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[Federal Register Volume 65, Number 26 (Tuesday, February 8, 2000)]
[Proposed Rules]
[Pages 6044-6046]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-2833]

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NUCLEAR REGULATORY COMMISSION

10 CFR Part 50

[Docket No. PRM-50-69]

Westinghouse Electric Company LLC; Receipt of Petition for 
Rulemaking

AGENCY:  Nuclear Regulatory Commission.

ACTION:  Petition for rulemaking; notice of receipt.

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SUMMARY:  The Nuclear Regulatory Commission (NRC) has received and 
requests public comment on a petition for rulemaking filed by 
Westinghouse Electric Company LLC (petitioner). The petition has been 
docketed by the Commission and has been assigned Docket No. PRM-50-69. 
The petitioner is requesting that the NRC regulations governing 
pressure and temperature limits for the reactor pressure vessel be 
amended to eliminate requirements for the metal temperature of the 
closure head flange and vessel flange regions. The petitioner believes 
the elimination of the flange requirement has no impact on Boiling 
Water Reactors (BWRs) and could improve plant safety in Pressurized 
Water Reactors (PWRs).

DATES:  Submit comments by April 24, 2000. Comments received after this 
date will be considered if it is practical to do so, but assurance of 
consideration cannot be given except as to comments received on or 
before this date.

ADDRESSES:  Submit comments to: Secretary, U.S. Nuclear Regulatory 
Commission, Washington, DC 20555. Attention: Rulemakings and 
Adjudications staff.
    Deliver comments to 11555 Rockville Pike, Rockville, Maryland, 
between 7:30 am and 4:15 pm on Federal workdays.
    For a copy of the petition, write: David L. Meyer, Chief, Rules and 
Directives Branch, Division of Administrative Services, Office of 
Administration, U.S. Nuclear Regulatory Commission, Washington, DC 
20555-0001. Documents related to this action are available for public 
inspection at the NRC Public Document Room (PDR) located at the Gelman 
Building, 2120 L Street, NW, Washington, DC 20555. Documents created or 
received at the NRC after November 1, 1999 are also available 
electronically at the NRC's Public Electronic Reading Room on the 
Internet at http://www.nrc.gov/NRC/ ADAMS/index.html. From this site, 
the public can gain entry into the NRC's Agencywide Document Access and 
Management System (ADAMS), which provides text and image files of NRC's 
public documents. For more information, contact the NRC Public Document 
Room (PDR) reference staff at 1-800-397-4209, 202-634-3273, or by email 
to [email protected].
    You may also provide comments via the NRC's interactive rulemaking 
website through the NRC home page (http://ruleforum.llnl.gov). This 
site provides the availability to view and upload comments as files 
(any format), if your web browser supports that function. For 
information about the interactive rulemaking website, contact Ms. Carol 
Gallagher, 301-415-5905 (e-mail: [email protected]).

FOR FURTHER INFORMATION CONTACT:  David L. Meyer, Office of 
Administration, U.S. Nuclear Regulatory Commission, Washington, DC 
20555. Telephone: 301-415-7162 or Toll Free: 1-800-368-5642 or E-mail: 
[email protected].

SUPPLEMENTARY INFORMATION:

Background

    The Nuclear Regulatory Commission received a petition for 
rulemaking dated November 4, 1999, submitted by Westinghouse Electric 
Company LLC (petitioner). The petitioner is requesting that Table 1 in 
10 CFR part 50, appendix G, be amended by removing requirements related 
to the metal temperature of the closure head flange and vessel flange 
regions. Specifically, the petitioner is requesting that footnotes 2 
and 6 be removed from Table 1. The removal of these footnotes would 
eliminate requirements that restrict heat-up and cool-down pressure 
temperature curves.
    In support of its petition, the petitioner has attached a 
Westinghouse document, WCAP-15315, ``Reactor Vessel Closure Head/Vessel 
Flange Requirements Evaluation for Operating PWR and BWR Plants'' 
(October 1999). The petitioner believes that this document sets forth 
the technical basis for the proposed modification, the grounds for and 
interest in the requested action, and the specific issues and facts 
that support the petition.
    On the basis of the information in WCAP-15315, the petitioner has 
concluded that the requirements pertaining to the reactor vessel 
closure head flange in 10 CFR part 50, Appendix G, Table 1, are not 
necessary and believes that removal of these requirements will have no 
impact on BWRs and could improve plant safety in PWRs. The petitioner 
requests that the regulations in 10 CFR part 50 be amended by removing 
footnotes 2 and 6 in Table 1 of Appendix G that pertain to the reactor 
vessel closure head flange.
    The NRC has determined that the petition meets the threshold 
sufficiency requirements for a petition for rulemaking under 10 CFR 
2.802. The petition has been docketed as PRM-50-69. The NRC is 
soliciting public comment on the petition for rulemaking.

Discussion of the Petition

    The petitioner notes that requirements pertaining to the reactor 
vessel closure head flange are contained in 10 CFR part 50, appendix G, 
Table 1 entitled, ``Pressure and Temperature Requirements for the 
Reactor Pressure Vessel.'' These requirements appear in footnotes 2 and 
6 of Table 1. These footnotes require that the metal temperature of the 
closure flange regions must exceed the material unirradiated RTNDT 
by at least 120 deg. F for normal operation when the pressure exceeds 
20 percent of the pre-service hydrostatic test pressure (621 psig for a 
typical PWR and 300 psig for a typical BWR). The petitioner believes 
that these requirements are unnecessary and requests that these 
footnotes be eliminated.

[[Page 6045]]

    In support of its petition, the petitioner has attached a 
Westinghouse document, WCAP-15315, ``Reactor Vessel Closure Head/Vessel 
Flange Requirements Evaluation for Operating PWR and BWR Plants' 
(October 1999) that it believes sets forth the technical basis for the 
proposed modification, the grounds for and interest in the requested 
action, and the specific issues and facts that support the petition. 
The Westinghouse document indicates that the method used to develop 
pressure-temperature limits on the reactor vessel closure head flange 
in NRC requirements is based on fracture toughness data from the mid 
1970s. Specifically, the margin of 120 deg. F and the pressure 
limitation of 20 percent of hydrotest pressure were developed using the 
KIA fracture toughness curve provided in Appendix G to 
Section XI of the American Society of Mechanical Engineers (ASME) 
Boiler and Pressure Vessel (B&PV) Code. The petitioner does not specify 
the editions of the ASME B&PV Code that contain the KIA or 
the KIC fracture toughness curves. The petitioner believes 
that improved knowledge of fracture toughness and other factors 
affecting the integrity of the reactor vessel have led to the recent 
change to permit the use of the KIC fracture toughness 
curve, provided in Appendix A to Section XI of the ASME B&PV Code, in 
the development of pressure-temperature curves as specified in ASME 
Code Case N640, ``Alternative Reference Fracture Toughness for 
Development of P-T Limit Curves for Section XI, Division 1.''
    The petitioner also believes the Westinghouse report demonstrates 
that a typical heat-up curve for both PWRs and BWRs using the KIC 
curve provides for a much higher allowable pressure through the entire 
range of temperatures. The petitioner concludes that the higher 
specified limits for a typical PWR are negated by the current NRC 
closure flange requirement. The petitioner contends that the 
Westinghouse report shows that the use of the KIC curve 
recently adopted by the ASME for flange considerations will lead to the 
conclusion that the current flange requirement can be eliminated.
    The petitioner contends that the Westinghouse report demonstrates 
that irradiation effects studies lead to the conclusion that the 
location of the closure flange region is in an area of the reactor 
where irradiation levels are very low, meaning that the fracture 
toughness of the closure head flange is not measurably affected. The 
Westinghouse report indicates that steady state operation stresses in 
several PWR designs are not very high, but in other designs the 
stresses are much higher. Loadings are primarily membrane stress with 
somewhat lower bending stresses for two PWR designs. In other PWR 
designs, the bending stresses are approximately twice (or more) the 
membrane stresses. In BWRs, the membrane stress is very similar to that 
in PWRs, but the bending stresses are higher in BWR designs, due to the 
larger diameter and smaller thickness.
    The report indicates that the relative impact of these stresses is 
best addressed through a fracture mechanics evaluation that postulates 
a semi-elliptic surface flaw at the outer surface of the closure head 
flange. The petitioner believes the report demonstrates that in both 
BWRs and PWRs, the stress intensity factors and fracture toughness 
variables at boltup provide a significant margin of safety and 
concludes that the integrity of the closure head/flange region is not a 
concern for any operating plant using the KIC fracture 
toughness curve. The petitioner also believes the report concludes that 
there are no known mechanisms of degradation in this region other than 
fatigue and that the calculated design fatigue usage level is so low 
that flaws are unlikely to initiate in the closure head/flange region.
    The Westinghouse document indicates that for PWRs the boltup 
temperature ranges from 10 deg. F to 51 deg. F, with a nominal boltup 
temperature of 60 deg. F. For BWRs the boltup temperature using the 
KIC fracture toughness curve ranges from 10 deg. F to 
66 deg. F, with a nominal boltup temperature of 80 deg. F. The 
petitioner believes that these comparisons make it clear that no 
additional boltup requirements are necessary and concludes that the 
requirements in footnotes 2 and 6 of Table 1 in 10 CFR part 50, 
appendix G can be eliminated.
    The Westinghouse report states that an important safety concern is 
the narrow operating window at low temperatures forced by the closure 
flange requirement. Because the flange requirement sets a pressure 
limit of 621 psi for a PWR (20 percent of hydrotest pressure), the 
pressure-temperature (P-T) limit curve may be superceded by the flange 
requirement for temperatures below RTNDT + 120 deg. F. The 
report also states that although this requirement was originally 
imposed to ensure the integrity of the flange region during boltup, it 
is no longer a concern as specified in the ``Flange Integrity'' 
analysis section of the report.
    The report indicates that the flange requirement can cause severe 
operational limitations when instrument uncertainties are added to the 
lower limit (621 psi) for the Low Temperature Overpressure Protection 
(LTOP) system of PWRs. Because the minimum pressure required to cool 
the seals of the main coolant pumps is 325 psi, the operating window 
between minimum system pressure necessary for seal cooling and maximum 
system pressure to comply with PT limits on the flange sometimes 
becomes very small. The report states that if the operator allows the 
pressure to drop below the pump seal limit, the seals could fail and 
cause the equivalent of a small break loss of cooling accident (LOCA), 
a significant safety problem. The petitioner believes that elimination 
of the flange requirement will significantly widen the operating window 
for most PWRs as stated in the report, reducing the likelihood of such 
an occurrence.
    The Westinghouse report cites the Byron Unit 1 facility as an 
example of a PWR that the petitioner believes illustrates how 
elimination of the flange requirement could improve plant safety. 
According to the report, Byron has LTOP setpoints significantly below 
the flange requirement of 621 psi, because of a relatively large 
instrument uncertainty. The setpoints of the two power-operated relief 
valves (PORVs) are staggered by about 16 psi to prevent a simultaneous 
activation. Because the two PORVs have different instrument 
uncertainties, the higher uncertainty is used for conservatism. The 
report states that:

    ``Elimination of the flange requirement for Byron Unit 1 would 
mean that the PORV curve could become level at 604/587 psig, which 
are the leading/trailing setpoints to protect the PORV downstream 
piping, through the temperature of the 350 deg. F down to boltup at 
60 deg. F. The operating window between the leading PORV and the 
pump seal limit rises from 121 psig (446-325) to 262 psig (587-325). 
This change will make a significant improvement in plant safety by 
reducing the probability of a small LOCA, and easing the burden on 
operators.''

    The report acknowledges that the Byron situation is only one 
example of the flange requirement's impact. The report also states that 
although each operating PWR facility will have different parameters, 
the operational safety will generally be improved by elimination of the 
flange requirement.
    The Westinghouse report further states that elimination of the 
flange temperature requirement would have no impact on BWRs:

    ``The saturation temperature corresponding to the 300 psig 
operating pressure (20% of the pre-service hydrostatic test 
pressure) is 420 deg. F. This is well in excess of the RTNDT 
+ 120 deg. F requirement. Therefore the flange temperature 
requirements are satisfied regardless of whether they exist or not.

[[Page 6046]]

Therefore, elimination of the flange temperature requirement has no 
impact on BWR flange integrity.''

The Petitioner's Conclusions

    The petitioner has concluded that the NRC requirements governing 
pressure and temperature limits for the reactor pressure vessel should 
be amended to eliminate reactor vessel closure head flange 
requirements. The petitioner has also concluded that the elimination of 
the flange requirement has no impact on BWRs and could improve plant 
safety in PWRs. The petitioner requests that the reactor vessel closure 
head flange requirement be eliminated from the regulations at 10 CFR 
part 50, appendix G, Table 1 as presented in its petition for 
rulemaking.

    Dated at Rockville, Maryland, this 1st day of February, 2000.

    For the Nuclear Regulatory Commission.
Annette Vietti-Cook,
Secretary of the Commission.
[FR Doc. 00-2833 Filed 2-7-00; 8:45 am]
BILLING CODE 7590-01-P
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