ML19325E829
| ML19325E829 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 10/30/1989 |
| From: | Croneberger D GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 5000-89-1832, GL-89-16, NUDOCS 8911090113 | |
| Download: ML19325E829 (6) | |
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OPU Neeleet Corporation One Upper Pond Road er Par 61ppany. New Jersey 07054 201 316 7000 i
TELEX 136 482 Writer's Direct Dial Number:
J October 30, 1989 5000-89-1832 l
U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.
20555 Gentlemen
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Subjects Oyster Creek !!uclear Generating Station Docket No. 50-219 Response to Generic Letter 89-16 Mark I containment Hardened Vent This letter constitutes CPU Nuclear's response to Generic Letter 89-16 for the Oyster Creek Nuclear Generating Station.
The generic letter was received by GPU Nuclear on September 14, 1989.
We commit to install a hardened vent provided the results of our IPE show that it is an appropriate risk reduction measure. We will notify you of our conclusion as soon as available but no later than our IPE schedule.
Diceussion s
Wetwell venting capability currently exists at Oyster Creek.
Procedures are in place and operators are trained to vent containment if needed to maintain containment integrity. The vent path is not " hardened" and thus could be expected to relieve pressure to the reactor building if used at high pressure.
However, the ability to remove decay heat through this path and/or avoid the primary containment pressure limit is provided by the current design.
Based on the NRC Staff's analysis in SECY-89-017 and on discussions between BWR owners' Group representatives and the Staff, we understand the principal risk reduction benefit associated with venting is expected for plants whose calculated core damage frequency (CDP) is dominated by accident sequences involving Long Term Loss of Decay Heat Removal (TW).
Oyster Creek is substantially different from the plants represented in the Staff's reference analysis.
It has several design features that would substantially reduce the likelihood of TW sequences and thus reduce t he benefit of the hardened vent.
8911090113 891030 ADOCKODOOg9 PDR P
C32035689 GPU Nuclear Corporation is a subsidiary of General Public Utihties Corporation
n h'kc Octoper 30, 1989 j
Page Two i
syecifically, the oyster Creek plant design employs kn Isolation condenser System (ICS, shown schematically in Attachment 1.
There are two independent ICS' trains (one is pictured), each fully redundant, which are capable of
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operating independent of AC power. The ICS is a passive system with each train j
capable of removing at least 3 percent reactor power without rejecting heat into containment, rurther, diverse sources of make-up water are available, including a source via redundant diesel fire pumps which are independent of l
the emergency AC power system.
Since the iaolation condensers remove decay
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heat directly to atmosphere, containment would not be chosen as a primary heat sink during reactor isolation sequences as long as IC's are available.
Even in
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very unlikely sequences involving loss of both ICs, oyster Creek has diverse i
heat removal paths not available at plants considered in the NRC's reference analysis. These include: 1) four containment spray heat exchangers with j
service water supplies which are powered from diesel generators and are I
i independent of IC's and other paths, and 2) three shutdown cooling loops with service water independent of ICs and containment sprays which could be used for sequences involving low reactor pressure.
Thus, the likelihood of core damage or containment over-pressure due to decay heat is extremely small.
In addition to these existing heat removal paths, our planned modification to add an alternate AC (AAC) power source during the 14R outage will improve the reliability of AC power to further assure the availability of these heat
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r removal paths in the event diesel generators are unavailable.
Early vintage PRA-type studies for oyster Creek did not show decay heat removal sequences to
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be significant contributors.
It is our expectation that the IPE, which is currently underway, will also show that TW sequences will represent a very low fraction of the total calculated CDP.
Therefore, the benefit of a harder.ed containment vent is substantially less than plants without ICS.
f In parallel with the IPE effort to evaluate ICS use, we will be working with the BWR owners'. Group to develop generic design criteria for the hardened vent.
The owners' Group anticipates that generic hardened vent design criteria will be available for NRC review by April 30, 1990.
L We have parformed preliminary engineering to develop a concept for a hardened vent which is schematically shown in Attachment 2.
This design is essentially l
the same as that which was described in Enclosure 1 to the generic letter, l
except for the use of remotely operated valves instead of rupture dises, which we currently consider to be more technically appropriate if a hardened vent is installed. Our preliminary cost estimate for implementing this design is $2.1 million based on installation in 1993. Our preliminary cost estimate for j
modifying the design to be independsnt of AC power is an incremental increaoe of $0.0 million.
The breakdown of these estimates by major element of cost is j
contained in Attachment 3.
This cost is well in excess of that assumed in the generic letter.
Major cost components include the distance and route of the vent path, the reactor building penetration, length of cable / conduit runs to the control room and the engineering of radiation monitoring and H2 combustion control features.
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As explained above, for Oyster Creek the installation of a hardened vent would
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U cost substantially more than the estimate in the generic letter and the expected benefits would be substuntially lower than the reference plant (s) due to.our unique design features.. Thus the cost / benefit ratio is far different.
. We will thoroughly examine the hardened vent issue in the IPE-in the context of r
'TW and all other sequences. We will also take into account other Mark I containment issues identified by the staff.
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D. K. Wonoberger j:
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Region 1 U.S. Nuclear Regulatory Commission 475 Allendale Road jy King of Prussia, PA 19406
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Mr. Alex Dromerick f
U.S. Nuclear Regulatory Commission
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b Washington, D.C. 20555 I
NRC Resident Inspector j
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OC MARDENED TORUS VENT COST EST! MATE o
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Sateline Engineering 8 4 Million Baseline Support
.2 Mard Vent (hc Powered)
Materials & Labor
.8 Nitrogen Purge Materials & Labor
.1 Subtotal 51.5 Million
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DC Powered System
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