Information Notice No. 79-13 – Indication of Low Water Level in the Oyster Creek Reactor

IN79013 

                               May 29, 1979 

MEMORANDUM FOR:     B. H. Grier, Director, Region I 
                    J. P. O'Reilly, Director, Region II 
                    J. G. Keppler, Director, Region III 
                    K. V. Seyfrit, Director, Region IV 
                    R. H. Engelken, Director, Region V 

FROM:               Norman C. Moseley, Director, ROI:IE 

SUBJECT:            Information Notice No. 79-13 - INDICATION OF LOW 
                    WATER LEVEL IN THE OYSTER CREEK REACTOR 

The subject Information Notice is transmitted for issuance on May 29, 1979. 
The Information Notice should be issued to all holders of Reactor Operating 
Licenses and Construction Permits. Also enclosed is a draft copy of the 
transmittal letter for this purpose. 


                                        Norman C. Moseley, Director 
                                        Division of Reactor Operations 
                                          Inspection 
                                        Office of Inspection and Enforcement

Enclosures:
1.   IE Information Notice
       No. 79-13
2.   Draft Transmittal Letter

CONTACT:  C. J. DeBevec, IE
          49-28180 
.

(Draft letter to all holders of Reactor Operating Licenses and Construction 
Permits) 

                                            Information Notice No. 79-13 

Addressee: 

This Information Notice is provided as an early notification of a possibly 
significant matter. It is expected that recipients will review the 
information for possible applicability to their facilities. No specific 
action or response is requested at this time. If further NRC evaluations so 
indicate, an IE Circular or Bulletin will be issued to recommend or request 
specific licensee actions. If you have questions regarding this matter, 
please contact the Director of the appropriate NRC Regional Office. 

                                        Sincerely, 


                                        Signature 
                                        (Regional Director) 

Enclosure:
IE Information Notice
       No. 79-13
.

                              UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                   OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D.C. 20555 
                                     
                               May 29, 1979 

                                           Information Notice No. 79-13 

INDICATION OF LOW WATER LEVEL IN THE OYSTER CREEK REACTOR 

Summary 

A loss of feedwater transient at the Oyster Creek facility on May 2, 1979, 
resulted in a significant reduction in water inventory within the reactor 
core shroud area as measured by one set of water level instruments (triple 
low level), while the remaining level instruments, sensing from the reactor 
annulus area indicated water levels above any protective feature setpoint 
(Figure 1). The water level within the core shroud area was reduced below 
the "triple low level" setpoint of 4-feet, 8-inches above the top of the 
fuel. 

Subsequent analysis by the licensee has determined that the minimum 
collapsed water level (solid, without steam voids) over the top of the fuel 
was 1 to 1-1/2 feet. 

Coolant sample analyses and offgas release rates indicate that no fuel 
damage occurred. 

General 

Oyster Creek is a non-jet pump BWR with licensed power of 1930 MWt. The 
plant was first made critical May 3, 1969. 

     Status Before Transient 

     Operating at near full power with the main parameters at levels as 
     follows: 

          1895 MWt power level 
          79" Yarway (13'4" over top of fuel) reactor water level 
          1020 psig reactor,- pressure 
          7.1 x 10 6 #/hr feedflow 
          14.8 x 10 4 gpm recirculation flow rate (4 pumps) 
          12 psid core Ap 

Equipment Out of Service (OOS) 

     "D" recirc pump OOS due to seal cooler problem 
     "B" startup transformer OOS for inspection of associated 4160v cabling 
.

Information Notice No. 79-13                               May 29, 1979 
                                                               Page 2 of 4 

Initiating Event 

The initiating event was a false pressure spike on the reactor high pressure
scram switches. This pressure spike was caused by an instrument technician 
who was performing Technical Specification required surveillance testing on 
isolation condenser pressure switches. 

Sequence of Events 

The most significant events following the reactor scram are listed in Table 
I, with the time in seconds following the scram. A discussion of these 
events is provided for further information. 

Thirteen seconds after the reactor scram on a false high reactor pressure 
signal, the turbine tripped at 25% low load setpoint. The turbine trip 
initiated a transfer of power from the auxiliary transformers to the startup
transformers (Figure 2). Because one startup transformer (SB) was out of 
service, two feedpumps and two condensate pumps on that 4160v bus (IB) lost 
power (pumps 1B and 1C). The third feedpump (1A) tripped due to low suction 
pressure resulting from the feedwater transient. An immediate attempt to 
restart IA was unsuccessful because of failure of an auxiliary oil pump to 
start. The oil pump is interlocked in the feedpump start sequence. 

Initially, water inventory was decreasing due to steam flow through the 
turbine bypass valves to the main condenser. This loss together with the 
void collapse associated with decreased feedwater temperature and the 
subsequent loss of feed flow, resulted in a rapid reactor water level 
reduction to the low water level alarm setpoint of 11-feet, 5-inches above 
the top of the fuel at 13.6 seconds. At 25 seconds, an emergency diesel 
generator (DG-2) had automatically fast-started following the power loss to 
bus 1D and picked up emergency loads as designed. This loading included the 
second control rod drive (CRD) pump which with the other CRD pump (powered 
through the retained startup transformer) provided the only coolant makeup 
during this time. The operator manually initiated, a main steam line 
isolation valve (MSIV) closure at about 43 seconds into the transient to 
conserve water inventory. The minimum indicated water level in the annulus 
area was 9-feet, 8-inches above the top of the fuel (the low low setpoint is 
7-feet, 2-inches above the top of the fuel). After closure of the MSIV the 
isolation condenser was condensing steam from the core and returning the 
condensate to the reactor annulus (downcomer) region through connection to a 
recirculation loop pump suction line (Figure 3). Reactor water level began 
to increase shortly after MSIV closure. 

Subsequently, at 76 seconds, an isolation condenser was manually placed in 
service for core decay heat removal. At approximately this time the 
discharge valves in "A" and "E" recirculation loops were closed in 
accordance with a Standing Order which was in effect at that time to prevent 
inadvertent isolation condenser isolation due to forced flow from operating 
recirculation pumps being 
.

Information Notice No. 79-13                               May 29, 1979 
                                                               Page 3 of 4 

sensed as a line break. This Standing Order was no longer appropriate since 
a plant modification had been made which tripped the recirculation pumps on 
any scram. The necessary procedure change had not been performed following 
the plant modification. The "D" loop discharge valve had been closed prior 
to the event since the associated pump was out of service. The "B" and "C" 
loop discharge valves were apparently closed in anticipation of restarting 
the recirculation pumps. 

The reactor triple low water level (4-feet, 8-inches above the top of the 
fuel) setpoint was reached at 172 seconds into the transient. Shortly after 
this the "Events Recorder," which records the time certain events occur 
following a reactor trip, was turned off. 

The triple low level in the core shroud area resulted from restriction of 
the isolation condenser return flow path to the core region due to closure 
of the recirculation pump discharge valves. With the recirculation pump 
discharge valves closed, the flow path back to the core shroud was via the 
2-inch bypass lines around the discharge valves. The effect was to reduce 
the water level in the core shroud area and to increase the level in the 
reactor annulus area. 

The core shroud area of the reactor was also receiving water from the CRD 
pumps. 

Reactor pressure was controlled during the transient by intermittent manual 
operation of the two isolation condensers. Reactor pressure and reactor 
annulus water level variations with time are shown on Figure 4. 

At 1922 seconds, a recirculation pump was started. It was manually tripped 
90 seconds later because of a rapid decrease in the annulus level. 

At 2208 seconds, a feed pump was started, following which at 2340 seconds, a 
primary recirculation pump and subsequently a reactor feedpump were operated 
for continued cooldown of the reactor. From this time on, water level within 
the core shroud area was normal. The plant was brought to a cold shutdown 
condition to analyze the cause of the triple low level and to evaluate the 
possibility of fuel damage. 

Conclusion 

Review of the occurrence by the licensee and NRC established that although 
the water level in the core shroud area went below the triple low level 
setpoint, no fuel was uncovered and no fuel damage is expected to have 
occurred. 
.

Information Notice No. 79-13                               May 29, 1979 
                                                               Page 4 of 4 

This Information Notice provides the details of a significant occurrence 
that is still under review by the NRC staff. If further NRC review 
indicates, an IE Circular or Bulletin may be issued to recommend or request 
specific licensee actions. 

No written response is required. If you desire additional information 
regarding this matter, please contact the Director of the appropriate NRC 
Regional Office. 

Enclosure:
List of Information Notices
  Issued in 1979 
.

                                                                   Table 1 

                            SEQUENCE OF EVENTS 

TIME (SEC.)                             EVENT 

     0                   REACTOR SCRAM/RECIRC. PUMP TRIP 

     13                  TURBINE TRIP/LOSS OF FEEDWATER/CONDENSATE PUMPS 

     13.6                LOW WATER LEVEL SCRAM POINT 

     16.8                #2 RPS MOTOR GEN. SET TRIP 

     31                  #2 DIESEL GENERATOR BREAKER CLOSED/2ND CRD PUMP 
                         STARTED 

     43                  MSIV CLOSED* 
     
     76                  B ISO. CONDENSER PLACED IN SERVICE* 

     90                  LOW WATER LEVEL ALARM CLEARED 

     172                 LOW LOW LOW WATER LEVEL TRIP POINT 

     186                 RECIRC. LOOP DISCHARGE VALVES NOTED CLOSED 

     1914                C RECIRC. PUMP STARTED THEN TRIPPED* 

     2208                FEEDWATER PUMP STARTED* 

     2304                RECIRC. PUMP STARTED/LOW LOW LOW WATER LEVEL ALARM 
                         CLEARED 

     2700                RPS #2 RESTARTED/SCRAM RESET* 3 

     600                 STARTUP TRANSFORMER SB RETURNED TO SERVICE 


* By Operator Action