ML19242B183

Responds to NRC 770927 Ltr.Forwards Info Re long-term Core cooling,long-term ECCS Realignment Following LOCA & long-term Cooling Plan & Performance Evaluation

ML19242B183
Person / Time
Site:	Fort Calhoun
Issue date:	07/30/1979
From:	Short T OMAHA PUBLIC POWER DISTRICT
To:	Reid R Office of Nuclear Reactor Regulation
References
NUDOCS 7908070631
Download: ML19242B183 (27)

Text

. ,

r~

.35 F-EK Omaha Public Power District 1620 HARNEY a OMANA, NE8RASMA 68102

• TELEPHON E 536-4000 AREA CODE 402 July 30, 1979 Director of Nuclear Reactor Regulation ATTN: Mr. Robert W. Reid, Chief Operating Reactors Branch No. 4 U. S. Nuclear Regulatory Coninission Washington, D. C. 20655

Reference:

Docket No. 50-285 Gentlemen:

The Omaha Public Power District received a letter from the Commission dated September 29, 1977, requesting additional information regarding the long term core cooling method used at the Fort Calhoun Station.

The District's reply, dated November 8,1978, provided responses to questions posed and indicated that a detailed quantitative response to Question 5 and a modifications schedule were forthcoming. Accord-ingly, the following information is provided by enclosure.

Enclosure (1) - Responses to Questions 1 through 5 of the Commission's September 19, 1977, letter. Question 4 has been revised for clarification purposes; Questions 1 through 3 are included for completeness; and Question 5 con-tains additional quantitative infonnation.

Enclosure (2) - Modifications Schedule.

Please note that the modifications schedule is preliminary; it is con-tingent upon the availability of equipment which must be procured.

The District be.seves that the proposed modifications will assure that long term core cooling can effectively be accomplished without baron precipitation difficulties.

Sincerely, kb(//bfdk!/5W

,f/ // T. E. Short

/

, Assistant General Manager 5l9 323 TES/KJM/BJH/lp xc: LeBoeuf, Lamb, Leiby & MacRae f\ gO\

1333 New Hampsnire Avenue, Suite 1100 Washington, D. C. 20030 pk 7 90807@ 91$

cl 3[ f'

ENCLOSURE (1)

RESPONSES TO THE COMMISSION'S CONCERNS REGARDING LONG TERM CORE COOLING Questicn 1 In the hot leg suction method a sufficient level of coolant must be available at the bottom of the hot leg (assuming cold leg break) to prevent degraded performance because of cavitation of the residual heat removal pump. The hot leg coolant level depends on the system pressure in the upper plenum as determined by the total 1000 b 'raulic resistance encountered by the steam escaping from the cold ler bi k. It has been demonstrated that in most cases this resistance will be sufficently low and the level of the water in the hot leg will y adequate. How-ever, for certain break locations the hydraulic resistance of the steam escape patn may be high enough to cause excessive loss of water level in the hot leg. Review the ECCS for this facility and provide detailed ar.alyses that demonstrate, regardless of the cold leg break size and location, that the hydraulic resistance of the escaping steam would be icw anough to maintain hot leg water as required to prevent pump cavi-tation.

Resconse 7.e hot leg suction method is not intended for use as a permanent post-LOCA long tem cooling procedure. Therefore, this question is not addressed.

Question 2 The pump used to draw water from the hot leg is designed to ocerate with relatively cold liquid. Show that this pump can satisfa.corily coerate in the hot leg suction mode. That is, show that the pump can simultaneously draw satura:ed water from the hot leg and subccoled water from the containment sump.

Resocnse The hot leg suction method is not intended for use as a permanent post-LOCA long term cooling procedure. Therefore, this questicn is not addres ed.

Question 3 The procedure for hot leg suction calls for a careful control of the ficw of water frca the hot leg and frca the containment sumo. 3how that:

a. The presently existing valve is adequate for controlling the flow.

b. The valve is located in a sufficiently low radiation area so tnat it would be accessible to *.he operator in a post-LOCA conditian.

519 324

c. There is sufficient instrumentation for monitoring the flow of water from the hot leg and from the sump.

Resconse The hot leg suction method is r.ot intended for use as a permanent post-LCCA long term cccling procedure. Therefore, this question is not addressed.

Question 4 In order to assure adequate flow of water through the core during simul-taneous hot and cold leg injection mode, the flow of water to the hot and cold legs should be carefully balanced. This requires the kncwledge of the flow path characteristics o' the system. In view of the fact that the hot leg flow path is vary complicated, involving several different lines and valves, you are requested to provide the followina information:

a. Show that all the lines in the hot leg injection flow path have sufficient capacity for maintaining adequate hot leg injection flow, regardless of the locatior of tha break.

b. Show that satisfactory procedures and instrumentation exist:. for monitoring hot leg injection flow.

c, Explain in detail the procedures used for aligning the flow nath for hot leg injection during the long tenn cooling after a LOCA.

Response

a. As indicated above, in response to Questions 1, 2, and 3, the hot leg suction method, involving a very complicated hot leg flow path, is not intended for use as a permanent post-LOCA long term cooling procedure. The District, instead, has dec ded to utilize the pressurizer auxiliary spray line as a means of hot leg iljection.

This path in conjunction with the cold leg injection paths ensures post-LOCA core flushing regardless of break location.

The proposed system for hot leg injecti n has been analyzed with regard to the hydraulic perfornance and system reliability. It has been calculated that the hot leg injection path and cold leg injec-tion paths will each have a flow of 175 gpm. This value is in excess of the requirements during tho time of core flushing. Als ,

modifications will ba made to the system in order to enhance the system reliability. n basic sketch of the modified system is pro-vided as Attachment 1.

b. The proposed system of simultaneous hot and cc' i leg injection is enhanced by its use of existing instrumentation. The safety injec-tion system instrumentat. ion in conjunction with the CVC5 flow instrument (FIA-236) is used for flow monitoring during hot and cold leg injection. The CVCS ficw instrument will be modified (increase range) to be able to read hot leg injection ficw.

c ~C 3\i Dh-2

c. The procedure for ECCS realignment for simultaneous hot and cold leg injection is provided as Attachment 2.

Question 5 During the long tem cooling mode following a postulated small LOCA, boron precipitation is orevented by maintaining ti,e system pressure, and 'herefore the saturation temperature, at sufficiently high levels.

However, the sistem must ultimately be depressurized and cooled in order to remove the head and inspect and/or replace the fuel. Describe the procedures that would be used to ultimately cool down and depressurize the system foilowing a small LOCA. Clearly specify the equipment that would be required and show that the equipment has adequate capacity.

Resconse A detailed description of the long term cooling plant and performance evaluation alc..g with the description of equipment functions and capacities, assumed in the analysis, is provided as Attachment 3.

Since Questien 5 addresses the small break LOCA response, the discussion in Attachment 3 provides detailed procedures for the small break LOCA.

However, for completeness in desc ibing the post-LOCA long term cooling procedures, a discussion of the I wge break response is also included.

5!9 7,26 3

r- U . , i m -

C"^

MOD!.:iCAT!O:", i On SU 'ULTM!COUS HO T /,'1D CC LD .- e _f"~.w v ^ tm LEG !;.' JECT!ON .

~FC FtA 23 i ki =_ ,v, _. CH tas

. 4 e,.s E'

C H 1'1 > '

" "cv ::s

- I n c c' c ' '

D<71 I }--D C-N' em C q.ra.. -'"r. ,cc,a

-t r

,NL ,9; I f l ,,- - wQ u, q[_ ~ *-

-* Xl -p , .--N' '

.- C H .12 4 '

c r4 0 s

b. . .c. .

' - > ( N E W V A *. , C ) Fo C H 'r* -

Cg,,, to \j, c %,:.

4_.

-* (.*4 !_w _.

v 4 .L., c 1 - *- i g _

W7 ~X M _ H.-', **, '

~

Cyc ( - hRCS

1. • P 3 "','

C f .=

CH 12 21',

HCV'3 0 3 C"'

p '

"-i L E C '-

CH-171/ / ( a. .:. .9 V A LY )

- ~

La 3 ..,

+l .aw~ ,.

.NL.--

- + - f3 fO J *

~ s J m%

Pn ,a.e6.,.

- -! s v% . a .

cm.j;3 P '. ..-

~ - CFF ff-

}

• Cri-~ YJ VA LV I) $ "/-

CL'~!C CL . ~. U .. '

n7.

-* s s' P V C 10 2 ;1 s' . . , -

UQ &j Q . >= C V .* 3 5

• I- ~

h ' ' ' -

gd LCV. **- % r' h ~/ ~ ,' I -,

213t LCV 033; ' C N" .,, '~' g l

v.N ~

l H OVS H k HOV 0?;3 x V

.I -I 7% _t_

h i . -, -C'i bcv ;15 C C ", FIC 101

--~ _

C1 G

0,,

g. }_.Nt#l -

. s%

~; ~-~1 N L___.

s ~

r Cv a r

/~

ns w ,. ..

Uo.u* n u c; >

_.1%t '~ .N-_- (. , ; -, v _. tv ;) %_._

v ,, l e v i 0 3. '

C .'

H C /-O i:7 pc , 013

[... g

.. o y

n' (.C h . 3 ; ~ - .

Mt.

os

& J v i

HC V-0 21 f; C ' 2 7

_.,1 fa . .

v O._

C -- i

&, *\t, pp,_. ~ -

.c a H cv .; ;; . ;.

g g.

HCV 2 317 ,

h*L

" N k

>l[1]

~,- H C / .2 2 4 r o.; t i

.] . , ..

A

_L

. N ^- _

• ~

---=-- b F CV- -

@ Cc-'. V >C ?k:r--- -

.) ) p -- .

-N-x- r a . . : , .~ H=v=,

w- Csz -

F CV ; . ' ' v% , _,,

p r. . ., ; ,. w - .:.

I ,:; ,3 L g'-

• P U:.%  %

rs,i - ,

v% s EV ~;; 3

p. 3 L .- u_. O ,s Sn T: M A t 1"'. '. E."? T F C a H O T A.N O

'J k / , .ln.l-

.) - -

C i j 'u' n 1. "_ v.' '..

' "u l~ ) ' .' .' "., r . v . .. . --

f;C T AI LC;'. ES g 6-  ;

v.. r. o.3,.. . _ . . . , , ,

C.,..

. p. _ _ ,c .a g

- *i u c v : ., 2 s.. .-

,Jg .

- NL . ), --- N ce t :< -

_, a e /

g

• s .

. /

oc.

..:s

_ \

N- - N ., 3, .

-,. . . . , - ' ' "'. - '".CF,E.l'.

3 .- .

p..m..- .

p. ,. , c , - r 1 ' ' '- -

Fort Calhoun Station Unit No.1 Long Term ECCa Realignment Following a LOCA (for simultaneous hot leg and cold leg injection)

A. Purcose To describe the operator action required to realign the ECCS to assure adequate core flushing.

B. Prerequisites

1. LOCA has occurred.

2. Safety injection has been initiated.

3. SIRWT has been emptied.

4. Safety injection system is operating in the recirculation mode.

5. RCS pressure <700 psia.

C. Preca u ti ons

1. Observe suitable radiological crecautions at manual operating stations.

2. Charging pumps must be stopped.

D. Procedure

1. Close HCV-238, HCV-239, CH-C, and CH-E.

2. Open HCV-240 (or CH-A).

3. Ocen HCV-303 (or CH-Y).

IF HPSI PUMPS 2A (or 2C) Atl0 HPSI PUMPS 22 ARE OPERATING, PROCEED WITH STEP 4:

4. Close HCV-304

5. Close HCV-312, HCV-313, HCV-321, and HCV-318 (or SI-X).

6. Mcnitor ficw through FI A-236 for a miniaium of 175 gpm.

IF ONLY HPSI PL"P 2A (or 2C) IS OPEPATING, PROCEED WITH STEP 7:

7. Close HCV-304 c3 'I 9 328ATTACEMENT 2 (2 pages)

D. Procedure (Continued)

8. Throttle HCV-312, HCV-315, HCV-318 and HCV-321 (or SI-X) until each HPSI cold leg flow is 44 gpm as indicated by FI-313, FI-316, FI-319, and FI-322.

9. Monitor flow through FIA-236 for a minimum of 175 gpm.

IF ONLY HPSI PL'MP 2B IS OPERATING, PROCEED WITH STEP 10:

10. Close HCV-312, HCV-315, HCV-318, and HCV-321, (or SI-X).

11. Throttle HCV-311, HCV-314, HCV-317, and HCV-320 (or HCV-306) until each HPSI cold leg flow is 44 gpm as indicated by FI-313, FI-316, FI-319, and FI-32?.

12. Monitor flow through FIA-236 for a minimum of 175 gpm.

E. References Drawings No. E-23866-210-130, Rev. 08 E-23866-210-120, Rev. 07 E-23866-210-110, Rev. 04 519 329 2

FORT CALHOUN STATION UNIT NO. 1 LONG TERM COOLING PLAN AND PERFORMANCE EVALUATION

1.0 INTRODUCTION

The post-LOCA Long Term Cooling ECCS perfomance evaluation for Fort Calhoun Station presented herein demonstrates conformance with criterion (5) of 10 CFR 50.46(b). The results of the post-LCCA long term cooling analysis demonstrate acceptable ECCS per-formance wherein the core temperatures are maintained at acceptably low values and decay heat is removed for an indefinite period of time. The following sections describe the long tem cooling procedure along with the results of the perfemance evaluation.

2.0 LCNG TERM CCCLING PLAN Long term cooling is initiated when the core is reflooded after a LOCA and is continued until the plant is secured. The objective of long term cooling is to maintain the core temperature at an acceptably low value while removing decay heat for the extended period of time required by the long-lived radioactivity remaining in the core. In satisfying this objective, the post-LOCA long term cooling plant makes provision for mr 7- 'ning core cooling and boric acid fluming by simultaneous hot and cold leg injection for the large break LCCA, or for initiating cooldown of the reactor coolant system (RCS) if the break is sufficiently small that the success of such operation is assured. Knowledge of RCS pressure gives the plant operator the indication of the break size ranc,9 For the small break LCCA, cooldown of the reactor coolant system (RCS) and long term decay heat removal is proviced by actuation of the pressurizer power operated relief valves (PORV) by releasing steam from the RCS. This action depressurizes and maintains the RCS pressure below thc high pressure safety injection (HPSI) pump shutoff head, allowing the HPSI pumps to flush the core and accelerate refilling of the RCS.

For the large break LOCA, the HPSI f L. is injected simul-taneously into the hot and cold legs. This injection mode provides cooling for the RCS and prevents bori; acid accumulation in the vessel following the large break LOCA. Hot side injection is pro-vided througn the pressuri r auxiliary spray system.

Figure 1 shows the basic sequenc.e of events and timing of operator actions in the long term cooling plan. As indicated in the diagram, the safety injection punps are automatically actuated by tne safety injection actuation signal. At 10 minutes post-LCCA, the auxiliary feedwater flow is confirmed or actuated;while at 30 minutes post-LOCA, the charging flow is terminated.

519 330 ATTACMdENT 3 (19 pages)

2.0 LONG TERM CIOLING PLAN (Continued)

At three hours af ter the LOCA, the operator detemines, based on RCS pressure, whether the small break LOCA or the large break LOCA procedures are to be implemented. If the RCS pressure is above 700 psia, then the small break procedure is aapropriate and the POR'/'s are opened. If the RCS pressure is below 700 psia, then the large break procedure applies and HPS!

pump discharge lines are realigned so that the total injection flow is split equally between the hot and cold legs. The hot side injection is achieved by injection in the RCS through the pressurizer auxiliary spray system. Both procedures provide sufficient injection flow to both cool the core and flush the reat. tor vessel for an indefinite period of time.

30 PERFORMANCE E'/ALUATION OF THE LONG TERM COOLING PLAN 3.1 Method of Analysis Th perfomance analysis for the long tem cooling plan was perfomed using the codes and methodologies documented in CENPD-254(1), However, the precedures used in implementing the long term cooling plan for Fort Calhoun Station differ samewhat from those described in CENPD-254. The difference between the Fort Calhoun Station and CENPD-254 procedures are due to different systems used in satisfying the cbjectives post LOCA long term cooling for both the small and large break LOCA.

The use of the different systems in the long term per-formance evaluation results in different system responses.

As a consequence of the different system responses, the decision pressures and decision times differ. A discussion of the major differences between the Fort Calhoun Station and CENPD-254 procedures is presented below in terms of the small and large break LOCA.

(1) In CENPD-254, in the small break LOCA procedure, RCS cooldown i: achieved using the steam generators.

In the Fort Calhoun Station plan, cooldown of the RCS is performed using the POR'/'s. Since the RCS response folluwing cooldown with the PCR'/'s differs from that if the steam generators are used, the decision time and decision pressure also differ, RCS cooldown for Fort Calhoun Stition, however, can also be initiated with the steam generator atmospheric damp system.

However, for additional conservatism, credit for (1)CENPu-254, " Post-LCCA Long Term Cooling Evaluation Mcdel," June,1977, b}h 2

3.0 PERFCPf!ANCE EVALUATION OF THE LONG TEPJ1 COOLING PLAN (Continued) 3.1 Method of An .ysis (Continued) this system was neglected since the response achieved with the cucidown with the f0RV's is the most limiting analysis condition. Even in the unli:<ely event that the PORV's are used, the perfcrmance analyses results contained herein demonstrate a large degree of margin, both in terms of boric acid accumulation and long term decay heat removal when this system is utilized to cool the RCS. Since CENPD-254 dces not make provision for the use of the PORV's, a modification to the model was made. The methods used in modeling the performance of the PORV's are described in Appendix A.

(2) In CENPD-254 and in the Fort Calhoun Station long term cooling plan, simultaneous hot and cold side injection is the appropriate procedure for the large break LOCA.

However, in CENPD-254, hot side injection is achieved by injecting directly into the not leg; whereas in the Fort Calhoun Station procedure, injection is achieved through the pressurizer auxiliary spray system. The results of the analysis presented in Section 3.4 demon-strate that injection into the hot legs via the pressurizer auxiliary spray system provides an effective and time increasing flow to flush the core very early following a LOCA.

3.2 Assumotions Used in the Performance Evaluation of the Long Tern Cooiing Plan The major assumptions used in performing the LTC analysis are the same as those listed in CENPD-254. Those assumptions which differ from LENPD-254 are listed below.

(1) The atmospheric dump valves on the steam generator secondary were assumed to remain closed.

(2) One of the two PORV's was assumed to fail closed.

3.3 Parameters Used in the Perfor~ance Evaluation of the LTC Plan (1) Reactor Pcwer Level (102% of Nominal) 1448 MWt (2) SCC Entry Temperature 300U F, max.

(3) SDC Entry Pressure 300 psig, max.

(4) Pressurizar PORY Capacity Per Valve 27.5 lb/sec (steam) min., at 2350 osia 3

519 332

3.0 PERFORMANCE EVALUATICN OF THE LONG TERM CCOLING PLAN (Continued) 3.3 Parameters Used in the Performance Evaluation of the LTC Plan (Cont'd)

(5) Operating Pressure Range of POR'l 2300 psia to 200 psia (6) Emergency Feedwater Storage Tank Volume 51,600 gal., min.

(7) The maximum possible boric acid concentration is assumed from each of these sources.

RCS = . 71 wt 3 RWT = 1.41 wt %

SIT = 1.41 wt BAST = 12.00 wt ..

(8) The water inventories from each source are deter-mined such that the effect of injection into the RCS maximizes the boric acid concentration in the RCS.

ECS 272,945 lb - minimum RWT = 2,590,484 lb - maximum SIT = 323,388 lb - maximum BAST = 98,456 lb - maximum (Injection terminated 91/2 hour, 30,000 lbm inje:ted)

(9) The following pumps inject water into the RCS.

Run Out Total Flow Rate No. Flow Pumo Source _gca)

( Pumos (acm)

HPSI RWT, sump 423 1 423 LPSI RWT 2200 1 2200 CSP'via RWT, sump 2550 1 2550 sump)

CHARGING BAST 40 3 120

, 5i9 j33

3.0 PERFOR".ANCE EVALUATION OF THE LONG TERM CCCLING PLAN (Continued) 3.4 Results of the Perfomance Evaluation of the LTC Plan The results of the performar.ce evaluation are discussed in tems of the small and large break procedures comprising 1.he Fort Calhoun Station long tem cooling plan. As discussed earlier, for small breaks cooling and boric acid flushino is provided by actuation of the PGRV's; while for large breaks, simultaneous hot and cold cide injection maintains core cooling and provides for boric acid flushing. In this plan, the operator implements the appropriate procadure based on RCS pressure at three hours after the LCCA. Three hours is the earliest time post-OCA in which the operator has cufficient information regarding RCS pressure and then can

i. ?lement the appropriate small or large break procedure.

That is, at three hours post-LOCA, the RCS pressure will have attained these values for the entire range of break sizes, small and large, wherein the operator can rc:dily identify whether the small or large break LOCA procedures are appli-cable.

(1) Small Break Procedure In evaluating the ECCS perfomance for the small break LOCA procedures, cooldown of the RCS is initiated by activating the PORV's if the RCS pressure is aoove 700 psia. Opening of the PORV's results in cooling and reducing RCS pressure sufficiently such that the HPSI pump refills and subcools the RCS. The refilling and subcooling of the RCS results ;n maintaining the boric acid concentraticn in the vessel well below the precipi-tation limit by dispersing the boron through the RCS by natural circulation. Fi g e 2 shows that for the range o# small breaks wherein the. 5) mall break procedure applies, breaks as large as .02 f t' result in refilling the RCS. Therefore, the small,braak procedure demon-strates that for breaks .02 ft' or smaller, the RCS will refill and subcool, thereby maintaining the boric acid concentration well below the precipitation limit and cooling the core for an indefinite period of time. The results of the smaller breaks are shown in F demonstrate that breaks smaller than .02 f t",igure 2 to are less limiting.

While the small break procedure demonstrates tnat the RCS will achieve a subccoled ccndition subsequent to refilling of the RCS for the small break LCCA, the boric acid conc (,tration in th; vessel is also maintained well 5!9 334 5

3.0 PERFORMANCE EVALUATION OF THE LONG TERM COOLING PLAN (Continued) 3.4 Results of the Performance Evaluation of the LTC Plan (Continued)

(1) Small Break Procedure (.ontinued) below the precipitation limit prior to refill . Figure 3 demonstrates that the small break procedure maintains the boric acid concentration well below the precipitation limit gf 75 wt % prior to refill for breaks as large as

.02 ft . AsshowninFic"re4,theminimumRCStempgra-ture determined for the small break procedure is 328 C (saturation at 100 psia)2 for the .02 ft2 break. The results of the .00037 ft break are also shown to amonstrate that smaller breaks will have higher RCS temperatures and thus higher solubility limits. However, the minimum temperature of 3280F for the 0.02 ft2 break establishes the boric acid solubility limit of 75 wt %

shown in Figure 3. Figure 3 also shows that the small break response is also well below the solubility limit of 32 wt I at the minimum temperature of 2280F (satura-tion at 20 psia), applicable to the large break results.

(2) Large Break Procedure In evaluating tne ECCS performance for the large break LOCA procedures, the limiting break with respect to long term boric acid accumulation in the inner vessel regions is the 9.8 ft2 break in the cold leg. This break is the most limiting because the rate of accumulation of boric acid will be greatest for this break size ia addition to having the lowest associated precipitation limit (32 wt ",). For this break and all other large breaks, the boric acid accumulation is reduced by the core flushing flow which i provided by the sialultaneous hot side and cold side injection from a aPSI pump. The simultaneous hot side and colo side injection mode is initiated at three hours post-LOCA if tne RCS pressure is below 700 psia.

Figure 5 shows that the initiation of simultaneous hot and cold side HPSI ficw at three hours results in a substantial and time increasing core flushing flow.

Figure 6 snows that even with no core flushing flow, the boric acid would not begin to precipitate until after 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> post-LOCA. The margin provided for the prevention of boric acid a c.umulation by the net core flushing flow over the minimun desired flushing flow of 5 gpm is shown in Figure 6.

519 335 6

3.0 PERFORMMlCE EVALUATION OF THE LONG TERM COOLING PLAN (Continued) 3.4 R_esults of the Perfonnance Evaluation of the LTC Plan (Continued)

(2) Large Break Procedure (Contine'd)

The time at which all hot leg stcam entrr'nment of injection water terminates has been calcu.ated to be 1.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> pcst-LOCA. Therefore, the initiation of hot and cold side injection at three hours post-LOCA occurs well after any potential for hot leg entrainment has been terminated and more than 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br /> prior to the time at which boric acid precipitation is predicted to occur.

The large break long tenn cooling procedure applies to those break sizes for which simultaneous hot and cold side injection can both flush and cool the core. Analyses of smaller breaks applying tha large break procedure demon-streates that the 0.005 ft 2 break is the smallest for which simultaneous injection can cool and flush the uore.

The plot of RCS pressure versus timc determined using che large break procedure is shown for several smaller break sizes in Figure 7. The .005 ft2 break is the smallest for which the large break procedure applies since the depressurization maintains the RCS pressure sufficiently low to allow the HPSI pump to flush and ccol the RCS.

The performance evaluation results discussed above demon-strate that the small break procedure is applicable for breaks 2s large 2

.02 ft , and the Igrge break procedure is applicable for brea s small as .005 ft ' e operator must choose the appropr' e procedure according ,o the RCS pressure at three hours put-LOCA. The RCS pressure is listed, for the entire range of break sizes, in Figure 8. As :how, the decision point pressure of 700 psia fits well within the break size range of .005 to .02 ft2 for which both the small and large break procedures are applicable. This cesult is also illus-trated in Figure 9.

The analysis results presented herein demonstrate that the small and large break LOCA procedures satisfy the objectives for pos;-LOCA long tena cooling. A summary of the margins in this procedure is presented in Table 1.

This analysis considered only the condition wherein offnite power i s ur. avail able. However, with offsite power available, it u possible to more quickly cooldown the RCS using the turbine bypass system and thereby initiate operation of the shutdown cooling system. An alternate procedure would be required to identify these condi*. ions. Hcwever, the analysis considered 7 519 336 4

3.0 PERFORMANCE EVALUATION OF THE LONG TERM COOLING PLAN (Continued) 3.4 Results of the Performance Evaluation of the LTC Plan (Continued) herein is based on the more limiting condition wherein offsite power is unavailable and cocidown of the RCS is accomplished with the PORV's. According to this plan, opening of the PORV's is sufficient to maintain decay heat removal for an indefinite period of time such that it is not necessary to initiate operation of the shutdown cooling system to assure continued heat removal. That is, the procedures identified in the long term cooling plan do not require evea+ual initiation of the shutdown cooling system although concitions will exist wherein this system can be operated. Because it is the intent of this report to present the most limiting condition, the analysis presented aerein addressed only the RCS cooldown with the PORV's.

4.0 CONCLUSION

The post-LOCA long term cooling plan demonstrates that the core temperature can be maintained at acceptably low values and decay heat can be removed for an indefinite period of time following a LOCA. This objective is accomplished by initiating simultaneous hot and cold leg injection to .001 and flush the reactoe vessel for the large break LOCA and opening the PORV's to cooldown and depres-surize the RCS for the small break LOCA. The performance analysis results also demonstrate that there is a large range of intermediate break sizes wherein either the small break or large break procedures satisfy the long term cooling performance objectives. Fu rth ermo re ,

the analysis demonstrates that even under the most limiting of conditions, wherein the PORV's arc used to cool the RCS, acceptable ERCS performance is assured during the long te m.

519 337 3

FIG:JRE 1 LO. . r.e T t .w.. ,i enGL.r mu ao c ee- i

c F0oa ~ ' ' " '

n6el

' E". 4' .l'.J J 'l' 'L 'a e '"I 1 '1 ' i 4' "1'0 L" L i ' J . 6 asat FC5 Iar i - -

c.9 L .' *.wLe L ri<i LOCA SIAS HPSI -iD LPSI s-,,,-

r..<,...,S

. nLitni tt (COLD SIDE)

AUTO

/m vuA.

ccu m .n).c.L U~ser a

ga, . . - - . ,..rio

- t, ,eni;

,, . - - t=,17 u..

.O '. U A L u

'( ~- ^

C i .e'. .D. LM i t' "'u.>v i*:..: cs G s.= = u , ,c.(J

.,.m YES p > 7co I;0 L-I  :=

f s' i  % .*

- . s W 4J

- y 5h

• f nL i 26 ; nF. "L..

.** - -

• i geeq g - 3 <

. .'[u -*lU $L l.-- C '.) ) 4l .,' (;)

a r, 7,:s. ., -, q-),

..q ,u ..,,. e ;

0 7 . yn y 6g ,f 9 9r= % 99

% s [4

.31.1 4 /* i s t fi f' (* JLf . . s C L l . ,i t e er , c- s. ,,

.s W / .

C 9 *94' i % P'*

b-- JI1--. *J cuw: - 3n i 7 . .. ~

. . ) . ,, 7, , 7 .

4'.s~. 4.,/*

b .s ( '[

.u. 1_.--

.- E $.\ .

f^_

,) (

'L

..c, , - . . ___ . , . . .-

..) .c.7.__.,

. . < . ;.. 'm - .. , ; ; i,._.. . . ,

iur.

^ <* i. _ l- . . -s.. ---

-. c- -

. .- .c 6 . .u, i is c= = c , ,r-j - , - - , ,.

..,,-,e w,39

.*'..s- 6 e i -,e .

o e em -

s s o -u

. e w . s g n'-c.-

. -. , . - . . _ - , .~. .

Q~ -,

519 S38

FIGURE 2 FT CALHOL::l llc PEK T !A:,'CE O!/1LUAT10i!

TlHE 10 !!EFILL T!iE 1;. S vs EREA!: AREA OPEll l'ORV'S AT 3 liCURS 60 -

50 -

11 0 en

$5 u3

r

_J 30 -

!b e

(.n e 20 -

10 - -

7 !R S , PCRV CPEliED 0

0 .005 .010 .015 .020 BREAK AREA, F7 2 519 339

FIGURE 3 FT. CA!.l:0'J.'l LTC PERFC!..Ai'CE CVALUATI0i!

BORIC ACID C0i!CLi!IRATIL. !il READOR VESSEL OPEi! PCRV'S AT 3 liRS.

100 -

80 -

SOLUBILITY LIMIT AT 323 Fg 22 2 '

3 60 -

tE w

S e

o 40 -

< RCS REFILLS 2  % _.

20 -

.015

/ .005 10

' '~ '

0 10 20 30 40 50 60 11ME AFTER BREAK, !!RS 519 340 11

FIGURE 4 FT. C6Ll!OL' LIC PLI:Fuis,i/u;CE EVALUAil0:1 RE/1CTOR C00i_l.:!T SA,: EM TEMPERai'J .E OPEil PCRV'S AT 3 iiouns 600 -

s M

E00

\ .

2

~ .00037 FT tu i00 4

\

t2 N ~

5 l2- .02 FT 2 S 300 -

E J

CD 8 '

m 200 -

E .

100 -

f I I I t I

0 10 20 30 40 50 60 TIME AFTER BREAK, HRS

FIGURE 5 FT CALHOUN LTC PERFORMANCE EVALUATION CORE F_JSHING FLOW DUE TO HOT SIDE INJECTION FOR A 9.8 F7 2 COLD LEG BREAK SIMULTANEOUS HOT SIDE / COLD SIDE E00 - INJECTICN FLCW INITIATED AT THREE FCURS POWER = 1448 i'IWT = 102% CF NOMINAL 500l l ECCS FLOW = 1 HPSI PUMP RCS TEMPERATURE = 228 op 400 -

E e

u3 - l s- s00 --

=

e.

__ HO T SIDE INJECTION 8

_; FLCW RATE u_

200 -

A NET CORE FLUSHING FLOW 100 -

Y CCRE EDIL-CFF RATE i ' ' I J O

0 5 10 15 20 25

-?

I . r_ i ci 7 c_.so r 7 . .e.s, e, x..

13 519 342

FIGURE 6 FT C!',Lil0Uii 1.TC PERF0ii,A:lCE EVALU/sil0:1 BORIC ACID CD: CE :I!: Ail 0:1 VS T!FiE lil IllE RE/',CIOR VESSEi.

rEAST = 12.00 WT7, 1,Ill WTZ BORIC ACID C0;;CE:JTRAT10l:S RWT =

ASSUIlED 111 T A!!:'S A:.D RCS : SIT = 1,lil WT%

RCS = 0,71 WTZ 35 , , i i

.c- ,0 r- n n 'u~

FLUSH SOLUBILITY LIMIT AT 20 PSIA -!

30 -

POWER = 1/018 MW(T) 25 - -- -

M ._

w -

2 o

~~ ~

y 20 -

e-CJ - :-COR E F LU S H=

hd r) GPM CO:,'5T A:

g 7, u

cg 15 -

-i E

u E

o i

' S IMULTA:,'EOUS CCLD/HO T S I DE 10 -

I NJ F C T I O:,' INITIATED AT 3 H0ut',S 5 -

Core Flush =

175 ';pm) -

I m

\,

/(Boil-off)

,r, (

0 0 5 10 15 20 25 mr '""

u 519 30

FIGURE 7 FC. CALHOUN LTL PtRFORMANCE EVALUATION RCS PRESSURE VS. TIME INITIATE SIMULTANEOUS liOT/ COLD SIDE IIJECTIC:: AT 3 !! CURS i i 1/10 0 -

i i 1200.-

~

N 1000'

\

\ -

800 J

\

i RCS REFILLS 8 ,

/ -

O d V -

0 600 -

\ \

s

\ yl 0.005 FT 2 400 -

' ~ 0.01 FT 2 200 -

N 0.02 F7 2

- 0.025 F7 2

' J I '

f 0 -

0 5 10 15 20 25 30

- TIME AFTER CREAK, HRS 1s 519 344'

FIGURE 8 FT. CALiiOUN LTC PERFORMAllCE EVALUATION OVERLAP OF ACCEPTABLE LTC PROCEDURES IN TERMS OF COLD LEr BREAK SIZE BREAK RCS PRESSURE SIZE, AT T=3 HOURS 2 pg13 FT r

SIMULTA:!EQUS 9.8 20 HOT LEG / COLD LEG 5 20 I:iJECTION COOLS CORE 2 20 a.ND FLUSHES ECRIC ACID 1 20 FRD1 VESSEL 0.5 20 0,030 229 q

0.025 276 0,020 344 PRESSURIZER FORys 0,015 445 RE":0VF DECAY HEAT 0,010 688 AND ALLOW liPSI FLCW t 0.005 1031 TO SUEC00L T;iE RCS '

0,0025 1055 A:iD FLUSH THE REACTOR 0.0010 1259 VESSEL 0,0005 1517 0.C0037 1331 519 345 16

FIGURE 9

~

FT, CAU!OUif I.TC PERF0lil/WCE EVALUATION RCS PRESSURE AT 3 HRS VS EREAK SIZE 1400

_ LARGE BREAK PROCEDURE FUNCTI0ilAL 1200 A

[

1000 -

5 a". -

800 W

B < DECIS10[1 Poli 1T ~ PRESSURE O

ce 600 -

O cc 400 -

~

t J V

00 -

SMALL b".EAK PROCEDURE FUNCTI0i!AL 0

0 .005 .01 .015 .02 .025 .03 BREAK AREA, FT 2 U 5]9 346

TABLE 1 MARGINS IN THE LONG TERM COOLING PLAN

. The boric acid will not precipitate before 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> post-LOCA in the absence of flushing. Simultaneous injection is initiated at 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> post-LOCA or 22 hours2.546296e-4 days <br />0.00611 hours <br />3.637566e-5 weeks <br />8.371e-6 months <br /> before precipitation will occur in the absence of flushing.

2 2

2. The range in break sizes, 0.005 ft to 0.02 ft , defines signifi-cant overlap wherein both the small and large break procedures apply.

3. The decision pressure of 700 psia at three hours post-LOCA has an associated allowable error of + 300 psi.

4. The operator need only make one decision; the decision at three nours pst-LOCA.

5. The operator need not make any decision before 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> post-LOCA.

6. The Long Term Cooling Plan does not require the availability of off-site power.

747 s '

519 13 o o

APPENDIX A MODEL USED FOR THE PRESSURIZER PCWER 'PERATED RELIEF "ALVES The post-LOCA Long hem Cooling evaluation model documented in CENPD-254 has been modified to include modeling of the pressurizer power operated relief valves (PORV's). The modification is summarized below.

a. An additional leak path was added :.o the CELDA code to model the PORV. The leak flow rate is calculated using the critical flow model described in Section A.3.6 in Appendix A of CENPD-254.

b. For conservatism, the discharge coefficient applied to the PORV, is defined as follows:

FD = 0.8 + 0.2 -Xvalve where:

F = discharge flow multiplier D

X valve = fluid quality exiting tne valve Use of this expressien for FD will result in a 20% reduction in the flow capacity through the PORV when liquid is expelled.

c. The enthalpy of the fluid exiting the RCS through the PORV is determined in the same manner as the methods presented in CENPD-254.

d. In computing the flushing flow for the purpose of calculating the boron concentration when the DORV is open, it is conservatively assumed that the core flow is equal to the liquid flow expelled through the PCRV.

519 348 19

MODIFICAT10ft SCHEDULE FOR

[0flG TERf1 C00LIrlG (BOR0ft PRECIPITATI0ft) 1979 1980 1981 Project Phase S 0 fl D J F M A M J J A S 0 fl D J F M A

1. Engineering (System Design, Equipaient Speci-fications,etc.)

2. Parts Procure-ment (Purchase Order, Fabrica-tion, and Delivery)

3. Construction ~~

(Si te Preparation, installation of new equipmer.t, hydro. , etc, )

Procurement for Safety Related Equipment

( )

15 Months Minimum L" m fl0TE : Every ef fort will be made to procure and install the necessary equipment during the 1981 refueling M outage, scheduled in March, 1931. Othemise, modifications will be performed during the 1982 E refueling outage. M en N

_t :. .s W 2