[Federal Register Volume 67, Number 36 (Friday, February 22, 2002)]
[Notices]
[Pages 8323-8325]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-4242]


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NUCLEAR REGULATORY COMMISSION

[Docket No. 50-247]


Entergy Nuclear Operations, Inc.; Indian Point Nuclear Generating 
Unit No. 2; Exemption

1.0  Background

    The Entergy Nuclear Operations, Inc. (ENO or the licensee) is the 
holder of Facility Operating License No. DPR-26 which authorizes 
operation of the Indian Point Nuclear Generating Unit No. 2 (IP2). The 
license provides, among other things, that the facility is subject to 
all rules, regulations, and orders of the U.S. Nuclear Regulatory 
Commission (NRC, the Commission) now or hereafter in effect.
    The facility consists of a pressurized-water reactor located in 
Westchester County in the State of New York.

2.0  Purpose

    Title 10 of the Code of Federal Regulations (10 CFR), part 50, 
Appendix G, requires that the Reactor Coolant System (RCS) Pressure-
Temperature (P-T) limits for an operating plant be at least as 
conservative as those that would be generated if the method of Appendix 
G to Section XI of the American Society of Mechanical Engineers Boiler 
and Pressure Vessel Code (ASME Code) (Appendix G to the Code) were 
applied.
    In summary, this action is in response to an application by the 
Consolidated Edison Company of New York, Inc.(Con Edison), the former 
licensee of IP2, for an exemption dated July 16, 2001. On September 6, 
2001, Con Edison's interest in the license was transferred to Entergy 
Nuclear Operations, Inc. (ENO). By letter dated September 20, 2001, ENO 
requested that the NRC continue to review and act on all requests 
before the Commission which had been submitted before the transfer. 
Accordingly, the NRC staff has acted upon the request. The exemption 
request of July 16, 2001, was supplemented by ENO on January 11, 2002. 
The exemption would permit the use of the ASME Code, Section XI Code 
Case N-640, ``Alternative Requirement Fracture Toughness for 
Development of P-T Limit Curves for ASME Section XI Division I,'' and 
ASME Code, Section XI Code Case N-588, ``Alternative to Reference Flaw 
Orientation of Appendix G for Circumferential Welds in Reactor Vessels, 
Section XI, Division I,'' in lieu of 10 CFR part 50, Appendix G, 
paragraph I.

2.1  Code Case N-588

    The requested exemption would allow use of ASME Code Case N-588 to 
determine stress intensity factors for postulated flaws and postulated 
flaw orientation for circumferential welds.
    10 CFR part 50, Appendix G requires that Article G-2120 of ASME 
Code, Section XI, Appendix G, be used to determine the maximum 
postulated defects in reactor pressure vessels (RPV) for the P-T 
limits. These limits are determined for normal operation and test 
conditions. Article G-2120 specifies in part, that the postulated 
defect be in the surface of the RPV material and normal (i.e., 
perpendicular) to the direction of maximum stress. ASME Code, Section 
XI, Appendix G, also provides a methodology for determining the stress 
intensity factors for a maximum postulated defect normal to the maximum 
stress. The purpose of this article is, in part, to ensure the 
prevention of non-ductile fractures by providing procedures to identify 
the most limiting postulated fractures to be considered in the 
development of P-T limits. Code Case N-588 provides relief from the 
Appendix G requirements, in terms of calculating P-T limits, by

[[Page 8324]]

revising the Article G-2120 reference flaw orientation for 
circumferential welds in RPVs. The reference flaw is a postulated flaw 
that accounts for the possibility of a prior existing defect that may 
have gone undetected during the fabrication process. Thus, the intended 
application of a reference flaw is to account for defects that could 
physically exist within the geometry of the weldment. The current ASME 
Section XI, Appendix G approach mandates the consideration of an axial 
reference flaw in circumferential welds for purposes of calculating the 
P-T limits. Postulating the Appendix G reference flaw in a 
circumferential weld is physically unrealistic and overly conservative, 
because the length of the flaw is 1.5 times the RPV wall thickness, 
which is much longer than the width of circumferential welds. The 
possibility that an axial flaw may extend from a circumferential weld 
into a plate or axial weld is already adequately covered by the 
requirement that defects be postulated in plates/forgings and axial 
welds.
    The fabrication of RPVs for nuclear power plant operation involved 
precise welding procedures and controls designed to optimize the 
resulting weld microstructure and to provide the required material 
properties. These controls were also designed to minimize defects that 
could be introduced into the weld during the fabrication process. 
Industry experience with the repair of weld indications found during 
pre-service inspection, in-service non-destructive examinations, and 
data taken from destructive examination of actual RPV welds, confirms 
that any remaining defects are small and do not cross transverse to the 
weld bead. Therefore, any postulated defects introduced during the 
fabrication process, and not detected during subsequent non-destructive 
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. ASME Code Case N-588 
addresses this issue by allowing consideration of maximum postulated 
defects oriented circumferentially in circumferential welds. ASME Code 
Case N-588 also provides appropriate procedures for determining the 
stress intensity factors for use in developing RPV P-T limits per ASME 
Code, Section XI, Appendix G procedures. The procedures allowed by ASME 
Code Case N-588 are conservative and provide a margin of safety in the 
development of RPV P-T operating and pressure test limits that will 
prevent non-ductile fracture of the RPV.
    The proposed P-T limits include restrictions on allowable operating 
conditions and equipment operability requirements to ensure that 
operating conditions are consistent with the assumptions of the 
accident analysis. Specifically, reactor coolant system pressure and 
temperature must be maintained within the heatup and cooldown rate 
dependent P-T limits specified in TS Section 3.1.B, ``Heatup and 
Cooldown.''

2.2  Code Case N-640

    The requested exemption would allow use of ASME Code Case N-640 in 
conjunction with ASME Code Section XI, Appendix G to determine the P-T 
limits for the RPV. Code Case N-640 permits the use of an alternate 
reference fracture toughness (KIc fracture toughness curve 
instead of KIa fracture toughness curve) for reactor vessel 
materials in determining the P-T limits. Because use of the 
KIc fracture toughness curve results in the calculation of 
less conservative P-T limits than the methodology currently required by 
10 CFR part 50, Appendix G, an exemption to apply the Code Case would 
be required by 10 CFR 50.60.
    The licensee proposed to revise the 
P-T limits for IP2, using the KIc fracture toughness curve, 
in lieu of the KIa fracture toughness curve, as the lower 
bound for fracture toughness.
    Use of the KIc curve in determining the lower bound 
fracture toughness in the development of P-T operating limit curves is 
more technically correct than the KIa curve because the rate 
of loading during a heatup or cooldown is slow and is more 
representative of a static condition than a dynamic condition. The 
KIc 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 KIa 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 KIa 
curve is well beyond the margin of safety required to protect the 
public health and safety from potential RPV failure. Additionally, P-T 
curves based on the KIc curve will enhance overall plant 
safety by opening the operating window, with the greatest safety 
benefit in the region of low-temperature operations.
    In summary, the ASME 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.

3.0  Discussion

    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 
(2) when special circumstances are present. Special circumstances are 
present whenever, according to 10 CFR 50.12(a)(2)(ii), ``Application of 
the regulation in the particular circumstances would not serve the 
underlying purpose of the rule or is not necessary to achieve the 
underlying purpose of the rule.''

Code Case N-588

    The first of these exemption requests would allow ENO to apply ASME 
Code Case N-588 as the basis for determining the most limiting material 
in the IP2 RPV. Code Case N-588 is applicable only for reactor vessels 
that have a circumferential weld as the most limiting material in the 
beltline region of the RPV. The Code Case methods allow licensees to 
apply the lower tensile stresses associated with a circumferential 
crack postulated in the circumferential weld, and thus allow the 
licensee to use the next most limiting base metal or axial weld 
material in the RPV as the basis for evaluating the vessel. Since the 
IP2 RPV is currently limited by circumferential shell weld for the 1/4T 
location, this Code Case is applicable to the evaluation of the IP2 
RPV.
    The staff has determined that Entergy has provided sufficient 
technical bases for using the methods of Code Case N-588 for the 
calculation of the 
P-T limits for the IP2 reactor coolant pressure boundary (RCPB). The 
staff has also determined that application of Code Case N-588 to the 
P-T limit calculations will continue to serve the purpose in 10 CFR 
part 50, Appendix G, for protecting the structural integrity of the IP2 
RPV and RCPB. In this case, since strict compliance with the 
requirements of 10 CFR part 50, Appendix G, is not necessary to serve 
the underlying purpose of the regulation, the staff concludes that 
application of Code Case

[[Page 8325]]

N-588 to the P-T limit calculations meets the special circumstance 
provisions stated in 10 CFR 50.12(a)(2)(ii), for granting this 
exemption to the regulation.

Code Case N-640

    Entergy has requested, pursuant to 10 CFR 50.60(b), an exemption to 
use ASME Code Case N-640 as the basis for establishing the P-T limit 
curves. Appendix G to 10 CFR part 50 has required use of the initial 
conservatism of the KIa equation since 1974 when the 
equation was codified. This initial conservatism was necessary due to 
the limited knowledge of RPV materials. Since 1974, the industry has 
gained additional knowledge about RPV materials, which demonstrates 
that the lower bound on fracture toughness provided by the 
KIc equation is well beyond the margin of safety required to 
protect the public health and safety from potential RPV failure. In 
addition, the RPV P-T operating window is defined by the P-T operating 
and test limit curves developed in accordance with the ASME Code, 
Section XI, Appendix G, procedure.
    The ASME Working Group on Operating Plant Criteria (WGOPC) has 
concluded that application of Code Case N-640 to plant P-T limits is 
still sufficient to ensure the structural integrity of RPVs during 
plant operations. The staff has concurred with ASME's determination. 
The staff has concluded that application of Code Case N-640 would not 
significantly reduce the safety margins required by 10 CFR part 50, 
Appendix G. The staff also concluded that relaxation of the 
requirements of Appendix G to the Code by application of Code Case N-
640 is acceptable and would maintain, pursuant to 10 CFR 
50.12(a)(2)(ii), the underlying purpose of the NRC regulations to 
ensure an acceptable margin of safety for the IP2 RPV and RCPB. 
Therefore, the staff concludes that Code Case N-640 is acceptable for 
application to the IP2 P-T limits.
    The staff examined the licensee's rationale to support the 
exemption requests and concluded that ENO has provided sufficient 
technical bases for using the methods of Code Cases N-588 and N-640 in 
the calculation of the 
P-T limits for IP2. The staff has also concluded that application of 
Code Case N-588 and Code Case N-640 to the 
P-T limit calculations will continue to serve the purpose in 10 CFR 
part 50, Appendix G, for protecting the structural integrity of the IP2 
RPV and reactor coolant pressure boundary. In this case, since strict 
compliance with requirements of 10 CFR 50.60(a) and 10 CFR part 50, 
Appendix G, is not necessary to serve the overall intent of the 
regulations, the staff concludes that application of the Code Cases N-
588 and N-640 to the P-T limit calculations meets the special 
circumstance provisions in 10 CFR 50.12(a)(2)(ii), for granting 
exemptions to the regulations, and that, pursuant to 10 CFR 
50.12(a)(1), the granting of these exemptions is authorized by law, 
will not present undue risk to the public health and safety, and is 
consistent with the common defense and security. The staff, therefore, 
considers granting exemptions to 10 CFR 50.60(a) and 10 CFR part 50, 
Appendix G, to allow ENO to use Code Cases N-588 and N-640 as the part 
of the bases for generating the P-T limit curves for IP2 is 
appropriate.

4.0  Conclusion

    Accordingly, the Commission has determined that, pursuant to 10 CFR 
50.12(a), the exemption is authorized by law, will not present an undue 
risk to the public health and safety, and is consistent with the common 
defense and security. Also, special circumstances are present. 
Therefore, the Commission hereby grants ENO an exemption from the 
requirements of 10 CFR 50.60(a) and 10 CFR part 50, Appendix G, for the 
calculation of P-T limits for IP2. The licensee shall use the methods 
Code Cases N-588 and N-640 in calculation of the P-T limits for IP2.
    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 (67 FR 7206).
    This exemption is effective upon issuance.

    Dated at Rockville, Maryland, this 15th day of February 2002.

    For the Nuclear Regulatory Commission.
John A. Zwolinski,
Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. 02-4242 Filed 2-21-02; 8:45 am]
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