ML20101C630
| ML20101C630 | |
| Person / Time | |
|---|---|
| Site: | Mcguire, Catawba, McGuire, 05000000 |
| Issue date: | 11/21/1984 |
| From: | Tucker H DUKE POWER CO. |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| IEB-84-03, IEB-84-3, NUDOCS 8412210148 | |
| Download: ML20101C630 (15) | |
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.A: P.o.'aox satse CH.* RLOrTE, N.C. S8949 HALB. TUCKER ~ "- m, a L m- -
gyggffMr%1,1 i Mr. James P. O'Reilly.. Regional Administrator
.U. S. Nuclear Regulatory Commission
. Region-II
'101 Marietta Street NW, Suite 2900 Atlanta, Georgia 30323-
Subject:
.McGuire. Nuclear Station Catawba Nuclear Station Docket Nos. 50-369 and 50-370; 50-413 and 50-414 NRC/OIE Bulletin 84-03
Dear Mr. O'Reilly:
Please. find attached Duke Power Company's response to NRC/0IE Bulletin 84-03.
This. bulletin concerns an incident in which the refueling cavity water seal failed and rapidly der.ined the refueling cavity, and requests certain. actions to assure that fuel uacovery during refueling remains an unlikely event.
The attached report provides a summary of our evaluation of the potential for
.and consequences of a. refueling cavity water: seal failure for the McGuire and
~ Catawba Nuclear Stations. Although the original seal was designed and tested by the. manufacturer establishing the adequacy of the seal configuration, a reevaluation of the seal integrity will be conducted. The seal configuration '
used at'McGuire and Catawba will be subjected to a series of tests designed l
.to determine the ultimate capacity of the seals, and if the minimum acceptance-criteria is not met on any test'the seal will be modified as necessary to obtain'the required capacity. This testing is scheduled to be completed the week of December.3, 1984, and the results along with a description of any planned modifications (if necessary) will be provided by December 31, 1984r' The first refueling of a McGuire or' Catawba Unit to occur after issuance of the bulletin will be the McGuire Unit 2/ Cycle 2' refueling which is currently scheduled to begin in late January, 1985. Operators involved in refueling-operations will be briefed on appropriate aspects .of"the bulletin prior to the outage.c LI declare under penalty of perjury that the statements set forth herein are true and correct to the best of my knowledge.
Very truly yours, ,
C k a 1 B.' Tucker.
-~ PBN/mj f
-. Attachment -
4 n - . - - - - - -
1 4
J*. Mr.-' Jcmea P.- O'Reilly, ~Rrgional Adzinistrator.
- Novamber 21, 1984 LPage two 'I cc: Mr.- R." C.- DeYoung, Director Office of Inspection and Enforcement ,
U. S. Nuclear Regulatory Commission JWashington, D. C. 20555
' Document-Control Desk-U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Mr. W. T. Orders NBC Resident Inspector McGuire Nuclear Station P. K. VanDoorn NRC Resident Inspector Catawba Nuclear-Station-
DUKE POWER COMPANY MCGUIRE NUCLEAR STATION, UNITS ~1, 2 CATAWBA NUCLEAR STATION, UNITS 1, 2 USNRC I&E BULLETIN 84-03 t
REFUELING CAVITY WATER SEAL November 21, 1984 l
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INTRODUCTION As a result of a failure of the refueling cavity water seal at the Haddam Neck Plant, described in NRC IE Bulletin No. 84-03, " Refueling Cavity Water Seal",
all power reactor facilities are required to evaluate the potential for and the consequences of a refueling cavity water seal failure and provide a summary report of the evaluation. This suninary report has been prepared in response to IE Bulletin No. 84-03 for the McGuire and Catawba Nuclear Stations.
. Seal Features The refueling cavity water seal at Catawba and McGuire is a one piece pneumatic ring, nine feet two inches in radius. It consists of a tapered top head plug with a protruding flange that is four inches wide. The bottom portion of the seal is the inflattable air bladder. The seal is composed entirely of one type of elastomer compound, EDPM E603, a Presray Company elastomer. The compounds durometer rating is 60. The seal is seated in a two inch annulus space between the reactor vessel flange and the primary shield wall. Figure 1 provides details of the seal and the seating surface.
The seal installation and operation is controlled by a station procedure and consists of two basic steps. The procedure specifies the air bladder of the uninflated seal to be inserted into the annulus area between the vessel flange and the primary shield wall. The seal bladde.r is placed in the. annulus. opening without any type of lubricants. Air pressure of 30-35 psi inflates the seal pulling the top portion _of the seal (the head) against the seating surface. This seats the seal in the annular opening enabling water to be retained in the refueling canal. , The seal is equipped with a pressure relief valve set at 35 psi thereby preventing the seal from over inflation.
When the seal is not in use, it is stored in accordance with the manufacturer's recommendations. After dewatering of the cavity, the seal is removed from the annulus opening. The surface is then wiped with daptha and placed in its storage crate. The seal is stored outside the containment, in the safety related equipment warehouse.
Several significant differences exist between the Catawba /McGuire design and that utilized at Haddam Neck. The differences listed below represent advantages over the Haddam Neck seal design.
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- ITEM CATAWBA-MCGUIRE HADDAM NECK
- 1) Elastomer Compound *Durometer Rating 60 *Durometer Rating 40 l 2 Number of Seals Required 1 2
! 3 Support Surfaces Rigid Both Sides Movable i
4 Seal Head Width 4" 3 1/2" 5 Annulus Width 2" Nominal 2 1/8" Nominal
!. 6 Air Pressure Requirements 30 - 35 psi 40 psi
- 7) Seal Alignment Positive and 'Jnmovable Requires adjustment and is subject to misalignment
(
- Durometer rating indicate the relative hardness 'of the seal material.
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The Catawba-McGuire seal is constructed of a stiffer elastomer compound with a larger head width. This coupled with a smaller annulus opening to seal and rigid supporting seating surfaces make the Catawba-McGuire seal conditions much different from that at Haddam Neck.
POSTULATED OCCURRENCES For the purpose of evaluation, three failure scenarios are considered:
- gross seal failure (100% of seal circumference) gross' seal failure (25% of seal circumference)
- seal leakage with a nominal 1/16 inch gap around entire circumference All failure scenarios assume that the water in the refueling cavity is at required elevation / depth and the water flows unobstructed through opening created >
by the failed seal. Figures 2 through 6 illustrate the layout of the Catawba Reactor Building and the Spent Fuel Pool. The McGuire Layout is similar.
The gross seal failure is a worst case failure scenario. This assumes that the seal, around the entire circumference of the reactor vessel, is immediately dislodged / removed from the annulus opening. Water then flows unobstructed.
through the annulus opening.
The second failure scenario is identical to the failure at Haddam Neck. This assumes that 25% of the seal circumference is immediately dislodged / removed from the annulus opening.
The third failure scenario postulates a nominal 1/16 inch gap between the seal and the intended seating surface for the entire circumference of the seal. A
. leakage is calculated based on this postulated gap.
-Even though the postulated failure scenarios are unlikely, Table 1 indicates the time to drain the refueling cavity to the level of the reactor vessel flange with the spent fuol pool isolated, with the fuel transfer tube open, and the maximum flow rate. Times are based on a . decreasing water head and flow rates are l
based on maximum water head.
TABLE 1 i
Time to Zero Flow (Min) l Failure Mechanism Refueling Refueling Cavity and Maximum Flow Cavity Only Spent Fuel Pool Rate (Gal./ Min.)
Gross Seal Failure 4.5 12.8 103,642
! Gross Seal Failure - 22 65 20,467 25% of Seal Circumference 1/16 Inch Gap Around Entire 144 414 3,210 Seal Seating Surface ,
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MAKE-UP CAPACITY After the refueling cavity is filled, there remains approximately 60,000 gallons of usable water in the Refueling Water Storage Tank (FWST). The only other adequate source of borated make-up to the refueling cavity is the spent fuel pool. However, if the fuel transfer tube is open, the spent fuel pool and
-refueling cavity will be draining at the same rate. The only assured source of make-up to the spent fuel pool is the nuclear service water pond, but in either case of gross seal failure, this source will not prevent the drain-down.
The drain down scenario does not affect core cooling, however, because the Residual Heat Removal (ND) System is more than adequate to remove decay heat from the core.
TIME TO CLADDING DAMAGE .
The following assumptions were made to conservatively estimate the time to cladding damage following complete uncovery of a spent fuel assembly and without credit for operator intervention.
- Reactor operating at 100% power (3425MWt) for long time prior to shutdown.
- Fuel and cladding at same temperature initially and throughout heatup period.
- Initial fuel /cadding temperature is 150'F and cladding failure occurs at 2200*F (10CFR50.46 limit)
- Fuel rod is insulated from surroundings
- Minimum time between shutdown and fuel movement is 100 hrs.
(Tech Spec requirements)
The following results are obtained:
DAYS AFTER SHUTDOWN TIME TO CLAD FAILURE (MIN) 4.17(100 hrs) 31 7 34 14 39 EFFECT ON STORED FUEL AND FUEL IN TRANSFER Fuel in Transit:
Fuel assemblies being moved by the fuel handling machines are fully withdrawn into the masts and, without operator action, could be uncovered following the drain-down. These fuel assemblies are in danger of being damaged by decay heat as described above, as well as exposing operators to high radiation doses.
However, operator action can assure that the fuel remains covered by lowering the assemblies into either the core, spent fuel storage racks, fuel transfer basket or RCC change fixture.
P Core:
I Fuel in the core will remain covered and adequately cooled by the' Residual Heat l RemovalSystem-(NO).
I Spent Fuel Sotrage Racks:
l' Fuel assemblies secured in the spent fuel storage racks in the spent fuel pool will remain covered by approximately 22 inches of water. Normal cooling will have~ ceased since the Spent Fuel Pool Cooling System (KF) intakes would have been uncovered early in the drain-down. Boiling will occur if cooling is not reestablished. This can be accomplished by closing the fuel transfer tube gate valve and refilling the pool. However, since high radiation in the fuel building may preclude closing this valve, an alternate cooling method is to recirculate water from the containment sump to the Refueling Water Storage Tank (FWST) and then to the spent fuel pool using an Residual Heat Removal (ND) pump.
Fuel Transfer Basket:
If the fuel transfer basket is.in the upender and in a vertical position, the top
, 3 1/4. inches would be uncovered following the drain-down; if horizontal, the L fuel will be covered and adequately cooled. The volume of water in the deep end
- of the refueling cavity will minimize the temperature increase and long term
)
cooling can be provided by either the Residual Heat Removal (ND) System or the-
{ !RefuelingWaterSystem(FW) System. Operator action can assure that these assemblies remain covered.
- RCC Change Fixture
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! Only a few fuel assemblies can be-stored in the RCC change fixture, but these assemblies will remain covered following the drain-down and adequately cooled'
, as described above.
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EMERGENCY OPERATING PROC'EDURES
. Steps are included in the core unloading and reloading procedures to direct the operators .in the event of decreasing level in either the refueling _ cavity'or the
- l. spent _ fuel pool.
1 INSTRUMENTATION Instrumentation is provided in the spent fuel pool so that if seal' failure occurs
- -while the fuel transfer tube is open, an annunciator alarm will be activated in the control room when the water level decreases 10 3/4 inches. In the case of
, .the full circumference gross seal failure, this will occur within 15 seconds; with the 1/16" gap, this will occur in about 8 minutes.
No instrumentation is provided in the refueling cavity to monitor water level. "
However, if seal failure occurs while the fuel transfer tube is closed, operators will still be alerted to the occurrence by area radiation monitors which will alarm locally when the radiation level exceeds 2.5 times background. Also, sumps in the lower containmer.t are provided with computer alarms which would indicate unusually high accumulation.
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- SEAL CAPACITY-
.The original seal was designed and tested to retain 24 feet of water. The
. seal manufacturer, Presray Company, established the adequacy of this seal ;
configuration. The refueling cavity has been flooded to the normal water level.
I in 2 occasions at McGuire Units 1.and 2,.and in 2 occasions at Catawba' Unit 1. 1 In each jnstance the seals have. satisfactorily served their function.
- In. light of the incident at Haddam Neck and the actions required by the bulletin,.
, a reevaluation of the seal integrity will be conducted. The seal configuration
- used at Catawba and McGuire will be subjected to a series of tests designed to determine the ultimate capacity of the seals.
The test set up will consist of a section of .the pneumatic seal placed in 'a test fixture constructed to represent the actual. seal layout as shown in the cross lsection in Figure 1. .The seal seating surfaces of all units will be surveyed to
-document as-built dimensions. The worst case dimensional condition'will be
! incorporated in the test set up. Test loadings will simulate the normal
- l hydrostatic loads. The following seal features will be tested: ,
Test l Type _ Test Seal Description 1 Seal inflated to design pressure, 35 psi
- 2. Seal inflated to design pressure, 35 psi .
Load seal to 24 ft. of water, deflate seal <
3 Seal uninflated 4 Inflate seal to syste.n capacity, (max. 70 psi)
, 5 Load seal with pull through device, seal uninflated
- The minimum acceptance criteria'will'be a seal capacity to withstand twice the normal static head of water,if the minimum acceptance criteria is not met on any ;
test, the seal will be modified, as necessary,,to.obtain the' required capacity
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[ The testing ~will be conducted at the McGuire Nuclear Station by Duke Power Company personnel. Testing is scheduled to start the week of November 26 and to be completed the week of December 3, 1984. -
CONCLUSION ,
, The preceding evaluation adequately addresses the potential for and consequences i
- of a refueling cavity water seal failure at the McGuire and Catawba Nuclear Stations.
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Although the seals have satisfactorily retained water in the refueling' cavity at McGuire, Units 1 and 2 and Catawba Unit 1, the testing, with the minimum acceptance criteria, assures that the refueling cavity water seal, present design f
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or mod'ified design, will have sufficient margin in capacity to preclude the possibility of a seal failure similar to the one experienced at Haddam Neck.
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