ML19257A513

Forwards Addl Response to 790821 Ltr,Per Joint Nrc/B&W Owners Group 790913 Meeting.Addresses Noncondensible Gas Discussion & Small Break & Power Operated Relief Valve stuck-open Discussion

ML19257A513
Person / Time
Site:	Davis Besse
Issue date:	12/28/1979
From:	Crouse R TOLEDO EDISON CO.
To:	Reid R, Reid R Office of Nuclear Reactor Regulation
References
TASK-2.K.3.30, TASK-TM 569, TAC-45817, NUDOCS 8001040535
Download: ML19257A513 (15)

Text

.

TOLEDO EDISON Docket No. 50-346 dce License No. NPF-3 m ai g39 3 2, Serial No. 569 December 28, 1979 Director of Nuclear Reactor Regulation Attention: Mr. Robert N. Reid, Chief Operating Reactors Branch No. 4 Division of Operating Reactors

• United States Nuclear Regulatory Commission Washington, D. C. 20555

Dear Mr. Reid:

This transmits additional responses to your letter of August 21, 1979 for Davis-Besse Nuclear Power Station, Unit 1, as defined in the joint NRC/B&W Owners Group meeting of September 13, 1979. Specifically the following items are addressed:

Attachment A - Noncondensible Cas Discussion - in response to item 3 of Attachment A to Enclosure 1 of your letter.

Attachment B - Small Break and PORV Stuck Open Discussion -

in response to item 2B of Attachment A to Enclosure 1 of your letter.

It is noted that these have been reviewed to be specifically applicable to the Davis-Besse Unit I design.

"ary truly yours, ffhrzu RPC:TJM: cts cc: Mr. Robert Capra Bulletins & Orders Task Force United States Nuclear Regulatory Cocmission Washington, D. C. 20555 kDYl 1685 031 essa

//

THE TCLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO, OHIO 43852 8 0 010 40 d3,

Docket tw . w-wu l

Am o -

License No. NPF-3

• - O i Serial No. 569

• w o . 3 . December 28, 1979 Attachment A.

Question 3 - Honcondensible Gases Regarding the presence of noncondensible gases within the reactor coolant system following a small break LOCA:

A. Provide the sources of noncondensible gases in the primary system.

B. Discuss the effect of noncondensible gases on:

(1) condensation heat transfer, (2) system pressure calculations and (3) natural circulation flow.

C. Describe any operator actions and/or emergency procedures

, necessary to preclude introduction'of sinnificant quantities '

of noncondensible gases into the primary 'ystem. s D. Describe' operator actions to be taken in the event of a significant accumulation of noncondensible gas;s in the primary system.

Resoonse A. Sources of Noncondensible Gases in the Primary System Table 1 lists the potential sources and amounts of noncondensible gases for a 177 fuel assembly plant. However, most of these gases would not be rele.ased for small break transients. Appendix K evaluations performed for the 177FA plants demonstrate that cladding temperatures remain low cnd no cladding rupture nor metal water reaction occur. Thus, these sources can be neglected. The core flooding tasks d only for breaks large enough to depressurize the RCSjscharce into Also, the the RCS steam generator (SG) is a heat sink only if primary system pressure is above that which corresponds to the sec,ondary system safety valve setpoint (% 1050 psia).

Therefore, gases present in the core flooding tank can be neglected in .

addressing the effect of noncondensibles. The only sources of noncondon-sibles which might separate in the RCS are the gases dissolved in the coolant, the gases in the pressurizer, gases in the makeup and borated water storage tank and gases released from an allowed 1% failed fuel in the core.

B. Effects of Noncondensible Gases on the Primary System Response followino a Small Break LOCA .

There are two possible ways in which the release of noncondensible gases in the primary system could interfere with the condensation heat transfer processes which occur in the steam generator during s, mall loss of coolant accidents. If noncondensible gases filled the U bend at the top of the hot 109, then water vapor would have to diffuse through the noncondensible gases before they could be condensed in the steam generator. This would be a very slow proces's and would effectively inhibi t natural circulation. Lesser amaunts of noncondensibles would reduce the heat transfer by condensation because the vapor would have to diffuse thitugh the noncondensibles to get to the condensate on the tubes.

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As discussed in response to Part A of this question, the

'only sources of noncondensibles which might separate in thr ?.CS are the gases dissolved in the coolant, the gasc.; in the pressurizer, gases in the makeup and borated water storage tank and gases released from an allowed 1% failed fuel in the core. Thus, the maximum amount of noncondensible gases in the system, assuming all gas comes out of solution, no noncondensibles are lost through the break flow, that there was one percent failed fuel, and the injection of 6.4 x 10 4 lbm from the makeup tank and BWST (typical of % 1500 sec of HPI),

would be:

Dissolved in coolant 563 scf In pressurizer 166 Fission gas 2 -

Fuel rod fill gas 11 MU tank 24 BWST 14 Total ,

780 scf 3

This gas would occupy a volume of 22.4 ft at a pressure of 1050 psia, the lowest pressure condition in the primary system for which condensation heat removal will occur. It should be noted that the assumed integrated injection flow does not have a significant effect on the total volume of noncondensibles which might be present in the primary system. Since the volume required to complMely fill the U-bend in the hot leg is 125 ft , the 3 noncondensible gases will not impede the flow of vapor to the steam generator.

The heat transfer during condensation is made up oV'the sensible heat trans-ferred through the diffusion layer and the latent heat released due to conden-sation of thq vapor reaching the interface (see Figure 1). The model of Colburn and Hougenlli gives the following equation for the heat transfer in the vapor phase:

4 = hg( gg - Tg j) + Kg Mg hfg (Pgg - Pgg ) (1) where 2 4 = condensation heat flux, btu /hr~ ft ~

hg = heat transfer coefficient for vapor layer, Btu /hr ft2 of Tgg = bulk temperature, OF Tgg = temperature of interface, O F I

• Kg = mass transfer coefficient, Mg = molecular weight, ibm /lb mole hfg = latent heat of vaporization, Btu /lbm lb Pgo = partial pressure of vapor at bulk conditions, Pgj = partial pressure of vapor at the interface, lb f D ft2 1685 033 Q

r <.373 Kg = 1.02 0 9* P - I) p/pam z RT s pD ,

2 D = diffusion coefficient, f t /hr z = height Ib ft f

R = gas constant,1545 lb mole O R T = absol'ute temperature at bulk conditions OR g = acceleration of gravity, ft/hr 2 p = density, lbm/f t 3 po = density at bulk conditions, lbm/ft 3 pi = density at interface cpnditions, lbm/ft3 ,

u = viscosity, lbm/hr ft pam = pai - gao in P#I pao pai = partial pressure of gas at interface, h pao = partial pressure of gas at bulk conditions, h

~

For the application to OTSG condensing heat transfer during small break tran-sients, the term hg(Tgo - Tgi) can conservatively be neglected since the vapor velocities would be very low. Thus,

& = Kg Mg hfg(Pgo - Pgi). (2) ,

The heat transfer with noncondensible gases present is obtained by iteration.

An interface temperature Tgj is assumed, which fixes Pgt, and the heat transfer across the liquid condensate film is computed from

& = hf (Tgj - Tg) (3)

• where 3', 1/4 P(Pf-P)9hfg f g k f hf = .943 Uf z(Igj-T)g .

of = density of fluid, lbm/ft3 pg = density of vapor, ibm /ft 3 kf = thermal conductivity of fluid, Btu /hr ft OF Tg = wall temperature, 'F A

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10f r D 'P D* n "

O k .

lhe partial pressure of the gas at the bulk conditions can be calculated from the nole fraction of noncondensible gases. When the heat flux con.puted from anuatinn 2 matches that computed by equation 3, the proper interface temperature i as been found.

The impact of noncondensibles on the condensation heat transfer process during l a small break was examined for the 0.04 ft2 and 0.01 ft2 cold leg breaks analy-

• zed for the 177-FA plants. TM breaks utilize the SG for heat removal for a significant portion of the transient. Hand calculations were performed, using l the theory presented above, to ascertain the effect of non-condensibles on the ,

transient. l t

The amunt of noncondensible gases, assuning that all gases come out of solu- i tien, would be 2.61 moles. The effect of these gases is to raise the pressure '

and primary temperature to obtain the same heat transfer. Assuming that the i noncondensibles accumulated only within the steam generator upper plenums and i the steam generator tubes, the system pressure increase, due to ncncondensibles,  ;

vould only be 25 osi, for a 0.04 ft2 break, and 40 psi, for a 0.01 ft2 break. .

It shculd be noted that this effect is predominantly due to the inclusion of *!

the partial pressure of the noncondensibles, which is 24 psi for the 0.04 ft2 l hreak and 34 psi for the 0.01 ft2 break, in the total system pressure. These ,

calculations represent the maximum impact as they were computed at the time -

of c.:ximum condensation heat flux for the respective cases.  ;

• s shm n, the influence of noncondensibles does not significantly effect the condensation heat transfer process. The estinates made are conservative in '

tnat they assumed all the gas is located in the steam generators (none is in the too of the reactor vessel or Dressurizer) and no cases escape through the t.r ea k . Thus, it is shown that the presence of noncondensible gases in the system considering the effect on condensation heat transfer, system pressure and natural circulation should not significantly affect the small break transient.

htions to Precl'ude Introduction of Noncondensible Gases into the P.ir.ary System introduction of significant quantities of noncondensible gases into the primary system following a small break LOCA is prevented if the core is not uncovered during a small break. The sma il break quidelines which have been developed by B&W, are designed to ,

prevent core uncovery by assuring continued ECC injection. Thus, t.he arount of loncondensibles which might separate in the RCS is small and would not significantly effect the small break transient (See Part B above).

D. Operator Actions During Accumulation of Noncondensible Gases in

. t,te Primary Systen A significant accumulation ^of rronromtens-tble gases within the primary system during a small break is not expected. This position is confirmed by small break transient predictions, using conservative Appendix K assumptions, which show that little core uncovery occurs.

(2,3,4) As a result of the small core uncovery fuel clad temperature excursions are limited to 1100f; .and, fuel clad failure or H2 gas format. ion due to metal water reaction' will not occur.

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Small amounts of noncondensible gases can be released into the primary system during a small break. For the break size range where noncondensible gases could have a detrimental effect (i.e., breaks where natural circulation is required for energy removal) the quantities of gases that are predicted to exist within the primary system are not significant. For larger quantities of noncondensible gases to exist, a core transient that is not predicted must occur. The probability for such an occurrence is believed to be small because of the detailed emergency procedures for post-LOCA conditions that have been developed and the extensive operator training that has been conducted in their use.

Emergency procedures have been developed to accommodate nonconden-sible gases, to maintain plant control, and to achieve a stable .

long term cool _ing condition. Provided below is a brief summary of plant control measures contained in present emergency procedures which will counteract the effects of noncondensible gases and additional guidance for operator action developed for an inadequate core cooling condition, which will be incorporated into emergency procedures in the near future. To upgrade the RCS venting and/or degassing capabilities, remote operated hot leg vents will be designed and installed by 1981. Small break-emergency procedures will also be revised a.t,that time to include use of the hot leg high point vents to aid the re-establish-ment of natural circulation and to vont noncondensible gases which '

may evolve during small break transient.

CURRENT PROCEDURAL ACTIONS During a small break, the principle effect of noncondensible gases is to minimize the performance of the steam generators during natural circulation (either single phase water flow- or reflux boiling). Table 2 lists the primary symptoms and the corresponding operator actions identified in current emergency procedures. As indicated in Table 2, a restart of the RC pumps (one per loop) is -

the optimum action. A return to forced circulation will aid in condensation of existing steam and removal of noncondensible cas (if present) within the hot leg piping. Noncondensible gases, originally within the loop pipinq, would then tend to be suspended within the coolant stream and collect within the upper regions of the reactor vessel (RV). A substantial quantity (s 1000 ft.3) of gas can be accommodated within the upper region of the RV; therefore, there is good assurance that natural circulation can be maintained if RC pump operation must be terminated. If the RC pumps cannot be started and/or no secondary side heat sink is available, the operator will utilize the PORV, HPI, Makeup Pumps and Startup feedwater pump for core cooling and RC pressure control until the RC pumps can be restarted and/or normal secondary cooling is re-established.

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D""D,*DlT os # J S N The above actions are suffic.ient to enable the operator to bring the unit to a stable, long term cooling condition based on expected plant performance using Appendix K evaluation methods. Although a large accumulation of noncondensible gases is not expected under these assumptions, the above actions are believed to be sufficient if the anticipated amounts of non-condensible gases are increased by an order of magnitude because of the larce volume available for gases in the upper head of the RV and the loss of noncondensible gases out the break.

Once stable long term cooling conditions are established, RCS venting and/or degassing procedures can be initiated. If the RC pump (s) are operative and pressurizer spray is available, the reactor coolant can be degassed within the pressurizer where the stean-gas space can be vented to the Quench Tank inside containment. If letdown is available, the reactor coolant can also be degassed utilizing the makeup tank. The reduction of the .

cmount of gases dissolved in the RC will encourage remaining gas pockets within the RCS to redissolve in the water. The operator can monitor the progress of dogassing activities via analysis of pressurizer fluid and/or letdown water samples.

SMALL JREAK - INADEQUATE CORE COOLING CONDITIONS An inadequate core cooling condition is not expected for B&W g 177 FA plants. However, guidelines which identify the symptoms and operator actions for several circumstances, including a small break, have been prepared by B&H. This information is discussed in detail in Reference 3.

The operator actions discussed in Reference 5 are aimed at restoration of core cooling (restart an RC pump) followed by an increased rate of plant cooldown and depressurization (via SG cooling and PORV operation) to acquire use of the high volumetric flow capability of the CFT and LPI system to maintain core cooling.

From a noncondensible gas standpoint, the actions accomplished the following: .,

1. Prevention: By initiating corrective action when cladding temperatures are below those for which metal water reaction is significant, gas accumulat4on is minimized. RC pump operation (if possible) to restore core cooling and to increase the plants cooldown/depressurization capability is the preferred action.

2. Venting: For the core to be inadequately cooled, the RCS must be in a highly void condition. Therefore, PORV operation in combination with the break should provide a vent mechanism for the noncondensible gas that do exist.

As discussed in the previeus section, normal venting and degassing procedures can also be undertaken once s. table long term cooling is established.

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REFERENCES

1. Colburn, A. P. and flougen, D. A. , " Design of Cooler Condensers for liixtures of Vapors with Noncondensing Gases", Ind. Ena.

Chem. 26(11), 1934

2. P. C. Jones, J. R. Biller, and B. M. Dunn, "ECCS Analysis of B&W's 177 FA Lowered Loop NSS", BAW-10103, Rev. 3, Babcock & Wilcox, J u l y , 19"

3. Letter from s. H. Tayl v.. B& to S. A. Varga, NRC, July 18, 1978

4. "Evaestion of T aasier,t Behavior and Small Reactor Coolant System Dreat:s in the li/ " A Assembly Plant", Volume 1, 2, and 3, Babcock &

Wilco.. May 7, 1979 . . . May 16, 1979.

5. R. B. Davis to B&W 177 Owners Group, "Small Break Operating Gui,delines", ,

November 7, 1979.

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- TA5LE 1 SOUFCF.S OF ECNCON;U S!fl.ES - 177 FA FIR;T Total a n 11abl ]" FAIIID } VEL ,

I t'IfAL-WATER REACTIO*3 Individual Individual Individual Individual Total cas Total Cas Total Total Cas Total Total Cas Volu:n Vclures thss  !!a nses Vol. Ind. Ces rucs tus<ca Vol. Ind. Cas 'tiss H-sres Sverce cas scf scf lb. Ib. nef Vol. ret th. Ib. ecf Vol sef 15. 15.

Lt.toived in reactor Hy&N2 563 H2 - 305 14 11 - I'#

2 coolant g2 - 158 N2 - I2* 3 Frc uurtter steam I12 I "2 136 H - 65 5.9 11 - 0.4 2

'Y*** Ng - 5.5 Ng - 11 Fressurizer water Hy&Ny 30 fl y - 20 0.91 11 - 0.11 2

'P*** N - 0.8 Ny - 10 2 Fission gases in Er & xe 1 86 Kr - 20 65.5 K r - 4. 8 1.9 Kr - 0.2 0.66 Kr - 0.05 1.9 . .

core le - 166 Xe - 60.7 Xe - 1.7 Ze - 0.61 Fuel roJ fill gas He & sore 1133 Ile - 1092 14.8 I!a - 11.5 11.3 Ile - 10.9 0.16 Ha - 0.12 11.3 N2 &02 N2 - 32 N2-28 N2 - 0.3 N2 - 0.02 02-9 02 - 0. 8 02 - 0.1 02 - 0.01 P:ctal water reaction Hy 416,500 - 2320 - 4165 - .* 3.2 -

(1002) 8:::23 1:U tank gas space H2 ' "2 726 H2 - 421 26.1 H2 - 2.3 H2 - 305 N2 - 23.8 .

3 t*J tank water space H2 ' "2 24 H2 - 16 0.71 H2 - 0.09 N2-8 N2 - 0.62 BWST Air (N2 1383 N2 - 902 121.2 N2 - 70.3

50) 2 02 - 481 02 - 50.9 p

CF tack gas space N2 26,248 - 2047 -

(two tanks)

CF tank water space H 964 -

75 -

g 2

(two tanks) g M suntions .

1. RCS contains 40 std. cc H2/Kg water & 20 std. cc N /Kg 2 water, with water volume = 10,690 f t at 583F and 2200 psia.

2. 'Fressurizer water contains 40 std. cc H /Kg 2 water & 20 std. cc N2/Kg water with Henry's Law relation between water space and steam space at 650F.

. *'ater

. volu=e = 825 ft3 and steam volume - 716 f t3

& 3. Fission gases based on inventory in core at 292 EFFD.

CO &. Fuct rod gas based on each rod containing 0.0375, geol Ite. 0.0011 gmol N2 and 0.00029 smol/02 .

W 5. Metal-water reaction based on 52,000 lb. Zr cladding.

6. MU t.uk values bascJ on taak containing 200 ft3 gas space and I.00 ft3 water space at 120F with the water containing 40 std. cc H2/Kg and 20 std.

C cc N 2 /K;; with Henry's Lae relationship betwecn cases in water and in gas space.

U EWST contains 450,000 Callons of water saturated with air, t.e.,15 std. cc N /Kg

7. 2 and 8 std. cc 0 /K8*

2 3

8. Each CF tank contains 1040 ft waterand370f[gasspacewith600pst C N2 at 120F with tienry's 1.aw relation between water and gas.

9. Values for 11 f atte3_ fuel based on Xe and Kr fis :lon product inventory acJ fuct rsd fill gas (!!e) in 12 of fuct rods being released to coolant.

10. Valws for 1% retal-witer reaction ba:,eJ on gases in Item 9 above and I'2 released f rom 12 of Zr cladding (520 lb.) reacting with coolant.

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s.

TABLE 2: Symptoms and Corrective Actions for a Loss of flatural Circulation During a Small Break (Current Procedures)

SYMPTOMS

1. Saturated coolant conditions

2. Increasing primary system pressure and temperature with stable or decreasing secondary pressure. -

CORRECTIVE ACTION

l. Maximize liPI (control HPI if a subcooled margin is re-established)

2. E,nsure secondary cooling (i .e'. , auxiliary feedwater available with proper steam generator level control), ,

3. Restore RCP flow (one per loop) when possible per the instructions below. If RC pumps cannot be operated and pressure is increasing go to Step 3.5.

3.1 If pressure is increasing, starting a pump is permissible at RC pressure greater than 1600 psig.

3.2 If reactor coolant system pressure exceeds steam generator secondary pressure by 600 psig or more " bump" one reactor coolant pump for a period of approximately 10 seconds (preferably in operable steam generator loop). Allow reactor coolant system pressure to stabilize. Continue cooldown.

If reactor coolant system pressure again exceeds secondary pressure by 600 psi, wait at least 15 minutes and repeat the pump " bump". Bump alternate pumps so that no pump is .

bumped more than once in an hour. This may be repeated, with an interval of 15 minutes, up to 5 times. After the fifth " bump", allow the reactor coolant pump to continue in

~

operation. -

3.3 If pressure has stabilized for greater than one hour, secondary pressure is less than 100 psig and primary pressure is greater than 250 psig, bump a pump, wait 30 minutes, and start an alternate pump.

3.4 If forced flow is established, continue plant cooldown at 100F/

hr. to achieve long term cooling with the LPI/DHR systems.

3.5 If a reactor coolant pump cannot be operated and reactor coolant system pressure reaches 2300 psig, open pressurizer PORV to reduce reactor coolant system pressure. Reclose PORV when RCS pressure falls to 100 psi above the secondary pressure. Repeat if necessary. If PORY is not operable, pressurizer safety valves will reliev overpressure.

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e 3.6 liaintain RC pressure as indicated in 3.5 if pressure increases.

Maintain this cooling mode until an RC pump is started or steam generator cooling is established.

3.7 If SG cooling is established, initiate plant cooldown at 100F/hr. to achieve long term cooling with the LPI/DHR systems. .

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FIGURE 1 T

L j =~cd DIFFUSION LAYEN

/ l p

/ Pgo

/ i j j g, _p 0

VAPOR AND j f l , NON-CONDENSIBLES

/ O21 L -T

} ,  !

/ pTgi

. / '

/(' T, l

/

/

/ # CONCENSATE

/ -

P = TOTAL PRESSURE P

PARTIAL PRESSURE OF GAS AT INTERFACE, Ibr/ft2 aj =

Pa = 2

, a PARTI AL PRESSURE OF GAS AT BULK CONDITl0NS,1bg/f t Pgj = 2 PARTIAL PRESSURE OF VAPOR AT' INTERFACE, Ibg/ft

=

Pgo PARTIAL PRESSURE OF VAPOR AT BULK CONDITIONS, Ibg/ft2' T, = WALL TEMPERATURE, F Tgj = TE!'PERATURE AT INTERFACE, *F

= BULK TEUPERATURE, Tgo F

REFERENCE:

1) COLBURN, A.P. AND HOUGEN, D.A., "DESICN OF COOLER CONDENSERS FOR MIXTURES OF YAPORS WITH NONCONDENSING GASES", IND. ENG. CHEM 26(11), 1934.

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ovv.sa ..v . au s,v License No. NPF-3 Serial No. 569

, December 28, 1979 Attachment B D

P*g *gM M &Ju SJu. 2_

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.t duestion23: Provide the reactor coolant system response to a stuck open PORV for the case of a small break which causes the reactor coolant system to pressurize to the PORV setpoint.

. i, Response

• The resultant system response for a case of.a small break which  !

causes the reactor coolant system to pressurize to the PORV setpoint {-

and result in a stuck open PORV can be qualitatively assessed based on previous analyses and is provided below. As is demonstrated .

the,small break op, crating guidelines which have been developed are

• adequate for control cf this transient.. +

Numerous small break calculations have been performed for the {3 operating 177 FA plants. These calculations are provided in .

References 1 through 6. As is demonstrated by these studies,  ;,

repressurization to the FORV following a small break is ppssible j only if the break is extremely small (<0.01 ft2) and if there is no feedwater available to the steam generators. For plants with a j,

i safety grade, redundant auxiliary feedwater system, sue.h as the Davis- .

Besse plant , the probability of a small break which pressurizes  :

to the PORV setpoint is considered extremely unlikely.. -

The system response of a very small break (<0.01 ft2) with a concurrent  :

loss of all feedwater is presented in Reference .4 .

• a>

The system will initially undergo a subcooled depressurization.  ;

During this period of the transient, the reactor trips, the pressurizer

• drains, and the initial SG inventory boils off. For these smaller -

sized breaks (<0.01 ft2), the SG initial inventory boils off prior .

to system depressurization to th,e ESFAS signal ~. Following the loss of the SG heat sink, the fluid *in the RCS increases in temperature ,. l, and becomes saturated. Since the volumetric flowrate out the ,,

break, following the establishment of saturation conditions in the ..

RCS, is less than the volumetric steam production caused by decay

• I!

heat removal, the RCS repressurizes the pressur'izer starts to  !'

refill. Thus, for these breaks, no ECCS equipment is automatically

~

actuated prior to system repressurization. .

l*

. System repressurization would continue until the PORV setpoint is '

reached if no operator action is taken to-prevent it. The earliest time that the PORV setpoint would be reached is >I 4 minutes, for a zero break case and % 20 minutes for the 0.01 ft break. It should be noted that actuation of the AFW system prior to these times would prevent opening of the PORV.

While analys'is of this break combination has not presently been performed, the present operator guidelines for small breaks were constructed to mitigate the consequences of such an event. The

~

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o'perator is instructed to maintain maximum HPI flow and're-establish feedwate.'

to the SG as soon as possible if AFW is not automatically initiated. Also, the guidelines require manual initiation of the startup feedwater pump upon loss of the SG heat sink. Should auxiliary feedwater continue to remain unavailable and the primary system pressure starts to increase, the operator is instructed to initiate the makeup system, open the PORV and leave it open in order to maintain the RCS pressure as low as possible and maximize the flows. These operator guidelines thus will minimize the consequences of a small break which repressurizes the RCS.

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References

1. BAW-10103A, Rev. 2, "ECCS Analysis of B&W's 177-FA Lowered-Loop NSS," July 1977.

2. Letter from J. H. Taylor to S. A. Varga of July 18, 1978, concerning 177 FA plants small break analysis.

3. BAW-10075A, Rev.1 "Multinode Analysis of Small Breaks for B&W's 177-Euel Assembly Nuclear Plants with Raised Loop Arrangement and Internals Vent Valves," March 1976.

4. Letter from J. H. Taylor to R. Mattson of May 'i,1979,

• " Evaluation of Transient Behavior and Small Reactoic Coolant System Breaks in the 177-Fuel Assembly Plant," Volume I,

• Section 6; and Volume III, Revision'1, by Toledo Edison letter dated May 22, 1979.

5. Letter from J. H. Taylor to R. J. Mattson of May 12, 1979, "Small Break in the Pressurizer (PORV) with No Auxiliary Feedwater and One HPI Pump."

6. Letter from R. B. Davis to B&W 177 Owners Group, Technical Subcommittee on TMI-2 Incident Related Tasks,

Subject:

Tasponses to IE Bulletin 79-05C Action Items, August 21, 1979.

s 1685 045