ML20058A225
| ML20058A225 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 11/08/1978 |
| From: | Short T OMAHA PUBLIC POWER DISTRICT |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7811140197 | |
| Download: ML20058A225 (9) | |
Text
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Omaha Public Power District OMANA, NE9mASMA 68102 TELEPHON E S36 4000 AREA CODE dO2 te23 MARNEW
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?loventer 8, 1978 Director of I!uclear Peactor Eegulation' ATCi:
I'r. Pctert W. Peid, Chief Operating Peactors Ersnch !!o.,%
U. S. ?!uelear Pegulatory,Lmksich Washingt;n, D. C.
205?3
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Pererence: Docket !!o. 50-285 i
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Gentienen:
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~'he Craha Public Power Dictrict received a letter frcm the Cenmission dsted Septenter 19, 1977, requesting additicnal infernation regarding the long tern core cooling method used at the Fort Calhoun Station.
In res-ponse, the District forwarded a schedule for supplying the information and, subsequently, provided letters describing progress made toward re-solving the issue.
This letter (see enclosure) supplies responses to the questions posed in the Cer.nissicn's September 19, 1977, letter.
It qualitatively describes the modifications which will te performed by the Distr.ct to insure a high degree of confidence that long term core eccling can effectively be a;ccr.plished without boron precipitation dif-ficulties.
Please note that a detailed quantitative response to Questica 5 and a =cdifications schedt:le vill be available for Cc=issicn review by July, 1979 Sincerely, l L ') I !
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4 4 T. E. Short
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.g e r Producticn vperaticns
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Tr.cle s ure 1
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LeBoeuf, 'amb, Leity & Mac?ae i
1757 ":i" Street, :1. W.
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Washiagten, D. C.
20036
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i E." CLOSURE Question 1 In the hot leg cuetion method a cufficient level of coolant must be available at the bottom of the hot leg (ascu=ing cold leg break) to prevent degraded performance be,cause of cavitation of the residual heat removal pump. The hot leg coolant level depends on the system pressure in the upper plenum as deternined by the total loop hydraulic resistance encountered by the steam escaping from the cold leg break.
It has been demonstrated that in most cases this resistance vill be sufficiently lov and the level of the water in the hot les vill be adequate. How-ever, for certain break locations the hydraulic resistance of the steam escape path may be hiCh enough to cause excessive loss of water level in the hot lec. Review the ECCS for this facility and provide detailed analyses that demenstrate, regardlect of the cold leg break site and location, that the hydraulic resistance of the escaping steam would te lov enough to maintain hot leg water as required to prevent pump cavi-tation.
Response
The hot leg suction method is not intended for use as a permanent post-LOC A long term ecoling procedure. Therefore, this questien is not addressed.
Question ?
The pump used to drav vater frcs the hot leg is designed to cperate vith relatively cold liquid. Shov that this pump can satisfactorily operate in the hct leg suction mode. That is, show that the pump can i
simultaneously draw saturated water from the het leg and subcooled vater from the containment sump.
Response
I The hot leg su:tien method is not intended for use as a permanent post-LOCA long term cooling procedure. Therefore, this question is not addre s sed.
Ques
- ien 3 The procedure for hot leg suction calls for a careful control of the flow of water from the hot leg and from the containment sump. Shov that:
a.
The presently existing valve is adequate for controlling the flev.
1
b.
The valve is located in a sufficiently low radiation area so that it would be accessible to the operator in a post-LOCA condition.
c.
There is sufficient instrunentation for monitoring the flow of water from the het leg and from the sump.
Pesponse The hot leg suction method is not intended for use as a permanent post-LOCA long term cooling procedure. Therefore, this question is not addressed.
Cuettien L In order to assure adequate flow of water through the core during sinultaneous hot and cold leg injection code, the ficv of water to the hot and cold legs should be carefully balanced. This requires the know-ledge of the flow path chsracteristics of the syste=.
In view of the fact that the het leg flev path is very complicat7d, involving several different lines and valves, you are requested to provide the following information:
a.
Show that all the lines in the het leg injecticn flow path have sufficient capacity for maintaining adequate hot leg injection flev, regardless of the location of the break.
b.
Shov that satisfactory procedures and instrumentatien exists for mcnitoring hot leg injection flow.
c.
Explain in detail the procedures used for aligning the flow path for hot leg injection during the icng term cooling after a LOCA.
i Ferrense a.
During the past year, the District has evaluated two approaches j
proposed by Conbustica Engineering to provide simultaneous hot and cold leg injection. Based on cost estimates and en-cineering parameters for the two approaches, the District has decided to utilize the pressurizer auxiliary spray line as a neans of hot leg injecticn. This path in conjunction with the cold les injection paths ensures post-LOCA core flushing regardless of break location.
The preposed system for hot leg injection has been analyzed l
vith regard to the hydraulic performance and system reliabi-li t.r.
It has been calculated that the hot leg injecticn path and cold leg injecticn paths will each have a flow of 175 spm. This value is in excess of the requirements during the tLne of core flushing. These flow rates vill be verified during precperational testing of the system. Also as a re-sult of the system analysis, modifications vill be made to 2
the system which will enhance the system reliability. A basic sketch of the modified system is provided by Figure 1.
b.
The proposed system of simultaneous hot and cold leg injection is enhanced by its use of existing instrumentation. The safety injection system instrumentation in conjunction with the CVCS flov instrument (FIA-236) is used for flow monitor-ing during hot and cold leg injection. The CVCS flow instru-cent vill be modified,(increase rance) to be able to read hot leg injection flow.
c.
The procedure for ECCS realignment for simultaneous hot and cold leg injection is provided by Attachment 1.
0 s_stion 5 2
Daring the 1cng tern cooling mode following a postulated small LOCA, boron precipitaticn is prevented by naintaining the system pres-sure, and therefore the saturation temperature, at sufficiently high levels. However, the system must ultimately be depressurised and cooled in order to remove the head and inspect and/or replace the fuel.
Describe the precedures that vould be used to ultimately cool devn and deprescurise the system following a small LOCA.
Clearly specify the equipment that vould be required and show that the equipment has ade-quate capacity.
Perponse The analysis required to demonstrate the post-LCCA 1cng term cool-
~
- ing perfennance for Fcrt Calhoun Unit 1 is currently in progress. Since the analysis is incor.plete only a qualitative description of the pcst-LOCA long tern ecoling performance is provided herein.
The final analy-sis vill be provided by July,1979, and vill centain a quantitative description of the icng term cooling performance. A description of the equipment functicns and c?.pacities assumed in the analysis will also be identified.
The functicn of long tern ecoling is to maintain the core tempera-ture al an acceptably lov value and provide for decay heat removal for the extended period of time required by the long-lived radicactivity remaining in the cere. Tc satisfy this objective the long term cool-ing procedures previde simultaneous hot and cold leg injecticn for the large break LOCA and decay heat removal fer the small break LOCA.
Since Questien 5 addresses the small break LOCA response, the dis-cussien belev emphasises only the small break LOCA procedures. Fcr l
completeness in describing the post-LOCA long term ecoling procedures, some discussion of the large break response is also included.
The sequence of events identifying the required operator actions to establish long term cooling for Fort Calhoun 1 is illustrated in Figure 2.
This procedure was developed to ensure that, regardless of l
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cl, A FORT CAlllOUM UtJIT NO.1 I/.ODIFICATIO*JS FOR Slt.1ULTAtJCOUS !!OT AfJI) COLD
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orve OUTSIDE CCtJTAltJr.ittJT ltJSIDC C0tJTAltJr.1Ct T
ntoucnmeiic,i Fort Calhoun Station Unit No. 1
.Long Tern ECCS P.calign.ent Folicwing a LOCA
.EP-A.
_ Purpose To describe the operator action required to realign the ECCS to assure adequate core flushing.
Precedure EP-describes the required realignment for simultaneous llot Leg and Cold Leg Injection B.
Frerequisites 1.
LOCA has 6peurred.
2.
Safety injection has been initiated.
3.
SIR',TT hes been emptied.
4.
Safety injecticn system is operating in the recirculatica mode.
5.' RCS pressure <
psia C.
Precautions
- 1. Obser.e suitable radiological precautions at manual operating stations.
C. Charging pumps must b6 stopped.
1 D.
Proc'edure t
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1.
Close !!CV-233, itCV-239, Cil-C, an'd :Cil-E.
E. Open !!CV-240 (or Cll-A).
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Procedure (centinued) 3.
Open llCV-308 (or Cil-Y).
IF llPSI PU!!PS 2A (or 2C) AND HPSI PUMPS 2B ARE OPERATItlG, PROCEED HITH STEP 4:
4.
Close !!CV-304.
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5.
Close HCV-312, HCV-315, HCV-321, and HCV-318 (or SI-X).
G.
Monitor flow through FIA-235 for a minimum of spm.
IF 0::LY HPSI PUMP 2A (or 2C) IS OPERATING, PROCEED WITH STEP 7:
7.
Close !!CV-304 8.
Throttle HCV-312, HCV-315, HCV-318 and HCV-321 (or SI-X) until each.
HPSI cold leg fica is,* gpm as indicated by FIA-313, FIA-316, FIA-3*
and FIA-322.
9.
Monitor flow though FIA-236 for a minimum of gpm.
IF OtiLY_ llPSI PUMP 2B IS OPERATIf;G, PROCEED llITH STEP 10:
- 10. Close HCV-312, HCV-315, HCV-313, and hCV-321, (or SI-X)
- 11. Throttle HCV-311, HCV-314, HCV-317, and HCV-320 (or HCV-305) until each HPSI cold leg ficw is.*_ gpm as indicated by FIA-313, FIA-316, FIA-319, and FIA-322.
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- 12. 1:enitor flow through FIA-235 for a minimum of,*
gpm.
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Pcrcrences c
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h Drawing !!o.
E-23SS6-210-130 Rev.Oh l
E-23866-210-120 Rev. 07 E-23055-210-110 Rev. 04
- to' be determined during final analysis.
s, FT. Call 10Vil LOCA E!4ERGE!;CY Plt 0CEDUltES SEQUEllCE DIAGRA !
FIGURE 2
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'To be detemined in final analy::is.
break size, boron precipitation is prevented and indefinite core cool-inc is establiched. This procedure minimizes the nwnter of operator actions required to establish post-LOCA long term cooling and does not require the operator to make an assessment of the break size (large break cr cmall break rance) for several hours following the LOCA. Know-ledge of the reactor system pressure providec the operator with the in-dication of the break cire (range) and hence defines the subsequent steps to be taken to establish core cooling for the long term.
The sequence of events leading to the establistnent of long term cooling is as follows. As indicated in the Figure 2, followinc a LOCA the safety injection pumps are automatically actuated by the safety injection actuaticn signal.
At 15 minutes after the LOCA, the auxiliary feedvater flow is con-firmed or activated. This ensare: that the steam Generators are main-tained as effective heat sinks during the long term.
At 30 minutes after the LOCA, the charcing pump flow is terminated to minimize the amount of high concentraticn boric acid added to the RCS from the boric acid stcrage system.
At one hour after the LOCA, reactor ecolant cystem (RCS) cooldown is initiated using the steam generators by supplying feedvater and re-lieving steam. Feedvater is supplied from the main condenser if AC power is available or frc= the condensate storage tank and demineralized water tank if AC power is not available. Stesn is relieved from the steam generator seccndaries through the turbine typass system if AC power is available or through the atmospheric dump system if AC power is not available.
If the RCS pressure at ((ime to be identified in the final analy-sis report 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> after the LCCA (indicated by point A in Figure 2) has remained above [ pressure to be identified in the finsi analysis report] psia, the BCS is filled with liquid, and there is assurance that all conditions for entering the shutdown cooling mode can te es-tablished.
If the RCS pressure at this time (indicated at point A in Figure 2) hss fallen or rensined below this pressure (ho be identi-fled], the break may be too larEe for absolute assurence that proper suction is available for the shutdown cooling mode. However, in this event, simultaneous hot and cold leg injection is initiated which vill both cool and flush (maintain the boren concentration at very lov values) the reacter vessel indefinitely.
In the simultanecus injec-tien mode, the high pr essure safety injection (EPSI) pump is realigned so that the total injection flov is dividei equally between the hot and cold lecc.
Hot leg injection is achieved by diverting half of the total HPSI flow thrcugh the pressurizer auxiliary spray line [a quanti-tative deceriptien of the HPSI flow and RCS response for this injection mode vill be provided in the final ECCS performance analysis repor(3 Simultaneous hot leg (via the precsurizer auxiliary cpray line) and cold leg injecticn frca the EPSI punps is prescribed by the long term ecoling procedure following any LOCA. This simultaneouc injecticn h
prevents boric acid prealpitation for an extensive rance of large mad l
intercediate sized breaks, in either the hot leg or the cold leg. For very small breaks, where the RCS pressure remains hich, the simultane-ous injection flow is not requir ed to provide effective flushing in the boric acid. Simultaneous injection is not required because for the very small breaks the system refills and the boric acid concentration remains lov due to dispersal throughout the RCS by natural circulation.
As a consequence, for the sr.all break LOCA the boric acid concentration is readily naintained at very lov values. However, a techanism for de-cay heat removal must be provided. As discussed above, the steam genera-tors are utilized to provide for decay heat removal and cool the RCS to shutdovn coolin6 conditions. While the RCS cooldown can be accomplished with the steam Eenerators, the pressurizer pcVer operated relief valves provide an additional cechanism to provide for indefinite decay heat removal as indicated in Fi ure 2.
The final ECCS performance analysis C
report vill also provide a quantitative description of the pressurizer power operated relier valve capacities and the accociated RCS response when this alternate system is used, i
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