ML20247F604
| ML20247F604 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 05/12/1998 |
| From: | Cruse C BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9805190452 | |
| Download: ML20247F604 (4) | |
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CHAntxs II. CuUsr Baltimore Gas and Electric Company Vice President Calvert Cliffs Nuclear Power Plant Nuclear Energy 1650 Calven Cliffs Parkway Lusby, Maryland 20657 410 495-4455 May 12,1998 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit No.1; Docket No. 50-317 Request for Temporary Relief from ASME Boiler & Pressure Vessel Code Section XI Requirement IWA-5250 Baltimore Gas and Electric Company requests temporary relief from American Society of Mechanical Engineers (ASME) Boiler & Pressure Vessel Code Section XI (1983 Edition), requirement IWA-5250, as allowed under 10 CFR 50.55a(a)(3)(i). We specifically request permission to delay locating and repairing the minor leakage identified in the liner of the refueling pool for Unit 1. The delay is requested until the period of time where the pool is in a long-term drained condition, i.e., prior to fuel movement from the reactor vessel during the next scheduled Unit 1 outage (spring 2000). The alternative proposed by this request will result in an acceptable level of quality and safety.
L Camponent for Which ReliefIs Requested Temporary reliefis requested for the liner of the refueling pool below elevation 45'. The refueling pool is a reinforced concrete pool with a steel liner. In accordance with guidance provided in Regulatory Guide 1.26, the portion of the refueling pool liner below 45' elevation is a Class 3 component subject to the requirements of ASME Section XI. The function of the Code portion of the liner is to provide a pressure boundary which prevents the Spent Fuel Pool (SFP) from draining if the transfer tube is open between the refueling pool and the SFP. An attempt has been made to locate the source of the leakage; however, due to the small nature of the leak, it has not been found.
II. Code Requirements for Which ReliefIs Requested American Society of Mechanical Engineers Boiler and Pressure Vessel Code Section XI (1983 Edition, through summer 1983 addendum), requirement IWA-5250, states:
"(a) The source ofleakages detected during the conduct of a system pressure test shall i
be located and evaluated by the Owner for corrective measures as follows:
... (2) repairs or replacements of components shall be performed in accordance with IWA-4000 or IWA-7000, respectively."
9805190452 900512 PDR ADOCK 05000317 P
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l Document Control Desk May 12,1998 L_
Page 2 III. Proposed Alternative Provides Adeaunte Level of Ouality and Safety Instead of conducting a repair at this time, we propose to monitor the leakage for the remainder of time that the refueling pool is flooded and the transfer tube is open to ensure that the leakage does i
not significantly increase. This will provide adequate assurance of safety until the defect can be l
located and, if the defect is located within the Code boundary, a Code repair can be made.
Reasonable efforts will be made to locate the defect prior to fuel movement from the reactor vessel j
during the next scheduled Unit I refueling outage (spring 2000).
Supporti== Information A.
Seauence of Events While performing general housekeeping on April 22,1998, evidence of leakage was found at the exit location of the overflow line for the refueling pool. The overflow line penetrates the pool liner at the 67'-6" elevation, and exits the concrete pool base at the 32' elevation. The
. age appeared to be on the order of one-to-two drops per second when the leak was found.
'i leakage was found to be substantially less with each subsequent visual examination. On L
by 4,1998, the visual examination found that there were no drops present; however, wetness remained at the leak location. The refueling pool was drained on May4,1998 as part of scheduled outage activities. After the refueling pool was drained, visual examinations and vacuum box testing were done on the most likely areas within the Code boundary for the leak.
3 The defect could not be located. At this time, it is not known if the leak originates from the Code portion of the refueling pool.
The following information was used to evaluate the ability of the refueling pool to perform its function:
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> The refueling pool is a reinforced concrete pool with a steel liner. Leakage from the pool appears to be migrating between the liner and the concrete wall, and exiting the concrete at the location where the pool overflow line comes through the concrete. An evaluation has been done to address possible rebar corrosion due to contact with borated water (similar to the water contained in the refueling pool). The evaluation shows that the corrosion rate of rebar in reinforced concrete is not accelerated under the conditions available in the refueling pool.
> The rate ofleakage from the defect is small. This would be indicative of a small flaw, which is supponed by our difficulty in locating it.
> The refueling pool is not subject to appreciable pressurization or thermal stresses. The pool is open to the containment atmosphere and, therefore, cannot be pressurized.
l Additionally, the water in the pool is cooled by the SFP Cooling System and the Shutdown Cooling System. Even if the cooling systems were to totally fail, the pool cannot be subject to temperatures greater than 212 "F.
> Due to the structural support provided by the concrete portion of the refueling pool and the small size of the flaw, it was determined that catastrophic failure of the liner due to this defect is not credible.
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Document Control Desk May 12,1998 '
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' Based on these observations, an initial determination was made that the refueling pool is able to perform I
its safety.and non-safety functions. Therefore, the system was determined to be operable. However, because of the identified leakage in the refueling pool liner and the possibility the leak may be in the Code portion of the refueling pool, Technical Specification Action Statement 3.4.10.1.c, Structural Integrity of ASME Code Class 3 Components, will be entered when fuel loading begins. His Action Statement does not restrict startup or continued power operation. We intend to attempt to locate the defect and restore the structural integrity of the litier as required by IWA-5250 prior to fuel movement from the reactor vessel during the next Unit I refueling outage (spring 2000), when the transfer tube is closed and the pool is drained.
. B.
Safetv Siname= ace As discussed above, the initial assessment determined that a catastrophic failure of the liner due to this defect is not credible; however, the system design and operation were reviewed to assess the ability to perform the system functions if the liner did fait catastrophically. The design functions performed by this system are to prevent draining the SFP when the transfer tube is open to ensure that spent fuel assemblies remain adequately covered at all times.
If the liner failed, the concrete pool would retain the water with some leakage. Because of the minimum number of penetrations in the concrete, the rate of water loss would be limited. The capability exists to makeup the refueling pool water with borated water from the Refueling
. Water Tank by gravity feed. His makeup flow path is designed to Seismic Category 1, Class 3 -
requirements. An alternative means of filling the refueling pool includes makeup water to the
- SFP, ' The Updated Final Safety Analysis Report Section 9.4.4 requires a minimum SFP makeup capability of 150 gpm.. These makeup sources.will ensure adequate time exists to safely store any fuel that is in transit through the transfer tube and close the transfer tube prior j
to any undesirable consequences.
The spent fuel assemblies in the SFP and the reactor vessel will remain covered at all times, as.
a result ofinherent design features that prevent inadvertent draining of the SFP and the reactor vessel below the top of the fuel assemblies. He presence of the water will provide the cooling
- function needed to maintain fuel integrity.
In addition to evaluating the effects of a catastrophic failure of the liner on the ability of the refueling pool to perform its design functions, the effects of a failure of the liner on other
- systems was also evaluated. For this type of failure, the only mechanisms that could result in a i
consequential failure are flooding and spray effects. The point of drainage from a liner failure j
is the lowest elevation of the Containment Building. Any leakage would accumulate in the j
containment sump. There is no equipment in the area of the Containment Building floor j
needed for. operation in Modes 5 and 6 that would be' affected by water on the floor.
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- Additionally, there is no equipment in the vicinity of the' exit point from the concrete that wou,ld be adversely impacted by any spray from a failure.- nese design features ensure flooding and spray effects resulting from a failure of the' 8.iner will not prevent other plant.
'j L systems from perh,rming their safety functions.
L i
Derefore, even'in' the event of the incredible catastrophic failure of the liner, the design
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functions of the system will be met using alternative means, as provided in the system design.
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Document Control Desk 1 May 12,1998
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C.
Code-Reanirement Performance Imnact Attempting to locate the defect and performing the Code repair of the refueling pool liner (if necessary) requires closing the transfer tube and draining the refueling pool while searching for -
the defect and repairing it if the defect is found in the Code boundary. We entered our Unit I refueling outage on April 3,1998, The leak was discovered during core off-load activities on 1
April 22,1998.' Core off-load was completed and the' transfer tube was closed. The refueling pool was drained and an inspection was done. As noted above, the defect could not be located.
1 A more time-consuming and dose intensive effort will have to be undertaken to find the source of this small leak. There is insufficient time between the identification of the leak and the-scheduled on-load of the core to perform the more intensive investigation that would be.
required. Therefore, we propose postponing further examinations and any repair of the liner that would be needed until the period 'of time where the pool is in a long-term drained condition, i.e., prior to fuel movement from the reactor vessel during the next scheduled Unit 1
.j
- outage (spring 2000). Granting this relief will not have an adverse affect on quality or safety.
V.. Compensatory Actions Instead of conducting a repair at this time, we propose to monitor the leakage for the remainder of time that the refueling pool is flooded and the transfer tube is open to ensure that the leakage does not significantly increase. Should the leakage from the liner increase substantially, we will reevaluate our analysis.
VI. Implementation Schedule A.
Daily visual examination to check for leakage from the liner - Will be started when the pool-is flooded and the transfer tube is open.
B.
Use more rigorous methods to attempt to locate the defect - Prior to fuel movement from the
- reactor vessel during the 2000 Unit I refueling outage.
SAFETY COMMITTEE REVIEW The proposed relief request has been reviewed by our Plant Operations and Safety Review Committee and they concluded that the refueling pool liner will provide an adequate level of quality and safety until the defect can be located and Code repairs as required by IWA-5250 can be made, if necessary, i Should you have questions regarding this matter, we will be pleased to discuss them with you.
Very truly yours,.
p h '"
,y CHC/ PSF / dim 1
1 cc:
R. S. Fleishman, Esquire H. J. Miller, NRC J. E. Silberg, Esquire Resident Inspector, NRC S. S. Bajwa, NRC R. I. McLean, DNR j
A. W. Dromerick, NRC J. H. Walter, PSC
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