ML20082B863
| ML20082B863 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 07/12/1991 |
| From: | Feigenbaum T PUBLIC SERVICE CO. OF NEW HAMPSHIRE |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NYN-91109, NUDOCS 9107170051 | |
| Download: ML20082B863 (11) | |
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%w Hampnire; Ted C, Feigenbaumf j
President and s <
Chief Executive Officer
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NYN 91109~
l July 12,1991 United States Nuclear-Regulatory Commission s.
. Washington, D.C. - 20555 -
L Attention:
Document Control Desk-~
C
-. Reference.
h(a):
Facility Operating License NPF 86, Docket No. 50 443 (b)-
NHY ' Letter NYN 91059 dated April.12,1991, " Request for License Amendment; Rod Cluster Control Assembly (RCCA) Repositioning
- Program
- T. _C. Felgenbaum to USNRC (c)_
USNRC Elettet dated May 3, _1991, ' ' Request for Modification of
. Aiaendment Request-for Roo Cluster. Control-Assembly Repositioning" Dr. G. E Edison to T. C. Feigenbaum
Subject:
Supplement to Request for License Amendment Rod Cluster Control Assembly
. (RCCA) Repositioning Program
- Gentlemen:
~
New + Hampshire l Yankee-(NHY) herein - provides supplemental information to the (license amendment. request regarding the Rod Cluster Control Assembly. (RCCA)
-Repositioning Program _[ Reference p)], - As requested by the NRC'in. a letter dated May 3,11991-[ Reference (c)] the enclosed information supplements the engineering evaluation and -
no lsignificant hazards consideration: evaluation provided in Enclosure 2 of Reference '(b)
E(RCCA Repositioning Program Engineering Evaluation and Significant Hazards Consideration Evaluation),
. __ ;The" request for a. license amendment was submitted to; support NHY's; plans to s
implement d Rod Cluster Control Assembly (RCCA) repositioning program. The proposed jRCCAs. repositioningL program permits the axial _-repositioning of the RCCAs between (and J including) 225 steps withdrawn and _232; steps withdrawn during. power operation, The 1'
implementation of the RCCA repositioning pregram is expected to yield even distribution of RCCAL wear'on the rodlet eladding and a longer ' operating lifetime for the RCCAsf The t
-RCCA_ wear phenomenon in-Westinghouse plants was described in USNRC Information Notice 8719s " Perforation and-Cracking of Rod Cluster Control Assemblies",
9107170051'910712 PDR ADOCK 05000443-
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PDR v
e 006G New Hampshire Yonkee Diision of Public Service Company of New Hampshire P.O Box 300
- Seabrook, NH 03874
- Telephone (603) 474 9521
'g a_
United States Nuclear Regulatory Commission July 12,1991 i
Attention:
Document Control Desk.
Page two
-1 The proposed changes affect th'e following Tect.nical Specifications and 11ases:
Technical Snecification 3.1.4 (Rod Dron Time) nace 3/41-20 Currently, rod drop times are determined by dropping rods from the ' fully withdrawn' position (228 steps withdrawn).
The change to this Technical Specification will iequire that rods -be dropped from the ' mechanical fully withdrawn' position which it, expected to be either 230 steps withdrawn or 231 steps withdrawn during hot conditions. Enginecting evaluations of the RCCA repositioning program hase addressed rod positions between 225 steps withdrawn and 232 steps withdrawn to envelope the expected mechanical fully withdrawa position. The drop time requirement of 2.2 seconds contained in this Technical Specification -is not changed, therefore all accident analyses which. credit rod insertion remain valid, New Hampshire Yankee will not utilize the rod positions above 228 steps withdrawn until drop times above 228 steps withdrawn are confirmed to be within this Technical Specification limit.
The maximum measured rod drop time at Seabrook Station of 1.45 seconds is estimated to increase by.048 seconds to a total of 1.498 seconds if rods were dropped from 232 steps withdrawn (i.e. 4 steps beyond 228), nevertheless, NHY will test the-drop. times for positions above 228 steps withdrawn prior to Jimplementation of the proposed RCCA repositioning program for these positions.
Technical Snecification 31.3.5 (Shutdown Rod Insertion Limiti nace 3/41-21 The change to this Technical Spccification involves the addition of a definition for " fully withdrawn" (i.e. 'The fully withdrawn position is defined as the -
interval within 225 to the mechanical fully withdrawn position, inclusive"). This change' allows the axial repositioning of the shutdown rod banks within this -
range during power operation. New Hampshire Yankee vill develop procedures
~ for implementation of the RCCA repositioning program for the shutdown rod banks p_rior to-implementation of the revised Technical Specification.
h Technical Specification 3.1.3.6 (Control Rod Insertion Limits) Fieure 3.1-1. pag.e.e 3/4 1-23 The change to Figure 3.11 which depicts the required positions for control rod banks as a function of thermal power level involves the addition of a definition for ' fully. withdrawn consistent with the change to Technical Spccification 3.1.3.5 abovci This. change. allows control rod banks that were previously maintained at a parked position of 228 steps withdrawn to be axially repositio'ned within the. range of 225 steps withdrawn to the mechanical fully withdrawn position, inclusive. New Hampshire. Yankee will develop procedures for implementation of the RCCA repositioning program for the control rod banks prior to the implementation of the revised Technical Specification.
v
. United States Nuclear Regulatory Commission July 12,1991 Attention:
Document Control Desk Page threc l
Technical Specification Hases 3/4.1.3 nace B 3/4 1-4 (Movable Control Assemblied i
i The changes to this Bases section are consistent with the proposed Technical Specification changes and specify that rod drop times are measured from the i
" mechanical fully withdrawn position" and that the fully withdrawn position of l
the shutdown rod banks and the control rod banks can be varied between 225 steps withdrawn and the mechanical fully withdrawn position (up to 232 steps l
withdrawn) inclusive. The changes to this Bases section also specify that the 225 to 232 step interval allows axial repositioning to minimize RCCA wear.
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The enclosed supplemental information does not affect the proposed Technical
)
Specification revisions, or the Bases revision previously provided nor does it rcvise the conclusions of the no significant ha7ards consideration evaluation provided in Reference (b),
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Should you have any further questions regarding this ma;ter please contact Mr. Terry
.l L, Harpster, Director of Licensing Services, at (603) 474-9521, extension 2765, l
\\
Very truly yours, I
ga-I f(ih l
Ted C. Feigenbaum l
(
Enclosure TCF:ALL/ss!
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United States Nuclear Regulatory Cominission July 12,1991 Attention:
Docupent Control Desk Page four ec:
Mr. Thomas T Martin Regional Administrator United States Nuclear Regulatory Commission Region 1 475 Allendale Road King of Prussia, PA 19406 Mr. Gordon E Edison, Sr, Project Manager Project Directorate 13 Division of Reactor Projects U.S. Nuclear Regulatory Commission Washington, DC 20555 Mr. Noel Dudley NRC Senior Resident inspector P.O. Box 1149 Seabrook, NH 03874 Mr. George Iverson, Director N. H. Office of Emergency Management State House Office Park South 107 Pleasant Street Concord, NH 03301 i
7 New llampshire. Yankee July 12,1991
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ENCLOSURE 1 TO NYN-9 109 I
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RCCA Repositioning Program Significant Hazards Consideration Evaluation 3
Summary of Sienificant Hazards Consideration Evaluation The RCCA repositioLing program proposed by NHY will allow the axial spositioning of the control rod banks and the shutdown rod be ks between 225 steps withdrawn and 232 steps withdrawn, inclusive, during power operation. Although the mechanical limit is 230 steps withdrawn during cold conditior,s, it is expected that the mechanical limit for certain rods may reach a limit of 231 steps withdrawn due to thermal expansion during ho, conditions. The actual mechanical limit for each rod will be determined in conjunction with the required rod drop tests of Technical Specification (TS) 3.1.3.4, "ad Drop Time. The 225 to 232 step range ' envelopes all possible mechanical fully withdrawn positions.
All shutdown rod banks and control rod banks, with the exception of Control Bank D, are currently required to be in a ' parked' position of 228 steps withdrawn during certain lesels of power operation.
Axial repositioning on monthly frequency will reduce the rate of a
frettir.g wear, extend the life of the RCCAs and, therefore, postpone the replacement of RCCAs.
The proposed RCCA repositioning program has been evaluated by Yankee Atomic Electric Company (Y A EC) wit h respect to its affect on reactor physics, transient analpis (non-LOCA), LOCA analysis, mechanical analysis and fuel management. The evaluations by YAEC and NHY have determined that the proposed changes do not involve a Significant Hazards Consideration pursuant to 10CFR50.92 as discussed below:
Sienificant Ha7ards Condderation Evaluation a.
Do the changes involve a stgnificant increase in the probability or co ssequences of an accident previously evaluated?
N.
The affect of control rod bank and shutdown rod bank repositioning at Seabrook Station has been esaluated by the Yankee Atomic Electric Company (YAEC). The YAEC evaluation determined that allowing control rod banks and shutdown rod banks to have a variable fully withdrawn position between 225 steps withdrawn and 232 steps withdrawn, inclusive, versus the current parked position of 228 steps withdrawn will have an insignificant affect on the Updated Final Safety Analysis Report (UFS AR) Chapter 15 accident analyses (both non-LOCA and loc'A transients). The bases for this determination are as follows:
Reactor Physics Considerations The proposed RCCA repos.uoning program involves the axial repositioning of both the control rod banks and the shutdown rod banks between 225 steps withdrawn and 232 steps withdrawn, inclusive. The program would replaec the stationary parked position of 228 steps withdrawn, which is required by the current Technical Specifications 3.1.3.5, " Shutdown Rod Insertion Limit", and 3.1.3.6, Control Rod insertion Limits" The proposed RCCA repositioning program will consist of monthly repositioning of both the shutdown rod banks and the control rod banks (excluding Control Bank D) by one step within the 225 - 232 step withdrawn range during power operation. Control Bank D is excluded from the program since this control bank is used as required for small incremental reactivity changes such as 1
boron dilutions or small load changes.
This control bank is. maintained within the requirements of the _ Technical _ Specification - Fig ire 3.1 1 rod bscrtion limits. Since both control rod banks and shutdown rod banks would u allowed to be inserted further into the core,-the potential impact - on axial and radial power _ distribution profiles as well as
- temperature dependent shutdown margins have been evaluated by YAEC. The conclusions
- of the YAEC evaluation are as follows:
The 228* step withdrawn position is actually 1.4f/ above the top of the active fuel region.
If rods _wcre repositioned to the 225* step withdiawn position, they would be approximately 4* inserted into the active core region. Yankee Atomic Electric Company has determined that repositioning the control rod banks and the shutdown rod bt.aks at the 225* step withdrawn position will have a insignificant affect which is not quantifiable within the accuracy of their computer model SIMULATE-3 for both acial and radial power distributions, critical boron concentrations and temperature dependent shutdown margins during Cycle 1 and Cycle 2.
The YAEC Topical Report 1659 for the SIMULATE 3 :omputer model was-accepted by the NRC for referencing on February 20, 1990. The Cycle 1 and Cycle 2 core
' designs each result in the 225* step withdrawn being approximately.4" inserted into the active core region. The fuel vendor will be informed that the RCCA repositioning program should be accounted for in subsequent core designs and safety analyses.
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, Transient Analysis Considerations j-As stated above, YAEC has determined raat there is no significant effect on axial or radial i
power distributions due to control rod bnks and shutdown rod banks insertion at 225 steps withdrawn consistent with th,. proposej RCCA repositioning program. Since there is no significant effect on power distributions with insertion at 225 steps withdrawn, there will be :
.no power distribution related effect'on the UFSAR Chapter 15 accident analyses. Therefore the proposed RCCA repositioning program does not involve a significant increase in the probability or consequences of an accident previously evaluated.
TM DCCA repositioning program also allows for the control rod banks and shutdown rod banks to be withdrawn to 232 steps, four - steps higher than the current Technical Specification limit. Withdrawing control rod banks and shutdown rod banks further out of 1
the core results in a longer time for insertion of these rod banks into the core. Technical Specification 3.1.3.4 states that for' Modes 1 and 2:
The individualfull-length (shutdown and control) rod drop time from the fully withdrawn position shall be less than or equal to 2.2 seconds from beginning of decay of stationary
- gripper coil voltage tc. dashpot entry with; a.
Tm for each loop greater than or equal to 551*F, and b.
All reactor coolant pumps operating.
l Rod drop times from 228 steps vithdrawn have been measured twice at Seabrook Station.
- The maximum measured rod drop time from the 228* step withdrawn under the Technical
. Specification required conditions was 1.45 seconds. Yankee Atomic Electric Company has o
conservatively calculated the additional drop time related to the extra four steps withdrawn to be.048 seconds utilizing Updated Final Safety Analysis Report (UFSAR) Figure 15.0-4, RCCA Posit;on Versus Time to Dashpot. The total calculated drop time of 1.498 seconds 2
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from a position of 232 step withdrawn is still well within the 2.2 securids requirement of Technical Specification 3,1.3A, Rod Drop Time. Additionally, NHY will not implement the RCCA repositioning program for-_the positions above 228 steps withdrawn until rod drop times at these positions have been measured and have-been determinea to meet the drop time requirement of Technical Specification 3.1.3.4.
Therefore the proposed _ RCCA repositioning ' program does not involve a significant increase in the probability or consequences of an accident previously' evaluated.
Loss Of Coolant Accident (l OCA) Considerations Tb impact of the RCCA repositioning program on the following areas has been evaluated by 'YAEC:
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'Large-and Small Break LOCA Analyses Hot Leg Switchover Calculation Post-LOCA Long-Term Core Cooling The small break LOCA analysis considers a top-skewed power shape and, therefore, could potentially be affected if the most limiting axial power shapes were affected by the proposed
- RCCA repositioning program, it has been determined by YAEC, as asserted above in the Transient Analysis Considerations, that the affect on power distributions from the repositioning program are insignificant. Additionally rod drop times as asserted above in the
- Transient Analysis Considerations are not significantly increased by the RCCA repositioning program It can, therefore, be concluded that the small break LOCA analysis will not be affected by the proposed RCCA repositioning program and the probability or consequences of such accidents are not increased. Additionally, the RCCA repositioning program does not affect large break LOCA analysis since power distributions are not significantly.affected and rod insertion is not credited during such an event.
The post LOCA long-term core cooling analysis and the hot leg switchover calculation address the potential for recriticality and boron precipitation.
The key parameters considered in this analysis are initial full power critical boron concentration and critical boron concentration under cold shutdown conditions (post LOCA). It has been determined by YAEC as asserted above in the Reactor Physics Considerations that inserting the control rod banks and the shutdown rod banks.4' into the actWe core region has an insignificant t..
impact on - critical baron concentrations. Therefore, n is concluded that the post-LOCA l-long-term cooling analysis is;not-affected by the RCCA repositioning program.
Mechanical Considerations The _ mechanical impact _ of implementation of the Rr'CA repositioning program has been
- cvaluated by YAEC, This evaluation addressed the following areas:
l RCCA Tip Characteristics -
LOCA Hydraulic Forces l
Mechanical Integrity _
l The. evaluation of RCCA tip. characteristics consisted of determining whether repositioning 1:
rods 'from 225 steps withdrawn te 232 steps withdrawn combined with the characteristics of
- the RCCA tips (geometry, material composition, etc.) would reduce the likelihood that the 3
rods would perform their function during design basis events. Chapter 4 of Updated Final Safety Analysis Report and as-built drawings show that withdrawing rods to the 232* step withdrawn still ensures that the tip< of the RCCAs remain engaged in the guide thimbles, thereby ensuring that alignment ben.een the RCCA fingers and the guide thimbles is always maintained. At a position of 232 steps withdrawn, the tips of the RCCAs are approximately four inches below the top of the fuel rods and approximately eight inches below the top of the nonle plate of the fuel assembly. This positioning ensures that the amount of bearing surface area at the tip of the RCCAs (against the inner surface of the guide thimbles) remains essentially unchanged compared to the 228 step withdrawn position.
The repositioning of the RCCAs within the 225"' step withdrawn and 232* step withdrawn range could position the tips so as to accumulate a 'iigher integrated flux and, therefore, a higher rate of embrittlement than would result at the 228"' step withdrawn position. Based on discussions with the fuel vendor, it is theit experience that the net affect on integrated flux for similar RCCA repositioning programs is insignificant and, therefore, the rate of embrittlement of the RCCA tips is unaffected. Additionally, as discussed above, inserting the RCCAs to the 225"' step withdrawn has no significant affect on axial power shapes.
This leads to the conclusion that repositioning the RCCAs to the 225"' step withdrawn will not lead to a significant increase in integrated exposure or embrittlement. Therefore, there is no adverse affect on the RCCA tips resulting from the proposed RCCA repositioning program.
The hydraulic forces resulting from a LOCA are applied to the RCCAs through openings in the guide thimbles within the fuel assemblies and through openings in the guide tubes in the upper internals. In the upper internals, a series of horizontal card type structures provide lateral support for the RCCA fingers at regular intervals along the length of the guide tube.
Fuel assembly guide thimbles provide lateral s"pport within the core region. Since the span lengths between lateral support locations will not be changed due to the RCCA repositioning program, forces and stresses will not be increased significantly.
Therefore, there is no adverse affect due to LOCA hydraulic forces resulting from the proposed RCCA repositioning program.
The mechanical integrity of the RCCAs during a design basis event has been evaluated. The RCCAs remain positively inserted in the guide thimbles by a safe margin even at the mechanical fully withdrawn position of 232 steps. The RCCAs and protective guide tubes (and thimbles) are subjected to the same mechanical stresses in any position from 225 steps withdrawn to 232 steps withdrawn due to the fixed lateral support locations in both the upper internals and the fuel assemblies. Therefore, the ability of the RCC As to perform their design function during a design basis event is not affected by the proposed RCCA repositioning program.
Overall, implementation of the RCCA repositioning program will have no adverse impact on the mechanical integrity / operability of the control rod banks and the shutdown rod banks and they will be able to satisfactorily perform their design functions.
Fuel Manacement Considerations Yankce Atomic Electric Company personnel have attended recent Electric Power Research Institute workshops related to RCCA fretting wear at which industry representatives reported that significant RCCA fretting wear has been experienced. Industry experience indicates that 4
Seabrook's RCCAs are susceptible to such fretting wear. With this industry experience in mind, YAEC has advised N11Y that the proposed RCCA repositioning program should be implemented as soon as possibt to minimire the risk of potential damage to the Seabrook Station RCCAs.
Secondly, Y AEC advised that the RCCA repositioning program should initially avoid the current fully withdrawn position of 228 steps until operating time at the other positions in the 225 step withdrawn to 232 step withdrawn range approximates that of the 228 step withdrawn position. This would allow for an even distribution of fretting wear within that range, b.
Do the changes create the possibihty of a new or different Lind of accident from any previously evahtuted.
No.
The following aspects of the RCCA repositioning program have been evaluated by YAEC.
The affect on rod drop times of withdrawing RCCAs further than allowed by the current Technical Specifications.
The affect on power distributions, critical boron concentrations and temperature dependent shutdown margin of inserting RCCAs deeper than currently allowed by Technical Specifications.
Whether withdrawal of RCCAs beyond the current Technical Specification limit may cause mechanical integrity / operability problems.
As asserted in the response to question a, above, the affect of withdrawing RCCAs another four steps beyond the current limit of 228 steps withdrawn has an insignificant increase on rod drop timer. The total rod drop time has been conservatively calculated to increase by a total of.048 seconds from L45 seconds to a new value of 1.498 seconds which is still significantly less than the maximum rod drop time of 2.2 seconds required by Technical Specification 3.1.3,4, Rod Drop Time.
The affect of inserting RCCAs three steps deeper than the current limit of 228 steps withdrawn has also been determined to have an insignificant affect on power distributions, critical boron concentrations, and temperature dependent shutdown margin as asserted in the Reactor Physics Considerations response to question a. above.
An evaluation of the affect of the proposed RCCA repositioning program on the mechanical integrity / operability of the RCCAs, was performed.
This evaluation determined that the proposed RCCA repositioning program does not introduce mechanical integrity / operability problems which might interfere with RCCA operation for the proposed repositioning range.
Therefore, the evaluations which have been performed have not identified any aspect of the proposed RCCA repositioning program that would lead to a new or different kind of accident from any accident previously evaluated.
c.
Do the changes involve a significant reduction in the margin of safety?
No. The proposed RCCA repositioning program does not involve a significant reduction in the margin of safety. The margin (s) of safety, potentially affected by the proposed Technical 5
~. _ _ -. _
m Specification changes-arc ~ related 'to Minimum Departure from -Nucleate lloiling Ratio requiremerts for non LOCA transients and to fuel failure assumptions included in the LOCA
- and rod ejection transient analyses. As discussed in response to question a. above, LOCA analyses and ' non LOCA transient analyses ate not significantly affected by~ the' proposed.
RCCA repositioning program due to its insignificant effect on core power distributions, rod-drop times and on the mechanical operability / integrity of the RCCAs. The margin of safety demonstrated by these analyses with respect to Minimum Departure from Nucleate Iloiting Ratio requirements is therefore not significantly reduced by the proposed RCCA repositioning program. The' mechanical integrity / operability of the RCCA'S is also not affected by the -
proposed RCCA repositioning program. The RCCAs will satisfactorily perform their design function during normal or postulated accident conditions. RCCA mechanical integrity ensures that the margin of safety associated with potential fuel failure and fission product release is not reduced.
With consideration and evaluation of' the above it has been determined that the proposed RCCA repositioning program does not involve a significant reduction in a margin of safety.
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