L-75-210, Submit Supplemental Response Re Post Accident Operation of Emergency Core Cooling System to Control Concentration of Boric Acid in the Reactor Vessel
| ML18227B026 | |
| 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 | |
| L-75-210 | |
| Download: ML18227B026 (8) | |
Text
NRC DISTRIBUTION FOR PART 50 DOCKET MATERIAL
~
ITEiVIPORARY FORM) ~
CONTROL NO;~iC.$
FILE F ROM Floxida Pwr & Light: Co.
Miami, Fla, DATE OF DOC 4-30-75 DATE R EC'D LTR TWX RPT 5-5-75 OTHER TO:
George Lear ORIG 3 Signed CC OTHER" SENT AEC PDR SENT I OCAL PDR xxx CLASS UNCLASS PROP INFO INPUT NO CYS REC'D 3
DOCKET NO:
50<<25 /251 DESC R I PTION:
Ltr. ref, our ltr. of 3-14-75, concerning ECCS trans the foll'owing.....,
ENCLOSURES:
Post Accident Operation of The Emergency Core Cooling System To Control'Concentration of Boric Acid gn the Reactor Vessel.os
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Cp April 30, 1975 L-75-210 Mr., George Lear, Chief Operating Reactors Branch
~f3 Division of Reactor Licensing Office of Nuclear Reactor Regulation U.
S. Nuclear Regulatory Commission Washington, D.
C.
20555
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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
'*'N THE REACTOR VESSEL
As a x'esult of additional work that has been accomplished since our original response to your letter of March 14,
- 1975, 4
J at @Qsv4tag t Ojlt Quilt ~ut 2vlt ol Doxie 4t LCJ J n t LlQ i QCk%
t ol VI'saeva
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we are submitting the attached supplemental response.
The supplemental response references the Westinghouse generic letter CLC-NS-309 dated April 1, 1975, for a general description and analysis of the phenomena surrounding the potential problem of boric acid concentration in the reactor 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.
Very truly yours,
/i~.
(/
gt!
Robert E.
Uhxig
., Vice President REU'HNP'tg Attachment cc; Mr. Norman C. Moseley Jack R.
Newman, Esquire HFLPING GUILD FLORIDA
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RILEY POXNT UNXT NOS.
3 A.
4 CONCENTI&TION Ol BORXC ACXD XN TIIE REACTOR VESSEL DURXNG LONG TERM CORE COOLXNG FOLLOWXNG A POSTULATED LOSS OF COOLANT ACCXDENT X.
Descri tion and Anal sis of t:he General Phenomena (See Westinghouse generic let:ter CLC-NS-309 dated April 1, 1975)
XX.
Significant: Parameter Differences Between.Turkey Point and the Westinghouse Generic Anal sis The followi.ng 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 btu (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 29 98 Turke Point 3
K 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 Xnjection 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 87.2 11 450 131.5
- This is a conservative estimate obt;ained by using a ratio of the 2200 core power x 29 = 23.
2786
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1 ~
The slightly higher initial concentration i.s offset by the smaller sump inventory. for Turkey Point.
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OC II
XXX.
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 Pioin RCS Cold Leg P'i 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 hot leg injection lines will be initiated.
Utilizing one low head safety injection pump and two high head S. I. pumps (minimum safeguards) flow is established downward through the'ore 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 3S) 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 wU.1 be suff'c'o.-.t 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'that of the safety injection water.
RCS Hot Le Pi e Ru ture For the hot leg'reak 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 conservai ively 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 abou" 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 vill 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
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 safety 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 hoi 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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