ML20112F743
| ML20112F743 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 04/30/1984 |
| From: | Chi L, Rogers A, Sozzi G GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20112F735 | List: |
| References | |
| AE-52-0484, AE-52-484, TAC-57308, TAC-57309, NUDOCS 8503270532 | |
| Download: ML20112F743 (19) | |
Text
r-s.
~,.
ENCLOSURE 1
~
p AE-52-0484 DRF B21-00289 April 1984 BYPASS TIMER CALCULATION FOR THE ADS MODIFICATION FOR HATCH UNITS 1 AND 2 Prepared by:
v-L. L. Chi, Senior Engineer Performance Requirements Engineering t
Approved by:
G. L. Sozzi, Manager Performance Requirements Engineering Approved by:
- 17 A[E. Rogers, Manager Plant Performance Fngineering 8503270532 850319
~
fDR ADOCK 05000366 PDR GENERAL $ ELECTRIC NUCLEAR ENERGY BUSINESS OPERATIONS GENERAL ELECTRIC COMPANY
- 175 CURTNER AVENUE e SAN JOSE, CAUFORNIA 95125 4
.. x s.
=
b CONTRIBUTORS L. L. CHI L. F. SANJINES P. T. TRAN
-i-i
LEGAL NOTICE Except as otherwise agreed to in writing, neither the General Electric Company nor any of the contributors to this document makes any warranty or representation (express or implied) with respect to the accuracy, completeness, or usefulness of the information contained in this document or that the use of such information may not infringe privately owned rights, nor do they assure any responsibility for liability or damage of any kind which may result from the use of any of the information contained in this document.
p._
..f I*
4 TABLE OF CONTENTS PAGE
1.0 INTRODUCTION
1 2.0 ANALYSIS GOAL 5
3.0 ANALYSIS 6
3.1 ANALYSIS METHOD 6
3.2 EVENT DESCRIPTION 7
3.3 RESULTS 8
4.0
SUMMARY
AND CONCLUSIONS 14
5.0 REFERENCES
15
-iii-1 b
t-
n
1.0 INTRODUCTION
The Automatic Depressurization System (ADS) through selected safety relief valves, functions as a backup to the operation of the high pressure injection systems: feedwater, High Pressure Coolant Injection (HPCI), Reactor Core Isolation Cooling (RCIC), for protection against excessive fuel cladding heatup upon loss of coolant over a range of steam or liquid line breaks inside the drywell. The ADS depressurizes the vessel, permitting the operation of the low pressure injection systems:
Low Pressure Coolant Injection (LPCI), core spray. The ADS is currently activated automatically upon coincident signals of low water level in the reactor, high drywell pressure, and low pressure ECCS pump running (tigure 1-1). A time delay of approximately 2 minutes after receipt of the signals allows the operator to reset the logic and prevent an automatic blowdown if the RPV water level is being restored or if the signals are erroneous. The ADS can be manually initiated as well.
For transient and accident events which do not directly produce a high drywell pressure signal and are degraded by a loss of all high pressure injection systems, adequate core cooling is assured by manual depres-surization of the reactor followed by injection from the low pressure systems. To reduce the dependence on operator action and to satisfy the intent of the Nuclear Regulatory Commission (NRC) requirements, Item II.K.3.18 of NUREG-0737 (Reference 1), Georgia Power Company (GPC) has elected to implement an ADS modification, known as Option 4, to the Edwin I. Hatch Nuclear Power Station, Units 1 and 2.
The Option 4 (Reference 2) modification adds a timer which bypasses the high drywell pressure permissive of the current ADS logic and adds a manual switch which allows the operator to prevent (inhibit) automatic ADS initiation (Figure 1-2).
The high drywell pressure permissive is bypassed by in-t.
stalling a second (" bypass") timer that is actuated on low water level (Level 1). When this timar times out, the high drywell pressure trip would be bypassed and the ADS initiated on a low water level signal alone. The additional logic would not affect the high drywell pressure-low water level initiation sequence insofar as it responds to pipe breaks inside the drywell. The addition of a manual inhibit switch to the ADS initiation logic has no effect on automatic ADS response to isolation or LOCA events.
This report presents the analysis which determines the setting for the bypass timer. The bypass timer will extend the ADS operation to transient events or loss of coolant accidents (LOCA) which do not result in a release of steam to the drywell but which may require depressuri-zation of the reactor pressure vessel to maintain adequate core cooling.
The selected event for determining the bypass timer setting is the main steam line (MSL) break outside the containment. This event will result in the most inventory loss without any release of steam to the drywell.*
The analysis method, assumptions, and results are discussed in the following sections.
The limiting event for this report should not be confused with the worst case event of Reactor Water Cleanup (RWCU) line break analyzed in NED0-24873 ("High Energy Line Break Evaluation for Edwin I. Hatch Nuclear Power Station", October 1980). This is because the " worst case" event in NED0-24873 did not include the case of MSL break and a complete loss of high pressure makeup systems. NED0-24873 also assumed manual depressurization at 10 minutes from event initiation.
With this assumption, the conclusion of NED0-24873, that the PCT for high energy line breaks outside the containment is significantly less than 2200 F is still valid.
Further, the event of stuck open relief valve at isolation and loss of all high pressure makeup systems is beyond the plant design basis.
e HIGH ORYWE LL PR ESSURE SEAL IN 1r LOW WATER LEVEL (LOW PR ESSURE ECCS ACTUATION) 1r CONFIRM WATER LEVE L IS BE LOW SCRAM LEVEL 1r 120 SECONO ACTUATION TIMER' if LOW PRESSUR E ECCS PUMPS RUNNING 1r ADS ACTUATION
- 120-second actuation timer will reset if reactor water level recovers above trip elevation before it times out.
The timer will restart if the low reactor water level signal occurs again.
Figure 1 1.
Current ADS Logic l
HIGH ORYWELL
- PRESSURE LOWWATER LEVEL (LOW PR ESSUR E SE AL IN ECCS ACTUATION) 1r SEAL IN LOW WATER LEVEL
'(LOW PRESSURE ECCS ACTUATIONI BYPASS TIMER if CCNFIRM WATER LEVEL IS BELOW SCRAM LEVEL 1r 120 SECOND ACTUATION TIMER
- 120 second actuation timer will reset if reactor water level recovers above trip elevation before it times out.
The timer will restart if the low reactor water level signal occurs again.
Figure 1-2.
Option 4 ADS ifodification -
Bypass High Drywell Pressure Trip and Add Manual Inhibit Switch
-4
c 2.0 ANALYSIS G0AL The bypass timer of the ADS modification is to assure adequate core
~
cooling for transient or accident events which may require rapid depressurization. Adequate core cooling can be assured if the peak cladding temperature (PCT) for an event is less than 1500 F.
Although the maximum PCT limit imposed by 10CFR50 Appendix K is 2200 F, a lower limit is established for the bypass timer. The lower limit will assure that the transient or outside line break events will not be the limiting events for the plant safety analyses. The current limiting events are large recirculation line breaks inside the containment which cannot be isolated and should be maintained as the limiting events. Thus, the goal for the analysis is to determine a setting for the bypass timer which will limit the PCT to approximately 1500 F for the worst case transient or outside line break event.
3.0 ANALYSIS 3.1 ANALYSIS METHOD The setting for the bypass timer is based on limiting the PCT of a transient or outside containment line break event to approximately 1500 F. The limiting event is the main steam line (MSL) break outside the containment. This event will result in a large amount of inventory loss before the break isolation and maintain the reactor at high pressure after the break isolation.
The event and the resultant PCT are evaluated in accordance with the approved Appendix K models (Reference 3) and the following conservative initial conditions and assumptions.
(1) The reactor is operating at 102'.' of rated power. This maxi-mizes the fuel cladding heatup and conforms with the require-ments of 10CFR50 Appendix K.
(2) The initial reactor. water level is at the scram level. This minimizes the time for ADS initiation.
(3) The initial system pressure and steam flow are consistent with the heat balance values for the assumed initial power and water level.
(4) The steam line is instantly severed by a complete circumfer-ential break. The break is physically arranged so that the.
coolant discharge through the break is unobstructed. These assumptions result in the most severe mass loss for the event. l I-
(5) The Main Steam Isolation Valves (MSIVs) are closed 5.5 seconds after the break occurs. This assumption is based on the 0.5 second time required to develop the automatic isolation signal of high steam flow and 5 second closure time for the MSIVs, which is the maximum value allowed by the plant technical specifications.
(6) Feedwater flow decreases linearly to zero in 1 second after the break occurs. This assumption minimizes the amount of inventory available to the reactor.
(7) The high pressure coolant injection (HPCI) and the reactor core isolation cooling (RCIC) systems are not available. A complete loss of high pressure makeup systems is a condition which may require rapid depressurization with the ADS.
(8) The low pressure coolant injection (LPCI) and the core spray systems are available for inventory makeup when the reactor is depressurized below the shut-off heads of the low pressure pumps.
(9) The decay heat value is 120% of the 1971 ANS standard which conforms to the requirements of 10CFR50 Appendix K.
3.2 EVENT DESCRIPTION The main steam line (MSL) break outside the containment is assumed to occur while the reactor is operating at 102% of rated power.
r s
The break results in steam flow through both ends of the break (Figure 3-1).
The steam flow increases to the value limited by critical flow considerations. The flow from the upstream side of the break is limited initially by the main steam line flow restrictor. The flow from the downstream side of the break is limited initially by the flow restrictors in the three unbroken lines. The high flow generates an isolation signal for the MSIVs.
The maximum response time for the flow sensing instrument is 0.5 second and the maximum valve closure time for the MSIVs is 5 seconds. Thus at 5.5 seconds after the break initiation, the MSIVs will be closed to isolate the break.
Following the isolation, the reactor pressure increases to acti-vate the safety relief valves (SRVs). Without feedwater, HPCI and RCIC, the SRV actuations gradually reduce the reactor water inventory down to Level I which activates the bypass timer. When the bypass timer times out, the existing ACS timer will start and automatic ADS initiation will occur within 120 seconds. The reacter pressure will then decrease and the low pressure ECCS pumps will inject to provide core cooling.
3.3 RESULTS Typical plant responses to the above event of MSL break outside the containment with the bypass timer for the ADS are shown in Figures 3-2 and 3-3.
Figure 3-2 shows the reactor pressure and water level responses. The reactor pressure drops initially due to the break.
After the break is isolated, the reactor pressure increases and the c
SRVs actuate. The reactor pressure remains within the operating range of the SRVs until the ADS actuates. Meanwhile, the reactor water level decreases gradually down to Level 1.
Before the by-pass timer and the existing ADS timer have expired, the water level drops below the top of the active fuel.
This period of uncovery causes an increa.se in PCT (Figure 3-3).
When the ADS actuates, the rapid depressurization results in a large water level swell to cover the core momentarily.and cool the fuel cladding. As the depressurization continues, the core once again uncovers and the PCT increases. The fuel cladding heat up decreases when LPCI and core spray begin to provide core cooling and eventually is termina-ted when the core reflood:.
The resultant PCT for bypass timer settings of 10, 13 and 15 minutes are shown in Figure 3-4.
The PCT for the 13 minute setting is approximately 1497 F which satisfies the established goal. The 13 minutes setting is greater than the generic value based on the previous evaluation (Reference 2). A longer timer setting will allow the operator more time to inhibit any unnecessary ADS and, therefore, is desireable as well as justifiable by this analysis.
An additional consideration to ensure the acceptability of the
~
bypass timer setting is to determine the affect of an ADS valve out-of service on the bypass timer setting. With an ADS valve out-of-service or failed during the event, the rate of reactor depressurization is reduced. This will affect the time when LPCI and core spray pumps can inject and have a direct impact on the resultant PCT.
If the effect is significant, it may be desirable to reduce the setting of the bypass timer.
Figure 3-4 shows that-the PCT for a 13 minute bypass timer with up to 2 out of the seven ADS valves out-of-service is approximately 1539 F.
This indicates that the PCT is not significantly affected even with two ADS valves unavailable or out-of-service.
Therefore, the 13 minute setting for the bypass timer is the recommended setting for the proposed ADS modification.
s s
i PRIMARY CON TAINWEN T BYPAS$ HEADER FLOAP
$ TOP VALVES
?"' xP s t Ic4 CONTROL VALVES I
N '2'
[
BREAK x
X X
>0-c<
REACTOR VES$EL TUR8INE 0)
J 1
r'e,
y/ f f g
g GENERATOR x
x o
U BYPAS$
FLOW X
RESTRICTOR$
TURBINE BYPA$$
ISOLATION VALVES SYSTEM t
CONO.
l l
L Figure 3-1 Location of !!ain Steam Line Break Outside Containment i. -
ll.
g-
. c q
I 2
5-i l
A-
. I -
S -
P
" '0 J'
1 TTT
. (
\\
=
EEE G
EEEE i
3 rFFF
'i
{
1 u
r
- S08, e
S38.E L
m E.
i R79V T
P12E L
s L
s
=
E-.
R a
p g
3 S
E y
SFFT B
EAAA VBTW h
n 2
i 0
~
1 0
1 3
2 ro
)
F
_S e
D s
n N
op O
s C
e 2
R 8E r
6S o
t 0(
cae E
R M
I 3
2 T
2 3
erug 1
1 i
3 F
.~
' 0 V
3 2
l 2
- _ _ ~
. 23 8
0 0
O 0
11
~
C~n_
[DDDJC JL(DJ>
ID L L
((LC t
(L
- l
,Ill,!lilil i!II i!
i t
,./
t j^'.
j, n
3 s-y E-o A
l RF u '0 u
fG0 1
i iE R00 E0 6
U1 3
3 F:1
\\
HT2 A
EF T - -
R' 2
DllT A/I LUM CTIBL l
3 K
ACT 0
ETC l[
PHP ia3.
2 0
r 1
en i
1 y
T
+
)
i s
S s
a D
p N
y C
O C
n s'
3 8E i
G. S 0
01 1
r E
o F
M I
TC T
P 3
2 i
3 3
l e
t3 ru 3
2
' 0 g
i F
l I
2
~1
_ - ~
.0 3 '0 2
1 O
1>
iDJOw
&xLl OEJ_U Ec b I
Lb L-4' e
E
r-
~
I 2000 O
1800 1600 o'
v
~
Analysis Goal = 15000F
^
e w
B
_U i!
(
E, 1400 6
E-E e
i G
1200
'E O
O All ADS Valves 1000 6 5 ADS Valves 9
l l
l l
l 800 10 11 12 13 14 15 BYPASS TIMER SETTING (Minutes)
Figure 3-4.
PCT vs. Bypass Timer Setting,
- 7. _.
4.0
SUMMARY
AND CONCLUSIONS Plant specific analyses were performed to determine the setting of the bypass timer.for the ADS modification to be implemented in the Edwin I.
Hatch Nuclear Power Station, Units 1 and 2.
The ADS modification is to add a bypass timer to the high drywell pressure permissive of the ADS logic. The bypass timer will activate if the reactor water level reaches Level 1 and automatic ADS will initiate when both the bypass timer and the existing ADS timer have expired. The modification provides automatic ADS initiation for transients or line breaks outside containment. Based on the evaluation of the limiting event of a MSL break outside the containment and a goal of limiting the maximum PCT to approximately 1500 F, the recommended setting for the bypass timer is 13 minutes.
s
5.0 REFERENCES
1.
" Clarification of TMI Action Plan Requirements",.
0ffice of Nuclear Reactor Regulation, U.S. Nuclear Regulating Commission, NUREG-0737, November 1980.
2._
"BWR Owners' Group Evaluation of NUREG-0737 Item II.K.3.18 Modification of Automatic Depressurization System Logic",
General Electric Company, NEDE-30045, February 1983.
3.
" General Electric Company Analytical Model For Loss-Of-Coolant Analysis In Accordance With 10CFR50 Appendix K", General Electric Company, NEDO-20566, January 1976. _
-