 and 
Appendix G to Part 50 would be required to approve the use of Code Case 
N-641. The staff examined the licensee's rationale to support the 
exemption request and agrees that the use of Code Case N-641 would meet 
the underlying intent of these regulations. Based upon a consideration 
of the conservatism that is explicitly incorporated into the 
methodologies of (1) 10 CFR Part 50, Appendix G, (2) Appendix G of the 
ASME Code, and (3) Regulatory Guide 1.99, Revision 2, the staff 
concludes that application of Code Case N-641, as described above, 
would provide an adequate margin of safety against brittle failure of 
the RPV. This is also consistent with the determination that the staff 
has reached for other licensees under similar conditions based on the 
same considerations. Therefore, the staff concludes that requesting 
exemption under the special circumstances of 10 CFR 50.12(a)(2)(ii) is 
appropriate and that the methodology of Code Case N-641 may be used to 
revise the P-T limits in the current and the proposed TSs for PBNP, 
Units 1 and 2.

IV

    Accordingly, the Commission has determined that, pursuant to 10 CFR 
50.12(a), the exemption is authorized by law, will not endanger life or 
property or common defense and security, and is, otherwise, in the 
public interest. Therefore, the Commission hereby grants the licensee 
an exemption from the requirements of 10 CFR 50.60(a), and 10 CFR Part 
50, Appendix G, for PBNP, Units 1 and 2.
    Pursuant to 10 CFR 51.32, the Commission has determined that the 
granting of this exemption will not have a significant effect on the 
quality of the human environment (65 FR 59472).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 6th day of October 2000.

    For the Nuclear Regulatory Commission.
Suzanne C. Black,
Deputy Director Division of Licensing Project Management, Office of 
Nuclear Reactor Regulation.
[FR Doc. 00-26472 Filed 10-13-00; 8:45 am]
BILLING CODE 7590-01-P