ML19319E222
| ML19319E222 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 10/17/1974 |
| From: | SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML19319E218 | List: |
| References | |
| NUDOCS 8003310730 | |
| Download: ML19319E222 (4) | |
Text
.
l s/9 s
1 v,
ABNORMAL OCCURRENCE REPORT
. DOCKET NO. 50-312-74-6 ReportkngDate:.
October 17, 1974 Occurrence Date:
- October 7, 1974 Time:
1110
-Facility: '
Rancho Seco Nuclear Generating Station Unit'No. 1
' Clay. Station, California Identification of Occurrence:
Exceeded the maximum cooldown rate established in the Technical Specifications.
Condition Prior to Occurrence:
The reactor was at steady state power producing 15% of rated steam load during the initial power testing program.
Reactor coolant pressure was at 2155 psig, average tempera'ture was at j76*F and control rod positions were O
Gr 1,2,3,4 and 5 at 100% withdrawn and-Gr 6 and 7 at 70%.
Boron was at 1339 ppmB and all auxiliary loads were being supplied by main (reactor) steam.
Description of Occurrence:
During operation at 15% the reactor operator noticed that the main condenser vacuum was decreasing.
Immediately the operator sent a man to put a second hogging air ejector on the line 'to help maintain condenser vacuum. The inieakage-into the condenser was too great to prevent decreasing the vacuum to 21 inches Hg.- At this time the operator realized the magnitude of the condenser leakage and in-formed the Shift Supervisor who in turn went to the condenser area in an attempt to visually determine the cause-of the'. low vacuum.
Six minutes later, with the continued
~
loss of vacuum,'the setpoint of 20 inches Hg was. reached. At this vacuum, to protect the condenser, the turbine bypass-valve controllers are automatically bypassed and a direct signal is inserted to close all the bypass valves. All six atmospheric relief valves werelisolated previously pending final adjustments on valve positioners. The
~
, operator tripped the reactor 30 seconds after the bypass valver shut-(time:
1109:30) whdi he determined that the heat input was inducing a transient. With all condenser bypass valves-closed and the ' atmospheric relief valves isola ~ted, the available heatsink was' the secondary sidei code. relief valves. The reactor pressure increased to 2250 psig-and.the a'erage: temperature' increased to 583*F.
The secondary. system pressure increased :
v toL1010 psig and at this pressure the "B" main steam line safety lifted'and disenarged J
my
_1_
0 g
a
,..f
-p
.4
\\
?
~,. - _
~a i
k r
The secondary system pressure was reduced to 5
re were reduced to 574*F I
ctcam for appcaximately one minute.
steam from the steam
[
963 p31g and the zaactor coolant temperatura and pressu The auxiliary steam loads continued to extractdecay heat was insufficien Since the reactor power history was minimal, ause a decreasing reactor coolant cnd 1940 psig.
The steam loads were high due to the..
g;n;rctors. the auxiliary steam load continuing to c d d the main feedwater pump, the hogging air k
cy;t:m temperature and pressure transient.
ta prevent in an Attempt to hold tcoting status of the plant and inclu e iously valved in, f
Gjcetors (a second hogger was just prev Fourth point heaters and several he condenser vacuum), pegging steam to tApproximately 4 1/2 minutes after th d~
ture was 533*F and decreasThg7 dn
.l High Pressure Injection Channels prccsure was 1840 psig and decreasing,stempera czall loads.
i pressurizer level was 30 inches and decreas ng.LA cnd IB w t
i nt:
I coolant system and maintain an indicateChannels lA and 13 s, ta k
d High Pressure Injection Puep A and the ass p
-l.
1 cuction valves from the Borated Water Storage l
(This component was
[
High Pressure Injection Pump B.with the Techni 2.
from the 9ovedfromserviceinaccordance Makeup Pump and the associated' suction valv 3.
Borated Water Storage Tank and the discharge va l of the pressurizer the operator needed to regain contro The above three items are whatThis channel also started:
A and C Units The Reactor Building Emergency Cooling Fans 1 vel.
4.
r Valves.
cnd the associated Nuclear Service Cooling WateThe Rea B and D
'5.
ling Water Valves.
Units and the associated Nuclear Service CooThe Nuclear S 6.
The Nuclear Service Cooling Water Pu=p B.
7.
The Nucicar Service Raw Water Pump A.
8.
The Nuclear Service Raw Water, Pump B.
9.
Reactor Building Isciation Valves.
10.
Auxiliary Turbine Steam Inlet Valve and Auxilia 11.
l transient but were part of Channe Feedwater Bypass Valves.
7~'
h Items 4 through 10 made no contribution.co t eHowever, Item 1 junction The steam en steam from the steam generators and in cont temperature and pressure.
1A and 1B, continued to decrease the reactor coolan
_g.
- %4b
w t
m..-
the fourth point heaters was reduced in order to conserve steam and the pressurizer level started increasing rnd returned to normal twenty-seven minutes later.
The cuxiliary boilers were put on the system and the auxiliary feedwater pump was secured ct 1130. Once the cold water injection into the steam generators was. stopped and the cteam valve to the auxiliary turbine closed the reactor coolant transient was terminated.
Stable conditions at 2155 psig pressure, 460*F and normal pressurizer level were obtained cpproximately forty minutes after the initial transient. The system was then slowly returned to the original pressure and temperature during the subsequent three hours.
At.2:00 p.m. the main steam pressure uas 880 psig, the pr2ssurizer level was 180 inches, coolant average temperature was 535'F, coolant pressure was 2155 psig and the steam generator levels and flows were controlling at minimum level of 30 inches.
Corrective Action Taken or Which Should be Taken:
The system was inspected and the main steam code safety In accordance valve PSV-20546 which lifted during the transient was leaking steam.
with the Technical Specifications, the valve was gagged.
Corrective actions were thoroughly analyzed by the on-site Plant Review Committee and are discussed at length under " Action Required to Prevent a Reoccurrence".
Designation of Apoarent Cause:
Procedure.
Analysis of Occurrence:
Thirty minutes prior to the transient the Gland Steam Spillover Valve PV-30103 was put into service according to the required valve lineup described in the procedure. The unit was running at low load and insufficient steam was leaking past the turbine throttle valves to supply the gland steam seals.
When the spillover control valve was opened a direct path to the condenser was established which decreased the gland steam pressure and with low gland stessThis pressure, air was sucked into the condenser through all the turbine seals.
caused the initial loss of vacuum which precipitated the transient.
The transient conditions reached were maximum reactor coolant pressure 2250 psig, minimum pressure was 1810 psig, maximum reactor average 11:35. The temperature increased to 583*F and was observed to decrease to 408*F at pressure / temperature remained within the established curve Figure 3.1.2-2 of the Technical Specifications but the cooldown rate from 530*F to 408"? a difference of 122*F exceeded the maximum rate of 100*F/hr as stated on the figure.
.The transient data was analyzed by the Babcock and Wilcox Mechanical Design Unit who reached the following conclusions:
1.
The transient of concern must be classified as an Emergency Condition in accordance with ASME Code Section III.
2.
The total AT was about 170*F in approximately 20 minutes, causing a peak strecs of 48 - 50 ksi. Peak stresses do not cause structural damage, Sh. e this is the first transient
- but are of concern only from a fatigue standpoint.
j iof this type at SMUD, no fatigue damage was incurred.
9 r..
~,
.c.
g 3.
An earlier study evaluated the pressurizer integrity
- (
)
clould the water level drop below the heater elements while they were on full load.
This: study proved the acceptability of the pressurizer because, as above, peak stresses were involved creating fatigue concerns; but not from a single occurrence.
4.
The transient must also be considered as an " emergency transient" on the OTSC's since it cannot be classified in the " normal" or " upset" The AShi Code Section III (1968), Summer 1968 Addenda, permits 25 such' category.
cvents. The transie : experienced is acceptable as one of the.25 allowable.
The particular transient keeps the OTSG tubes in tension; therefore, tube buckling is not a problem. The tension load was such-that-the.__.
tube stresses were well below yield str'ess of the material, and no tube bowing will result from any permanent set.
In summary, there was no concern'of structural damage nor any limitations on operating capability. The occurrence will be classified as an " Emergency Transient" in--
cccordance with ASME. Code Section III.
l Equipment I.D.:
No equipment malfunctiened'during this transient.
J Action. itequired to Prevent a Reoccurrenca:
1.
Prior to returning to power operation a complete anclysis must be made by B&W.
(Note: This was accomplished as stated in " Analysis
~~of Occurrence. )
)
\\s /
2.
Guidelines vill be put into the procedure to warn the operator not to open the Gland Steam Spillover block valve if the control valve in open since this may lead to a loss of condenser vncuum.
3.
PV 30103 (the Gland Steam Sp111over Control valve) shcred be tested to assure proper operation. This was accomplished after the tronsient.
4.
Prior to power operation a minimum of two atmospheric dump valves per' steam generator must be operable. These valves were' put back into service October 8,.1974, prior to returning to power operation.
5.
The " Lose.of Coolant Accident" and " Main Steam Line Break" Procedures should be reviewed. This review is underway and procedure revisions will be initiated if required.
6.
The Icaking Code Safety valve has been gagged.
7.-
Generation Engineering will review the possibility of' transferring the' Auxiliary Feedwater Pumps and Valves from Safety Channels LA cnd 1B to 2A and 2B.
Removing the auxiliary feedwater components will permit operating the~HPI independently and prevent excessive transients as stated in this report.
1 Failure Data: None.
.,s
/
T
\\
/
~-
l K
-