B16189, Documents Current Conditions & Future Plans for Spent Fuel Pool
| ML20135C557 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 02/21/1997 |
| From: | Mcelwain J NORTHEAST NUCLEAR ENERGY CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| B16189, NUDOCS 9703040121 | |
| Download: ML20135C557 (4) | |
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V Nuclear Energy wn,.ione Nm iear power sias,o Northeast Nuclear F.nergy Canpany P.O. Box 128 Waterford. CF 0638~>-0128 (860) 447-1791 i
Fax (860) 444-4277 The Nortleast Unditics System February 21,1997 Docket No. 50-245 B16189 U.S. Nuclese Regulatory Commission Attention: Document Control Desk Washington, DC 20555 Millstone Nuclear Power Station, Unit No.1 i
Soent Fuel Pool Conditions The purpose of this letter is for Northeast Nuclear Energy Company (NNECO) to document the current conditions and future plans for the Millstone Unit No.1 Spent Fuel Pool (SFP). NNECO is providing this letter to the NRC staff due to several issues NNECO has recently identified in the Millstone Unit No.1 SFP.
The conditions found in the Millstone Unit No.1 SFP in and by themselves, and i
in the aggregate, are not reportable under Commission regulations. However, j
there exists the potential for genaric implications.
This informational letter provides a summary of the as found conditions, method of discovery, current activities, and the proposed corrective actions.
in July of 1996, NNECO identified a significant amount of debris (foreign material) on the floor and cask pad area of the Millstone Unit No.1 SFP. The July inspection also noted foreign material on the tops of fuel assemblies. As a result, in early January 1997, NNECO installed remote cameras in the SFP to investigate pool conditions, and produced several hours of video tapes that document the extent of the problems. The tapes were reviewed to evaluate the condition of the spent fuel pool, fuel storage racks, and the stored fuel bundles.
A review of these tapes noted the following 11 conditions:
1.
Debris on top of fuel bundles and racks.
2.
Improperly seated bundles supported vertically on their channel J
'7 fasteners.
3.
Improperly seated bundles for unknown reasons.
4.
Channel problems.
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5.
Debris on SFP floor and other debris (not including that on top of bundles and racks).
6.
Damaged SFP rack vents.
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U. S. Nuclear Regul: tory Commission B1618g4Page 2 l
7.
Storage of a damaged irradiated fuel assembly in a fuel container l
designed for damaged fuel located in control rod storage rack.
8.
Velocity limiter sections of control rod blades stacked without support on SFP floor.
9.
Small dont in SFP floor liner.
l 10.
Boron tube stuck up into the bottom of fuel bundle.
11.
Blade guide hardware condition problems.
Conditions 1 and 5 involve debris on the fuel bundles, fuel racks, and the floor of the SFP. The review of the video tape identified that this debris includes rope, l
cable, boron tubes, a broom head, filter hose, nuts and unidentifiable objects. In addition, the bottom of the SFP is covered by a layer of-sediment.
The preliminary operability determination performed by NNECO concludes that the presence of debris identified during the SFP inspection does not affect operability or qualifications of components installed in the SFP.
l Condition 6 involves two spent fuel storage racks that were noted to have damaged vents. One vent is missing a cap and the other is bent. These vents ensure gases, which can build up in the rack walls due to neutron interaction with the poison material, do not cause swelling of the rack wall. A follow-up i
video inspection determined that the vents are not blocked by debris or completely pinched off. The operability determination performed by NNECO concludes both damaged vent fittings are capable of venting gases created j
l during fuel storage and therefore, the fuel storage racks are operable.
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l The review of the video tapes also identified improperly seated fuel bundles as listed in conditions 2, 3, and 10. The investigation has concluded that the i
improperly seated fuel bundles are caused by one of three conditions. For 55 of i
the fuel bundles, the bundles are elevated on their channel fasteners. For 14 l
fuel bundles, the fuel bundles are elevated but not vertically supported by the l
channel fasteners. The reason for these 14 elevated bundles is unknown at this time. One fuel bundle is resting on what is suspected to be a boron tube that is lying on the floor liner and bends upward into the bottom of the fuel storage cell.
The operability determination performed by NNECO concludes that the storage l
racks are operable based on reactivity and seismic characteristics, but are not fully qualified.
Full qualification requires that fuel assemblies are properly seated. The design function of the racks is not challenged in the current configuration provided that the seated adjacent fuel is not raiud. This condition l
does not affect cooling flow to these bundles; therefore, there is no change in l
decay heat removal capability. In addition, a restriction has been put in place on fuel movement until resolution of the raised bundles issue.
The blade guide hardware condition problem listed as condition 11 involves several missing lockwires and nuts from the top yoke of several double blade l
guides. These double blade guides were not used in the vessel this outage and i
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U. S. Nuclear Regulatory Commission l
B1,6189Page 3 i
therefore, any loss of nuts and lock wire would have occurred during use in i
previous outages.
The preliminary operability determination performed by i
NNECO concludes that the presence of nuts and lockwire in the SFP or the j
reactor vessel does not affect operability of safety related components. As part of pre-reload activities, accessible areas of the reactor vessel will be checked for 4
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debris and foreign material.
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Channel problems, condition 4, were also found during the review. Some of the i
problems identified were channels that are not fully seated on the fuel l
assemblies and channel corner tab problems. One channel appeared to have
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both corners broken off with the clip still attached. This channel was observed to I
have slipped slightly down. Other channels were found to have cracked corners.
i in all cases, the fuel assemblies with channel problems were observed to be fully i
seated. The slight change in weight distribution due to the fuel channel being l
elevated on the channel fastener was evaluated in the operability determination i
for the elevated fuel assemblies. In addition, fuel channels provide no design l
basis function while the fuel assembly is in Spent Fuel Pool storage.
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i Condition 8 addresses the part of the video review that revealed the velocity i
j limiter portion of four control rod blade assemblies are stored vertically on top of
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j one another without support. The velocity limiter sections are located on the
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spent fuel pool floor in the space between a spent fuel rack and the control rod blade storage rack. An evaluation of the unsupported velocity limiter storage configuration showed that existing design basis analysis envelopes the potential j
impact of the velocity limiters on fuel storage racks, the control rod storage rack i
and the spent fuel pool liner. Therefore, it was concluded that the structural l
integrity of the spent fuel rack, the control rod blade storage rack and the pool liner would be maintained in the event of an impact caused by a postulated fall of the velocity limiters.
i A damaged irradiated fuel assembly stored in a damaged fuel container in the control rod storage rack is identified as condition 7. The bundle was dropped in 1974 and was placed in a storage container in 1976. The bundle was placed in
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its current location in 1989. A restriction has been put in place that prevents storing fuel in rack locations that are adjacent to the storage location of the damaged bundle.
The preliminary operability determination has found the l
current storage configuration to be in compliance with Spent Fuel Pool storage j
requirements and the storage racks to be operable.
Another discrepancy identified was a dent in the spent fuel pool floor liner that is approximately 4 inches in diameter, condition 9. The spent fuel pool liner is j
relied upon to maintain leak tightness within the spent fuel pool concrete structure under design basis conditions.
The preliminary operability determination concludes that dent does not challenge the leak tightness or 1
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U. S. Nuclear Regulatory Commission B1618mPage 4 structural integrity of the pool. A subsequent analysis of the liner under SSE i
loading concluded that it meets all design basis requirements.
As part of the reload activities, new and reload fuel bundles will be visually l
inspected from below to check for foreign material. The corrective actions to be taken after the refueling operation include removing debris from the pool and the fuel storage racks to prevent contamination of the bundles.
The used components with activity levels permissible for shipping including velocity l
limiters, control rod blades, and blade guides will be removed from the SFP prior to the next refueling.
The following are NNECO's commitments in this letter. Other statements within l
the letter are provided for information only.
l B16189-1 The SFP will be cleaned up to remove debris and various used l
components prior to Refueling Outage 16.
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Please contact R. Walpole at (860) 440-2191 if you have any further questions.
l Very truly yours, 1
l NORTHEAST NUCLEAR ENERGY COMPANY 1
A&EJ
/Jiih'n P. McElwdn
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'Wiillstone Unit No.1 Recovery Officer
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cc:
H. J. Miller, Region i Administrator S. Dembek, NRC Project Manager, Millstone Unit No.1 i
T. A. Easlick, Senior Resident inspector, Millstone Unit No.1 Dr. W. D. Travers, Director, Special Projects
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