Texas Utilities Electric Company (Comanche Peak Steam Electric Station, Units 1 and 2); Exemption

[Federal Register Volume 64, Number 91 (Wednesday, May 12, 1999)]
[Notices]
[Pages 25520-25522]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-11996]


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NUCLEAR REGULATORY COMMISSION

[Docket Nos. 50-445 and 50-446]


Texas Utilities Electric Company (Comanche Peak Steam Electric 
Station, Units 1 and 2); Exemption

I.

    Texas Utilities Electric Company (the licensee/TU Electric) is the 
holder of Facility Operating Licenses No. NPF-87 and No. NPF-89, which 
authorize operation of the Comanche Peak Steam Electric Station 
(CPSES), Units 1 and 2. The licenses provide, among other things, that 
the licensee is subject to all rules, regulations, and orders of the 
Commission now or hereafter in effect.
    These facilities consist of two pressurized-water reactors at the 
licensee's site located in Somervell County, Texas.
    TU Electric seeks this exemption to the 2 percent above licensed 
power level assumption to allow for uncertainties specified by Title 10 
of the Code of Federal Regulations (10 CFR), Part 50, Appendix K, 
``ECCS [Emergency Core Cooling System] Evaluation Models,'' Section 
I.A., to support license amendments for modest increases of up to 1 
percent in the licensed power levels for both units. This will result 
in an exemption from the requirements of 10 CFR Part 50, Appendix K to 
allow ECCS evaluation model assumptions to be conducted at no less than 
1.01 times licensed power level. The licensee seeks this exemption 
based on its proposed use of a new feedwater flow measurement system to 
allow more accurate measurement of thermal power (known as the Leading 
Edge Flowmeter (LEFM) System), manufactured by Caldon, Inc. The LEFM is 
described in Caldon, Inc., Topical Report ER-80P, ``Improving Thermal 
Power Accuracy and Plant Safety While Increasing Operating Power Level 
Using the LEFM System.'' The subject topical report was approved 
subject to the limitations stated in a letter and Safety Evaluation 
(SE) dated March 8, 1999.

[[Page 25521]]

II.

    Part 50, Appendix K, Section I. A. states, in part, that ``it shall 
be assumed that the reactor has been operating continuously at a power 
level at least 1.02 times the licensed power level (to allow for such 
uncertainties as instrument error).'' The Appendix K rule was written 
to ensure that adequate margin for ECCS performance would be available 
if a design-basis loss-of-coolant accident (LOCA) ever occurred (39 FR 
1002, January 4, 1974). The margin was provided by incorporating 
several conservative features into the ECCS performance criteria as 
well as maintaining conservative requirements and recommendations for 
evaluation models.
    The basis for the requirement is discussed in background 
documentation, such as the Statement of Consideration for Appendix K 
(39 FR 1002, January 4, 1974). The 102 percent assumption is one of 
several items listed as conservative factors used to model the energy 
available from reactor operation. The Statement of Consideration also 
associates the preaccident power level assumption with the modeling of 
the rate of heat generation after the LOCA occurs. A comparison is made 
between the estimated uncertainty associated with the decay heat 
assumption (i.e., 20 percent above the American Nuclear Society (ANS) 
standard) and the estimated effect on heat generation resulting from 
the 102 percent power assumption. This is a natural connection since 
the preaccident power level directly affects the decay heat generation 
rate after reactor shutdown.
    When it was considering changes to Appendix K to accept the use of 
best-estimate evaluations, the staff understood that the rule 
incorporated substantial conservatisms (see SECY 83-472, ``Emergency 
Core Cooling System Analysis Methods,'' November 17, 1983). These 
conservatisms were necessary when the rule was written because of 
limited experimental evidence. The major analysis inputs and 
assumptions that contribute to the conservatism in Appendix K are 
grouped together under Sections A through D of the rule: (A) Sources of 
Heat During the LOCA (the 102 percent power provision is one factor); 
(B) Swelling and Rupture of the Cladding and Fuel Rod Thermal 
Parameters; (C) Blowdown Phenomena; and (D) Post-blowdown Phenomena: 
Heat Removal by ECCS. In each of these areas, several assumptions are 
typically used to assure conservatism in the analysis results. For 
instance, under sources of heat during the LOCA, in addition to the 102 
percent requirement, decay heat is modeled on the basis of an ANS 
standard with an added 20 percent penalty, and the power distribution 
shape and peaking factors expected during the operating cycle are 
chosen to yield the most conservative results. As discussed in SECY-83-
472, experimental programs provided ample data, which shed light on the 
considerable margin provided by Appendix K, giving the staff confidence 
to consider alternative ECCS evaluation models.

III

    Section 50.12(a), states that . . .
    The Commission may, upon application by any interested person or 
upon its own initiative, grant exemptions from the requirements of 
the regulations of this part, which are--
    (1) Authorized by law, will not present an undue risk to the 
public health and safety, and are consistent with the common defense 
and security.
    (2) The Commission will not consider granting an exemption 
unless special circumstances are present. . . .
    Section 50.12(a)(2), states that special circumstances are 
present whenever . . .
    (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; or
    (iv) The exemption would result in benefit to the public health 
and safety that compensates for any decrease in safety that may 
result from the grant of the exemption; or
    (vi) There is present any other material circumstance not 
considered when the regulation was adopted for which it would be in 
the public interest to grant an 
exemption. . . .

IV

    The staff has reviewed the applicable regulations and the 
regulatory history for Appendix K as well as for Section 50.46, and 
finds that those regulatory documents do not prohibit the licensee's 
proposal to use Caldon Inc.'s, Leading Edge Flowmeter System (Caldon 
LEFM System) instrument. Accordingly, the exemption is authorized by 
law, as required by 10 CFR 50.12(a)(1).
    The staff used Regulatory Guide 1.174 and Standard Review Plan 
Chapter 19 to review the application for the exemption. Specifically, 
the staff reviewed the application considering the defense-in-depth 
philosophy, the maintenance of sufficient safety margin, and the fact 
that the increase in risk was small and consistent with the Commission 
safety goals. A slightly higher power level will result in a small 
increase in decay heat load that could affect required response time of 
the ECCS and the available operator response time following transients 
and accidents. Results of core and containment consequence analyses 
from higher power levels could also be affected. However, NUREG-1230, 
``Compendium of ECCS Research for Realistic LOCA Analysis,'' considered 
the risk impact of changes associated with the revised ECCS rules, 
including power increase, and considered a power increase of 5 percent 
or less to have little risk significance. The staff concludes that this 
increase of 1 percent is bounded by the NUREG-1230 considerations.
    In the safety evaluation for the Caldon topical report ER-80P dated 
March 8, 1999, the staff accepted statistical treatment of 
uncertainties attributed to the LEFM and venturi-based flow measurement 
instruments and the uncertainty values associated with these two types 
of flow measurement instruments at CPSES. The use of the Caldon LEFM 
System and quantification of power measurement uncertainty do not raise 
inconsistencies with the Commission's safety goals. Further, the 
Commission has determined that, pursuant to 10 CFR 50.12, the requested 
exemption is authorized by law, will not result in an undue risk to the 
public health and safety, and is consistent with the common defense and 
security and is otherwise in the public interest.
    The Commission also finds that special circumstances exist. By 
seeking to apply a smaller margin for power measurement uncertainty, 
the exemption does not violate the underlying purpose of Appendix K. 
The application of 1.02 times the licensed thermal power is not 
necessary to achieve the underlying purpose of Appendix K. Indeed, by 
quantifying a contributor to the uncertainty where the uncertainty was 
not specifically known, the exemption may better serve the underlying 
purpose of the requirement. The use of the Caldon LEFM System and the 
quantification of power measurement uncertainty appear to offer safety 
benefits.
    By requesting this exemption, the licensee has undertaken to 
quantify a contributor to the uncertainty in power measurement. 
Although there is a small safety impact expected from the associated 
power increase, it is not considered significant. The use of the LEFM 
system and the quantification of power measurement uncertainty appear 
to offer safety benefits.
    The Caldon LEFM System and the quantification of power measurement 
uncertainty associated with use of the Caldon LEFM System constitute

[[Page 25522]]

material circumstances that did not exist when the rule was written. 
The current Appendix K rule presumes that the 2 percent margin accounts 
for uncertainties associated with measurement of thermal power. 
Contributors to the uncertainty were not identified at the time the 
rule was written and the magnitude of the uncertainty was not 
demonstrated by experiment or analysis. The rule does not require 
quantification of actual uncertainties, nor does the regulatory history 
reflect any detailed technical basis for the choice of a 2 percent 
margin. Therefore, the Commission has determined that special 
circumstances as defined in 10 CFR 50.12(a)(2)(ii), (iv), and (vi) are 
present.
    The Commission hereby grants the licensee an exemption from the 
requirements of 10 CFR Part 50, Appendix K to allow ECCS evaluation 
model assumptions to be conducted at no less than 1.01 times licensed 
power level when the quantification of power measurement uncertainty 
can be justified by the use of the Caldon LEFM System instrumentation. 
The granting of this exemption does not, however, provide authority to 
increase the licensed power of CPSES, Units 1 and 2. A separate license 
amendment to increase licensed power level, for each licensed unit, 
will be required to be submitted and approved before such authority may 
be provided for that unit.
    Pursuant to 10 CFR 51.32, the Commission has determined that 
granting of this exemption will have no significant effect on the 
quality of the human environment (64 FR This exemption is effective 
upon issuance.

    Dated at Rockville, Maryland, this 6th day of May 1999.

    For the Nuclear Regulatory Commission.
John A. Zwolinski,
Director, Division of Licensing Project Management, Office of Nuclear 
Reactor Regulation.
[FR Doc. 99-11996 Filed 5-11-99; 8:45 am]
BILLING CODE 7590-01-P