ML20151R752
| ML20151R752 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 02/03/1986 |
| From: | Wilson R GENERAL PUBLIC UTILITIES CORP. |
| To: | Zwolinski J NRC |
| References | |
| RFW-0776, RFW-776, NUDOCS 8602060221 | |
| Download: ML20151R752 (3) | |
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Forked River.New Jersey 08731-0388 609 971-4000 Writer's Direct Dial Number:
February 3,1986 RP4-0776 John A. Zwolinski, Chief Onerating Reactors Branch No. 5 Division of Licensing U.S. Nuclear P.egulatory Commission Washington, D. C. 20555
Dear Mr. Zwolinski:
Subject:
Oyster Creek Nuclear Generating Station Docket No. 50-219 Isolation Condenser Vent Exemption Pursuant to your letter of August 30, 1985 concerning GPUN's request for exemption from 10CFR50.44(c)(3)(iii), please find attached our response.
Should you have any questions, please contact Mr. M. W. Laggart at (201) 299-2341.
ry tr 'ly yours, G
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R. d Wil on Vice Pres dent Technical Functions RFW:gpa 2799f Attachment cc: Administrator, Region I Jack N. Donohew, Project Manager U.S. Nuclear Regulatory Commission U.S. Nuclear Regulatory Commission 631 Park Avenue 7920 Norfolk Avenue King of Prussia, PA 19406 Bethesda, Maryland 20014 NRC Resident Inspector Oyster Creek Nuclear Generating Station Forked River, New Jersey 08731 l
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GPU Nuclear Corp 6 ration is a subsidiary of the General Pubhc Utihties Corporation
ATTACHMENT t,,
0YSTER CREEK IS0l.ATION CONDENSER VENT ENTION RE@EST NRC Request 1.
The analysis in Attachment II to the July 23, 1985 exemption request is incomplete. Low pressure systems are always assumed to be available in the analysis, provided the reactor can be depressurized. Other events which result in hydrogen generation plus the need for the isolation condensers may be postulated. One example of such an event would involve a LOCA with core damage followed by isolation of the break and a loss of low pressure systems (CRD and feedwater also not available).
In' order to adequately assess the impact of isolation condenser venting versus r.o venting, the full spectrum of events requiring isolation condenser venting must be analyzed.
Please provide these additional analyses.
GPUN Response All cases (both with and without low pressure systems available) were evaluated in the risk assessment and are included in the Event Sequence Diagrams and Event Trees.
However, our analysis discussed only those small break LOCA sequences in which adequate long-term isolation condenser performance was required to successfully depressurize the reactor vessel and result in low pressure (core spray) injection.
The type of event referred to is of very low frequency and has no impact on the need for Isolation Condenser (IC) venting.
The Core Spray System (CSS) is a highly redundant system containing two completely independent loops, each with two trains of pumps (main and booster).
Realistic system performance analysis over the small break size range show that operation of a single main pump and associated booster pump is sufficient to prevent significant fuel clad damage. As a result of the high reliability of the CSS, sequences in which it is not available have very low frequencies.
We can use the Event Trees to determine sequences in which the CSS fails i
and leads to a core damage condition.
Using the LOCA below core outside containment Event Tree, core damage sequence #14 involves the path requiring IC operation (and possible venting) and failure of the CSS.
The mean frequency is 2.36 X 10'*/ year.
Similarly, for the LOCA below core inside containment Event Tree, core damage sequences #31, 32 and 33 involve the path requiring IC operation (and possible venting) and failure of the CSS.
The mean frequency for these sequences is 1.34x10-'*/ year.
The total frequency for these LOCA conditions with the IC initially available and failure of the CSS is therefore 2.37 X 10'*/ year.
Taking a broader view, we can examine all sequences in which the Automatic Depressurization System (ADS) falls (LOCA below core outside containment) and ADS and Feedwater fail (LOCA below core inside containment) to determine the potential impact of venting on reaching core d6' age conditions.
Sequences potentially requiring IC venting resul'. In end states #9 through 15 for the LOCA below core outside containment.
Sequences 9 through 11 were previously evaluated.
Sequences #12 through 15 are core damage end states with a mean frequency of 5.69 X 10-*/ year.
PAGE 2
'~r Similarly, sequences #25 through 36 are the end states that potentially require IC venting for the LOCA below core inside containment.
Sequences 25 and 26 were previously evaluated. Sequences #27 through 36 are core damage end states with a mean frequency of 1.58 X 10-' / year.
When all sequence frequencies are corrected for the range of break sizes as was done in car previous report:
LOCA below core 1
Outside containment Sequences 9-11 1.76 X 10-5 Sequences 12-15 4.55 X 10-*
1 LOCA below core Inside containment Sequences 25-26 5.15 X 10-*
Sequences 27-36 1.26 X 10-
TOTAL 1.770 X 10-5 This total is only 0.37. larger than the frequency calculated for Attachment II to our exemption request (1.765 X 10-5) which was rounded and reported as 1.77 X 10-5 This, combined with the conservatisms previously discussed (in Attachment II of our previous exemption request) confirms our conclusion that isolation condenser venting can be of little benefit in reducing core damage frequency, and should not be required for the Oyster Creek Nuclear Generating Station.
NRC Request 2.
Are there any negative safety impilcations to adding isolation condenser vents?
GPUN Response GPUN is not aware of any negative safety impilcations associated with the addition of the isofation condenser vents.
NRC Request 3.
Will the installation of isolation condenser vents involve a significant increase in radiation exposure for workers?
GPUN Response GPUN estimates that 5-10 man rem would be associated with the installation of the isolation condenser vents.