ML20080M295
| ML20080M295 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 09/07/1983 |
| From: | Eisenhut D Office of Nuclear Reactor Regulation |
| To: | TOLEDO EDISON CO. |
| Shared Package | |
| ML20080M297 | List: |
| References | |
| TAC-48593, NUDOCS 8310030600 | |
| Download: ML20080M295 (6) | |
Text
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UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of
)
TOLED0 EDIS0N COMPANY AND THE
_)
CLEVELAND ELECTRIC ILLUMINATING
)
Docket No. S0-346 COMPANY
)
(Davis-Besse Nuclear Power Station, )
Unit No.1)
)
3 i
EXEMPTION I.
The Toledo Edison Company and the Cleveland Electric Illuminating Company (the licensees) hold Facility Operating License No. NPF-3, which authorizes The Toledo Edison Company to operate the Davis-Besse Nuclear Power Station, Unit No.1 (the facility) at steady-state power levels not in excess of 2772 megawatts thermal. This license provides, among other things, that it is subject to all rules, regulations and Orders of the Nuclear Regulatory Commission (the Commission) now or hereafter in effect.
The facility is a pressurized water reactor (PWR) located at the licensees' site in Ottawa County, Ohio.
II.
On December 2,1981, the Comission published a revised Section 10 CFR 50.44, " Standards for Combustible Gas Control System in Light-Water-Cooled Power Reactors (46 FR 58484
).
Sectio.4 10 CFR 50.44(c)(3)(iii) of the regulation requires:
"To provide improved operational capability to maintain adequate core cooling following an accident, by the end of the first scheduled outage beginning after July 1,1982, and of sufficient 8310030600 830907 PDR ADOcK 05000346 P
duration to permit required modifications, each light-water nuclear power reactor shall be provided with high point vents for the reactor coolant system, for the reactor vessel head, and for~other systems required to maintain adequate core cooling if the accumulation of noncondensable gases would cause the loss
.of function of these systems."
The vent for the reactor vessel head is the subject of this exemption.
By letter dated July 1, 1982, the licensees requested an exemption from the requirement of 10 CFR 50.44(c)(3)(iii)' for a reactor vessel head vent.
The licensees, by letter dated January 30, 1980, committed to install high point vents at the top of the hot leg U-bends and at the top of the pressurizer.
The installation of these vents will be completed prior to startup, scheduled for September 1983, from the curredt refueling.
The licensees' exemption request stated that installing an additional vent in the reactor vessel head would not be necessary to vent noncondensable gas trapped undar the vessel head to prevent-the loss of natural circulation.
III.
We have reviewed the licensees' exemption request and the bases for that rGquest.
However, the lack of integral system test data which would demonstrate the feasibility of this approach and the lack of a verified code capable of modeling the complex phenomena associated with non-condensable gas in contact with steam-water mixtures prevents our con-ciuding that noncondensable gases that evolve in the primary system can be safely vented by the hot leg high point vents alone.
The Davis-Besse facility is expected to have the capability of venting noncondensable gas through the hot leg vents before natural circulation could be lost.
However, if gas were trapped under the reactor vessel h;ad, the procedure by which the gas could be vented through the hot leg vents by the operator during any required depressurization could be diffi-cult.
It is our understanding that the head venting capability via the
' hot. leg vents has not been analyzed with a verified computer code capable of trescing noncondensable gases in contact with steam-water mixtures, nor has any acceptable analysis been verified against integral systems data applicable to the Babcock and Wilcox (B&W) reactor coolant system configura-tion.
As such, we do not have sufffeient assurance from the licensees that venting noncondensable gases under the reactor vessel head via the hot leg high point vents only can be safely and successfully accomplished.
The ability of the operator to safely accomplish head venting via the hot legs has not been demonstrated, either with a simulator, a test facility, or a verified analysis code.
The consequences of excessive depressurization t
and resultant interruption of natural circulation through the venting pro-cess have not been examined.
The staff believes that the ability of the operator to safely and successfully vent noncondensable gas trapped under the vessel head with hot leg vents and in the absence of vessel head vents should'be confirmed by (1) conducting experiments in an appropriate integral system test facility to verify analytical methods and venting procedures, or (2) demonstrating, with a simulator, the ability of the operators to perform safely and successfully head venting via the hot legs.
The simulator must be shown to be capable of properly simulating the phenomena of interest by verification against appropriate integral system test data.
Such test
data could be obtained as part of the test program rcquired to verify small break 1.oss of Coolant Accident methodology in Item II.K.3.30 of NUREG-0737.
By letter dated March 9, 1983, the licensees committed to participate in the B&W Owners Group, Integral System Test program to demonstrate the effi-cacy cf their proposed method of noncondensaole gas removal from the reactor vessel head and to submit their evaluation of the test results to verify analytical methods and operating procedures.
The licensees further committed to have the hot leg vents installed and declared operable, have procedures in place and operators trained for using these vents to vent noncondensable gases trapped under the reactor head prior to startup, scheduled for September 1983, from the current refueling outage.
Our present judgment is that the sequence of events necessary to lead to a degraded core condition which might involve the need to remove non-condensable gas from the vessel head region is of sufficient low probability that it is unlikely to occur during the interim period needed to obtain the necessary experimental data.
Therefore, until the test results are received and reviewed, an interim exemption should be granted.
IV.
1 Accordingly, the Commission had determined that, pursuant to 10 CFR 50.12, l
an interim exemption is authorized by law and will not endanger life or property or the common defense and security, and is otherwise in the public interest.
l The requested exemption from the requirements,of 10 CFR 50.44(c)(3)(iii) pertaining to the installation of a reactor tessel head vent is nereby granted, modifiec and conditioned as follows:
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~
The date July 1,1982, from which the installation schedule for the reactor vessel head vent is established, is extended to December 31, 1985, which means that the head vents must be installed by the end of the first scheduled outage of sufficient duration after that date to ;ermit the required modification.
This exemption is based upon the Commission's expectation that sufficient actual test data will be available by mid-1985 to permit the licensees to make a decision and plan accordingly sven though the Integral System Test Report may not have been
. issued in final form.
The licensees shall conduct or participate
-in the B&W Owners Group Integral Test System Test Program to demonstrate the efficacy of their proposed method for noncondensable gas removal from the reactor vessel head and submit their evaluation of the test results to the NRC.
It is recognized by the Commission that this testing is expected to confirm that the hot leg high point vents are sufficient to remove any noncond'ensable gases trapped in the reactor vessel head and that a head vent is not necessary for this purpose.
Prior to startup from the current refueling outage, the hot leg vents shall be operable and the licensees shall have procedures in place and operators trained for using the hot leg vents to vent non-condensa'61e gases trapped under the reactor head.
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6-The Cow,ission has determined that the granting of this exemption will not result in any significant environmental impact and that pursuant to-10' CFR 551.5(d)(4), an environmental impact statement, or negative declaration and environmental impact appraisal need not be prepared in connection with this action.
This exemption is effective upon issuance.
FOR THE NUCLEAR REGULATORY COMMISSION s
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/fdtM4 lut Lt.L
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1senh Director Division of Licenring
. Dated at Bethesda, Maryland, this 7th day of September 1983.
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