ML20059H599
| ML20059H599 | |
| Person / Time | |
|---|---|
| Site: | 05200002 |
| Issue date: | 11/03/1993 |
| From: | ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY, ASEA BROWN BOVERI, INC. |
| To: | |
| Shared Package | |
| ML20059H479 | List: |
| References | |
| PROC-931103-04, NUDOCS 9311100140 | |
| Download: ML20059H599 (134) | |
Text
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SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT RECOVERY GUIDELINE EMERGENCY OPERATIONS "
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SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT RECOVERY GUIDELINE
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EMERGENCY OPERATIONS ,
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Page GUIDELINES PURPOSE ;
Thir guideline provides operator actions which must be accomplished in the' event of a Loss of Coolant Accident (LOCA). The actions in this. guideline ~are' necessary to ensure that the plant is placed in a stable, safe condition. The goals of this guideline are to mitigate the effects of a LOCA, to isolate the break, and if this is not possible, to establish either long term core cooling l using the safety injection system or core cooling using the shutdown cooling. j system. This guideline achieves this goal while maintaining adequate core !
cooling and minimizing radiological releases to the environment. This guideline provides technical information to be used by utilities in developing !
a plant specific procedure. .l ENTRY CONDITIONS !
- 1. The Standard Post Trip Actions have been performed E !
l All of the following conditions exist l
- a. Event initiated from MODE 3 or MODE 4 f
- b. SIAS has NOT been blocked
- c. LTOP has NOT been initiated and -;
- 2. Plant conditions indicate that a loss of Coolant Accident has occurred. l Any one or more of the following may be present: f
- a. Pressurizer level low (for a break in the pressurizer, the. level i
may be high). j
- b. Safety injection system (SIS) actuated automatically. ;
- c. Increase in containment pressure, temperature, radiation, humidity and Holdup Volume level. ;
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- d. IRWST Temperature increasing j
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- f. RVLMS indicates head voiding
- g. Loss of subcooling i
- h. CIAS n ease in Nuclear Annex Radiation, Temperature, Humidity or Sump Level.
EXIT CONDITIONS r
- 1. The diagnosis of a Loss of Coolant Accident is not confirmed. j E
- 2. Any of the Loss of Coolant Accident Safety Function Status Check acceptance criteria are not satisfied.
E
- 3. The Loss of Coolant Accident E0G has accomplished its purpose by ,
satisfying ALL of the following:
- a. All Safety Function Status Check acceptance criteria are being
-i satisfied. ;
- b. Shutdown Cooling System Entry Conditions are satisfied, g the r break has been isolated, g the RCS is in long term core cooling. :
f
- c. An appropriate, approved procedure to implement exists or has been approved by the [ Plant Technical Support Center or the Plant Operations Review Committee]. ;
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SYSTEM 80 +" TITLE LOSS'0F COOLANT ACCIDENT '
RECOVERY GUIDELINE ,
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INSTRUCTIONS CONTINGENCY ACTIONS '!
- 1. Confirm diagnosis of Loss of 1. Rediaonose event and exit to Coolant Accident by: either appropriate Optimal
- a. verifying Safety Function Recovery Guideline or to the Status Check acceptance Functional Recovery Guideline. .;
criteria are satisfied, ,
, and
- b. referring to the Break '
Identification Chart (Figure 5-2), l and [
- c. sampling both steam generators ;
for activity. ,
I
- 2. If pressurizer pressure 2. Jf pressurizer pressure decreases i decreases to or below [1825 to or below [1825 psia] and an j psia], Then verify an SIAS is SIAS has NOT been initiated [
actuated. automatically, Then manually ;
initiate an SIAS. j i
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- - Step 'ontinuously A g l.Aw. l P
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GUIDELINES INSTRUCTIONS CONTINGENCY ACTIONS ,
- 3. Ensure maximum safety 3. If safety injection and charging injection and charging flow to flow NOT maximized, Then do the l the RCS by the following: following as necessary:
- a. start idle SI pumps and verify a. ensure electrical power to SIS flow in accordance with valves and pumps l Figure 5-3, b. ensure correct SIS valve and lineup,
- b. start charging pump if c. ensure operation of necessary necessary. auxiliary' systems.
- 4. If pressurizer pressure 4. Continue RCP operation.
decreases to less than [1400 psia) following a SIAS. t'an do either of the following:
- a. If RCS is subcooled then .
ensure two of four RCPs are [
tripped (in opt isite loops).
EE .i
- 5. Verify RCP operating limits 5. Trio the RCP(s) which do not are satisfied. satisfy RCP operating limits. ,
- 6. Record the time of day. 6.
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GUIDELINES INSTRUCTIONS CONTINGENCY ACTIONS
- 7. Attempt to isolate the LOCA by 7. 9 performing the following:
- a. verify letdown line is a. manually _ isolate letdown, ,
isolated,
- b. verify sample lines are b. manually isolate sample lines, isolated,
- c. Verify N0 leakage into CCW c. H RCS to CCW leak is evident, system by CCW radiation Then attempt to isolate CCW i monitor NOT alarming and no affected RCPs and trip abnormal increase in CCW surge affected operating RCPs.
tank level.
- d. verify rapid depressurization d. manually isolate rapid valves are closed depressurization valves. ]
e .- verify reactor coolant gas e. manually isolate reactor .j vent valves are closed coolant gas vent valves. l
- 8. Verify LOCA NOT occurring 8. -H LOCA occurring outside of outside of containment by the containment, Then do the ,
following: following: .
- a. nuclear annex radiation a. attempt to locate and isolate ;
temperature, humidity alarms leak, NOT alarming, b. isolate the nuclear annex
- b. no unexplained increase in ;
nuclear annex sump levels. !
- c. no unexplained increase in !
subsphere sump levels. l r
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- 9. H containment pressure is 9. Ensure normal containment .
greater than or equal to [2.7 equipment cooling / air psig] Then ensure the recirculation systems operating. l following:
- a. containment isolation is a. H containment isolation does actuated automatically from not occur automatically or all the ESF panel containment isolation valves j and are not in their accident
- b. all available containment positions, Then manually recirculation fans operating initiate containment isolation !
'F
[ plant specific method of' manual containment isolation insertion here].
t e
- 10. H containment pressure is 10. j greater than or equal to ,
[8.5 psig], Then do the following:
- a. ensure containment spray a. manually actuate containment actuation, spray ;
and b. ;
- b. ensure adequate containment temperature-pressure control by one'of the following:
i) all containment ;
recirculation fans and cooling units are operating ;
]
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- 10. (Continued)
- c. Take action to place external c. ;
hydrogen recombiners in service
system ventilation system
- e. verify subsphere building e. manually start subsphere :
ventilation system operating building ventilation system i
operating.
- 11. Jf containment spray system is 11. Continue containment spray operating and containment system operation pressure is less than [5.5 ,
psia), Then containment spray may be terminated. Upon termination the CSS must be 4 aligned and reset for ,
automatic operation [or manual restart] and the annulus ventilation system secured.
- 12. Place the hydrogen monitors in 12. l i
service i
- 13. Verify containment hydrogen 13. Operate hydrogen recombiners l concentration is less than until containment hydrogen !
[0.5%]. concentration is less than !
[0.5%]. !
i LOCA 8 ABB CE SYSTEM 80+" -!
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- 14. Monitor containment radiation 14. Operate CSS, as necessary ,
level and provide input to
[ Plant Technical Support j Center) for evaluating the impact of potential l environmental releases.
perform steps 16 through 36. Then perform steps 37 through !
55.
- 16. H the LOCA has NOT been 16.
' isolated, Then perform a rapid cooldown to SCS entry conditions at a rate within ;
I Technical Specification Limits by (listed in preferred order):
- a. H the condenser is available,
~!
Then cooldown using the steam bypass system, )
1r_
- b. H the condenser or steam f bypass system NOT available, Then cooldown using the atmospheric dump valves.
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INSTRUCTIONS CONTINGENCY ACTIONS
- 17. Maintain steam generator 17. !
levels in the normal band 7 throughout the cooldown using main, startup or emergency ,
feedwater. i
- 18. Ensure the available 18. [
g condensate inventory is -
i adequate per Figures 5-4 and ,
5-5. ;
- 19. When pressurizer level is 19. Continue to operate available greater than or equal to [2%), charging and SI pumps for !
Then ensure charging and maximum available flow.
letdown, and the SIS (unless SIS termination criteria met) ,
are being operated to maintain ;
pressurizer level [2 to 78%] 4
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- 20. Depressurize the RCS to s [450 20.
psia] by using the following:
- a. pressurizer spray.
E
- b. control of charging and letdown.
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- c. operating / throttling SI pumps or -;
- d. " sing reactor coolant gas vent :
system.
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TITLE j SYSTEM 80 +" LOSS OF COOLANT ACCIDENT REC 0VERY GUIDELINE :
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- 21. Maintain RCS pressure within *21. If RCS subcooling greater than the Post Accident P-T limits P-T limits or cooldown rate l of Figure 5-1. greater than [100*F/Hr.], Then do the following as appropriate:
- a. stop the cooldown
- b. depressurize the plant using rum >r v.jul G<d WM hb# main or auxiliary spray or reactor coolant gas vent
-system to restore and maintain :
pressurizer pressure within the Post Accident P-T limits of Figure 5-1.
- c. attempt to maintain the plant in a stable pressure-temper-ature configuration or continue to cooldown within 1 the limits of Figure 5-1.
- d. If overpressurization due to :
SI/ charging flow, Then -
throttle or secure flow (refer .
to step 27 and manually !
control letdown to restore and maintain pressurizer pressure within the limits of Figure
. 5-1.
LOCA 11' ABB CE SYSTEM 80+ 4 I
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SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT REC 0VERY GUIDELINE EMERGENCY OPERATIONS "
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l INSTRUCTIONS CONTINGENCY ACTIONS 1
- 22. J,f. RCPs are NOT operating, 22.
Then evaluate the need and de-sirability of restarting RCPs.
Consider the following:
- a. adequacy of RCS and core heat a. H RCP operation NOT desired, removal using natural circu- Then go to step 25.
lation, o_r
- b. existing RCS pressure and tem- b. H at least one RCP is oper-peratures, ating in each loop, then go to
- c. the need for main pressurizer step 27. i spray capability,
- d. the duration of CCW inter- ,
E uption to RCPs,
- e. RCP seal staging pressures and ,
temperatures. .
- 23. Determine whether RCP restart 23. Go to step 25 criteria are met by ALL of the following:
- a. electrical power is available t to the RCP's
]
ting, and there are no high {
temperature alarms on the ;j selected RCPs, !
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- 23. (Continued)
- c. at least one steam generator ,
is available for removing heat from the RCS (ability for feed and steam flow), ,
- d. pressurizer level is greater .,
than [33%) and not decreasing,
- f. [other criteria satisfied per RCP operating instructions).
- 24. If RCP restart desired and 24. Go to step 25.
restart criteria satisfied, Then do the following:
- a. start one RCP in each loop, i
- c. operate charging (and SI) pumps until pressurizer level ,
greater than [R %)
- 4 ~/,
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- 25. H no RCPs are operating, Then 25. Ensure proper control of steam verify natural circulation generator steaming and feeding flow in at least one loop by (refer to steps 16 and 17) and ALL of the following: RCS inventory and pressure
- a. loop AT(T n - T,) less than nor-control (refer to steps-19 and mal full power aT, 20).
- b. hot and cold leg temperatures 7 constant or decreasing,
- c. RCS subcooled based on repre- ;
sentative CET temperature, j
- d. no abnormal difference
[ greater than 10*F] between T g i RTDs and representative CET f temperature. -$
- 26. H no RCPs are operating and 26. ,
single-phase natural circu- ,
lation can NOT be maintained, ,
then flow through the break j and two-phase natural circu-lation can maintain the heat i removal process. The operator should ensure the following: .l
- a. SIS flow per Figure 5-3, i and ,
- b. proper steaming and feeding of ,
the SG (refer to steps 16 and 17),
and LOCA 14 ABB CE SYSTEM 80+"-
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- 26. (Continued) ,
- c. representative CET temperature i is less than superheated. i
Then they may be throttled or stopped, one pump at a time, e if All of the following are i
satisfied-I
- b. pressurizer level is greater l than [33%] and not decreasing, I
- c. at least one steam generator f is available for removing heat d from the RCS (ability for feed f and steam flow),
- d. the RVLMS indicates a minimum {
level at the top of the hot leg nozzles. l t
- 28. If the criteria of-step 27 28. l cannot be maintaine'd after SI j pumps throttled or stopped, 'I Then appropriate SI pumps must be restarted and full SIS flow !
restored.' ]
= o_e , ________ __-____ _.____.____ ,r w ev 1 -
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- 29. Monitor In-containment 29. Maintain IRWST level by Refueling Water Storage Tank replenishment from available b
(IRWST) level and verify sources as necessary, reactor cavity sump level or ;
Holdup volume Tank (HVT) increases as IRWST level decreases.
! 30. Bypass or lower the automatic 30.
5 initiation setpoint of [MSIS) .,
as the cooldown and ;
depressurization proceed. j
- 31. When pressurizer pressure 31.
reaches [740 psia] Then reduce safety injection tank pressure to [300 psia]. ,
i f
- 32. When pressurizer pressure 32.
reaches [445 psia), Then !
isolate, vent or drain the safety injection tanks (SITS). ,
- 33. Initiate low temperature 33. .
overpressurization protection at T, [259'] .
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- 34. H SI throttle stop criteria 34. :
of step 27 are met, Then go to Step 36.
- 35. At [2-4 hours] after start of 35. !
LOCA, H at least one steam t generator is available for RCS heat removal, Then do the following:
- a. establish simultaneous hot leg ,
and direct vessel injection j (unless SCS operation can be
^
established before the [4 hour] time limit), ;
and !
- b. maintain steam generator heat i removal and continue RCS ;
cooldown (refer to steps 16 l and 17). ,
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SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT REC 0VERY GUIDELINE .
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- 36. When the following SCS entry 36. If SCS entry conditions can.
- conditions are established: NOT be established, then do j the following as appropriate:
- a. pressurizer level > [33%) and a. maintain natural circulation -l constant or increasing, (refer to steps 25 and 26),
- b. RCS subcooled, b. maintain simultaneous hot and
~
- c. RCSpressuresh50 psia direct vessel injection if ;
- d. RCS aT s [400*F], .necessary (Refer to step 35),
plant specific limits surize and voiding is sus-pected, Then monitor for voids Then exit this guideline and by the following indications, initiate SCS operation per parameter changes,'or trends:
[ operating instruction]. Include 1) letdown flow greater- l any special precautions or than charging flow, .
procedure modifications from the ii) pressurizer level in-Plant Technical Support Center or creasing significantly-Plant Operations Review Committee, more than expected f while operating pres- !
surizer spray iii) the RVLMS indicates j that voiding is present [.
in the reactor vessel, [
iv) HJTC unheated thermo- .
couple temperature'in-dicates saturated con- i ditions in the reactor .
vessel upper head, .;
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GUIDELINES INSTRUCTIONS CONTINGENCY ACTIONS l i
- 36. (Continued) d. Jf voiding inhibits RCS de- I pressurization to SCS entry ,
pressure, Then attempt to eliminate the voiding by i) verify letdown is iso-lated, and
- 11) stop the depres-surization -
and iii) pressurize and depres- !
surize the RCS within the limits of Figure 5-1 by operating pres- l surizer heaters and j spray or SI and the charging pump. Monitor ,
pressurizer level and the IWLMS for trending ,
of RCS inventory.- i
- f. Jf depressurization of the RCS to the SCS entry pressure is- i still not possible, and void- :
ing is suspected to exist in
.the steam generator tubes, i Then attempt to eliminate the. ;
voiding by: l LOCA 19 ABB CE SYSTEM 80+"
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SYSTEM 80+" l TITLE LOSS OF COOLANT ACCIDENT. i REC 0VERY GUIDELINE EMERGENCY OPERATIONS "^"
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- 36. (Continued) i) cool the suspected steam generator (by steaming and/or ;
blowdown, and feeding) l to condense the stean generator tube void, t and i ii) monitor pressurizer !
level for trending RCS ,
inventory.
- g. If depressurization of th-e RCS to the SCS entry pressure is still not possible, t!Le.n ;
attempt to eliminate the voiding by:
i) operate the pressurizer vent.or the reactor coolant gas vent to -
clear trapped }
non-condensible gases.
and ii) monitor pressurizer level and/or the RVLMS :
for trending of RCS inventory.
- 37. If LOCA is isolated, Then 37.
perform steps 38 though 55.
SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT
. RECOVERY GUIDELINE EMERGENCY OPERATIONS 2'- ^^"
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- 38. H SI pumps are operating, 38. Continue SI pump operation, j Then they may be throttled or stopped, one pump at a time, ,
if ALL of the following are ,
satisfied: ..
- b. pressurizer level is greater ;
than [33%] and not decreasing,
- c. at least one steam generator ,
is available for removing heat from the RCS (ability for feed ,
and steam flow),
- d. the RVLMS indicates a minimum -
level at the top of the hot !
leg nozzles. ,
- 39. H criteria of step 38 cannot 39. j be maintained after SI pumps ;
throttled or stopped, Then ap- l propriate SI pumps mus't be re- ]
started and full SIS flow , ;
restored.
- 40. Control charging if available 40. H RCS subcooling can NOT be and letdown, and SI (unless maintained, Then [78%] may be ,
SIS termination criteria met) exceeded to restore RCS sub-to restore and maintain pres- cooling.
surizer level [2% to 78%).
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- 41. Depressurize the RCS to s [450 41. ;
psia] by using the following: e
- a. pressurizer spray,
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- b. control of charging and letdown ,
E
.[
- c. operating / throttling SI. pumps. !
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- d. operating reactor coolant gas .
vent system j
- 42. Maintain pressurizer pressure 42. RCS subcooling greater than .l within the Post Accident P-T P-T limits or cooldown rate !
limits of Figure 5-1 by greater than [100*F/Hr], Then 1!
do the following as appropriate: .
- a. stop the cooldown - i depressurize the plant using R
- b. f c,id M Ve.d fysb e $ main or auxiliary spray if- ;
available or use the reactor 'j coolant gas vent system to re- -
- 1. store and maintain pressurizer. !
l pressure within the Post Acci - j dent P-T limits of Figure'5-1. l
- c. attempt to maintain the plant f in a stable pressure-temper- j ature configuration or con- j inue to cooldown within the i limits-of Figure 5-1.
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- 42. (Continued) d. Jf overpressurization.due to SI/ charging flow, Then I throttle or secure flow (refer l to step 38) and manually f control letdown to restore and l maintain pressurizer pressure .
within the limits of Figure [
5-1.
- i
- 43. Maintain steam generator 43.
levels in the normal band j using main, startup or ,
emergency feedwater. !
- 44. Ensure the available 44. ;
condensate inventory is l adequate per Figures 5-4 and f 5-5. i
- 45. Borate the RCS to maintain 45.
shutdown margin in accordance with Technical Specifications. ;
and !
Prevent boron dilution by l pressurizer outsurge by the ,
following (listed in preferred f order): ;
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- 45. (Continued) !
- a. borate the entire RCS (in- f luding the mass in the pres-surizer) to cold shutdown con-ditions.
E
- b. use main or auxiliary spray if available to increase and maintain pressurizer boron -
concentration within [50 ppm]
- 46. Perform a controlled cooldown 46. !
in accordance with Technical .
Specifications by (listed in preferred order): ;
- a. steam bypass system E
- b. atmospheric dump valves. ,
- 47. If RCPs are NOT operating, 47. !
Then evaluate the need and j desirability of restarting l RCPs. Consider the following:
- a. adequacy of RCS and core heat a. If RCP operation NOT desired, f removal using natural Then go to step 50. j circulation E
temperatures, operating in each loop, Then !
- c. the need for main pressurizer go to step 51. I l
spray capability, l LOCA 24 ABB CE SYSTEN 80+*
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- 47. (Continued) ;
- e. RCP seal staging pressures and temperatures. ;
- 48. Determine whether RCP restart 48. Go to step 50.
criteria are met by ALL of the !
following: :
- a. electrical power is available l to the RCP bus, -
- b. RCP auxiliaries.(CCW) to maintain seal cooling, bearing, and motor cooling are operating, and there are no high temperature alarms on the :
selected RCPs,
- c. at least one steam generator is available for removing heat from the RCS (ability for feed j and steam flow), .;
- d. pressurizer level is greater ,
than [33%) and not decreasing, !
(Figure 5-1),
- f. [other criteria satisfied per ]'
RCP operating instructions].
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- 49. H RCP restart desired and 41 restart criteria satisfied, l Then do the following.
- a. start. one RCP in each loop, ~l
- b. ensure proper RCP operation by )
monitoring RCP amperage and NPSH, !
- c. operate charging (and SI) pumps until pressurizer level [
t
+1 T/-
greater than [33%)'(and SI j termination criteria met.
Refer to step 38). ;
verify natural circulation inventory and pressure control ,
flow in at least' one loop by (refer to steps 40 and 41) and ALL of the following: steam generator feeding and
- a. loop AT(in - T,) less than steaming (refer to steps 43 normal full power 4T, and 46). !
- b. hot and cold leg temperatures constant or decreasing, ,
- d. no abnormal difference ;
[ greater than 10*F] between Tg RTDs and renresentative CET temperature. i LOCA 26 ABB CE SYSTEM 80+*
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REC 0VERY GUIDELINE EMERGENCY OPERATIONS 27 of
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- 51. Bypass or lower the automatic 5I.
initiation setpoints of MSIS, and SIAS as the cooldown and depressurization proceed.
- 52. When pressurizer pressure 52.
reaches [740 psia] Then reduce safety injection tank pressure to [300 psia].
- S3. When pressurizer pressure 53.
reaches [445 psia), Then isolate, vent or drain the safety injection tanks (SITS).
- 54. Initiate low temperature 54.
overpressurization protection (LTOP) at T, < [259'F].
7 p t 1
'*' 55. s,,en the following SCS entry 55. Jf the RCS fails to de-conditions are established: pressurize, Then a void should be suspected.
- a. pressurizer level > [33%] and a. voiding in the RCS may be.in-constant or increasing. dicated by any of the follow-
- b. RCS subcooled ing indications, parameter
- c. RCS pressure s [450 psia] changes, or trends:
- d. RCS gT 's [400*F], i) letdown flow greater
- e. RCS activity level within than . charging flow, plant specific limits LOCA 27 ABB CE SYSTEM 80+'-
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GUIDELINES INSTRUCTIONS CONTINGENCY ACTIONS i
- 55. (Continued) ii) pressurizer level in-I creasing significantly.
more than expected ,
while operating pres-surizer spray. ,
~iii) the RVLMS indicates 'I that voiding is present in the reactor vessel-iv) HJTC unheated thermo-couple temperature in-dicates saturated con- ,
ditions in the reactor vessel upper head,
'/) [et % r Sdiceti a in:
-scrt here]
- b. If voiding inhibits RCS de-pressurization to SCS entry- >
pressure, Then attempt to eliminate the voiding by:
- 1) verify letdown is isolated, and ii) stop the depres-surization, j and LOCA -28 ABB CE SYSTEM 80+"
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GUIDELINES INSTRUCTIONS CONTINGENCY ACTIONS
~
- 55. (Continued) iii) pressurize and de-pressurize the RCS within the limits of Figure 5-1 by operating pressurizer heaters and. !
spray or SI and charg-ing pumps. Monitor pressurizer level and the RVLMS for trending of RCS inventory.
- c. If depressurization of the RCS to the SCS entry pressure is still not possible, and void-ing is suspected to exist in the steam generator tubes, ;
Then attempt to eliminate the voiding by:
i) cool the suspected steam generator (by ,
steaming and/or blow-down, and feeding) to condense the steam gen-erator tube void, and ii) monitor pressurizer ;
level for trending RCS i inventory. !
l l
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. i RECOVERY GUIDELINE i
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GUIDELINES -
INSTRUCTIONS CONTINGENCY ACTIONS -
a
- d. If depressurization of the RCS to the SCS entry pressure is ;
still not possible, Then at-l tempt to eliminate the voiding !
r by:
i) operate the pressurizer ;
vent or the reactor I coolant gas vent to clear trapped non-condensible gases, and ii) . monitor pressurizer level and/or the RVLMS '
for trending of RCS j go.y 4lps (Mv- inventory.
insWoc% s4 cps Then exit this guideline and initiate SCS operation per ,
operating instruction. Include any special precautions or procedure modifications from the Plant Technical Support Center or
< Plant Operations Review Committee. ;
)
SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT REC 0VERY GUIDELINE ,
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j, GUIDELINES I
The LOCA Guideline has accomplished its purpose if the plant is in a condition i
where all of the Safety Function Status Check acceptance criteria are being satisfied, and the RCS is either in long term core cooling (i.e., ,
recirculation through the SIS), the break has been isolated, or SCS entry '
conditions are satisfied. Further recovery actions must be identified by the
[ Plant Technical Support Center].
END i
i L.
7 l
L l
l SYSTEM 80+" TITLE LOSS OF COOLANT ACCIDENT !
RECOVERY GUIDELINE l
EMERGENCY OPERATIONS 52 Page of
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GUIDELINES SUPPLEMENTARY INFORMATION This section contains items which should be considered when implementing E0Gs and preparing plant specific E0Ps. The items should be implemented as precau-tions, cautions, notes, or in the E0P training program.
I. During all phases of the cooldown, monitor RCS temperature and pressure to avoid exceeding a maximum cooldown rate greater than Technical . ,
Specification Limitations.
i
- 2. Do not place systems in " manual" unless misoperation in " automatic" is apparent. Systems placed in " manual" must be checked frequently to -f ensure proper operation.
- 3. All available indications should be used to aid in the evaluation of plant conditions since the accident may cause irregularities in a particular instrument reading. Instrument readings must be corroborated when one or more confirmatory indications are available (e.g., during rapid depressurization the indicated level in the pressurizer may be too high).
- 4. If there is a high radioactivity level in the reactor coolant system, ,
then circulation of this fluid through the SCS or the CVCS may result in high area radioactivity readings in the subsphere or nuclear annex. The ,
activity level of the RCS should be determined prior to initiating SCS or letdown flow. ;
- 5. For small breaks in the RCS where the steam generators are important for l heat removal, one steam generator must be used for this purpose even if primary to secondary leaks are detected. Use the unaffected steam .;
generator, or the least affected steam generator, if both have primary to secondary leaks. ;
1' i
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SYSTEM 80 +" TITLE TOSS OF COOLANT ACCIDENT:
RECOVERY GUIDELINE EMERGENCY. OPERATIONS ^^"
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- 6. If operation of the containment spray system is necessary,_the oiinulus ventilation should be operated in conjunction with containment spray system.
- 7. If the initial cooldown rate exceeds Technical Specification Limits, then there may be a potential for pressurized thermal shock (PTS) of the reactor vessel. Post Accident Pressure / Temperature Limits should be maintained within the limits of Figure 5-1.
- 8. Minimize the number of auxiliary spray cycles whenever the temperature differential between the spray water and the pressurizer is greater than
[200*F] in order to minimize the increase in the spray nozzle thermal stress accumulation factor.
- 9. High containment temperature conditions may adversely impact the accuracy of instruments whose transmitters are located inside containment (e.g., pressurizer level and pressure, steam generator pressure and level, RCS loop RTDs) and may impact the continued availability of equipment located in centainment.
- 10. Verification of an RCS temperature response to a plant change during natural circulation cannot be accomplished until approximately 5 to 15 minutes following the action due to increased loop cycle times.
- 11. Solid water operation of the pressurizer should be avoided unless subcooling cannot be maintained in the RCS (Figure 5-1). If the RCS is solid, closely monitor any makeup or draining, and any system heatup or cooldown, to avoid any unfavorable rapid pressure excursions.
- 12. Hot leg and cold leg RTD temperature indication may be influenced by charging pump or SIS injection water temperatures. Use multiple RTD indicationsfand/orCETindications}fortemperaturewheninjectionis occurring.
)
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GUIDELINES
- 13. During the process of establishing entry conditions (RCS pressure and temperature) for SCS operation, it may be necessary to eliminate or reduce the size of the steam void in the reactor head. Ensure sufficient condensate availability to continue steam generator heat removal until the RCS pressure and temperature are reduced sufficiently, and SCS operation is accomplished.
- 14. When a void exists in the reactor vessel, and RCPs are not operating, the HJTC RVLMS provides an accurate indication of reactor vessel liquid inventory. When a void exists in the reactor vessel, and RCPs are operating, it is not possible to obtain an accurate reactor vessel liquid level indicatico Joe to the effect of the RCP induced pressure head on the HJTC RVLhS. Information concerning reactor vessel liquid inventory trending may still be discerned. However, the operator is cautioned not to rely solely on the HJTC RVLMS indication when RCPs are operating, and to use other means of level indication if available.
- 15. The operator should continuously monitor for the presence of RCS voiding and take steps to eliminate voiding any time voiding causes the heat removal, or inventory control, safety functions to begin to be threatened. Void elimination should be started soon enough to ensure heat removal and inventory control are not lost.
- 17. Small breaks located at the top of the pressurizer (e.g., stuck open safety relief valve) will result in flashing and steam production in the reactor vessel and hot legs. This steam will flow towards the break through the pressurizer surge line and oppose the draining of the pressurizer liquid. Thus, the liquid level in the pressurizor may increase or exhibit erratic behavior due to the competing steam-water LOCA 34 ABB CE SYSTEM 80+'
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l i
counter current flow condition. A similar behavior may be observed if the break is in the surge line. 1
- 18. Operation of any equipment in the containment building when containment hydrogen concentration 2[4%]should consider the possibility of hydrogen ignition. Consideration should oe given to the following:
- a. The importance to safety of equipment operation,
- b. The urgency of equipment operation,
- c. The use of alternative equipment located outside containment,
- d. The current hydrogen level and the anticipated time to reduce H2 5 [4%)
- 19. Measured containment hydrogen typically represents a value of hydrogen i in units of percent by volume of dry air. The measured hydrogen will typically ir.dicate higher than the actual containment hydrogen for a steam / air mixture inside containment. The indicated value should, ,
therefore, be corrected to account for any steam / air mixture inside .
containment.
shy Ow The loss of one-444a1 AC or DC tsa4n will not prevent the operators from
- 20. ;
performing the actions of this guideline. However, it is desirable to have a complete complement of electrical equipment to mitigate and to recover from an event. Therefore,theoperatorsshou{dat,temptto Del $f N3 l
restore electrical power to M-1 v4t+1 AC or ved DC,tr;9 ra g/s54i r. ( 0 :) .
- 21. SI pumps 1 and 2 are provided with low flow throttle valves installed in parallel to the SIAS actuated main discharge path valves. Low flow throt- valves .should be used when very low SI pump flow rates are !
required for contolling RCS pressure.
1 M5f#1 pc'&O hJc-ver.h lept w
- 7. 2 . N or Ju E C P re d .~ T , !
yp, ;n mdu ru l c rcokk m c d.nuwsQ Er Ur ^'l v,;n v ic s LOCA 35 ABis CE SYSTEM 80+"
SYSTEM 80+" TITLE LOSS-0F COOLANT ACCIDENT l RECOVERY GUIDELINE EMERGENCY-OPERATIONS Page " of
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GUIDELINES l
r l
~
t i
i i
Figure S-I TYPICAL POST ACCIDENT PRESSURE-TEMPERATURE LIMITS l (TO BE DEVELOPED DURING DETAILED ENGINEERING) i I
SYSTEM 80 + " TITLE LOSS-0F COOLANT ACCIDENT RECOVERY GUIDELINE.
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Figure 5-2 .
BREAK IDENTIFICATION CHART I
PRIMARY BREAK OR SECONDARY BREAK SUSPECTED ,
e mSERT SusCOOuNG WCREASWQ' QB *ONE OR BOTH SGs IND4CATE 1f PRES $URE LOW
- A. ,
YES NO o MAY SE SLOW W THE CASE OF SMALL BREAK LOCA IN .
I CONTAINMENT 1I EXCESS STEAM ,
DEMAND EVENT (ESDE)
If PRIMARY l SoE BREAK If II C'
B.
YES ONTAINMENT go YES CONTAINM No PRESSURE PRESSURE NCREASING INCREASING f
D.
YES N" mAM NO i
PUUfT lf If II II 1!
88 LOCA >
ESDE W ESDE OUTOF LOCA INSIDE g N CONTAINMENT CONTAWMENT CONTAMMDfT g 5
SYSTEM 80 + " TITLE LOSS OF COOLANT ACCIDENT' l REC 0VERY GUIDELINE EMERGENCY OPERATIONS Page ' of
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Figure 5-3 ;
TYPICAL ACCEPTABLE SIS FLOW VS RCS PRESSURE "'
t2 .;
INJECTION MODE .,
-t
?
= .;
mo --
i saea - ,
A N
~
'"'~~
- _ _\, _ _ _ _ =_= _ __
s
' e
. - - s N .
_ _ __ _ L. _ _ m m __ _. _ __ __
.\ \ ,
_a . _ - -
N N
- c g .- -
a .
s '* ~ \ \
t n
u na -
t- -
NN :
r s": N n
a N\ ;
g .w -
-- t
~ .
30 -
m-
\
iiijiiii.iiijiiiiiiiiiiiiiii
. ~ .. a ,a now (crs)
- V}>NoY"E'EYAiUs*c"nNE"ns"e rma*El:s%YunT*
"' 'N'E"$MdI"h EW ,
i.,1 = . = .w =a n. _'_"J/L*TJ' _ , - W r!"
f
.l SYSTEM 80+" TITLE LOSS OF COOLANT ACCIDENT-RECOVERY GUIDELINE i
EMEHGENCY OPERATIONS Page " of
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t Figure 5-4 ;
TYPICAL FEEDWATER CAPACITY VS TIME UNTIL SHUTDOWN COOLING REQUIRED 4lY 4 i i a i i i 4 i i 4 4 . e i sitM - -
r :
C C
D 5
w 3 10 _
A f Tire after trip when ric hones R
a 23i/ - 4 -
E Q
U 1
R 21/ - 16hans - .
D, G
A '
L t.515 -
't
?
?
I l*lE -
f Basis:
~
Secondary Pressure = 1100 psia
/[
/
Feedwater Temperature = 1200F
, / .
/
/ *"
3 10" -
i e i , e * , t i e ' t i i 0 2 4 6 8 ID 12 14 86 13 20 22 24 26 it 30 32 DG (hours) From start of feedwater i
i LOCA 39 ABB CE SYSTEM 80+* ,
~.
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GUIDELINES ;
t i
Figure 5-5 TYPICAL FEEDWATER REQUIRED FOR SENSIBLE HEAT REMOVAL Tm (Required) vs T,,,, (InWal)
(TO BE DEVELOPED DURING DETAILED ENGINEERING) .
a i
1 i
SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT l REC 0VERY GUIDELINE EMERGENCY OPERATIONS "
P a g e of
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SAFETY FUNCTION ACCEPTANCE CRITERIA
- 1. Reactivity Control 1.a. Reactor power decreasing !
.and
- b. Negative Startup Rate and
- c. Maximum of 1 CEA NOT fully inserted or borate per Tech.
-f Specs.
b l
i LOCA 41 ABB CE SYSTEM 80+' ,
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i SYSTEM 80 + = TITLE LOSS OF COOLANT ACCIDENT -
REC 0VERY GUIDELINE Ll EMERGENCY OPERATIONS Page 'z of
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GUIDELINES ]
'i SAFETY FUNCTION STATUS CHECK SAFETY FUNCTION ACCEPTANCE CRITERIA-
- 2. Maintenance of Vital Auxiliaries 2.a. Safety Load Division I , [
Safety Load Division II energized i
and
[125V) DC and [120V) AC Safety -
Bus C energized .
RC ii)[125V]DCand[120V]ACSafety i Bus C energized a_ILd
[125V) DC and [120V] AC Safety ,
Bus D energized I L
l l
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.. l SYSTEM 80 + TITLE LOSS OF' COOLANT RCCIDENT RECOVERY GUIDELINE 1
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EMERGENCY OPERATIONS P a g e of
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GUIDELINES i
i) charging and letdown, and SIS flow (per i Figure 5-3) maintaining -
or restoring pres- l surizer level [2% to - ;
78%] (unless SIS termi- l nation criteria met) ,
and ,
ii) the RCS is subcooled and iii) the RVLMS indicates the core is covered OC I
i
?
h f
i i
r ,
SYSTEM 80 +' TITLE - LOSS 0: COOLANT ACCfDENT .
REC 0VERY GUIDELINE- :
EMERGENCY OPERATIONS Page " of
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GUIDELINES ;
SAFETY FUNCTION STATUS CHECF, j!
SAFETY FUNCTION ACCEPTANCE CRITERIA i
i) available charging pump ,
is operating and the SI pumps are injecting ,
water into the RCS per Figure 5-3, i and ii) the RVLMS indicates the ,
core is covered.
- 4. RCS Pressure Control 4.a. Pressurizer heaters and spray, orchargingpumpfandSI pumps, are maintaining or restoring pressurizer pressure within the limits of Figure 5-1.
- b. available charging pump is operating and the SI pump (s) ;
are injecting water into the RCS per Figure 5-3 (unless SIS l termination criteria are met).
l LOCA 44 ABB CE SYSTEM 80+" 4 l
SYSTEM 80 + C TITLE LOSS OF COOLANT ACCIDENT-EMERGENCY OPERATIONS Page " of
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- 6. RCS Heat Removal 6.a. At least one steam generator l has level: l i) within the normal level 1 band with feedwater avail-able to maintain level l E I l
l ii) being restored by main, emergency or startup feed-water flow ;
- 7. Containment Isolation 7.a. No steam plant activity moni-tors alarming i and l
- b. i) Containment pressure less -
than [2.7 psig]
E ii) CIAS present or manually ,
initiated t
and
- c. i) No containment area radiation monitors alarming
= ,
ii) CIAS present or i
manually initiated and annulus vent sy, stem is ;
operating. M__ ___ ,
0
&%) St.htM b'iIdi9 vfd {
sysk yh.) .
SYSTEM 80 + " TITLE LOSS OF COOLANT ACCIDENT- !
RECOVERY GUIDELINE F EMERGENCY OPERATIONS 1 Page " of
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GUIDELINES SAFETY FUNCTION STATUS CHECK ,
)
. SAFETY FUNCTION ACCEPTANCE CRITERIA ;
- 8. Containment Temperature & Pressure 8.a. 1) Containment temperature L Control less'than [236*F] !
and .
ii) Containment pressure less than [8.5 psig] i E ,
- b. At least one containment spray header delivering at least [
[5000 gpm]. ,
- 9. Containment Combustible Gas 9.a. Hydrogen concentration less !
Control than [0.57.] .
E
- b. 1) available hydrogen ;
recombiners energized and ii) Hydrogen concentration less than 4Y..
E ,
- c. Hydrogen mitigation system operating in accordance with plant specific operating ;
instructions. ,
2-,. w e - ,4s.
SYSTEM 80+" TITLE LOSS OF COOLRNT ACCIDENT l REC 0VERY GUIDELINE j EMERGENCY OPERATIONS Page " of
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GUIDELINES BASES ,
i The bases section of the loss of Coolant Accident (LOCA) Recovery Guideline l
describes the LOCA transient in relation to the actions which the operator !
takes during a LOCA. The purpose of the bases section is to provide the }
operators with informat%a which will enable them to understed the reasons j for, and the conseque ce ,f, the actions they take during a LOCA.
Characterization of a LOCA A LOCA is an accident which is caused by a break in the reactor coolant system (RCS) pressure boundary. The break can be as large as a double ended !
guillotine break in the hot leg or as small as a break which results in' a loss
- of RCS fluid at a rate that is just in excess of the available charging f capacity of the plant. j; I
Small and large break LOCAs differ in their effect on the post-LOCA RCS heat >
removal process. For a large break, the only path necessary for RCS heat' removal in both the short and long term is the break flow with core boiloff.
For small breaks, heat removal via the flow out the break is not sufficient to provide cooling and, therefore, steam generator heat removal is required. The guidelines take this into account with the decisions which must be made. l Although distinct small and large break LOCA information is contained in the bases section of this guideline, the action steps to be used during the actual ,
emergency do not require the operator to distinguish between break sizes. i A LOCA is characterized by an initial decrease in RCS pressure and inventory.
Subsequent RCS inventory and pressure response depends on the size of the break. For large breaks inside containment, an increase in containment ;
temperature and pressure occurs relatively soon after the LOCA. However, a small LOCA may not be detectable on containment temperature and pressure l instruments in the short term. The actions taken by the operator during a l
i
SYSTEM 80 + " TITLE LOSS OF COOLANT ACCIDENT RECOVERY GUIDELINE ,
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LOCA, and more detailed descriptions of LOCA response, are provided in the !
following sections.
Safety Functions Affected The LOCA primarily affects RCS inventory and pressure control, and RCS and core heat removal. To a lesser degree, reactivity control, containment :
isolation, and containment temperature and pressure control are also affected.
All safety functions should be monitored to assure public safety or to detect failures which might lead to unsafe conditions.
RCS inventory control is initially lost since the break flow rate exceeds the available charging pump capaci'r. For small breaks, RCS inventory control is regained via injection fr the safety injection (SI) pumps and the charging !
pumps. It is maintained in the long-term by injection from these pumps. For large breaks, inventory control is regained through the injection of water into the RCS by the safety injection tanks (SITS) and the safety injection (SI) pumps. It is maintained in the long-term through the recirculation of i sump water through the RCS by the HPSI pumps. Note that for large breaks, the RCS may not totally refill and pressurizer level may not be reg &ined. If the large break is unisolable, continuous injection is required to make up for the loss out the break and to prevent boron precipitation.
RCS pressure control is initially lost as the RCS depressurizes because of the loss of inventory out the break. For large breaks, the RCS depressurizes in 10 seconds to 3 minutes to pressures typically below 300 psia. In the case of the largest breaks, the RCS pressure will reach equilibrium with containment I pressure, and will be nea. ly equal to that pressure. Because of the size of the break, the operator never regains direct control of RCS pressure and the RCS remains depressurized. For small breaks, the RCS depressurizes during the short-term (10 to 30 minutes) to an equilibrium condition with the steam generators. It then continues to depressurize as the operator cools down the steam generators. Pressure control is regained when the safety injection LOCA 48 ABB CE SYSTEM 80f"
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GUIDELINES e system (SIS) refills the RCS and pressurizer level is regained. Once pressure control is regained, subsequent small break post-LOCA operator actions which are associated with pressure control are (1) decreasing RCS pressure by-means of auxiliary sprays, (2) controlling SI pumps and charging, (3) heat removal via the steam generators in order to establish shutdown cooling entry B conditions and, (4) isolating or depressurizing the SITS. For small break LOCAs, during the period of time when the RCS is refilling (pressure control has not yet been achieved), there may be significant voiding in the RCS. The voided areas may be located in the reactor vessel head region as indicated by the HJTC RVLMS, the RCS loops, or the steam generator u-tubes, and may be made ;
up of steam or non-condensible gases. Steam voids may occur from fluid :
flashing in local hot spots within the RCS. This voiding is not a problem as long as heat removal is not inhibited or the ability to reduce primary pressure is not greatly reduced. The presence of small amounts of non-condensible gases may be present from sources such as gases evolving from the primary coolant and pressurizer vapor space. If their presence is detected in the RCS the reactor vessel head vent may be operated. The presence of non-condensible gases in the steam generator tubes is ,
characterized by a decrease in primary to secondary heat removal capability.
RCS heat removal is not jeopardized by the presence of non-condensibles until -
a significant number of steam generator tubes are blocked. A significant -
number of tubes will not be blocked unless there is considerable oxidation of ,
fuel cladding, and this is not expected for the small break LOCA, unless significant core uncovery occurs.
l There are twc paths initially available for RCS heat removal: heat transfer to the secondary side via the steam generators, and heat transfer via the fluid flowing out the break. Large break LOCAs have sufficient fluid flowing out the break to provide adequate heat removal without relying on steam generators. Small break LOCAs do not have sufficient fluid flowing out of the break to provide adequate heat removal. Therefore, steam generator heat removal is required in addition to break flow for adequate heat removal.
Because the LOCA ORG does not distinguish between large and small break LOCAs, LOCA 49 ABB CE SYSTEM 80+*
. & ' d>
l(O k [kN* IMAGE EVAL.UATION (fD, s\/f//
'[
'9h* TEST TARGET (MT-3) ((' [ #[*fF (j
\ fp %'
/g ,<(44e
'%o#)W 9 #%
l.0 - W
- '
- : %1
.. m pme q l,l
\ \ll I.25 ! 1.6 l _l.4- llmm 4 -
150mm >
4---- - - -
6"
- a x%ss,$h W r 4f%+ ,,O+ l, l
$fzy, hy}gg, s- s ibh,[4
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S
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f[j // % g W R ig, ,$ 4 ,
5'; # 1 IMAGE EVALUATION TEST TARGET (MT-3) N p (g,
}//g/77 Q qs gy;s %,,
fv l.0 L"*
9 ;" ??d ip=e j,l _ m ll 1.8 Im 1.25 1.4 i'l g1I.6-h 4_-------- 150mm - >
6" >
4________.--
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og, /// ,. y.
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%e 0 4 IMAGE EVALUATION / k(0/s9fa
\;/g/ ',' '"O $N:ff
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TEST TARGET (MT-3) 4 ,
=
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92 4 32 R 2.2
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g _ _ . _ _ _ _ . _ _ . ~ -
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.% '& / (g a% s
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7 VMAGE EVALUATION ((,j///
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k e 's %
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,fk{[dkk!?4gf N '~: ,
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- 9$$f h to Aft
~
1.0 L. ~m "
n 22
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1.25 !! l.4 M 1.6 p ___
6 4-------- 150mm
- 4__.------ - - - - -
6" *
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yy *% 4 p.p 4 ++ss'a .,
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/ . 4
SYSTEM 80 +" TITLE LOSS of COOLANT ACCIDENT REC 0VERY GUIDELINE EMERGENCY OPERATIONS Page " of
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i GUIDELINES steam generator heat removal capability is required at all times during a LOCA.
The large break LOCA heat removal process is not complex. For cold leg breaks the SIS refills the reactor vessel (RV) and provides only enough fluid to the core to match boil off. The excess injected fluid spills out of the cold leg break. The steam from core boil off passes out the >~+ leg and tnrough the steam generators on its way out the cold leg break. For the hot leg brer.,
the injected water builds up in the enld legs and orovides the core with water for boil off heat removal and some single phase cooling. In the long term, heat removal is provided by simultaneous hot .,d cold leg injection. This process provides heat removal for eitner ..ot or colo leg large break LOCAs while providing the added benefit of ensuring adequate flushing of the RV to avoid buildup of non-volatile materials produced in the boil off cooling process. Figures 5-6 and 5-7 illustrate the heat removal process for large break LOCAs.
The small break LOCA heat removsl process is more complex than that described above for the large break. In the short-term, after the RCPs are tripped, core heat removal is maintained by natural circulation. Since the break is not large enough to adequately remove the heat, heat removal via a steam generator is required. This requires that the operator maintain feedwater (either main, startup or emergency) to the steam generators and control steam flow from the steam generators via the steam bypass system or the atmospheric dump valves; Figures 5-8 and 5-9 il?ustrate the heat removal process for typical small break LOCAs. The typical percer.tage of required RCS heat removed by the steam gen:rators for various break sizes is illustrated in Figures 5-10 and 5-11.
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GUIDELINES Figure 5-6 HEAT REMOVAL VIA LARGE HOT LEG BREAK (ILLUSTRATIONS WILL REFLECT THE PROCESSES DESCRIBED IN THE GUIDELINE) i l
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GUIDELINES Figure 5-7 HEAT REMOVAL VIA LARGE COLD LEG BREAK (ILLUSTRATIONS WILL REFLECT THE PROCESSES DESCRIBED IN THE GUIDELINE)
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Figure 5-8 ,
HEAT REMOVAL VIA SMALL (RCS FILLED) f i
(ILLUSTRATIONS WILL REFLECT THE PROCESSES DESCRIBED IN THE GUIDELINE) t i
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Figure 5-9 i HEAT REMOVAL VIA SMALL BREAK (REFLUX COOLING r
r (ILLUSTRATIONS WILL REFLECT THE PROCESSES DESCRIBED IN THE GUIDELINE) i l
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Figure 5-10 BREAK DIAMETER VS % OF DECAY HEAT REMOVED BY STEAM GENERATORS ,
(T0 BE DEVELOPED DURING DETAILED ENGINEERING)
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4 Figure 5-11 BREAK DIAMETER VS % OF DECAY HEAT REMOVED BY STEAM GENERATORS -
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GUIDELINES The small break natural circulation process can take different forms. These. j forms include single phase nttural circulation and a more complex two phase natural circulation. The simplest form of natural circulation is single i phase, liquid cooling. Sin 3 1 e phase natural circulation is possible for cases where RCS inventory and pressure are controlled. Single phase cooling i transports heat using the same flow path involved in forced circulation !
i cooling with the liquid density difference between SG and RV driving the flow. l Two phase natural circulation involving steam and water is more complex and !
can take several forms, which depends on the amount of decay heat, the amount i of inventory and pressure control degradation, the break size and the status ;
of the SIS and the steam generators. One form of two phase natural !
circulation is known as reflux. In the reflux process, steam leaves the core j region and travels to the steam generator via the hot leg; the steam is condensed in tne steam generator before reaching the top of the "U" tubes and l flows back to the core via the 'ot leg where it is once again turned to steam.
Another two phase natural circulation process is similar to reflux but differs ;
t in that the steam from the core goes past the steam generator "U" bend and is j condensed in the tubes on the cold leg side; thus condensate flows back-to the core via the cold leg. A combination of the two processes is also possible.
I The operator has adequate instrumentation to monitor natural circulation for -
l the single phase liquid natural circulation process. The RCS temperature .
instrumentation, and loop aT can be used along with other information to ;
confirm that the single phase natural circulation process is effective. The j natural circulation processes involving two phase cooling are complex and f varied enough so that RCS loop AT may not be a meaningful indication of j adequate natural circulation cooling. The guidelines are written to alert the operator to use explicit acceptance criteria for natural circulation only when >
RCS inventory and pressure are controlled. ,
i For cases where two phase natural circulation cooling is the heat removal l process, the operator relies upon maintaining the steam generator heat removal !
process and the strict rules that require the SIS to remain operating to LOCA 57 ABB CE SYSTEM 80+* !
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restore inventory control. In addition, the core exit thermocouple temperature and Tn temperature indication are important in monitoring heat :
t removal during two phase natural circulation cooling. As long as these temperatures remain within acceptable limits they indicate that heat removal {
and inventory functions are being satisfied. l The time frame for the transition from single phase liquid natural circulation cooling to the reflux mode is determined by the relative size of the small break. The operator should be aware that this transition may cause confusing ,
temperature indications as the RCS loop ATs readjust to reflect the transition in progress. The emphasis in the guideline is to continue the steam generator j heat removal process, continue restoring inventory control, and to continue }
monitoring the core exit thermocouples to confirm the heat removal process is l adequate.
Once RCS pressure and temperature are reduced, RCS heat removal is provided by !
the shutdown cooling system-if possible. In the event that liquid inventory
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in the steam generators is not adequate to remove decay heat, a source of feedwater is unavailable, and the SCS is inoperable, the operator is instructed to implement the Functional Recovery Guideline because a multiple l casualty condition is in effect (LOCA and Loss of All Feedwater). Specific ]
guidance for initiating once-through-cooling is provided here. As discussed ;
previously, although steam generator heat removal is only required for the i
small break LOCA event, the LOCA EPG does not require the operator to distinguish between large and small break LOCAs so the action is taken l whenever SG heat removal capability is lost.
Short-term reactivity control is accomplished by the negative moderator j effects for large breaks and by the reactor trip for small breaks. The j reactor trip decreases core heat generation to decay heat levels which aids in the control of heat removal. Long-term reactivity control is accomplished through injection of borated water by the safety injection system and the ;
charging pumps.
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Containment isolation occurs either automatically, or is performed manually after an evaluation of the plant conditions (containment temperature, !
pressure, and activity level; and for plants which generate a CIAS on SIAS, l, pressurizer pressure). j If the LOCA occurs inside containment, then containment temperature and pressure control can be accomplished by various combinations of containment l fan coolers fin the emergency mv&)-and/or the containment spray system.
These systems act to remove heat from the containment atmosphere, thus >
reducing the temperature and pressure. j Containment Combustible Gas Control may become a concern due to hydrogen !e generated during LOCA events. The ultimate goal of the Containment 1 Combustible Gas Control safety function is to prevent a hydrogen burn from causing containment pressure to reach or exceed containment design pressure. l, Preferentially this is accomplished by operation of the hydrogen recombiner. l If recombiner operation is not possible or sufficient, then a hydrogen purge may be performed if deemed necessary by the Plant Technical Support Center. j These actions are performed to prevent or minimize the release of fission products to the environment. !
i Three significant sources of hydrogen exist during LOCA events. These are: j t
(1) Metal-water reactions involvina zircaloy or stainless steel in the RCS j These reactions take place at high temperatures during the core uncovery phase of a LOCA. Thus, hydrogen generated will be >
released to the containment atmosphere if the primary break is j inside containment. The amount of hydrogen produced depends on the duration of core uncovery and the maximum core temperature reached.
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Radiolysis of water by fission product decay (2)
As a result of the decay of the fission products, water molecules l in the RCS and in the RCS fluid which has been released into the ,
containment may be broken down into hydrogen and oxygen. The .
gases are released to the containment atmospheres This is a slow f process but over a period of time can be the most significant l source of hydrogen. It may take [12 to 16] days for hydrogen j concentration to reach 4%. The rate of buildup will increase with an increase of fission products in the RCS.
(3) Corrosion of aluminum and zine by the containment sprays '
i The reaction between the aluminum and zinc materials in the containment with the borated spray solution generates hydrogen.
The reactions occur at higher rates with increasing temperatures. :
t Hydrogen may be generated in this way during the first hours of a ,
LOCA event. ,
Figure 5-12 provides the results of a typical safety analysis calculation of 1 the hydrogen concentration for a large break LOCA event. The initial increase ,
in hydrogen concentration is due to the metal-water reactions and the corrosion reactions. The long term increase is due to the radiolysis of !
water. ,
i The containment hydrogen concentration can be reduced by recombining hydrogen and oxygen to form water. The hydrogen recombiners do this by raising the
- temperature of the air passing through them to the point where the ;
recombination reaction takes place. Electric heating elements are used to heat the incoming mixture, while flow through the units is provided by natural j circulation. l LOCA 60 ABB CE SYSTEM 80+*
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i Figure 5-12 TYPICAL HYDROGEN CONCENTRATION BUI JP AND REMOVAL FOLLOWING A LARGE BREAK LOCA (TO BE DEVELOPED DURING DETAILED ENGINEERING)
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GUIDELINES Since the recombination rate (cubic feet of hydrogen removed per hour) depends l on the hydrogen concentration in the atmosphere, use of the recombiners will l result in an exponential decrease in the hydrogen concentration. Typically, l one recombiner will remove hydrogen at a rate that is compatible with the long !
term hydrogen generation rate following a large break LOCA due to radiolysis i of reactor coolant water. !
i Figure 5-12 provides typical curves showing the effect of one and two i recombiners that are started nine days after the LOCA.
i The containment hydrogen concentration can also be reduced by purging the l containment atmosphere with fresh air. The hydrogen purge system accomplishes f this by providing controlled intakes and exhausts to the containment :
atmosphere. This method of hydrogen control is utilized after the Plant j Technical Support Center has evaluated several factors - including the expected effects of a hydrogen burn. -
The hydrogen removal ratt (cubic feet of hydrogen removed per hour) depends on j the purge system flow rate, the containment free volume, and the containment hydrogen concentration. Typically, the hydrogen purge system will remove j hydrogen at a rate that is comparable with the long term hydrogen generation }
rate following a large break LOCA. Higher purge rates will result in higher !
removal rates. The hydrogen purge rate can be approximated by the hydrogen ;
removal rate of one recombiner as shown in Figure 5-12. ;
Trendina of Kev Parameters (Representative of small break LOCAs) 7 Reactor Power (Figure 5-13) ,
A reactor trip will occur on thermal margin / low pressure, and reactor power will be decreasing as a result of the reactor trip. Additional negative reactivity insertion will be provided by moderator voiding, and boron addition by charging pump and/or SIS flow.
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RCS Temperature (Figures 5-14, 5-15) f Following the reactor trip, RCS temperature initially decreases for all size LOCAs due to the reduction in heat input into the RCS, and due to the heat ,
removed out the break and by the steam generators. ,
i Pressurizer Pressure (Figure 5-16)
Pressurizer pressure initially decreases due to the loss of coolant and ;
reactor power reduction following reactor trip.
Pressurizer Level (Figure 5-17) i Pressurizer level may decrease or increase. For breaks not located in the pressurizer, the pressurizer will empty and, depending on the size of the break, not refill during the course of the accident. Breaks located in the j pressurizer may lead to increased pressurizer level since water from the hot l leg flows into the pressurizer surge line while significant voiding of the RCS loop is occurring. If there is a break on or near the pressurizer level ;
instruments, this may cause this instrument to be grossly inaccurate and misrepresent pressurizer level (high or low).
For small break LOCAs where the pressurizer refills as a result of safety injection, pressurizer level may not be representative of RCS inventory or core coverage. As indicated above, the depressurization associated with a leak in the RCS will usually result in the formation of voids in RCS hot spots (reactor vessel head, hot legs, S/G tube bundle). The growth or ;
persistence of these voids, after refill of the pressurizer by the SIS, may cause pressurizer level to increase or remain constant in spite of continuing loss of inventory through the break.
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Some degree of voiding is expected for LOCAs; but the extent and duration is !
I largely dependent on break size and location. Most small break (58) LOCA events will not result in core uncovery without some other failure occurring concurrently. Some small breaks can lead to some core uncovery. However, l when SI delivery is established, the core will be covered. For very small breaks, the RCS will repressurize to slightly below the shut-off head of the t HPSI pumps and voiding will not uncover the core. For large breaks, the RCS l saturates almost immediately and voids start to form. Core uncovery is !
expected in the short term but RCS pressure decrease is also very rapid and SIS flow restores core cooling. I i
Steam Generator Pressure (Figure 5-19)
Steam generator pressure may increase or remain constant in the short term if the break is small. However, for all sized LOCAs, steam generator pressure l will usually decrease in the long term as a result of operator action. f t
Steam Generator Level (Figure 5-20)
Steam generator level will decrease rapidly following the reactor trip and then increase to the hot standby level. Level may then remain constant or increase somewhat based on automatic or manual control of feedwater. !
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Figure 5-13 ;
REPRESENTATIVE SMALL BREAK LOCA ,
i REACTOR POWER l i
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Figure 5-14 l REPRESENTATIVE SMALL BREAK LOCA RCS HOT LEG TEMPERATURE >
l (TO BE DEVELOPED DURING DETAILED ENGINEERING) 1 LOCA 66 ABB CE SYSTEM 80+*
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Figure 5-15 REPRESENTATIVE SMALL BREAK LOCA >
RCS COLD LEG TEMPERATURE (To BE DEVELOPED DURING DETAILED ENGINEERING) 4 l
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REPRESENTATIVE SMALL BREAK LOCA ,
PRESSURIZER PRESSURE (TO BE DEVELOPED DURING DETAILED ENGINEERING) f i
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GUIDELINES Figure 5-17 REPRESENTATIVE SMALL BREAK LOCA PRESSURIZER LEVEL LOCA 69 ABB CE SYSTEM 80+"
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Figure 5-18 REPRESENTATIVE SMALL BREAK LOCA ,
REACTOR VESSEL LEVEL !
(TO BE DEVELOPED DURING DETAILED ENGINEERING)
- (TG BE DEVEL0 rib UURiHG DETAILED EW6ihEERiM0} ,
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Figure 5-19 REPRESENTATIVE SMALL BREAK LOCA STEAM GENERATOR WIDE Ra.NGE LEVEL (TO BE DEVELOPED DURING DETAILED ENGINEERING)
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i Figure 5-21 provides a summary of the LOCA Recovery Guideline's strategy. If ,
a LOCA is initiated from MODE 1 or MODE 2, the operator performs the Standard ;
Post Trip Actions and diagnoses the event prior to entering the LOCA Recovery [
Guideline. However, if the event is initiated from MODE 3 or MODE 4, the operator is not directed to the Standard Post Trip Actions since they may not ,
apply. Instead, the operator ensures that the LOCA is properly diagnosed and !
that the specified entry conditions are met prior to entering the LOCA Recovery Guideline. Once in the LOCA Recovery Guideline, the operator would have performed the Standard Post Trip Actions and diagnosed the event. In the +
LOCA Recovery Guideline, the operator begins using the Safety Function Status ,
Check to confirm that the plant is recovering. The next steps can be broken i into six major recovery actions.
The six major recovery actions bring the plant to a stable condition which can >
be maintained indefinitely. The first major action consists of maximizing safety injection flow into the RCS and attempting to isolate the source of the leak. This step reduces the risk of core uncovery and facilitates recovery from the LOCA. The second and third major actions apply to the situation when ;
the leak has been isolated. The second major action involves regaining l control of the RCS pressure and inventory and maintaining sufficient RCS heat removal. The third major action is to perform a controlled cooldown to the !
SCS entry conditions. The fourth through sixth major recovery actions are applicable to the situation when the leak cannot be isolated. The fourth j major action involves a rapid plant cooldown using the SGs. This step is particularly important for small breaks which require the SGs to remove the core decay heat. The fifth major recovery action is the commencement of post-LOCALong}ermfooling(LTC). Safety injection flow is switched to q u'
simultaneous het/n%..Cy:g injection from the normal cold leg injection. Also a
pp. c. v.8 s h y f L the suction for the charging pumps is switched to the L mfsd i% nier tan l for boron concentration control. The sixth major action is a determination of .
whether SCS operation is appropriate (small breaks) or whether simultaneous f LOCA 72 ABB CE SYSTEM 80+"
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hot / cold leg injection in a recirculation mode should be continued (large breaks).
A more detailed chart illustrates the recovery guideline strategy and lists the guideline steps which correspond tc each strategy objective. f.efer to Figure 5-26, W nc; 15.2}r i
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Figure 5-21A LOSS OF COOLANT STRATEGY CHART ,
(FLOW AND STRATEGY CHARTS WILL REFLECT THE DETAILED STEPS IN THE GUIDELINE.)
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i Figure 5-21B LOSS OF COOLANT STRATEGY CHART i
(FLOW AND STRATEGY CHARTS WILL REFLECT THE DETAILED STEPS IN THE GUIDELINE.) ,
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Bases for Operator Ac(ions ,
The operator actions are directed at placing the plant in a safe, stable condition. One of two paths is followed, depending upon whether or not the j break has been isolated.
- 1. The diagnosis of a Loss of Coolant Accident should be confirmed by using the Break Identification Chart (Figure 5-2) and by comparing control board parameters to the acceptance criteria in the Safety Function !
Status Check to ensure that all safety functions are being satisfied.
In particular, the operator should note the status of RCS subcooling and ,
containment and steam plant activity. These parameters provide a means of discriminating between LOCAs/SGTRs and ESDEs. For LOCAs, the RCS reaches saturation conditions and containment activity monitors may be !
alarming but steam plant activity monitors should not be alarming. For l I
a SGTR, steam plant activity monitors may be alarming but containment activity monitors should not be alarming. For ESDEs, neither steam f plant or containment activity monitors should be alarming. For. plants which exhibit SG tube leakage, however, steam plant or_ containment activity monitors may alarm during ESDEs. [ Sampling both steam j generators for activity will assist in confirming the diagnosis.] These actions ensure the proper guideline is being used to mitigate the effects of a LOCA. I If the initial diagnosis of a LOCA is confirmed, then the operator i continues with the actions of this guideline. However, if the Break Identification Chart indicates that a SGTR or an ESDE has occurred, then the LOCA Guideline is exited and the actions of the proper guideline are implemented. This step allows the operator to switch to the proper guideline for those events similar to LOCAs which may have occurred.
LOCAs, ESDEs, and SGTRs have similar initial symptoms and could be confused early in the event.
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If a correct diagnosis cannot be made, then the operator is directed to !
exit this guideline and to implement the Functional Recovery Guideline. ;
The Functional Recovery Guideline is safety function based and will ;
ensure that all safety functions are addressed regardless of what !
event (s) is occurring.
- 2. If pressurizer pressure decreases to or below the SIAS setpoint of [1825 !
psia], then an SIAS should be initiated automatically. If this does not {
occur, then the operator should manually initiate an SIAS.
- 3. A LOCA will result in the actuation of the safety injection system.
Pressurizer pressure will respond during the accident according to the f break size. Safety injection system (SIS) flow rate will follow _
pressurizer pressure according to the SIS delivery curves (see Figures j 5-23 and 5-24). The SIS and charging flowrate should be checked (Figure :
5-3 provides information which can be utilized to verify adequate SIS j flow is occurring) and maximized for RCS inventory replenishment and/or j core heat removal. The charging pump may have to be manually restarted if an interruption of electrical power to the charging pump bus has i occurred. The following guidance will assist in ensuring maximum injection of water into the RCS: i
- a. idle SI pumps should be started and system flow should be verified l to be within the limits of Figure 5-3, !
- b. The charging pump should be started, if necessary.
i If any SI pump that should be operating won't start, any charging pump won't start, or SIS flow is not in accordance with Figure 5-3, then the '
following guidance is provided:
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- a. the operator should verify that electrical power is available to valves ano pumps necessary for inventory control,
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- b. the SIS "alve lineup should be verified to be morrect from control !
4 board indications,
- c. auxilia.ry systems necessary for SIS or charging operation should 1 be checked.
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It must be noted, however, that the maximization of charging and safety l 4
injection can result in excess RCS inventory, possible filling of the ,
pressurizer to a solid condition, and a PTS concern upon RCS heat up, l fluid expansion, and subsequent RCS pressure excursion. Operators must j be aware of these concerns and terminate the SIS operation when ti.c {
termination criteria are met.
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- 4. Steps 4 and 5 contain guidance regarding the RCP operating strategy for '
a LOCA (Figure 5-22). A generic RCP trip strategy has been developed which results in the tripping of all four RCPs for depressurization events where RCS is not subcooled, but allows the continued operation of two RCPs (in opposite loops) for depressurization events where RCS is ,
subcooled. For undiagnosed events, where the Functional Recovery Guideline is implemented, the RCP trip strategy is identical to that '
followed in the LOCA guideline. Steps 5 and 6 detail the two l significant operational aspects regarding the RCP trip strategy for a f LOCA. Skfc. cme 15.u) j 4
The first operational strategy results in the operator tripping two RCPs -i (in opposite loops) if pressurizer pressure decreases to less than [N f i
psia] following a SIAS and RCS is subcooled. This action may occur in the Standard Post Trip Actions and, in this case, the operator would i simply verify that two RCPs (in opposite loops) have been tripped. The !
I operator trips all four RCPs if pressurizer pressure decreases to less than [1400 psia) following a SIAS and RCS is not subcooled. If the operator cannot confirm that a LOCA has occurred, and the Functional Recovery Guideline is implemented, the RCP trip strategy is identical to
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GUIDELINES be diagnosed and is determined to be other than a LOCA (i.e., ESDE or SGTR), then only two RCPs (in opposite loops) are tripped. The other two RCPs remain operational until one or more of the RCP operating requirements (e.g., NPSH, temperatures, seal flow, oil pressures, motor amperage, vibration) are no longer satisfied, then, any pump which does not satisfy these requirements should be tripped. This gives the operator maximum flexibility in plant control because a normal plant cooldown can be performed while still ensuring a conservative approach to event recovery.
- 5. The second aspect of the RCP operating strategy concerns the verification that RCP operating limits are satisfied. The RCPs will be operating in a pressure-reduced RCS and may not satisfy NPSH requirements. The operator must continuously monitor RCP operating limits (e.g., temperatures, seal flow, oil pressures, NPSH, motor
. amperage, vibration) and trip any RCPs which do not satisfy RCP operating limits. Plant specific RCP operating limits should appear in this step, either directly or, by referencing the applicable operating instructions.
- 6. The operator records the time of day, since some of the follow-up actions need to be performed within a defined time window relative to the start of the accident.
- 7. Potential so .es -i leakage which can be rapidly and remotely isolated are checked a .. isolated, if possible, to minimize RCS inver. tory losses and to attempt to isolate the break. The following guidance is provided to isolate the leak:
- a. Letdown is isolated to possibly isolate the break and to preclude loss of RCS inventory to the CVCS.
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Figure 5-22 RCP TRIP STRATEGY FOR LOCA (FLOW AND STRATEGY CHARTS WILL REFLECT THE DETAILED STEPS IN THE GUIDELINE.)
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- b. RCS sampling should be terminated and all sampling lines should be isolated. If necessary, this isolation should be performed i I
manually. Isolating sampling lines minimizes the possibility of inadvertent personnel exposure, and minimizes RCS inventory l losses. l
monitor. An increase in CCW surge tank level may also be an indication of reactor coolant to CCW in-leakage. An increased CCW !
heat load, possibly caused by high containment temperatures will also cause surge tank level to rise to the point where an l abnormally high level increase may possibly be discerned. If RCS to CCW Ieakage is evident, then isolate the CCW affected kCPs and trip affected operating RCPs. i i
- d. The rapid depressurization valves should be verified closed. If they are not closed, the operator should manually close the rapid !
depressurization valves. This will minimize the loss of inventory l through these valves.
- e. Another potential leak path is the reactor coolant gas vent l valves. The operator should verify these valves are closed and if
- necessary, manually close the valves. -
i
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i t
P 2
t Figure 5-23 TYPICAL SAFETY INJECTION DELIVERY CURVE NO FAILURES t
(T0 BE DEVELOPEu DURING DETAILED ENGINEERING) t f
5
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GUIDELINES Figure 5-24 TYPICAL SAFETY INJECTION DELIVERY FAILURE CONDITION - LOSS OF ONE EMERGENCY GENERATOR (TO BE DE\ILOPED DURING DETAILED ENGINEERING)
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- 8. A LOCA outside of containment is a very low probability event but if it .
does occur, and appropriate actions are not taken, the consequences can .
be severe. In this step, the nuclear annex temperature, humidity, and j radiation alarms and sump levels and subsphere sump levels are monitored ;
i for indications that RCS fluid has breached containment. If it is evident that a LOCA is occurring outside of containment, then an attempt to locate and isolate the break should be made, if possible.
Plant-specific instructions for isolating the nuclear annex and its ;
ventilation systems should be inserted here. This is provided to limit ;
the release of fission products to the environment. l I
- 9. If containment pressure is greater than or equal to [4 psig], then the i operator ensures the following
- a. The operator verifies that containment isolation occurs at the !
appropriate automatic setpoint. If containment isolation does not occur automatically or all containment isolation valves are not in their accident positions, then the operator should manually }
initiate containment isolation. The plant-specific method of j manual containment isolation inserted here. The purpose of this l step is to prevent direct communication between the containment j atmosphere and the environment. Operators should be alert to the ;
loss of auxiliaries to the containment (in particular component ;
cooling water) which may occur with containment isolatian.
Re-est+11shing letdown should also be considered if it is )
availe 9. This will enable the operator to better control RCS l inventory during a possible RCS heatup and subsequent fluid !
t expansion. This action can minimize the possibility of PTS. )
[
- b. High pressure in the containment may pose a threat to containment integrity. Furthermore, high containment temperature adversely impacts the accuracy of instruments whose transmitters are located inside containment (e.g., pressurizer level and pressure, steam !
generator pressure and level, RCS loop RTDs) and may impact the l LOCA 84 ABB CE SYSTEM 80+*
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4 continued availability of equipment located in containment. The effect of temperature on hydrogen generation (by corrosion ;
reactions) is described in the bases of step 10. I t
If containment pressure has not reached or exceeded [2.7 psig], then the (
operator should ensure normal containment equipment cooling and air l recirculation systems are operating.
- 10. The containment spray system is automatically actuated at a containment !
pressure of [8.5 psig] or greater. If containment pressure reaches [8.5 l psig], then the operator should ensure containment spray actuation. In i order to maintain containment pressure below design pressure, there exists redundant containment Spray systems each capable of delivary j
[5000 gpm]. :
i When containment sprays are actuated, the conditions created in the j containment may generate Hydrogen. Hydrogen may be generated by the reaction of boric acid (from containment spray flow) and metals'in the i i
containment. Aluminum and zinc are two metals which are reactive with boric acid. The reaction rates of boric acid and aluminum and zinc are !
a function of temperature. Therefore, if the containment spray system !
a has been spraying boric acid onto zinc and aluminum surfaces in a high j temperature environment, then conditions exist for the generation of {
hydrogen in the containment. l t
i The operator should take action to place external hydrogen recombiners i in service to minimize the hydrogen concentratinn.
W www hu h sa+A The oneratobshould h sp ve. .
also verify the annulus ventilation systemp operlting. If it is not, j the system should be manually started. l
- ll. Containment spray system operation may be terminated when containment pressure has been reduced to an acceptable level. Continued operation of the sprays after pressure has been reduced to an acceptable level LOCA 85 ABB CE SYSTEM 80+*
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GUIDELINES increases the possibility of wetting electrical connectors which may l result in electrical grounds, shorts and other malfunctions. Therefore, l if containment sprays have actuated and containment pressure is reduced j below [5.5 psig], then containment spray may be terminated. After i terminating containment spray, the containment spray system should be realigned for automatic [or manual] operation in case containment i pressure again increases to the actuation setpoint. In addition, when -
the containment spray system operation is terminated, the annulus l ventilation system should be secured. t
- 12. Subsequent operator actions and performance of the containment j combustible gas control portion of the Safety Function Status Check will i require measurement of the containment hydrogen concentration. The ;
i hydrogen monitors should be placed in service in order to enable the ;
operator to monitor containment hydrogen concentration. [The actions
" required for operation of the hydrogen monitors should be performed l concurrent with the following steps] (h f = ce 15.16.) ;
- 13. Although hydrogen is not flammable until it achieves a concentration of at least 4%, it is prudent to reduce hydrogen to as low a concentration ;
as possible. (i.e., less than the minimum detectable hydrogen )
concentration of [0.5%).) Such action minimizes the possibility of f reaching the flammability limit and of forming pockets of high !
concentration hydrogen. Therefore, the [ hydrogen recombiners] should be j run until hydrogen concentration is reduced to less than [0.5%). The recombiners take approximately [1 hour] to reach operating temperature so no decrease in measured hydrogen co:. centration should be expected !
before this time.
- 14. Containment radiation levels should be monitored in order to provide the
~
[ Plant Technical Support Center) input to evaluate the environmental impact of any planned, or unplanned releases.
l
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- 15. At this point in tre guideline, the operator will pursue one of two strategy paths. 11 the LOCA has not been isolated, the operator is ;
directed to follow th3 path which contains recovery actions for that ,
hema. condition (steps 16 through 36). If the leak or rupture has h- isolated, the operator is directed perform those steps aimed at !
stabilizing the plant (steps 37 through 55).
- 16. If the LOCA has not been isolated, then the following actions are directed toward re-establishing RCS inventory control while maintaining l RCS heat removal. The goal of this section is to establish shutdown cooling, if possible, as the means of core heat removal. A rapid plant ;
cooldown via the steam generators is beneficial for all LOCAs, ,
particularly small breaks. For small breaks, the steam generators ~ are the major heat sink for RCS heat removal. An aggressive cooldown (while holding the cooldown rate within Technical Specification Limitations) improves RCS heat removal by enhancing natural circulation and reflux i boiling. Furthermore, an aggressive cooldown hastens the depressurization of the RCS. This results in higher safety injection l flows which aid in regaining RCS inventory control. Figures 5-23 and j 5-24 show typical SIS flowrates as a function of RCS pressure.
For the largest breaks, the RCS depressurizes to an equilibrium pressure !
with the containment. In this condition, the RCS fluid is at a lower !
temperature than that of the steam generators. The steam generators, therefore, act as a heat source, superheating any steam in the RCS which may be flowing through the S/GS to the break. By cooling down the steam '
generators, heat input to the RCS is reduced.
The turbine bypass system or the atmospheric dump valves are utilized depending on the availability of the condenser and turbine bypass ;
system.
)
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- 17. Steam generator level should be maintained in the normal band using ,
main, startup or emergency feedwater. This ensures that a heat sink is available for RCS heat removal and cooldown. This is especially important in the case of a small break LOCA (Reference 15.9).
Maintaining steam generator in the normal band also ensures that the steam generator tubes remain covered. By raintaining level above the l top of the tubes, sufficient static pressure head will be available to ,
prevent migration of containment radioactivity through pre-existing tube defects to the secondary side of the steam generator in the long term. ,
This minimizes the release of radioactivity to the atmosphere.
- 18. The available condensate inventory should be monitored and replenished from available sources as necessary to continually provide a source for ,
a secondary heat sink. Examples of alternate sources of condensate are nonseismic tanks, fire mains, lake water supplies, potable tanks, etc. '
Plant specific alternate sources of feedwater should be identified and cited in the procedure 4Sefa m.ce-45.!!}= The condensate required to either maintain the plant at hot standby or to cooldown may be determined from Figures 5-4 and 5-5.
- 19. Once pressurizer level has been restored to greater than or equal to
[2%], then level should be maintained [2 to 78%] by control of charging and letdown (preferentially) as necessary, and the SIS. If SIS termination criteria are met, then SI pumps may be throttled or stopped.
When pressurizer level is being controlled at [2%] or greater, than charging pumps may be operated as necessary. If pressurizer level is not restored to [2%), then all available charging and SIS pumps should be operated for maximum flow.
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Figure 5-25 POSI H 2BURN CHARACTERISTICS (TO BE DEVELOPED DURING DETAILED ENGINEERING) f' t
l l
1 i
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GUIDELINES A pressurizer level of [2 to 78%] with a saturated bubblein the
?
pressurizer should be established if possible, as the means of RCS pressure control. If pressurizer level drops below the top of the pressurizer heaters, then pressurizer heater operation will be .
interlocked off for overheating protection. It may be necessary to ;
exceed [78%) pressurizer level if the operator is attempting to restore t i
RCS subcooling since pressurizer heaters may be unavailable and solid water operation may be necessary to restore subcooling. l r
- 20. For small break LOCAs, especially where RCS inventory and pressure are controlled, a deliberate depressurization of the RCS will be necessary >
to permit entry into shutdown cooling. This step directs a ,
depressurization to SCS entry pressure, [450 psia], and provides the available depressurization success paths-depending on existing plant ,
conditions. For large breaks, all that may be required to depressurize to or below [300 psia] is throttling of SIS flow (if SIS termination 4
criteria are met). ,
i
- 21. Throughout the cooldown and depressurization, the operator should verify ,
that the pressurizer pressure is being maintained within the Post j Accident P-T limits of Figure 5-1. If the Pressure-Temperature limits 7 of Figure 5-1 are being violated, then the operators should take actions to restore the RCS to within the P-T limits. Depending on the situation j (pressure too high or too low), the operator should perform the following actions as appropriate: j
- a. Stop the cooldown w ng.vs v :
- b. Operate, main or auxiliary spray or reactor coolant gas vent system as necessary to restore pressurizer pressure to within the P-T limits of Figure 5-1. j
- c. Attempt to maintain the plant in a stable pressure-temperature l configuration. If low RCS subcooling exists, then the cooldown l should be continued if desired, within the limits of Figure 5-1.
LOCA {
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- d. If an overpressure situation exists and is caused by SI and/or charging flow, then throttle or stop SI (refer to Step 31) or i charging pumps and manually control letdown to restore and maintain pressure within the Post Accident P-T limits of Figure 5-1.
- 22. The plant conditions should be carefully assessed before any RCPs are restarted. The need for forced circulation operation should be balanced against the risk of damage to the RCP seals.
The need for operation of the RCPs should be evaluated based on: ,
- a. the adequacy of the RCS and co.e heat removal under the existing natural circulating conditions,
- b. the existing RCS pressure and temperatures,
- c. the need for main pressurizer spray capability. [
If the existing natural circulation is providing satisfactory RCS and 4 core heat removal, a transfer to forced circulation operation may not be necessary. This would be particular true if the RCS_ had already been l cooled and depressurized to SCS entry conditions. If the RCS pressure and temperatures are closer to hot standby conditions, it may be f desirable to restart the RCPs in order to' allow a normal forced circulation cooldown. Consideration should also be given to the necessity of having main pressurizer spray capability if auxiliary spray is not providing the desired depressurization rate.
i The potential for RCP seal degradation should be evaluated based on: :
i i
- a. how-long [CCW) to the RCPs was interrupted, j
- b. RCP seal staging pressures and temperatures. j i
l I
_ . - . _ _ _ .- ]
SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT REC 0VERY GUIDELINE !
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interrupted for longer than 10 minutes. The seal staging pressures ,
provide an indication of degraded seal stages (a low pressure drop i across a stage indicates a problem). Restart of an RCP with one or more degraded seal stages should be avoided if possible. ;
i
- 23. If RCP restart is to be attempted, then select two RCPs (in opposite loops) for operation, if RCP restart criteria are met. This will ensure continued forced circulation of coolant through the core, cooling of the [
RV head region, provide the capability for the normal mode of pressurizer spray, condense RCS steam voids, and remove non-condensible gases from the S/G tube bundle. Furthermore, this action enhances the strategy to obtain an uncomplicated cooldown whenever possible during a ,
recovery from a LOCA. However, only one reactor coolant pump in each ;
loop should be operated to minimize heat input to the RCS -(Refer =r 4 5. 22 F.
Determine whether RCP restart criteria are met by the following: l i
i
- a. Electrical power available to the RCPites,
- b. RCP auxiliaries (In particular component cooling water) to
- LW ';.
- ~~ c maintain seal i.e d eacct46, bearing, and motor cooling should be !
.,2 _ g .-
operating in order to prevent damage to the pump and/or motor. ;
, ,,.y_,
j
. f.w - >There should be no high temperature alarms on the RCPs to be '
operated. l
[c. At least one steam generator is available for removing heat from .
[S ' h
the RCS. A steam generator having the ability for feed flow and j
m ,. _, s[e steam flow is available for removing heat from the RCS. [
' C d. Pressurizer level is greater than [33%] and not decreasing. A- i pressurizer level above [33%] provides the operator with a margin s
, u :a:, < ,
p.a ,
., ]
for maintaining plant control during a LOCA. A level of [33%) !
provides a margin above the heaters to offset the possible l pressurizer level decrease due to loop shrinkage and/or steam void .i condensation. ,
LOCA l
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subcooled condition, taken in conjunction with (d) above, F indicates that adequate inventory control has been established,
- f. All plant specific RCP operating criteria should be satisfied ,
before the RCPs are restarted to prevent damage to RCPs resulting from abnormal operating conditions. ;
- 24. Upon restarting two RCPs in opposite loops, pressurizer level and pressure may decrease due to loop shrinkage and/or steam void j condensation. It is possible that this action will drain the pressurizer. Steam voids present in the reactor vessel will condense upon restarting RCPs. The RVLMS should be monitored for the trending of reactor vessel liquid level. This trending information may be ;
correlated to pressurizer level dt.:rease. RCP operation with a drained pressurizer may continue provided certain actions are taken and certain criteria are satisfied G h ence 15.15)r The following constitutes the actions to be taken, and the criteria to
' be satisfied, when restarting RCPs: ;
i i
- a. Start one RCP in each loop.
- b. Ensure proper RCP operation by monitoring RCP amperage and pump j NPSH. NPSH is determined by pressurizer pressure and corresponding T, on Figure 5-1. j
- c. Ope ate charging (and SI) pumps.vton,restoie and maintain I
pressurizer level greater than [33%). If SI pumps are operating, !
continue their operation until SIS termination criteria are met (refer to step 27). This action will ensure that pressurizer heaters remain covered.
i If all RCP operation is terminated and inventory and pressure are j
- 25.
controlled, then natural circulation is monitored by heat removal via at least one steam generator. Natural circulation flow should occur within 5-15 minutes after the RCPs were tripped.
4
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GUIDELINES The operator has adequate instrumentation to monitor natural circulation for the single phase liquid natural circulation process. The RCS temperature instrumentation, namely loop 4T, can be used along with the other information to confirm that the single phase natural circulation t process is effective. The natural circulation process involving two phase cooling is complex and varied enough so that RCS loop aT may not :
be a meaningful indication of adequate natural circulation cooling. The guidelines are written to alert the operator to use explicit acceptance criteria for natural circulation only when RCS inventory and pressure are controlled. t t
The RCS temperature response during natural circulation will be slow (5-15 minutes) as compared to a normal forced flow system response time of 6-12 seconds, since the coolant loop cycle time will be significantly larger.
When single phase natural circulation flow is established in at least one loop, the RCS should indicate the following conditions: ,
- a. Loop AT (Tg - T,) less than normal full power 4T,
- b. Hot and cold leg temperatures constant or decreasing,
- d. No abnormal differences between Tg RTDs and core exit thermo-couples. Hot leg RTD temperature should be consistent with the '
core exit thermocouples. Adequate natural circulation flow '
ensures that core exit thermocouple temperatures will be approximately equal to the hot leg RTDs temperature within the bounds of the instrument's inaccuracies. An abnormal difference between T g and the CETs is greater than (10*F].
Natural circulation is governed by decay heat, component elevations, j primary to secondary heat transfer, loop flow resistance, and voiding. )
SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT RECOVERY GUIDELINE EMERGENCY OPERATIONS "
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circulation decay heat removal is obtained by fluid density differences i between the core region and the steam generator tube sheet. '
As a contingency, if the criteria listed are not met, then natural circulation in the RCS is not effectively transferring heat from the core to the steam generators. Both RCS and Core Heat Removal Safety Functions may become jeopardized if any of the above criteria continue to be violated. Operators should ensure that RCS pressure and inventory, and SG steaming and feeding are being controlled properly to prevent violation of a safety function (RJerence u.u ) .
- 26. During a LOCA, the natural circulation process can take different forms.
These forms include single phase natural circulation and a more complex two phase natural circulation. The simplest form of natural circulation is a single phase liquid cooling. Single phate natural circulation is possible for most cases where RCS inventory and pressure are being controlled properly. Single phase cooling transports heat using the '
same flow path involved in forced circulation cooling with the liquid density difference between SG and RV driving the flow. Two phase natural circulation is more complex and can take several forms. Two phase natural circulation depends on the amount of decay heat, the amount of inventory and pressure control degradation, the RCS leak rate, i and the status of the SIS and the steam generators. One form of two 7 phase natural circulation is known as reflux. In the reflux process, ,
steam leaves the core region and travels to the steam generator before !
reaching the top of the "U" tubes where it condenses and the condensate flows back to the core via the hot leg where it is once again turned to~ -
steam. Another two phase natural circulation process is similar to reflux, but differs in that the steam from the core goes past the steam generator "U" bend and is condensed in the tubes on the cold leg side and the condensate flows back to the core via the cold leg. A combination of the two processes is also possible.
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The operators have adequate instrumentation to monitor natural circulation for the single phase liquid natural circulation process.
The RCS temperature instrumentation, namely loop AT, can be used along with other information to confirm that the single phase natural !
circulation process is effective. The natural circulation processes !
involving two phase cooling are complex and varied enough so that RCS l loop 4T may not be a meaningful indication of adequate natural circulation cooling.
t For cases where two phase natural circulation cooling is the core heat removal process, establishing heat removal via at least one steam generator utilizing main, startup or emergency feedwater and steam f discharge through the atmospheric dump valve becomes more critical. The monitoring of representative CET temperatures, to confirm the adequacy of the heat removal process, also becomes a critical indicator of natural circulation cooling 4Rcftren c 15 4 If RCS subcooling cannot be maintained, then the core heat removal process will be maintained utilizing two-phase natural circulation and !
flow through the break. If two phase natural circulation is utilized !
the operators must ensure that the following are observed: [
- a. The charging pumps and available SI pumps are operating and adequate flow per Figure 5-3, j and
- b. steam generator feeding and steaming are procerly controlled {
(refer to steps 16 and 17.) . [
and
- c. the representative CET temperature is maintained less than superheated. A superheated condition indicates that core uncovery :
has occurred and that the core heat removal process is no longer !
effective.
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- 27. If the SI pumps are operating, then they must continue to operate at full capacity until SI termination criteria are met. Termination of SI should be sequenced by stopping one pump at a time while observing the termination criteria. Throttling of SI flow is also permissible if all l of the following SI termination criteria are satisfied: [
- a. RCS is subcooled based on representative CET temperature (Figure 5-1). Establishing subcooling ensures the fluid surrounding the core is subcooled which ensures heat transfer to the RCS !
inventory. Voids may exist in some parts of the RCS (e.g.,
reactor vessel head as determined by the HJTC RVLMS), but these l are permissible as long as core heat removal is maintained. [
- b. Pressurizer level is greater than [33%] and not decreasing. A pressurizer level greater than [33%] and not decreasing, in r conjunction with criterion a) above, is an indication that RCS ;
inventory control has been established. ,
- c. At least one steam generator is available for removing heat from the RCS. A steam generator having the ability for feed flow and ,
steam flow is available for removing heat from the RCS. ;
- d. The HJTC RVLMS indicates a minimum level at the top of the hot leg j nozzles. This provides an extra margin of core coverage and, taken in conjunction with the above, serves as an additional !
indication that adequate RCS inventory control has been established. !
If all of the SI termination criteria are met, then the operator may f either stop or throttle the SI pumps. The operator may decide to ,
throttle, rather than terminate the flow, if the SIS is to be used to control pressurizer level or plant pressure. A general assessment of the SIS performance can be made from the control room.
The operator should confirm that at least one train and preferably both trains of SI are operating and that system delivery rate is consistent LOCA 97 ABB CE SYSTEM 80+"
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GUIDELINES with RCS pressure as shown in Figures 5-23 and 5-24. Injection flow rates to each cold leg should be approximately equal. Departures from this would indicate a closed flow path or some system leakage.
- 28. If the criteria of step 27 cannot be maintained after the SIS pumps are throttled or stopped, then the appropriate SIS pumps should be restarted and full SIS flow restored.
- 29. The op_erator should monitor In-containment Refueling Water Storage Tank
~ZR W5 1
-(WT-)- l evel .
For RCS breaks inside containment, a decreasing trend in
[IRWST] level should correspond to an increasing trend in Holdup Volume Tank (HVT) or Reactor Cavity sump level. This action enables the operator to trend [IRWST) level and to anticipate possible problems (LOCA is outside of containment). If a decreasing trend in [IRWST) level cannot be correlated to an increasing HVT or reactor cavity _ sump level, then the LOCA may be outside of containment. For LOCAs outside I
containment, [IRWST) level should be replenished from available sources.
This will prevent the inadvertent air binding of the SI pumps. l 1
- 30. During a controlled cooldown and depressurization the automatic initiation of an MSIS is undesirable, particularly when primary to !
secondary heat transfer via the steam generators is a necessary method of heat removal. Therefore, the MSIS setpoint must be manually reset as the cooldown progresses to ensure that automatic engineered safeguards protection for an MSIS remains available until the RCS is cooled down and depressurized. !
- 31. During plant cooldown and depressurization, it may be necessary for the operators to vent the Safety Injection Tanks (SITS) at a pressure above the maximum SIT pressure to prevent inadvertent SIT injection. This allows the operator to maintain control of the RCS inventory. In addition, it may be desirable for the operators to have the SITS available for injection at a lower pressure during lower mode I
i I
l
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GUIDELINES operations. Therefore, this step instructs the operator to reduce the oo SIT pressure to [f'te psia] to prevent inadvertent injection but maintain its availability during lower mode operations.
- 32. When pressurizer pressure reaches [445 psia] the safety injection tanks (SITS) must be vented, drained, or their discharge valves shut to prevent the nitrogen cover gas from being discharged into the RCS when RCS pressure is reduced below the SITS pressure during a controlled cooldown. For a large break LOCA, this step will not be applicable l
because SITS will have discharged as designed to maintain adequate inventory for heat removal V ere. m.e 10.9).
- 33. Low temperature overpressurization protection (LTOP) is instituted at T,
[259'F)toprotectagainstsubjectingtheRCSpressureboundarytolow temperature brittle fracture.
- 34. If the SI throttle /stop criteria can be satisfied, then there is no need to initiate simultaneous hot and direct vessel injection. This step directs the operator to skip step regarding hot and direct vessel j injection.
- 35. If shutdown cooling system operation cannot be initiated, then ,
simultaneous hot and direct vessel injection is used for both small :
break and large break LOCAs at [2-4] hours after the start of the LOCA.
In this mode, the SI pump discharge lines are realigned so that the ,
total injection flow is divided equally between the hot leg and the- f reactor vessel. Simultaneous injection :nto the hot leg / and reactor l vessel is used as the mechanism to prevent the precipitation of boric acid in the reactor vessel following a break that is too large to allow ;
the RCS to refill.
Injecting to both sides of the reactor vessel ensures that fluid from the reactor vessel (where the boric acid is being concentrated) flows LOCA 99 ABB CE SYSTEM 80+*
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GUIDELINES l out of the break regardless of the break lccation and is replenished with a dilute solution of borated water from the other side of the reactor vessel. The action is taken no sooner than [2 hours] after LOCA ,
since the fluid injected to the hot leg may be entrained in the steam j being released from the core and hence possibly diverted from reaching l the reactor vessel. After [2 hours], the core decay heat has dropped l sufficiently so that there is insufficient steam velocity to entrain the i fluid being injected to the hot leg. The action is taken no later than
[4 hours) after the LOCA in order to ensure that the buildup of boric acid is terminated well before the potential for boric acid precipitation occurs. Even though the action is required only for large breaks, it is taken for any LOCA so that the operator need not be required to distinguish between large and small break LOCAs.
Simultaneous hot)nd ccYq injection is not required for small breaks because the buildup of boric acid is terminated when the RCS is refilled. Once the RCS is refilled, the boric acid is dispersed J
throughout the RCS via natural circulation. If entry into shutdown d
cooling system operation is anticipated before the [4 hour] limit, and the criteria of step 36 are met, then the realignment to hot /eek leg / SVI injection is unnecessary (Reference 15.17 and see detailed plant specific long term cooling analysis).
- 36. For certain sized breaks (small breaks), entry into shutdown cooling may be possible and may be initiated if certain plant conditions exist.
- a. pressurizer level control should be established and verified by a level greater than [33%] and constant sr increasing,
- b. RCS is subccoled,
- c. RCS pressure should be at or below the shutdown cooling system entry pressure of [450 psia]
- d. RCS hot leg temperature should be at or below the shutdown cooling system entry temperature of [400*F],
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- e. Before the SCS is operated, RCS activity levels must be determined since the RCS fluid will now be circulated outside of the containment building. The operator must decide whether to '
circulate high activity RCS coolant outside containment if high activity is present and such circulation has the potential for i release to the environment. If the potential for significant releases exists, it may be more desirable to continue cooling with ,
the steam generators. i If SCS operation is determined to be appropriate, then the SIS is cuv aligned for eeM349-injection and the SCS is initiated. The [ Plant Technical Support Center or Plant Operations Review Committee] may approve changes to these procedures which accommodate the LOCA conditions.
If the RCS cannot be depressurized, then voiding may be causing RCS pressure to remain high. Any time it is found that voiding inhibits RCS depressurization to SCS entry pressure, when SCS operation is desired, j then an attempt at elimination of the voiding should be made (hierences l 15.11 a i;. M).
.3 The operator should continuously monitor for the presence of voids.
Voiding in the RCS may be indicated by any of the following indications, parameter changes, or trends:
- a. letdown flow greater than charging flow, i
- b. pressurizer level increasing significantly more than expected ;
while operating pressurizer spray, ;
- c. the HJTC RVLMS indicates that voiding is present in the reactor vessel, {
- d. HJTC unheated thermocouple temperature indicates saturated !
)
conditions in the reactor vessel upper head, t
_c. b+her Nicat wns occrt h;rc]. - ,
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If voiding should be eliminated, then proceed as follows:
1
- a. letdown is isolated or verified to be isolated to minimize further inventory loss, i
- b. the depressurization is stopped to prevent further growth of the void,
- c. pressurizing and depressurizing the RCS within the limits of Figure 5-1 may condense the void. Pressurizing has the effect of filling the voided portion of the RCS with cooler fluid which will remove heat from the region. Subsequent depressurization and a repeating of this process several times will cool and condense the steam void. In the case of a void in the reactor vessel, the pressurization / depressurization cycle will produce a fill and drain of the reactor vessel. The pressurization /depressurization cycle may be accomplished using pressurizer heaters and spray (preferred method) or the SIS / charging system (alternative method). Monitor pressurizer level and the RVLMS for trending of RCS inventory. This will assist the operator in assessing the effectiveness of void elimination.
- d. if indications of unacceptable RCS voiding continue, and voiding is suspected to exist in the steam generator tubes, then cool the steam generator (by steaming or blowdown, and/or feeding) to condense the tube bundle void. This will be effective for condensing steam voids but will not have an effect on non-condensible gases trapped in the tube bundle. A buildup of non-condensible gases in the tube bundles will not hinder natural circulation event with a large number of the tubes blocked. This is due to the small amount of heat transfer area required for the removal of decay heat. Monitor pressurizer level' for trending of RCS inventory. This will assist the operator in assessing the effectiveness of void elimination.
- e. if indications of unacceptable RCS voiding continue, then voiding may be caused by non-condensible gases. Operate the [ pressurizer LOCA 102 ABB CE SYSTEM 80+*
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vent and/or the] reactor coolant gas vent system to clear trapped '
non-condensible gases. Monitor pressurizer level and/or the RVLMS for trending of RCS inventory. This will assist the operator in {
assessing the effectiveness of void elimination.
- 37. This step is the lead-in for the second flow path mentioned in step 15.
ine LOCA has been isolated and operator actions in the subsequent steps !
(33 through 55) are performed to stabilize plant conditions for long-term recovery. ;
- 38. If the SI pumps are operating, then they must continue to operate at l full capacity until SI termination criteria are met (Reference 15.97- l For most LOCAs, the SI pumps will run continuously for a long period of time while RCS inventory, pressure, and heat removal control are being regained. In some cases, control of these three safety functions is not regained during the accident (i.e., largest breaks) and the SI pumps run for the duration of the recovery period. Early termination is expected only when the SIAS was spurious, or if the leak was identified and promptly isolated.
i Termination of SI should be sequenced by stopping one pump at a time while observing the termination criteria. Throttling of MSI flow is l also permissible if all.of the following criteria are satisfied: j a) RCS is subcooled based on representative CET temperature (Figure 5-1). Establishing subcooling ensures the fluid surrounding the l i
core is subcooled. Voids may exist in some parts of the RCS (e.g., reactor _ vessel head as determined by the RVLMS], but these '
are permissible as long as core heat removal is maintained. ,
b) Pressurizer level is greater than [33%] and not decreasing. A ,
pressurizer level greater than [33%] and not decreasing, in conjunction with criterion a) above, is an indication that RCS T inventory control has been established.
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steam flow is available for removing RCS heat. I d) The RVLMS indicates a minimum level at the top of the hot leg nozzles. This provides an extra margin of core coverage and, taken in conjunction with the above, serves as an additional j indication that adequate RCS inventory control has been established.
If all of the SI termination criteria are met, then the operator may ,
either stop or throttle the SI pumps. The operator may decide to !
throttle, rather than terminate the flow, if the SIS is to be used to ]
control pressurizer level or pressure. A general assessment of the SIS performance can be made from the control room. The operator should confirm that the charging pump is operating and that at least one train, ;
and preferably both trains, of SI are operating and that system delivery rate is consistent with RCS pressure as shown in Figure 5-23 and 5-24.
Injection flow rates to each reactor vessel nozzle should be l approximately equal; departures from this would indicate a closed flow !
- path or some system spillage in addition to the LOCA. ;
- 39. If the criteria of steps 38 cannot be maintained after SIS pumps j throttled or stopped, then the appropriate SIS pumps should be restarted ;
and full SIS flow restored. l
- 40. Pressurizer level should be restored and maintained at [2 to 78%) by l control of charging and letdown (preferentially) as necessary,- and SI j pumps. If SIS termination criteria are met, then SI pumps may be j throttled or stopped. When pressurizer level is being controlled at
[2%] or greater, then the charging pump may be operated as necessary. A pressurizer level of [2 to 78%] should be restored and maintained _to avoid losing pressure control with a saturated bubble in the pressurizer. If the pressurizer level drops below the top of the LOCA 104 ABB CE SYSTEM 80+"
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There should be no high temperature alarms on the RCPs to be j operated. ,
- c. At least one steam generator is available for removing heat from l the RCS. A steam generator having the ability for feed flow and !
steam flow is available for removing heat from the RCS. ;
- d. Pressurizer level is greater than (33%) and not decreasing. A i pressurizer level above [33%) provides the operator with a margin ;
for maintaining plant control during a LOCA. A level of [33%) '
provides a margin above the heaters to offset the possible ;
pressurizer level decrease due to loop shrinkage and/or steam void condensation. !
subcooled condition, taken in conjunction with (d) above, l indicates that adequate inventory control has been established. l
- f. All plant specific RCP operatir.g criteria should be satisfied i before the RCPs are restarted to prevent damage to RCPs resulting !
from abnormal operating conditions. !
- 49. Upon restarting two RCPs in opposite loops, pressurizer level and pressure may decrease due to loop shrinkage and/or steam void' I condensation. It is possible that this action will drain the pressurizer. Steam voids present in the reactor vessel will condense j upon restarting RCPs. The RVLMS should be monitored for the trending of .
reactor vessel liquid level. This trending infurmation may be correlated to pressurizer level decrease. RCP operation with a drained pressurizer may continue provided certain actions are taken and certain l criteria are satisfied w m.m.m... m.w,.
The following constitutes the actions to be taken, and the criteria to l be satisfied, when restarting RCPs:
- a. Start one RCP in each loop. :
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NPSH. NPSH is determined by pressurizer pressure and corresponding T, on Figure 5-1. ,
- c. Operate charging (and SI) pumps, and letdown as necessary to maintain pressurizer level greater than [N]% If SI pumps are operating, continue their operation until SI termination criteria are met (refer to step 38). This action will ensure that -
pressurizer heaters remain covered. l
- 50. If all RCP operation is terminated and inventory and pressure are controlled, then natural circulation is monitored by heat removal via at least one steam generator. Natural circulation flow should occur within >
5-15 minutes after the RCPs were tripped. <
The operator has adequate instrumentation to monitor natural circulation for the single phase liquid natural circulation process. The RCS temperature instrumentation, namely loop AT, can be used along with the other information to confirm that the single phase natural circulation i process is effective. The natural circulation process involving two phase cooling is complex and varied enough so that RCS loop AT may not be a meaningful indication of adequate natural circulation cooling. The guidelines are written to alert the operator to use explicit acceptance :
criteria for natural circulation only when RCS inventory and pressure ;
are controlled.
The RCS temperature response during natural circulation will be slow I
(5-15 minutes) as compared to a norr al forced flow system response time of 6-12 seconds, since the coolant loop cycle time will be significantly !
larger.
When single phase natural circulation flow is established in at least one loop, the RCS should indicate the following conditions:
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- a. Loop AT (Ts - T,) less than normal full power AT, j
- b. Hot and cold leg temperatures constant or decreasing,
- d. No abnormal differences between Tg RTDs and core exit thermocouples. Hot leg RTD temperature should be consistent with {
the core exit thermocouples. Adequate natural circulation flow f ensures that core exit thermocouple temperatures will be l approximately equal to the hot leg RTDs temperature within the 1 bounds of the instrument's inaccuracies. An abnormal difference [
between Ts and the CETs is greater than [10*F].
Natural circulation is governed by decay heat, component elevations, l primary to secondary heat transfer, loop flow resistance, and voiding.
Component elevations on C-E plant are such that satisfactory natural circulation decay heat removal is obtained by fluid density differences ,
between the core region and the steam generator tube sheet. ,
As a contingency, if the criteria listed are not met, then natural circulation in the RCS is not effectively transferring heat from the core to the steam generators. Both RCS and Core Heat Removal Safety Functions may become jeopardized if any of the above criteria continue j to be violated. Operators should ensure that RCS pressure and
inventory, and SG steaming and feeding, are being controlled properly to prevent violation of a safety function.
- 51. During a controlled cooldown and depressurization, the automatic ;
operation of certain safeguard systems is undesirable. Therefore, the setpoints for SIAS, and MSIS must be manually reset (lowered) as the cooldown progresses to ensure that automatic engineered safeguards I
protection remains available until the RCS is cooled down and depressurized. t LOCA 111 ABB CE SYSTEM 80+"
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52, During plant cooldown and depressurization, it may be necessary for the operators to vent the Safety Injection Tanks (SITS) at a pressure above the maximum SIT pressure to prevent inadvertent SIT injection. This ;
1 allows the operator to maintain control of the RCS inventory. In addition, it may be desirable for the operators to have the SITS available for injection at a lower pressure during lower mode operations. Therefore, this step instructs the operator to reduce the 3m SIT pressure to [MO psia] to prevent inadvertent injection but maintain its availability during lower mode operations. ,
1
- 53. If pressurizer pressure reaches [445 psia] the safety injection tanks (SITS) must be vented, drained, or their discharge valves shut to prevent the nitrogen cover gas from being discharged into the RCS when i RCS pressure is reduced below the SITS pressure during a controlled cooldown. ,
- 54. Low temperature overpressurization protection (LTOP) is initiated at T,
< 259'F to protect against subjecting the RCS pressure boundary to low- l temperature brittle fracture. I t
- 55. For certain sized breaks (small breaks), entry into shutdown cooling may j be possible and may be initiated if certain plant conditions exist.
i
- a. pressurizer level control should be established and verified by a level greater than [33%] and constant or increasing,
- b. RCS subcooling is subcooled,
- c. RCS pressure should be at or below the shutdown cooling system 7 entry pressure of [450 psia] ;
- d. RCS hot leg temperature should be at or below the shutdown cooling system entry temperature of [400*F], i
- e. Before the SCS is operated, RCS activity levels must be determined since the RCS fluid will now be circulated outside of the containment building. The operator must decide whether to .
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U SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT RECOVERY GUIDELINE EMERGENCY OPERATIONS ""
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- f. Other plant specific prerequisites for SCS operation must be considered (e.g., component cooling water, instrument air and valve control power). [
If SCS operation is determined to be appropriate, then the SIS is :
aligned for cold leg injection and the SCS is initiated. The [ Plant !
Technical Support Center or Plant Operations Review Committee] may [
approve changes to these procedures which accommodate the LOCA conditions. !
l If the RCS cannot be depressurized, then voiding may be causing RCS !
pressure to remain high. Any time it i:: found that voiding inhibits RCS depressurization to SCS entry pressure, when SCS operation is desired, l then an attempt at elimination of the voiding should be made (-Rete.er.ces ;
15.11 1-i5.14).
The operator should continuously monitor for the presence of voids. :
Voiding in the RCS may be indicated by any oir the following indications, parameter changes, or trends:
i
- a. letdown flow greater than charging flow, '
- b. pressurizer level increasing significantly more than expected ,
while oparating pressurizer spray,
- c. the HJTC RVLMS indicates that voidino is present in the reactor vessel, !
- d. HJTC unheated thermocouple temperature indicates saturated l conditions in the reactor vessel upper head, j
- e. Evthe. niuicauons instet- Scre] .
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GUIDELINES If voiding should be eliminated, then proceed as follows: ;
i
- a. letdown is isolated or verified to be isolated to minimize further inventory loss,
- b. the depressurization is stopped to prevent further growth of the 5
void,
- c. pressurizing and depressurizing the RCS within the limits of ,
Figure 5-1 may condense the void. Pressurizing has the effect of ;
filling the voided portion of the RCS with cooler fluid which will remove heat from the region. Subsequent depressurization and a j repeating of this process several times will cool and condense the ,
I steam void. In the case of a void in the reactor vessel, the pressurization / depressurization cycle will produce a fill and ,
drain of the reactor vessel. The pressurization /depressurization !
cyt.le may be accomplished using pressurizer heaters and spray (preferred method) or the SIS / charging system (alternative :
method). Monitor pressurizer level and the RVLMS for trending of RCS inventory. This will assist the operator in assessing the !
effectiveness of void elimination. .
- d. if indications of unacceptable RCS voiding continue, and voiding is suspected to exist in the steam generator tubes, then cool the steam generator (by steaming or blowdown, and/or feeding) to condense the tube bundle void. This will be effective for condensing steam voids but will not have an effect on non-condensible gases trapped in the tube bundle. A buildup of j non-condensible gases in the tube bundles will not hinder natural circulation event with a large number of the tubes blocked. This is due to the small amount of heat transfer area required for the ,
removal of decay heat. doniter pressurizer level for trending of .
RCS inventory. This will assist the operator in assessing the effectiveness of void elimination.
- e. if indications of unacceptable RCS voiding continue, then voiding j may be caused by non-condensible gases. Operate the [ pressurizer LOCA 114 ABB CE SYSTEM 80+*
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GUIDELINES qu vent and/or the] reactor coolant 3vent system to clear trapped l non-condensible gases. Monitor pressurizer level and/or the RVLMS for trending of RCS inventory. This will assist the operator in assessing the effectiveness of void elimination.
When shutdown cooling system entry conditions are met, the LOCA guideline should be exited and SCS operation initiated per plant-specific operating instructions. The Plant Technical Support Center or Plant Operations Review Committee may have modified the SCS procedure or added special precautions to SCS operation because of the LOCA condition.
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Safety Function Status Check The Safety Function Status Check (SFSC) is used to continually verify the status of safety functions. The safety function acceptance criteria are j selected from best estimate analysis to rrflect the range for each parameter which would be expected following a Loss of Coolant Event. If all SFSC acceptance criteria are being satisfied, then the adequacy of this guideline for mitigating the event in progress is confirmed and the health and safety of the public is ensured.
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SAFETY FUNCTION STATUS CHECK BASES LOSS OF COOLANT ACCIDENT ;
l 1
The safety functions and their respective acceptance criteria listed below are j those used to confirm the adequacy of the LOCA Guideline in mitigating the event. ,
SAFETY FUNCTION ACCEPTANCE CRITERIA BASES
- 1. Reactivity Control a. Reactor Power For all emergency Decreasing events, the reactor must i and be shutdown. The
- c. Maximum of I CEA NOT borated observes typical fully inserted or Technical Specification borated per Tech. requirements.
spec.
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GUIDELINES SAFETY FUNCTION ACCEPTANCE CRITERIA BASES
- 2. Maintenance of Vital a. Safety Load Division One vital AC bus is Auxiliaries (AC and I energized required to power -
DC power) or equipment necessary to -
Safety Load Division maintain control of all II energized other safety functions.
y One DC train is required -l as a minimum to provide monitoring and limited control of the other safety functions.
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SAFETY FUNCTION ACCEPTANCE CRITERIA BASES
- 2. Maintenance of Vital , igg. ,
Auxiliaries (AC and b. 125V DC and 120V AC DC power) Safety Bus A ;
(Continued) energized j and 125V DC and 120V AC j Safety Bus C energized 9.C 125V DC and 120V AC :
Safety Bus B energized and 125V DC and 120V AC Safety Bus D energized
[
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- 3. RCS Inventory a.
Control Then ensure: pressurizer level should ,
i) charging and let- be restored to the band down, and SIS of [2 to 78%] by con-flow (per Figure trol of charging and [
5-3) maintaining letdown and SIS flow.
or restoring SIS flow may be ter-pressurizer level minated or throttled
[2 to 78%) (un- when SIS termination less SIS termi- criteria are met. The nation criteria value of [78%), was ;
met). chosen as an upper limit ,
and for pressurizer level to ii) the RCS is sub- ensure an adequate bub-cooled ble is in the pressur-and izer following an inad-iii) the RVLMS indi- vertent initiation of cates the core is auxiliary spray for 20 i
covered seconds. A value of o_r [2%], was chosen as the
- b. H LOCA NOT iso- lower limit to ensure lated, Then ensure: the operator does not i) Available charg- drain the pressurizer.
ing pump is oper- Subcooling coexisting i
ating and the SIS with a pressurizer level pumps are in- of [2" to 78%) indicates ,
jecting water adequate RCS inventory into RCS per control via a saturated Figure 5-3 i and ,
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- 3. RCS Inventory Con- ii) the RVLMS in- bubble in the pressur-trol (Continued) dicates the core izer. Representative .
is covered. CET Temperature is to be used during natural cir- ;
culation flow conditions l and Tg RTDs are to be used during forced cir-culation flow condi-tions. An RVLMS indi-cation that the core is covered, taken in con-junction with subcool-ing, is an additional indication that RCS in- ,
ventory control has been !
established.
For cases where RCS in-ventory has badly de- l graded, the SIS oper-ation provides implicit assurance that control ,
is being regained. At RCS pressures greater than the shutoff head of the SIS, the use of the charging pump is emphasized. f LOCA 121 ABB CE SYSTEM 80+*
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SAFETY FUNCTION ACCEPTANCE CRITERIA BASES'
- 3. RCS Inventory Con- The charging pump is trol (Continued) emphasized because until t pressure lowers, this will be the sole means of injecting water into ,
the RCS.
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- 4. RCS Pressure Control a. Pressurizer heaters The expected RCS and spray, or pressure range of the charging and SIS LOCA event is very pumps are broad, therefore, the maintaining or acceptance criteria are restoring written to cover the pressurizer pressure expected range which may within the P-T result from a LOCA.
limits of Figure 5-1, E '
- b. Available charging pump is operating and the SIS pump (s) are injecting water t into the RCS per Figure 5-3 (unless SIS termination i criteria are met).
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SAFETY FUNCTION ACCEPTANCE CRITERIA BASES l
- 5. Core Heat Removal Tu RTDs and Super-heat condition in representative CET the RCS can only occur ;
temperatures less than with core uncovery. .
superheated. Core uncovery results from a loss of RCS in-ventory which generally results from two ac-cident scenarios: LOCA or loss of steam gener-ators as a heat sink.
LOCA results directly in a loss of inventory.
Very small break LOCAs will not result in de-pressurization much be-low the SI pump shutoff head. For these small break LOCAs superheat is :i indicative of core un- I covery occurring at high ;
pressure. For large break LOCAs which result.
in rapid depressur-ization to less than 300 .
psia, superheat which'is ,
indicative of core .
uncovery occurs at low pressure. A loss of inventory (leading to ,
core. uncovery) can also
[
result from a loss of .
[
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- 5. Core Heat Removal S/G heat sink which -
(Continued) causes RCS pressure to ,
rise high enough to lift :
the primary safety ,
valves. Core uncovery l and, therefore, superheat on the [CETs]
indicate an advanced ,
phase in the approach to. i inadequate core cooling-and are undesirable. If at anytime superheat is :
approached or indicated, 1 the operator should review the effectiveness of earlier measures and take all possible steps ,
to restore the inventory to at least a core ,
covered condition as indicated by saturation i or subcooling on the !
CET, Subcooled Margin Monitor, or as an indication of core l coverage on the RVLMS. ;
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i) within the normal maintained if.at least level band with one steam generator is feedwater available for removing available to heat (capable of steam ;
maintain level flow and feed flow). ;
9C ii) being restored by f main, emergency, or startup feedwater flow. ;
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- 7. Containment a. No steam plant Steam plant activity is ,
Isolation activity monitors an indication of a SGTR alarming and is not anticipated and for a LOCA regardless of *
- b. i) Containment containment conditions. j pressure less than [2.7 psig] [2.7 psig] is the CIAS p_t setpoint. If pressure ,
ii) CIAS present or does reach [2.7 psig],
manually containment isolation initiated valves should shut-and automatically (i.e., or
- c. i) No containment CIAS should be present).
area radiation monitors alarming If CIAS does not occur pr automatically, the ii) CIAS present or operator should manually manually initiate a CIAS.
initiated and annulus vent The containment should system is in be isolated if operation with containment area annulus pressure radiation monitors are [
'?p:in alarming.
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SAFETY FUNCTION ACCEPTANCE CRITERIA BASES
- 8. Containment a.i) Containment [236*F] corresponds to Temperature and Temperature less the saturation temper-Pressure Control than [236*F] ature associated with and the CSAS setpoint. [8.5 ii) Containment psig) is based on CSAS ,
Pressugeless p setpoint.
than [1e psig] ;
or Containment temperature
- b. At least one and pressure may exceed containment spray the above limits during :
header delivering at inside containment LOCA least [4500 gpm]. events. If this hap-pens, the containment i
cooling systems should be operating to minimize the temperature and ,
pressure. Each contain- ;
ment sprays train which will remove 100% of the design basis heat load should be specified.
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GUIDELINES SAFETY FUNCTION ACCEPTANCE CRITERIA BASES i
- 9. Containment Com- a. Hydrogen concen- The Containment Combus-bustible Gas Control trations less than tible Gas Control safety l
[0.5%) function is satisfied if I p_t hydrogen levels are less i
- b. i) [All available than the minimum detect- ;
hydrogen able concentration recombiners ([0.5%]). If hydrogen i energized] is 2 [0.5%) then oper-and ation of the hydrogen ii) hydrogen recombiners- should main-concentration tain the hydrogen con- i
, less than [4%] centration below the p_t lower flammability limit
accordance with gation system can be ;
plant-specific operated to ensure con-operating tainment integrity is 1 instructions. maintained. .The [ Plant Technical Support Cen-ter] will review containment conditions and recommend a hydrogen mitigation if conditions warrant. The safety function is satisfied if the mitigation system is operating in accordance l l
with [ plant specific j operating instructions). !
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SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT RECOVERY GUIDELINE EMERGENCY OPERATIONS GUIDELINES Page
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i Event Strateov This section contains the detailed LOCA operator actions strategy flow chart, Figure 5-26. The flow chart pictorially depicts the strategy around which the LOCA guideline is built. It is intended to assist the reader in understanding the intent of the guideline writer and for use in training. Operators should understand the major objectives of the guideline in order to facilitate their ;
progress toward the guideline goals.
The strategy charts show the LOCA Recovery Guideline strategy in detail and list the guideline steps which correspond to each strategy objective. Some steps in the guideline may be performed at any time during the course of an -
event. Those steps which have an asterisk next to the step number.can be performed at any time during the event.
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SYSTEM 80 +" TITLE - LOSS OF COOLANT ACCIDENT :
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Figure 5-26a :
LOSS OF COOLANT ACCIDENT RECOVERY .
STRATEGY CHART (FLOW AND STRATEGY CHARTS WILL REFLECT THE DETAILED STEPS IN THE GUIDELINE.)
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GUIDELINES ;
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t Figure 5-26b t LOSS OF COOLANT ACCIDENT RECOVERY ,
STRATEGY CHART (FLOW AND STRATEGY CHARTS WILL REFLECT THE DETAILED STEPS IN THE GUIDELINE.)
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SYSTEM 80 +" TITLE LOSS OF COOLANT ACCIDENT.
RECOVERY GUIDELINE EMERGENCY. OPERATIONS 5-GUIDELINES Page of
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Figure 5-26c LOSS OF COOLANT ACCIDENT RECOVERY STRATEGY CHART (FLOW AND STRATEGY CHARTS WILL REFLECT THE DETAILED STEPS IN THE GUIDELINE.)
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Figure 5-26d LOSS OF COOLANT ACCIDENT RECOVERY STRATEGY CHART (FLOW AND STRATEGY CHARTS WILL REFLE::T THE DETAILED STEPS.IN THE GUIDELINE.)
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