ML20116G263
| ML20116G263 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 03/29/1985 |
| From: | Brons J POWER AUTHORITY OF THE STATE OF NEW YORK (NEW YORK |
| To: | Murley T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| IEB-84-03, IEB-84-3, IP-WDH-744, NUDOCS 8505010427 | |
| Download: ML20116G263 (8) | |
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- > NewWrkPbwer tv Authority March 29, 1985 IP-WDH-744 Dr. Thomas E. Murley Regional Administrator Region I U. S. Nuclear Regulatory Commission 631 Park Avenue King of. Prussia, PA 19406
Subject:
Indian Point 3 Nuclear Power Plant Supplementary Information in Response to I&E Bulletin 84-03, Refueling Cavity Water Seal
Reference:
(1)
J. C. Brons letter to T. E. Murley, dated November 27, 1984.
Dear Dr. Murley:
The referenced letter provided the Authority's response to I&E Bulletin 84-03 for Indian Point 3 (IP-3).
The Authority's response identified evaluations-which were underway to determine the effects of a fuel assembly drop onto the reactor cavity seal. The results of this evaluation are attached in fulfill-ment of our comunitment in Reference (1).
While we have evaluated the consequences of a fuel assembly drop onto the seal, we consider such-an event to be highly improbable particularly for the scenario where the feet of a fuel assembly must impact precisely on the seal over the annular gap.
The Authority is also providing updated information regarding the results of
. evaluations previously performed to determine the stability of the IP-3 seal under plant specific installation conditions. The results of the evaluations presented herein continue to support our conclusion that the current seal design, acting as a passive device, is adequate and capable of performing its intended design function.
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The Authority is currently preceding with its review of the INPO SOER No. 85-1, Reactor Cavity Seal Failure. We intend to close out this SOER prior to com-mencement of the Cycle 4/5 refueling outage.
8505010427 850329 PDR ADOCK 05000286 l
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Dr. Thomas E. Murley March 29, 1985 Page Two a
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We trost you find the attached information satisfactory.
If you have any questions regarding this matter, please contact Mr. W. Hamlin of my staff.
Sincerely, g
J. C. Brons Resident Manager 3
Resident lbspector's Office cc:
Indian Point"3 U. S. Nuclear, Regulatory Comunission P. O. Box 66 '
Buchanan, New York 10511 Director of Nuclear Reactor Regulation i
Atta:
Mr. Steven A. Varga. Chief
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Operating Reactors Branch 1 Division of Licensing U. S. Nuclear Regulatory Conunission 3
Washington, DC 20555
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ATTACHMENT 4
SUPPLEMENTARY RESPONSE TO 4
IE BULLETIN 84-03 REACTOR CAVITY WATER SEAL New York Power Authority Indian Point 3 Nuclear Power Plant Docket No. 50-286 DPR-64
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Consequences of a Fuel Assembly Drop onto Seal An evaluation of a fuel assembly drop onto the reactor cavity water seal has been performed.
In this scenario, it is assumed that a fuel assembly in transit unlatches from the refueling machine and impacts the cavity seal. As was' discussed in Reference (1), a precise impact is required to affect the seal due to the dimensions of the fuel assembly and the small gap width under
. consideration.
i The ability of the cavity seal to maintain its integrity following a postulated fuel assembly drop was based on the extent of push-through of the seal during
-the event and the seal performance following the event. Conservatises in the evaluation include the following:
1.
Precise fuel assembly impact on the seal by two legs, 2.
All friction between the seal, cavity wall, and reactor vessel flange is ignored, and 3.
Bouyant forces on the fuel assembly are neglected.
A comparison of the potential energy of the dropped fuel assembly to the ability of the seal to resist downward motion was performed. Based on the results of this comparison, the segment of the seal under the fuel assembly 4
feet would undergo distortion and could be pressed into the annular gap. This would be a local distortion in the vicinity of the fuel assembly feet. The seal will only be compressed into the gap until the remaining feet of the assembly contact the reactor vessel flange or cavity floor.
Figure 1 illus-trates-the resulting configuration of the seal with the fuel assembly legs resting over the gap.
The behavior of the-seal following the fuel assembly drop was evaluated to determine if it would continue to provide a sealing function. The effects of the hydrostatic pressure on the seal subsequent to the fuel assembly impact and the consequences of a potential puncture of the seal bladder by the fuel assembly feet were assessed.
The evaluation of the seal for hydrostatic loading in the post-fuel assembly drop configuration of Figures 1 and 2 was performed utilizing a flexible
" cable" model. The deflection of the seal due to the head of water was deter-mined neglecting any lateral support for the portion of the seal pressed into the gap and no friction between the seal and the reactor vessel flange or cavity wall.
The results of this evaluation demonstrate that the portion of the seal under the two fuel assembly feet will be displaced approximately 2.12 inches into the gap. This displacement is less than the 2.25 inch thickness of the sealing surface on the reactor vessel flange (see Figure 1 for the relative dimensions of the reactor vessel flange), therefore, seal contact will be maintained and gross seal failure is not expected.
The potential for the dropped fuel assembly to puncture the seal was also investigated and the consequences determined.
In the event the fuel assembly 3
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' i feet punctures the seal bladder and the bladder fills with water, an additional load will be placed on the seal. Since the seal is reinforced, the bladder will not expand but the shape of the cross section will change as water fills the bladder. Assuming the bladder becomes circular in shcpe to hold the maxi-mum amount of water, the additional load due to this water (distributed over 2
the 2 inch gap) is calculated to be 0.33 lb/in,
This additional load is considered negligible. When this load is added to the hydrostatic load nominally present on the seal, the resulting deflection following the fuel assembly drop is 2.13 inches into the gap. This deflection is less than the thickness of the sealing surface on the reactor vessel flange.
The additional load on the undistorted portion of the seal is negligible. It is not expected that puncturing the seal would result in push through due to the additional water load in the seal bladder.
It is noted that the post seal behavior is more favorable if only one of the four feet on the fuel assembly impacts the seal over the annular gap. This is
'due to the less severe seal distortion which would occur if only one foot impacted the seal. The predicted displacement of the seal under this scenario is 0.725 inches below the top of the reactor vessel flange.
The results of these evaluations support the Authority's conclusion that the reactor cavity water seal will perform its intended function under the adverse scenarios postulated herein.
While we have evaluated the consequences of a fuel assembly drop onto the seal, such a scenario is of extremely low probability for the following reasons:
1.
the period of time during which fuel assemblies are above the seal l
and therefore available to strike it is small; 2.
the target area of the seal is small (4 inches in width) with the target area of the annular gap being only 2 inches wide; 3.
the design of the lower nozzle of the fuel assembly requires a precise l
impact with the feet of.the assembly oriented in a manner to impact the 2 inch wide annular gap region; and, l
I 4.
the fuel assembly must impact the seal in a cocked position to maxi-mize the force imparted to the seal, otherwise a portion of the force will be transmitted to the reactar vessel flange or cavity floor since the width of the fuel assembly is over four times that of the annular gap.
Interlocks provided on the refueling machine are designed to preclude a fuel I
assembly drop event. Redundant interlocks prevent the fuel assembly gripper l
from releasing a fuel assembly if the assembly is suspended. The primary interlock detects a suspended assembly via a force gauge. The back-up inter-lock uses a mechanical spring lock in the gripper. The primary interlock prevents the opening of the solenoid valve in the air line to the gripper i
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except when zero suspended weight is indicated by the force gauge. The mechanical lock prevents operation of the gripper even if air pressure is applied to the operating cylinder.
In addition, only one of the three drives on the refueling machine can normally be operated at any given instance.
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. svaluation of Hydrostatic Forces on Seal Reference (1) provided'the results of an evaluation performed to determine the stability of the reactor cavity water seal under the hydrostatic forces due to the nominal head of water present during refueling. Tne results of this I
evaluation have been updated to account for the extension of the. bladder into the wedge portion of the seal. The extension of the bladder into the wedge required that the beam height in the beam model utilized for the evaluation be reduced accordingly.
1
'The results of the evaluation with the revised beam model inputs demonstrate that the maximum deflection of the top of the seal is 0.268 inches at a water
. head four times that which is normally present on the seal.
This revised deflection does not represent a concern with respect to seal integrity and the conclusions presented in Reference (1) are maintained.
Furthermore, the' Authority is aware of hydrostatic loading tests which have been performed on seals and cavity designs very similar to that which exists at IP-3.
While the Authority has not had plant specific tests on the seal
. performed, the results of these tests performed for other plants have demon-strated outstanding results regarding seal performance. Similar tests for IP-3 would be expected to yield similar results.
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