ML20052F166
| ML20052F166 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood, 05000000 |
| Issue date: | 05/05/1982 |
| From: | Tramm T COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| 4029N, NUDOCS 8205120188 | |
| Download: ML20052F166 (8) | |
Text
. - - _.
Commonwe:lth Edison
) one First National Plata. Chicago, Illinois C
1 O'
Address Reply to: Post Office BE767 1
Chicago, Illinois 60690 k
i j
May 5, 1982 i
J Mr. Harold R.
Denton, Director l
Of fice of Nuclear Reactor Regulation cg U.S. Nuclea r Regulatory Commission Washington, DC 20555 4
9 o
%,,h Y*.
4 1
Subject:
Byron Station Units 1 and 2 rM Braidwood Station Units 1 & 2 9j 4 ( );
l Boration o f Reactor Coolant Q
.(
System
'\\
v b,
t
)
NRC Docket Nos. 50-454, 50-455, D
[')'
l 50-456, 50-457
/
...J t
Dear Mr. Denton:
This is to provide information regarding boration of the j
Byron /Braidwood reactor coolant systems during an extended loss of 1
off-site power.
NRC review of this information should close Con firma to ry Issue 13 o f the Byron SER.
a
{
Attachment A to this letter explains the manner in which a typical Byron /Braidwood reactor can be brought to the cold shutdown condition without the use o f reactor coolant pumps, the normal charging and letdown paths and the excess letdown path.
Two methods i
are identified which will maintain the required shutdown margin j
during the reactor coolant system cooldown and depressurization.
i A summary of the attached explanation will be provided in i
response to FSAR question 212.154 in the next amendment.
Pleas e direct questions regarding this matter to this o ffice.
One signed original and fif teen copies of this letter are provided for your use.
i Very truly yours, Jt d ef.Aku~
T.R.
Tramm 4
Nuclea r Licensing Administrator a
2 00I j
1m V
3 i
4029N
//
1 8205120188 820505 PDR ADOCK 05000454 i
E PDR 1
ATTACHMENT A 4
i BORATION FOR COLD SHUTOOWN WITHOUT LETDOWN 4
A calculation was performed examining the feasiliby of reaching cold 0
shutdown (defined to be 200 F and atmospheric pressure) without letdown for a typical Byron /Braidwood unit.
The results show that the baron concentration as a function of time and temperature is suf ficient to maintain the core subcritical with the required shutdown margin.
i Initial Conditions l
i The plant is presumed to be operating at power with boron concentration Ci and xenon concentration Xi.
The reactor is tripped and brough to zero load hot standby condition (defined as g'
Tavg o f 5570, 2250 psia, and pressurizer liquid level at 25% o f span).
The most reactive control rod is presumed to stick during the trip.
After reaching zero load hot standby conditions, the normal and excess letdown lines are lost.
The operator must then proceed to cold shutdown via either o f two methods.
In the first method, all RCS depressurizations are accomplished oy opening the pressurizer power operated relie f valves.
termal pressurizer spray 1
is presumed to be unavailable because the reactor coolant pumps may i
not be operating.
Table 1 lists the equipment requrired.
Shutdown Procedure Initially, independent of the method used to reach cold shutdown, 4 wt.% boric acid from the boric storage tanks will be used to fill the pressurizer liquid level from 25% o f span to 95% o f span while i
the plant is held at zero load hot standby conditions.
This will provide sufficient boron to compensate for xenon decay at hot standby.
The 95% pressurizer level indication will ensure that the pressurizer is not water solid.
The pressurrizer pressure will be i
held constant at 2250 psia using manual control of pressuzier heaters and the reactor coolant termperature will be reduced from 0
j 557 F to 3500F by relying on natural circulation though steam generators.
At 3500F, the pressure will be reduced, using either i
o f the two depressurization methods, from 2250 psia to 415 psia.
The RHR system will then be used to reduce the temperature from-350 F to 2000F while maintaining a constant pressure of 415 0
psia.
At 200 F and 415 psia, the pressure will be reduced to atmospheric using the same method as used during the previous depressurization.
Depressurization with Spray The operator must select one of two methods for depressurization -
either via CVCS auxiliary spray or the PORV's.
If the CVCS auxili-i ary spray is to be used (Table 2 and Figure 1), the pressurizer l
liquid level at the beginning of the depressurization cycle (i.e.,
0 0
at 350 F and again at 200 F) should be as low as possible while still keeping the heaters covered.
This will minimize the mass o f
. saturated liquid in the pressurizer which will flash to steam as the pressurizer pressure is reduced.
It will also provide space in the pressurizer for accepting the spray water without " pegging" the pressurizer level indicator.
When cooling from 5570F to 3500F to 2000F, the operator first allows the coolant to contract to 25%
o f pressurizer level indication span, and thereafter adds 4 wt.%
ooric acid to maintain 25% o f span indication and increase boron concentration.
In this way, the pressurizer heaters will be kept covered and the operator will avoid a situation where there is too much liquid in the pressurizer without the ability to letdown.
Depressurization from 2250 psia to 415 psia at 3500F, and from 415 psia to atmospheric pressure a t 2000F, will be accomplished by spraying until pressurizer level indication increases to 95% o f span.
Depressurization with PORV's If the PORV's are to be used for depressurization (Table 3 and Figure 2), the pressurizer liquid level at the beginning of each depressurization cycle (i.e., a t 3500F and again a t 2000F) should be as high as possible to maximize the mass o f steam which can be discharged without covering the pressurizer heaters.
When cooling f rom 5570F to 3500F, the operator will maintain the pressurizer level at 95% of level indication span by adding 4 wt.%
boric acid, via some other method than spraying, to makeup for coolant contractions in the pres-surizer.
Oepressurization from 2250 psia to 415 psia at 3500F, and from 415 psia to atmospheric pre sure at 2000F, will be accomplished by opening one PORV, discharging steam and allowing the pressurizer liquid level to decrease.
4029N
TABLE 1 b
3
SUMMARY
OF SYSTEMS AND EQUIPMENT RE0UIRED FOR COLD SHUTDOWN B0 RATION WITHOUT LETDOWN Boric Acid Tank Boric Acid Transfer Pump l
Centrifugal Charging Pump I Charging Line Pressurizer Level Indication Pressurizer Heater CVCS Auxiliary Spray or Pressurizer Relief ~ Valve Residual Heat Removal Loop i
==
i w
<+-y-
---.r.-1.-
..,..,-_v_
,,___.mm_._y_,,
TABLE 2 b
)
i COLD SHUTDOWN VIA CVCS AUXILIARY SPRAY TIME RCS T BORON CONCENTRATION AVERAGE HOURS PPM op 0
557 Ci 3
557 536 +.923 C1 4
500 543 +.935 Ci 450 842 +.89 Ci 400 1072 +.857 Ci 9
350 1266 +.83 Ci 12 350 1581 +.77 Ci I
2 18 /37 200 1583 +.77 C1 I
2 24 /43 200 2125 +.693 Ci I
2-Train RHR Cooldown.
2 Single Train Cooldown.
m
r TABLE 3 b
)
COLD SHUTDOWN VIA PORV'S TIME RCS T BORON CONCENTRATION AVE N E HOURS ppg
.p 0
557 Ci I 3.0 557 536 + Ci 5.5 500 927 + Ci 7.5 450 1185 +.9 Ci 9.0 400 1389 +.87 C1 10.5 350 1159 +.84 C1 11.0 350 1617 +.87 C1 1
2 15.0 /36.0 200 1996 + 81 C1 l
2 16.0 /37.0 200 2029 +.824 Ci I 2-Train RHR Cooldown.
2 Single Train RHR Cooldown.
i l
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