ML083030432
| ML083030432 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 10/21/2008 |
| From: | Smith J D Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TVA-SQN-TS-08-06 | |
| Download: ML083030432 (18) | |
Text
October 21, 2008
10 CFR 50.59(c)(2) TVA-SQN-TS-08-06 10 CFR 50.90
U.S. Nuclear Regulatory Commission
ATTN: Document Control Desk
Washington, D.C. 20555-0001
Gentlemen:
In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority (TVA) ) 50-328 SEQUOYAH NUCLEAR PLANT (SQN) - UNITS 1 AND 2 - "LICENSE AMENDMENT REQUEST (LAR) TS-08-06 TO REVISE ICE CONDENSER LICENSING BASIS" Pursuant to 10 CFR 50.90, Tennessee Valley Authority (TVA) is submitting a request
for an amendment (TS-08-06) to Licenses DPR-77 and DPR-79 for SQN. The proposed amendment will modify the SQN U pdated Final Safety Analysis Report (UFSAR) by requiring an inspection of each ice condenser within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of
experiencing a seismic event greater than or equal to an Operating Basis Earthquake (OBE) within the 5-week period after ice basket replenishment has been completed.
The intent of the proposed change is to confirm that adverse ice fallout has not
occurred, which could impede the ability of the ice condenser lower inlet doors to
open. This action would be taken in order to ensure the generic qualification of the ice
condenser containment design is maintained in accordance with Topical Report
WCAP-8110, Supplement 9A, which is referenced in the SQN UFSAR.
TVA has determined that there are no significant hazards considerations associated
with the proposed change and that the UFSAR change qualifies for categorical
exclusion from environmental review pursuant to the provisions of 10 CFR 51.22(c)(9).
Additionally, in accordance with 10 CFR 50.91(b)(1), TVA is sending a copy of this
letter and enclosure to the Tennessee State Department of Public Health.
TVA does not have specific schedule needs for this proposed change and processing
can be pursued as appropriate.
U.S. Nuclear Regulatory Commission Page 3 October 21, 2008
Enclosure
cc (Enclosure):
Mr. Brendon T. Moroney, Project Manager
U.S. Nuclear Regulatory Commission
Mail Stop 08G-9a
One White Flint North
11555 Rockville Pike
Rockville, Maryland 20852-2739
Mr. Lawrence E. Nanney, Director
Division of Radiological Health
Third Floor
L&C Annex
401 Church Street
Nashville, Tennessee 37243-1532
E1-1 ENCLOSURE
EVALUATION OF THE PROPOSED CHANGE
Subject:
Application for license amendment to revise the Ice Condenser Licensing Basis to include requiring the inspection of each ice condenser within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of experiencing
a seismic event greater than or equal to an Operating Basis Earthquake (OBE) within
the 5-week period after ice basket replenishment.
1.0
SUMMARY
DESCRIPTION This evaluation supports a license amendm ent request (LAR) to amend Operating Licenses DPR-77 and DPR-79 for SQN Units 1 and 2.
The proposed change would revise SQN's Updated Final Safety Analysis Report (UFSAR) to require an inspection of each ice condenser within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of experiencing
a seismic event greater than or equal to an OBE (OBE is defined as 1/2 of a Safe
Shutdown Earthquake [SSE]) within the 5-week period after ice basket replenishment is
completed. This will confirm that ice condenser lower inlet doors have not been blocked
by ice fallout.
The proposed amendment provides a procedural requirement to confirm the ice condenser maintains the ice condenser generic qualification as set forth in the UFSAR.
Justification for the use of the proposed procedural requirement is based on reasonable
assurance that the ice condenser lower inlet doors will open following a seismic event
during the 5-week period and the low probability of a seismic event occurring coincident
with or subsequently followed by a Design Basis Accident (DBA).
In 2007, an NRC Region III Inspector identified a potential concern that typical ice
condenser maintenance practices at Donald C. Cook Nuclear Plant (CNP) did not ensure
compliance with the licensing basis for ice fusion time requirements in that procedures do
not recognize a 5-week storage period for freshly loaded ice baskets prior to power
ascension.
TVA began discussions with the other ice condenser plant licensees (CNP and Duke
Power Company) and Westinghouse Electric Company regarding the ice fusion concern.
The ice fusion issue was discussed in a public meeting at NRC Headquarters on
December 12, 2007. Consistent with those discussions, TVA has elected to change the
SQN UFSAR as described above to address the ice fusion concerns.
2.0 DETAILED
DESCRIPTION The SQN ice condenser consists of a completely enclosed annular compartment located around approximately 300 degrees of the perimeter of the upper compartment of the containment, but penetrating the operating deck so that a portion extends into the
containment lower compartment. The lower portion has a series of hinged doors (lower
inlet doors) exposed to the atmosphere of the lower containment compartment and
designed to remain closed during normal plant operation. At the top of the ice
condenser is another set of doors (top deck doors) that are exposed to the atmosphere
of the upper compartment; these doors also remain closed during normal plant
operation. Intermediate deck doors are located below the top deck doors. These doors E1-2 form the floor of a plenum at the upper part of the ice condenser and remain closed during normal plant operation. Within the ice condenser, ice is held in baskets arranged
to promote heat transfer to the ice. During normal plant operation, the ice condenser
performs no function and is not required for a controlled shutdown of the unit.
The ice condenser is structurally designed to withstand an SSE plus a DBA.
In the event of a loss-of-coolant accident (LOCA) or high energy line break (HELB),
which includes a steam or feedwater line break inside containment, the pressure rises in
the lower compartment and the ice condenser lower inlet doors open. This allows air
and steam to flow from the lower compartment into the ice condenser. The resulting
pressure increase within the ice condenser causes the intermediate deck doors and the
top deck doors at the top of the ice condenser to open, allowing air to flow out of the ice
condenser into the upper compartment. Steam entering the ice condenser is condensed
by the ice, thus limiting the peak pressure and temperature buildup in containment.
Condensation of steam within the ice condenser allows a continual flow of steam from
the lower compartment to the condensing surface of the ice, thus reducing the lower
compartment pressure.
Sufficient ice heat transfer surface and flow passages are provided in the ice condenser
so that the magnitude of the pressure transient resulting from an accident does not
exceed the containment design pressure. The lattice frame and support column
assemblies allow passage of steam and air through the space around the ice baskets.
The floor drains are passive structural components during normal operation. During a
small pipe break, the condensed steam and melted ice will collect on the floor of the ice
condenser and then flow out through the drains. For intermediate and large pipe breaks, water will drain through both the lower inlet doors and the drains.
The lower inlet doors are provided with shock absorber assemblies to dissipate the
kinetic energy generated by opening the doors during a large pipe break scenario.
As part of the ice condenser qualification program, seismic testing of ice baskets was
conducted at the Westinghouse Waltz Mill facility to determine the amount of ice fallout
from ice baskets subjected to simulated plant time history seismic disturbances.
Ice condenser qualification program test results were reported in WCAP-8110, "Test
Plans and Results for the Ice Condenser System," and ten supplements. Supplement 9
to the WCAP, entitled "Ice Fallout From Seismic Testing of Fused Ice Basket,"
addresses ice retention during a seismic event.
This document describes the test apparatus and methodology for verifying that flaked ice
will be retained in an ice basket subjected to cumulative worst-case SSE seismic
loading. In the Atomic Energy Commission's (AEC [now NRC]) evaluation of
WCAP-8110, Supplement 9, dated November 21, 1974, (renamed WCAP-8110, Supplement 9-A) it is stated that a flaked ice basket stored for at least 5-weeks exhibited
adequate retention capability when subjected to Design Basis [Safe Shutdown]
Earthquake seismic response spectra.
The AEC's November 21, 1974 letter, included within WCAP-8110, Supplement 9-A, contains the following statement: "As a result of our review, we have concluded that the
data presented in WCAP-8110 Supplement 9 (the Westinghouse test report) are
adequate to conclude that land-based plants using ice condenser type containments E1-3 should begin their initial ascent to power after a minimum of 5-weeks following ice loading." The same November 21, 1974 letter, accepts the document as a topical report
which may be referenced in license applications. SQN's UFSAR references WCAP-
8110, Supplement 9-A as part of the generic qualification of the ice condenser
containment design.
The term "ice fusion" refers to a condition established when an ice basket freshly loaded
with flake ice achieves stability at the operating temperature of the ice condenser, i.e.,
when the ice freezes or otherwise solidifies such that it tends to stay in the ice basket
when agitated. If the ice were not sufficiently fused during a seismic event, it is possible
that ice could fall from the ice baskets and impede the ability of the ice condenser lower
inlet doors to open.
In order for the ice condenser to perform its energy absorption and pressure mitigation
functions, the ice condenser lower inlet doors must open to allow the mass release from
a LOCA or HELB to enter the ice condenser, and the ice bed ice mass and geometry
must be adequate to support heat transfer to the ice bed.
3.0 TECHNICAL EVALUATION
10 CFR 50.59(a)(6) defines a test or experiment not described in the UFSAR to mean
any activity where a structure, system, or component is utilized or controlled in a manner which is either: (i) outside the reference bounds of the design basis as described in the
UFSAR, or (ii) inconsistent with the analyses or descriptions in the UFSAR.
In this case, the reference bounds of the design basis are incorporated by reference to
WCAP-8110, Supplement 9-A in the SQN UFSAR. The reference bounds of the design
basis is: "land-based plants using ice condenser type containments should begin their
initial ascent to power after a minimum of 5 weeks following ice loading." This bounding
waiting period assures that ice in the ice baskets will be sufficiently fused such that ice
fall out during an SSE does not impede the ice condenser's design function. The activity
to be analyzed is the ability for the SQN units to start an ascent to power operations
without waiting for the bounding 5-week period if an alternate method of meeting the
requirement is utilized for either a complete charging of the ice bed or following routine
ice bed servicing.
10 CFR 50.59 (c)(1) states, in part, that the licensee may make changes to the licensed
facility as described in the UFSAR and conduct tests and experiments not described in
the UFSAR without obtaining a license amendment only if the changed test or
experiment does not meet the criteria in paragraph (c)(2) of this section.
10 CFR 50.59 (c)(2) states, in part, that the licensee shall obtain a license amendment
pursuant to 10 CFR 50.90 prior to implementing a proposed test or experiment which
would: (ii) result in more than a minimal increase in the likelihood of occurrence of a
malfunction of a structure, system, or co mponent important to safety previously evaluated in the UFSAR; or (viii) result in a departure from a method of evaluation
described in the UFSAR used in establishing the design basis or in the safety analyses.
A review of the activity showed that the criterion for a license amendment was met.
Thus, a request for an alternate means of meeting the requirements is described below:
The current text of the SQN UFSAR, Section 6.5.9.1, entitled "Lower Inlet Doors, Design
Basis, Interface Requirements," reads as follows:
E1-4 Sufficient clearance is required for the doors to open into the ice condenser.
Items to be considered in this interface are floor clearance, lower support
structure clearance and floor drain operation.
The proposed revision to this paragraph reads as follows:
Original ice basket qualification testing (Topical Report WCAP-8110, Supplement 9-A), has shown freshly loaded ice is considered fused after 5 weeks. In the
event of an earthquake (OBE or greater) which occurs within 5 weeks following
the completion of ice basket replenishment, plant procedures require a visual
inspection of applicable areas of the ice condenser within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to confirm
that opening of the ice condenser lower inlet doors is not impeded by any ice
fallout resulting from the seismic disturbance. The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> time frame for
inspection is applicable during modes where the lower inlet doors are required to
be operable, otherwise perform this inspection prior to startup. This alternative
method of compliance with the requirements of General Design Criteria (GDC) 2
is credible based upon the reasonable assurance that the ice condenser doors
will open following a seismic event during the 5 week period and the low
probability of a seismic event occurring coincident with or subsequently followed
by a Design Basis Accident.
Under the proposed change to the licensing basis, power ascension and normal plant
operation could occur for a period of up to 5 weeks prior to achieving full qualification of
the ice condenser as defined in the current licensing basis. One of 5 scenarios could
occur during this "period of potential exposure," specifically: i. No seismic disturbance, LOCA or HELB occurs ii. A seismic disturbance occurs without a LOCA or HELB occurring iii. LOCA or HELB occurs without a seismic disturbance iv. A seismic disturbance occurs coincident with a LOCA or HELB
- v. A seismic disturbance occurs with a subsequent LOCA or HELB Under the first three scenarios, there is no impact as a result of the proposed change. In
the first two scenarios, the ice condenser would not be called upon to perform an
accident mitigation function. In the third scenario, although the ice condenser would be
called upon to mitigate an accident, absent a seismic disturbance, there is no driver to
dislodge ice, and the ice condenser would function as designed.
In the fourth and fifth scenarios, if a LOCA or HELB occurred coincident with, or subsequent to a seismic disturbance, it is possible that ice in freshly loaded ice baskets
could fall out. However, several factors provide defense-in-depth and tend to mitigate
the safety significance of the proposed change:
There is Reasonable Assurance That the Ice Condenser Would Function Following a Seismic Event Reduction in total ice mass:
The basis of the current 5-week ice fusion time requirement was derived
from qualification testing (c. 1974) conducted by Westinghouse Electric E1-5 Company during development and licensing of ice condenser containments. Determination of a minimum ice fusion time was not an
objective of the test program.
As a result of the review of test results captured in WCAP 8110, Supplement 9, the Ice Condenser Utility Group (I&M, TVA and Duke)
concluded that the 5-week ice fusion time selected as the licensing basis
was conservative and that ice condenser design has substantial margin
with respect to ice fallout. A key consideration in reaching this conclusion
was inherent conservatisms in the 1974 test program: The test baskets floated freely in the lattice frames and were not fixed at one end. The floating end exacerbates the movement
resulting from application of a given seismic excitation, which
would tend to overstate the ice fallout in the test compared to
expected fallout from an actual plant event. The test basket was only six feet tall and had an open top, whereas an actual ice condenser basket typically consists of four
vertically stacked twelve-foot sections, with only the uppermost
section having an open top. The majority of ice fallout during the
tests occurred from the open top of the basket. Since
proportionally less ice would be expected to fall out of the lower
sections of an actual ice condenser basket, the percentage of ice
falling out of the test basket section overstates what would be
expected during an actual plant event.
Flow channel blockage:
The successful completion of SQN Technical Specification Surveillance
Requirement 4.6.5.1.b ensures that the ice accumulation on the structural
steel members comprising flow channels through the ice bed is less than
or equal to a 15 percent blockage of the total flow area for each safety
analysis section.
Therefore, it can be reasonably assumed that any loose, granular ice that
would be shaken free during a seismic event from a recently replenished
ice basket cannot block flow passages that were verified to be at least 85
percent clear during the preceding surveillance inspection.
Restriction of lower inlet door movement:
The SQN ice condenser baskets typically consists of four vertically
stacked twelve-foot sections, with only the uppermost section having an
open top. The majority of ice fallout during the tests occurred from the
open top of the basket. Since ice fallout at SQN could only occur from
the top portion of the uppermost basket, the quantity of ice that could
fallout in a seismic event is much less than estimated in the tests. The
quantity of ice that falls out would be loose, and therefore unlikely to block
the inlet doors. The inspection of the ice condenser doors within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />
of a seismic event provides assurance that the ice fallout would not be a
sufficient quantity or in a fused state that could block the free movement
of the ice doors.
E1-6 Floor drain blockage:
As discussed in the SQN UFSAR, containment peak pressure is not
affected by drain performance impacted by ice accumulation due to a
seismic event. There are a total of 20 ice condenser floor drains among
the 24 ice condenser bays. The ice condenser design is such that for
blockage of any floor drain, water would flow to adjacent bays and
eventually would spill over the lower inlet door openings if necessary.
Additionally, any ice on the floor of the ice condenser would be melted by
the rise in temperature of the ice condenser and flowing meltwater.
In conclusion, there is reasonable assurance that the ice condenser would
function properly following a seismic event within the 5 week period due to
inherent conservatisms in the 1974 test data, the low likelihood of flow channel
and floor drain blockage, and improbable blocking of the lower inlet doors by any
potential fallout.
The Probability of a Seismic Disturbance Coincident With or Subsequently Followed by a LOCA or HELB is Low The proposed amendment revises the SQN UFSAR by requiring an inspection of
each ice condenser within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of experiencing a seismic event greater than
or equal to an OBE within the 5-week period after the completion of ice basket
replenishment to confirm that adverse ice fallout has not occurred which could
impede the ability of the ice condenser lower inlet doors to open. This action
would be taken in order to ensure the generic qualification of the ice condenser
containment design is maintained in accordance with Topical Report WCAP-
8110, Supplement 9A, which is referenced in the SQN UFSAR.
Although this license amendment request is not presented as a risk-informed
change under the guidance of Regulatory Guide 1.174, "An Approach for Using
Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific
Changes to the Licensing Basis," consideration of the probability of occurrence
provides an insight into the very small risk involved in the proposed change.
The annual probability of exceedance for the OBE level earthquake at Sequoyah was derived from EPRI RP 101-53 (EPRI NP-6395-D), "Probabilistic Seismic Hazard Evaluation." The ice condenser was conservatively assumed to be required by the applicable operating mode for the entire 5-week fusion period.
The probability that the ice condensers doors could become impeded during the
5-week period was computed. The likelihood of a LOCA or HELB, which would
require the ice condenser, following the impediment was then estimated with time
constraints as noted below. The ice condenser inspection is required within 24
hours. If the ice condenser lower inlet doors are determined to be impeded and
cannot be restored, the unit must be in Mode 5 within the next 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />.
Therefore, the total exposure time for consideration of a subsequent event is 61
hours. The frequency of LOCAs and HELBs were derived from NUREG/CR-
6928, "Industry-Average Performance for Components and Initiating Events at
U.S. Commercial Nuclear Power Plants" and NUREG/CR-5750, "Rates of
Initiating Events at U.S. Nuclear Power Plants: 1987 - 1995."
As a result, the probability of ice condenser impairment and subsequent E1-7 challenge is estimated to be less than 3.89E-09 for Sequoyah during the "period of potential exposure." This is a very low probability as would be expected by the
nature of the events.
Approval of the proposed amendment is justifiable based upon the low probability
that a LOCA or HELB would occur coincident with or subsequent to an OBE (while the plant is shutting down) during the "period of potential exposure." After
the 5-week fusion time has been reached, the Westinghouse Topical Report
WCAP-8110, Supplement 9-A test report concludes that acceptable levels of ice
fallout occur for all expected seismic events, up to and including the SSE.
4.0 REGULATORY EVALUATION
4.1 Applicable
Regulatory Requirements/Criteria The proposed inspection of each ice condenser within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of experiencing a
seismic event equal to or greater than an OBE within the 5-week period after ice
basket replenishment provides an alternate method of confirming that the lower
inlet doors would open subsequent to a seismic event. Justification for the use of
the proposed procedural requirement is based upon reasonable assurance that the
ice condenser doors would function following a seismic event, and the low
probability of a seismic event coincident with, or immediately followed by a DBA.
This LAR does not alter or revise the current bounding safety analyses of record in
any way. Consequently, SQN will remain in compliance with the applicable
regulations and requirements. These are:
10 CFR50, Appendix A, General Design Criterion (GDC) 2, "Design Basis For Protection Against Natural Phenomena," which requires that
structures, systems and components im portant to safety be designed to withstand the effects of natural phenomena such as earthquakes; GDC 16, "Containment Design," which requires that the reactor containment and associated systems pr ovide an essentially leak-tight barrier against the uncontrolled release of radioactivity to the
environment; GDC 38, "Containment Heat Removal," which requires that a system be provided to remove heat from the reactor containment; and GDC 50, "Containment Design Basis," which requires that the reactor containment structure be designed with conservatism to accommodate
applicable design parameters (pressure, temperature, leakage rate).
This LAR is being submitted in accordance with 10 CFR 50.90.
E1-8 4.2 Precedent
The NRC approved a similar license amendment request from Indiana Michigan Power, the licensee for Donald C. Cook Nuclear Plant (CNP) Units 1 and 2, on
April 16, 2008. The NRC approved a similar license amendment request from
Duke Power Company for McGuire Nuclear Station on April 2, 2008. The SQN
proposed change is consistent with these amendments.
4.3 Significant
Hazards Consideration
The proposed inspection of each ice condenser within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of experiencing a seismic event equal to or greater than an Operating Basis Earthquake (OBE) within
the 5-week period after ice basket replenishment provides an alternate method of
confirming that the lower inlet doors would open subsequent to a seismic event.
Justification for the use of the proposed methodology is based upon reasonable
assurance that the ice condenser doors would function following a seismic event, and the low probability of a seismic event coincident with, or immediately followed
by a Design Basis Accident (DBA).
TVA has evaluated whether or not a significant hazards consideration is involved with the proposed amendments by focusing on the three standards set forth in
10 CFR 50.92, "Issuance of Amendment," as discussed below:
- 1. Does the proposed amendment involve a significant increase in the probability or consequences of an accident previously evaluated?
Response: No.
The analyzed accidents of consideration in regard to changes potentially affecting
the ice condenser are a loss-of-coolant accident (LOCA) and a steam or
feedwater line break inside containment. The ice condenser is an accident
mitigator and is not postulated as being the initiator of a LOCA or high energy line
break (HELB). The ice condenser is structurally designed to withstand a Safe
Shutdown Earthquake (SSE) plus a Design Basis Accident (DBA) and does not
interconnect or interact with any systems that interconnect or interact with the
reactor coolant, main steam or feedwater systems. Because the proposed
changes do not result in, or require any physical change to the ice condenser that
could introduce an interaction with the reactor coolant, main steam or feedwater
systems, there can be no change in the probability of an accident previously
evaluated.
Under the current licensing basis, the ice condenser ice baskets would be
considered fully fused prior to power ascension and the ice condenser would
perform its accident mitigation function even if a safe shutdown seismic event
occurred coincident with or just preceding the accident. Under the proposed
change, there is some finite probability that, within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following a seismic
disturbance, a LOCA or HELB in containment could occur within 5 weeks of the
completion of ice basket replenishment. However, several factors provide
defense-in-depth and tend to mitigate the potential consequences of the proposed
change.
E1-9 DBAs are not assumed to occur simultaneously with a seismic event. Therefore, the coincident occurrence of a LOCA or HELB with a seismic event is strictly a
function of the combined probability of the occurrence of independent events, which in this case is very low. Based on the Probabilistic Risk Assessment model
and seismic hazard analysis, the combined probability of occurrence of a seismic
disturbance greater than or equal to an OBE during the 5-week period following
ice replenishment coincident with or s ubsequently followed by a LOCA or HELB during the time required to perform the proposed inspection (24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />) and if
required by technical specifications, complete unit shutdown (37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />), is less than 3.89E-09 for Sequoyah
. This probability is well below the threshold that is typically considered credible.
Even if ice were to fall from ice baskets during a seismic event occurring
coincident with or subsequently followed by an accident, the ice condenser would
be expected to perform its intended safety function. There is reasonable
assurance that the ice condenser would function properly following a seismic
event within the 5-week period due to inherent conservatisms in the 1974 test
data, the low likelihood of flow channel and floor drain blockage, and improbable
blocking of the lower inlet doors by any potential fallout.
Based on the above, the proposed changes do not involve a significant increase
in the probability or consequences of an accident previously evaluated. The ice
condenser is expected to perform its intended safety function under all
circumstances following a LOCA or HELB in containment.
Therefore, the proposed change does not involve a significant increase in the
probability or consequences of an accident previously evaluated.
- 2. Does the proposed amendment create the possibility of a new or different kind of accident from any accident previously evaluated?
Response: No.
The proposed change affects the assumed timing of a postulated seismic and
DBA applied to the ice condenser and provides an alternate methodology to
confirm the ice condenser lower inlet doors are capable of opening. As
previously discussed, the ice condenser is not postulated as an initiator of any
DBA. The proposed change does not impact any plant system, structure or
component that is an accident initiator. The proposed change does not involve
any hardware changes to the ice condenser or other changes that could create
new accident mechanisms. Therefore, there can be no new or different
accidents created from those previously identified and evaluated.
Therefore, the proposed change does not create the possibility of a new or different kind of accident from any previously evaluated.
- 3. Does the proposed amendment involve a significant reduction in a margin of safety?
Response: No.
E1-10 Margin of safety is related to the confidence in the ability of the fission product
barriers to perform their design functions during and following an accident
situation. These barriers include the fuel cladding, the reactor coolant system, and the containment system. The performance of the fuel cladding and the
reactor coolant system will not be impacted by the proposed change.
The requirement to inspect the ice condensers within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of experiencing
seismic activity greater than or equal to an OBE during the 5-week period
following the completion of ice basket replenishment will confirm that the ice
condenser lower inlet doors are capable of opening. This inspection will confirm
that the ice condenser doors remain fully capable of performing their intended
safety function under credible circumstances.
The proposed change affects the assumed timing of a postulated seismic and
DBA applied to the ice condenser and provides an alternate methodology in
confirming the ice condenser lower inlet doors are capable of opening. As
previously discussed, the combined probability of occurrence of a LOCA or HELB
and a seismic disturbance greater than or equal to an OBE during the "period of
potential exposure" is less than 3.89E-09 for Sequoyah. This probability is well
below the threshold that is considered credible.
Therefore, the proposed change does not involve a significant reduction in the
margin of safety. The SQN ice condenser will perform its intended safety
function under credible circumstances.
The changes proposed in this license amendment request (LAR) do not make
any physical alteration to the ice condensers, nor does it affect the required
functional capability of the ice condenser in any way. The intent of the proposed
change to the UFSAR is to eliminate an overly restrictive waiting period prior to
unit ascent to power operations following the completion of ice basket
replenishment. The required inspection of the ice condenser following a seismic
event greater than or equal to an OBE will confirm that the ice condenser lower
inlet doors will continue to fully perform their safety function as assumed in the
SQN safety analyses.
Thus, it can be concluded that the proposed change does not involve a
significant reduction in the margin of safety.
Therefore, the proposed change does not involve a significant reduction in a margin of safety.
Based on the above, TVA concludes that the proposed amendment does not involve a significant hazards consideration under the standards set forth in
10 CFR 50.92(c), and accordingly, a finding of "no significant hazards
consideration" is justified.
4.4 Conclusions
In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be
endangered by operation in the proposed manner, (2) such activities will be
conducted in compliance with the Commission's regulations, and (3) the issuance E1-11 of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
5.0 ENVIRONMENTAL CONSIDERATION
A review has determined that the proposed amendment would change a requirement with respect to installation or use of a facility component located within the restricted area, as
defined in 10 CFR 20, or would change an inspection or surveillance requirement.
However, the proposed amendment does not involve (i) a significant hazards
consideration, (ii) a significant change in the types or significant increase in the amounts
of any effluents that may be released offsite, or (iii) a significant increase in individual or
cumulative occupational radiation exposure. Accordingly, the proposed amendment
meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or
environmental assessment need be prepared in connection with the proposed
amendment.
6.0 REFERENCES
The following documents were consulted:
- a. WCAP-8110, Supplement 9, dated May 13, 1974 b. AEC Evaluation of WCAP-8110, Supplement 9-A, dated November 21, 1974
- c. Memorandum from P. S. Tam, NRC, "Summary of December 12, 2007, Meeting with I&M on the Issue of Ice Condenser Ice Fusion (TAC No. MD6756)," dated December
20, 2007 (ADAMS Accession Number ML073470330)
ATTACHMENTS
- 1. List of Regulatory Commitments
UNITS 1 AND 2
LIST OF REGULATORY COMMITMENTS
Implement SQN station procedures requiring the inspection of each ice condenser within
24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of experiencing a seismic event greater than or equal to an Operating Basis
Earthquake (OBE) within the five (5) week period after the completion of ice basket
replenishment.
A2-1 ATTACHMENT 2 TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT (SQN)
UNITS 1 AND 2
PROPOSED UPDATED FINAL SAFETY ANALYSIS REPORT CHANGES (MARK-UP)
I. AFFECTED PAGE LIST
6.5-37
II. MARKED PAGES See attached.
A2-2 SQN ice condenser. The opening rate of the inlet doors is important to insure minimizing the pressure buildup in the lower compartment due to the rapid re lease of energy to that compartment. The rate of pressure rise and the magnitude of the peak pre ssure in any lower compartment region is related to the confinement of that compartment. T he time period to reach peak lower compartment pressure due to the design basis a ccident is approximately 0.05 seconds.
- 4. Doors shall be of simple mechanical design to minimize the possibility of malfunction.
- 5. The inertia of the doors shall be low, consistent with producing a minimal effect on initial pressure.
Design Criteria - Normal Operation
- 1. The doors shall restrict the leakage of air in to and out of the ice condenser to the minimum practicable limit. (See Section 6.5.6.3.)
- 2. The doors shall restrict local heat input in the ic e condenser to the minimum practicable limit. Heat leakage through the doors to the ice bed should be a to tal of 20,000 BTU/hr or less (for 24 pairs of doors).
- 3. The doors shall be instrumented to provide indicati on of their closed position.
Testing of prototype doors has established that their normal position under zero differential pressure conditions is 3/8" 1/8" open.
- 4. Provision shall be made for adequate means of inspecting the doors during reactor shutdown.
- 5. The doors shall be designed to withstand earthquake loadings without damage so as not to affect subsequent ice condenser operation for normal and a ccident conditions. These loads are derived from the seismic analysis of the containment.
- 6. The door system shall provide a flow propor tioning capability for small break conditions in accordance with Figure 6.5.9-1.
Interface Requirements
- 1. Crane wall attachment of the door frames is via st uds with a compressible seal. Attachment to the crane wall is critical for the safety function of the doors.
- 2. Sufficient clearance is required for doors to open in to the ice condenser. Ite ms to be considered in this interface are floor clearance, lower suppor t structure clearance and floor drain operation.
- 3. Door opening and stopping forces will be transmitt ed to the crane wall and lower support structure, respectively.
Design Loads
Pressure loading during LOCA was provided by t he Transient Mass Distribution (TMD) code from an analysis of a double-ended hot leg break in the cor ner formed by the refueling canal, with 100
S6-5.doc 6.5-37 INSERT A2-3 INSERT Original ice basket qualification testing (Topical Report WCAP-8110, Supplement 9-A), has shown freshly loaded ice is considered fused after 5 weeks. In the event of an earthquake (OBE or greater) which occurs within 5 weeks following the completion of ice basket
replenishment, plant procedures require a visual inspection of applicable areas of the ice
condenser within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to confirm that opening of the ice condenser lower inlet doors is not
impeded by any ice fallout resulting from the se ismic disturbance. The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> time frame for inspection is applicable during modes where the lower inlet doors are required to be operable, otherwise perform this inspection prior to startup. This alternative method of compliance with
the requirements of GDC 2 is credible based upon the reasonable assurance that the ice
condenser doors will open following a seismic event during the 5 week period and the low
probability of a seismic event occurring coincident with or subsequently followed by a Design
Basis Accident.