ML20106A994
| ML20106A994 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 09/25/1992 |
| From: | Cottle W ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GNRO-92-00123, GNRO-92-123, NUDOCS 9209300215 | |
| Download: ML20106A994 (7) | |
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September 25, 1992 4
U.S. Nut lent Regulatory Commis.sion finil Stat ion PI-137 Wo*;hington, D.C.
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Sub}cct:
G ratui Gul f Nutionr Station Unit 1 Docket No. 50-416 1,1 cense No. NIT-29 Response to Request for Add it ional Informat ion Relnted t o Ground Wnter I, eve 1 Cont rol and Monit oring GNRO-92/00123 Ge n t. l e rnen :
On April 30, 1992, Entergy Operations, Inc. provided n f Inal report. on high ground water levels nt t.he Grand Gulf Nuclear St at ion (CGNS).
'ihla t epot t sommnrized the out stand ing ground wat er issnes at GGNS and described actions taken t.o renolve thesn issues.
This report n ino conta.itied a pr.t.-cons t ruct ion ground wa t e r level contour enop nnd evaluntion results providing the nnximum expect ed post-construction ground wnter level wit hin t
the power block aren, ily letter dated July 17, 1992, the Staf f raquest ed additional lufotantion to puppot t. completion of it s review.
Thn nt.tachment prov iden. our i nsponse t o this requos, for additionni informatlon.
i Should you have n,y quest ions or require nddit ional clar i ficu lon, plense l
con t n c.t Jewel Summers a t. (601) 437-2149.
l-l Yours truly, I
.l wPW WTC/JS/nmn attachment:
Requent for Addit.ional Infor mat ion on Ground Water cc:
(See.Next Page) r.
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Sept' ember 25, 1992 i
GNRO-92/00123 Page 2'of 3 cc:
Mr. R.11. lintnha rd (w/a )
Mr. D. C. Ilintz (w/a)
Mr. P. B. McGehee (w/a)
Mr. N. S. Reynolds (w/a)
Mr.11. L. Thomas (w/o)
Mr. Stowart. D. F. hunter (w/4)
Regional Administrator U.S. Nuclear Regulatory Commission Region 11 l
101 Mariett.a St., N.W.,
Suito 2900 Atlanta, Georgin 30323 Mr. P. W. O'Connor, Project Manager (w/2)
Of fice of Nuc]nar Reactor Rot,ulation U.S. Nuclear Regulatory Com.nission Ma11 Stop 13113 Washington, D.C.
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Attachment to GNRO-92/00l?3 Page 1 of 5 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION j
i Ot:ESTION NO. 1 Thn licensee proposed to raise the Design Ground Water Level (DGWL) from El.
109.0 ft. above mean sea level to El. 114.5 ft. for the Cont.rol Building and Standby Servjco Water (SSW) basins, and to El.117.0 f t, for the remaining safety i-related structures. The licensee stated that several studies and calculations since 1983 have been performed t.o justify raising of the DGWL, but no details i
and document 9 tion of thesn studies have been presented.
Pleasn provide a summary of those studies and technical reports, including report titles, date of issuance, brief descriptions and documentations, for future reference and retrieval.
RESPONSE
Note: As discussed in the final report dsted April 30, 1992, the Control Building and SSW Basins have been evaluated for a ground water elevation of 114.5 ft. and the remaining safety related structures have been cva'unted for a ground water clovation of 117.0 ft.
llowever, Entergy has sta,ed the DGWL will be raised from 109 f t.. to 114.5 ft, for all structures within the power block.
The f ollowing is a list of t he major documents generated in the evaluation of high ground water !cvels and available for review at GGNS. The reference section within each document cites additional reinted documents.
S tt;-lies 19$.3_ St udy rate:
December 1983
Title:
liigh Ground Water Level St.uc'y, Grand Gulf Unit 1.
Performed by Bechtel Corporation (
Reference:
i AECM-85/0035, dated February 14, 1985).
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Descriptton:
This study was conducted-to determine if the integrity of safety related struct ures was compromised t.y the high ground water levels experienced in 1983.
A r< view of the structural analysis for stability and hydrostatic loading was performed.
1989-1990 Study Date:
November 1990
Title:
Status Report - Program to Resolve liigh ground water Level Is<ue.
Performed by Bechtel Corporation.
==
Description:==
This study was initiated to investigate the source (s) of ground water flow into the backfill adjacent to the power block structures, i
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Attachment to GNRO-9./00123
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.Il91_Sl"! J Date:
January 1991 Title-Addendum to Status Report - Program to Resolve liigh Ground Water Level Issue.
Performed by 13cchtel Corparation.
==
Description:==
St udy was initiated to er,.and on the previous studies and prc. vide an action plan for resointion of the high ground water level issue.
Engineering Report Date:
April 28, 1992
Title:
GGNS Ground Water Assessment.
Report No.
GGNS-92-0026 Revision 0.
r Descriptlon:
This report presents thn results of ef forts begun in 1969 to determine why ground water levels at GCNS had exceeded the design ground water level.
It reflects the recommended resolution to the ground water level J r. sues,
including raising of the DGWL.
Calculations Date:
May 28 1992
Title:
Ground kater Level Evaluation Calculation Review.
(GEXI-92/00722) i i
Pescript lon:
This letter references calculations reviewed by liechtel Corporation to support resolution of the GGNS ground water issue.
Quest.lon No. 2 l
The licensee reported that the major sources of recharge to the ground water at GGNS are infilt ration from precipitat ion and leakage from the cooling tower.
a.
W he t.
is the probable maximum precipitation (PMP) rate that has been considered at the GGNS site?
Is it consistent with the latest position of NRC Standard Review Plan rection 2.4.3, Revision 3, April 3, 19897 l
RESPONSE
Thn PMP analysis-for GGNS was conducted in accordance with-Regulatory Guido 1.59, Revision-2. This analysis determined that approximately 30.5 inches of rainfall-would be received during a 6 hr storm event (based on llMR-33 for 10 square mile area with a maximum intensity of 16,4 in./hr).
Acceptance of this analysis is documented in NUREG-0831, Section-2.4.4.
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Attachment to GNRO-92/00123 page 3 of 5
~ A storm event consistent with the 19 test revision of NRC Standard Review plan Section 2.4.3, Revision 3. April 1,
19fM would be based on li!1R-51, where a 6 br storm event would produce npproximately 31.5 inches of rainfall with a riximum int ensit y of 28.2 in./hr.
Timrefore, t he overall rainfall j
amount in not signi ficant ly rii f ferent than that already evaluated.
Iloweve r,
ns shown nhove the maximum rainfall intensity is significantly increased.
Altbough, changes to inteneIty may have a s igni f t cant. effect on PHP, the i
durntlon of these ininfall rates are for a short time period (less thnu 30 minut es). Other parameters being enunl, n higher intensity rainfall would promote runof f and provide less time for t he rain fall t o percolate for a given storm event.
Also, saturated ground conditions would tend to promote runoff and dry ground conditions would provide a buffer.
Additionally, as stated in a letter from Entergy Operations, Inc. dated April 30, 1992, water levels typically rise when precipitation Js high for sew n! consecut ive months and f all during simlinr periods of lower thn:. averegn precipitation, i
Although short durat ion rainf all event s do af fect the ground water level, th-effects dir.sipate quickly.
Therefore, it is reasonable to assume that this short durnt lon, high intensity rainf all would not adversely affect ground water levels.
b.
Although the cooling tower hn, been repaired and the lenkage stopped at present, what is the basis ta believe that lenkage will not happen again in the future?
RESPONSE
A walkdown of t he cooling tower t unnels during the fourth refueling ontage revealed a major leak at one of t he expansion joints.
The influrn of this expansion joint sen] was due primarily to the type of sen) installed at an expansion joint that was misaligned durin;; construct ion.
A dif ferent type of seal was installed at the expansion joint during the fifth refueling ou t.n g e.
In nddition, several ee nnsion/ contraction cracks in the tunnel walls were also repnired.
These tracks were very small in width and didn't contribut e signif f(antly to cooling tower lenkage.
lloweve r, these cracks were repaired to prevent degradation of rebar in the tunnel walls.
Other than the (niled expansion joint seal, no degradation mechanisms were identified during the walkdown which could lead to significant cooling tower
.l e n k a g e. Nonetheless, as committed in our final report, dated April 30, 1992, a visual inspection of the cooling tower will be performed during each tofueling outnge t o veri fy na potent ial leakage prths exist.
r Based on periodic inspection, repair of the failed expansion joint and the l
nhsence of mechanical / chemical degradat ion mechanisms that could lend t o significant un identi f ied leakage, we are conf ident that cooling tower leeknge of this magnitude will rot recut.
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Attachmnnt to GNRO-92/00123 page 4 of 5 i
QUESTION NO. 3 The licennen stated that no downtering wolls will be required to maintain ground water levnis below El. 114. 5 f t.. nd,) a ce n t to safety rel4.ted structures. What necessary steps should bn taken in case the ground water invel of El. 114.5 ft.
is exceeded? Ilow can we monitor the ground water level in the future J f all the monitoring devices nro removed?
RESPONSE
Exceeding 114.5 ft is not considered crediblo from an historical perspectivo (no such exceedance has ever been recorded within the power block).
T' e ground water level dat1 that has been recorded indicates that extended periods of hnavy precipitatton have the greatest effect on ground water levels. Thesn pnriods of heavy precipit ation af fect primarily the southeast.
nren of the pinnc whnre dewatering well DW-8 i located.
In determining the maximum expected ground water level for the p. ant, the highest recorded levn) (El. 110.2 f t.. ) with minimal influence f rom plant recharge sources was ndded to the highest. ground wnter level change (3 ft.) from a pnriod of heavy precipitntion. This results in a conservatively det.ertined maximum expected ground wat er levnl ' f approximately 113 f t. within thn power block nren.
Therefore, ground water levels are not expected to rise to or even approach elevation 114.5 feet.
i The construction dewatering system was originally installed to remove scopnge of ground unter into the excavntion and inflow of precipitation during constructfan (
Reference:
UFSAR Section 2.S.446).
Monitoring un-cor s hiered a temporary measurn until complet ion of Unit 2 construct. ion.
Since the Unit 2 Gonstruction Permit has been revoked and construction on this unit terminated, the Unit 2 backfill compinted, repairs to the cooling; tower completed and the expncts' maximum ground water levnl determined, thern is no longer n need to continue monitoring the plant ground water level.
llowever, as previously noted, a visual inspection of the cooling tower will be pntformed during each future refueling outngo to verify no potentini j
innkage paths exist.
QUESTION NO. 4 l
provide for comparison thn following responso spect ra of design ground mot.lon to l
demonstrate that ndditional evaluat ion of seismic structural design is not l-required for the new DGWI. change:
(n) Spectra for the old DGWh El. 109.0 ft.
(b)'Brondened-(+/-15%) spectra for the old DGWh El. 109.0 ft.
(c) Spoetra for the new 10Wb El. 117.0 ft
RESPONSE
The design spect ra for GGNS design ground motion is provided in UFSAR Figures 3 7-1 and 3. 7-2.
These spect ra were obtained by mmli fying Newmark's curves to account for variations in site conditions, foundation properties, G9209181/SN1,1CFI.R - 7
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- and ef fects of focal and epicentral distance from the site. Ground water elevation is not a parameter directly considered in the development of the GGNS fIce field ground motion desict, spectra.
The plant site specific design synthesized time-history was obtained through malification of the 1940 f.i Centro carthquake since no recorded earthquake motions were available.
Using the synthesized time-history, response spectra were developed that enveloped the modified Newmark design spectra (UFSAR Figures 3.7-4 through 3.7-15) at a sufficient number of frequencies.
Th!s time-history was used to determine in-structure seismic response.
Ilowever, ground watei levels could pc,tentially af fect the in-structure response spectra.
The areas of concern are the dynamic soil properties and the analysis methodology. The dynamic soll properties are affected by the raised ground wat.cr icvel and the analysis methodology is af fected by the dynamic soil properties. The ef fect of raising the IXiWh on the key soil parameters has been investigated (Ref. GGNS Ground Water Assessment Repoct No. GGNS-92-0026, Revision 0, April 28, 1992) and found that the effect of these changes in the soll properties on the analysis methodology is negligible.
These slight variations in soll properties woald have a minimal cifect on response and would be more than adequately enveloped by the broadening of the in-structure <lesign response spectra (4-15%) discussed in UFSAR Section 3.7.2.5.
Therefore GUNS in-structure design response spectra remain unchangen and are applicable to a ground wat er elevation of 114.5 ft..
or 117.0 ft. (see note under response to Question No. 1).
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