ML18227B314

Letter Post Accident Operation of the Emergency Core Cooling System to Control Concentration of Boric Acid in the Reactor Vessel

ML18227B314
Person / Time
Site:	Turkey Point
Issue date:	04/30/1975
From:	Robert E. Uhrig Florida Power & Light Co
To:	Lear G Office of Nuclear Reactor Regulation
References
Download: ML18227B314 (10)

Text

NRC DISTRIBUTION FOR PART 50 DOCKET MATERIAL

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CONTROL NO:

FILE'ROM Florida Pwr 6 Light Co.

Miami, Flao TO:

George Lear 4-30-75 ORIG 3 Signed 5-5-75 CC OTHER DATE OF 'DOC DATE REC'D LTR TWX RPT OTHER SENT AEC PDR XXX SENT I.OCAL PDR CLASS UNCLASS PROP INFO DESCR IPTION:

INPUT NO CYS REC'D 3

ENCLOSURES:

DOCKET NO:

50-250/ 5i Ltr. ref. our ltr. of 3-t4-75, concerning

'MS trans the fol1'owing Post Accident Operation of The Emergency Core Cooling System To Control Concentration of Boric Acid fn the Reactor Vessel.o....

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3 cys. Encl. Rec'd).

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FLORIDA POWER 5 LIGHT COMPAN'r April 30, 1975 L-75-210 Mr. George Lear, Chief Operating Reactors Branch g3 Division of Reactor Licensing Office of Nuclear Reactor Regulation U.

S. Nuclear Regulatory Commission Washington, D.

C.

20555 Dear Mr. Lear TURKEY POINT UNIT NOS.

3 AND 4 DOCKET NOS.

50-250 AND 50-251 POST ACCIDENT OPERATION OF THE EMERGENCY CORE COOLING SYSTEM TO CONTROL CONCENTRATION OF BORIC ACID IN THE REACTOR VESSEL

's a result of additional work that has been accomplished since oux original response to your letter of March 14,

1975, regarding concentration of boric acid in the reactor vessel, we axe submitting the attached supplemental response.

The supplemental xesponse references the Westinghouse generic lettex CLC-NS-309 dated April 1, 1975, for a general description and analysis of the phenomena surrounding the potential pxoblem of boric acid concentration in the xeactor vessel.

The attachment further describes the differences between the Turkey Point Unit Nos.

3 and 4 and the 3 loop plant referenced in the generic letter and provides some added discussion of the Turkey Point units'pecific capability for long term core cooling following the rupture of either coolant system cold or hot leg pipe.

Vexy truly yours,

~y Robert E. Uhrig Vice Pxesident REU:HNP:tg Attachment cc; Mr, Norman C. Moseley Jack R.

Newman, Esquire HELPING BUILD FLORIDA

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TURKEY POXNT UNIT NOS.

3 AND 4 CONCENTRATXON OF BORIC ACID XN THE REACTOR VESSEL DURXNG LONG TERM CORE COOLING FOLLOWING A POSTULATED LOSS OF COOLANT ACCXDENT

'X.

Descri tion and Anal sis of the General Phenomena

.XX.

(See Westinghouse generic letter CLC-NS-309 dated April 1, 1975)

Significant Parameter Differences Between.Turkey Point and the Westin house Generic Anal sis The following table provides a comparison of the key parameters.

Significant Parameter Differences Between Turkey Point Unit Nos.

3 and 4 and the Westinghouse 3 Loop Plant Referenced in the Generic Anal sis Core Power (MWt)

,Total Sump Xnventory (ibm)

Xnitial ppm Boron in System Effective Vessel Volume (ft. )

3, Weight Percent Boric Acid in Vessel at 24 Hours Using (h -h.

.) where h.

.=h -80 g

inj inj f ibm Safety Injection Enthalpy (btu/ibm)

W Generic Report

'('3 Loo Plant) 2786 3.3 x 10 6 2000

'854 29 98 Turke Point 3

6 4

2200 3.0 x 10 6 2030 854 23*

93 Sensible Heat.

(h t-h.

~ )(btu/ibm) sat inj Decay Heat Energy Addition at 24 Hours (btu/sec)

,Safety Injection Flow Rate needed to keep core below saturated conditions at 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (ibm/sec) 82 14-, 520 178 8 "/. 2 11,450 131.5

• This is a conservative estimate obtained by using a ratio of the 2786 x 29 = 23.

. '2200

.The slightly higher initial concentration

.is offset by the smaller sump inventory for Turkey Point.

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~IXX.

Discussion of the Plant's Capability for Long Term Core Cooling Following a Rupture of Either the Reactor Coolant System (RCS)

Cold or Hot Le Pi in RCS Cold Le Pi e Rupture For the boric acid concentrating phenomena that occurs during the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following the rupture of an RCS cold leg

pipe, we wish to reference the Westinghouse generic letter.

As shown by the table contained in section XX of this report, the concentration (23%) that would be reached at time 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> in the Turkey Point reactor vessel is still well below the solubility

.limit for 212 F water.

At time 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after the accident, high head recirculation via the two'ot leg injection lines will be initiated.

Utilizing one low head safety injection pump and two high head S.

X. pumps (minimum safeguards) flow is established downward through the core and out, of the broken cold leg piping.

The flow of the liquid through the core and out of the break will result in

. termination of the concentrating effect.

As a result of the slight amount of steam that is still being generated, the con-centration of boric acid in the reactor vessel will approach a

value slightly greater'approximately 3%) than the concentration in the safety injection water rather than an equal concentration.

This slightly higher reactor vessel concentration will not present any problems to long term core cooling.

At about time 55 hours6.365741e-4 days <br />0.0153 hours <br />9.093915e-5 weeks <br />2.09275e-5 months <br /> after the accident, the flow from the hot leg will be sufficient to terminate boiling and all concentrating effects will also be terminated.

The concentration of boric acid in the reactor vessel will then become equal to'hat of the safety injection water.

B.

RCS Hot. Le Pi e Ru ture For the hot leg break there will initially be no concentrating effect since the safety injection water will flow into the cold leg, through the core and out of the broken hot leg.

At time 24

'hours hot leg safety injection flow will be initiated.

Assuming the worst. case (minimum safeguards and flow from one of the hot leg injection lines spills out of the break) a flow of approxi-mately 42 ibm/sec will be delivered to the vessel.

Nith this

.flow rate decay heat will generate a steaming rate of approximately 8 ibm/sec.

Xf we conservatively assume that this is the steaming rate that will exist for the remainder of the accident a mass balance around the reactor vessel shows that about 34 ibm/sec of liquid must exit the vessel through the break.

Taking credit for the mixing 'that will occur in the core as a result of the boiling action it can be seen from a mass balance on the boric acid that the boric acid concentration in the reactor vessel will approach

. a concentration equal to the ratio of the "liquid flow rate in" (S.

X. flow of 42 ibm/sec) to that of the "liquid flow rate out" (34 ibm/sec).

Therefore, the concentration in the core can be conservatively estimated to increase to a maximum of approximately 1.25 times the concentration of approximately 2000 ppm that. exists

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at time 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

Such a slight concentrating effect clearly poses no problem to maintaining long term core cooling.

As soon as the second train of the sa'fety injection system is available, cold leg injection (in addition to the hot leg injec-tion) will be initiated and this flow through the core and out of the broken hot leg will subcool the core and equalize the concentration of boric acid between the liquid in the reactor vessel and the safety injection water.

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