United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 84-81: Inadvertent Reduction in Primary Coolant Inventory in Boiling Water Reactors During Shutdown and Startup

                                                           SSINS No.: 6835 
                                                           IN 84-81        

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

                             November 16, 1984 

Information Notice No. 84-81:   INADVERTENT REDUCTION IN PRIMARY COOLANT 
                                   INVENTORY IN BOILING WATER REACTORS 
                                   DURING SHUTDOWN AND STARTUP 

Addressees: 

All boiling water reactor (BWR) facilities holding an operating license (OL)
or construction permit (CP). 

Purpose: 

This information notice is being provided to inform licensees of a 
potentially significant problem pertaining to the inadvertent reduction of 
reactor pressure vessel (RPV) coolant inventory at BWRs. It is expected that
recipients will review this notice for applicability to their facilities and
consider actions, if appropriate, to preclude a similar problem from 
occurring at their facilities. However, suggestions contained in this 
information notice do not constitute NRC requirements; therefore, no 
specific action or written response is required. 

Description of Circumstances: 

There have been five relatively recent events at BWR facilities involving 
reductions of RPV inventory while the reactor was shut down or starting up. 

Washington Nuclear Power Unit 2 

On August 23, 1984, Washington Nuclear Power Unit 2 (WNP-2) experienced a 
loss of 25 inches of RPV coolant inventory through the residual heat removal
(RHR) system to the radwaste system. The reactor was going to cold shutdown 
from low power (~l%). While warming the B loop of the RHR system for 
shutdown cooling, the shutdown cooling isolation valve closed because of a 
shutdown line high-flow signal. Because it was not alarmed in the control 
room, this condition was not noticed for about 15 minutes while the isolated 
line continued to drain to the radwaste system. When the valve was reopened, 
25 inches of RPV inventory drained into the evacuated RHR line. The drop in 
RPV level was noticed by the operator, who reclosed the suction valve. The 
reactor protective system (RPS) initiated a scram and the primary 
containment isolation system (PCIS) isolated the RHR system with the vessel 
level at +12.5 inches. This is approximately 174 inches above the top of the 
core. The loop was refilled and warmup was continued. A plant modification 
was made to provide audible annunciation in the control room of the closure 
of the isolation valves. 

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On August 7, 1984, WNP-2 was starting up with the RPV at 400 psig and 
feedwater flow not yet established with a condensate booster pump. The main 
steam line drains were opened to the main condenser and RPV level decreased 
to +13 inches in about 15 minutes. RPS and PCIS initiated to terminate the 
event. The drain lines were closed and RPV level was restored.  A caution 
statement was added to the minimum startup checklist to prevent opening a 
steam line flow path before establishing feedwater flow via the condensate 
system. 

LaSalle Unit 1 

On June 11, 1982, LaSalle 1 experienced a loss of approximately 3,000 
gallons of RPV inventory to RHR piping. LaSalle 1 had an unirradiated core 
and was in initial startup. The B loop of the RHR system was aligned in the 
shutdown cooling mode and the A loop was in the standby mode. While 
performing a local leak rate test on the A loop drywell spray outboard 
isolation valve, a portion of RHR piping was drained. When the test was 
completed and the RHR A loop was returned to the standby mode, water from 
the RPV drained into the RHR piping. The RPS initiated a scram at a vessel 
level of +12.5 inches, and the PCIS isolated the RHR system. Makeup water 
was then supplied to the A loop from condensate and the B loop was verified 
filled and vented. The scram and isolations were reset. The procedures for 
the initiation of shutdown cooling were rewritten to include cautions for 
the operator concerning level fluctuations. 

On September 14, 1983, while LaSalle 1 was in cold shutdown and performing 
an RHR system relay logic test on the B loop, 50 inches of RPV inventory was
drained to the suppression pool. To align the RHR system for the test, 
several valves were open: both drywell spray valves, the suppression pool 
spray valve, the test return to suppression pool valve, and the C loop 
injection valve. When the B loop injection valve was opened to perform the 
test, the only remaining valve available to isolate the RPV was a testable 
check valve. This valve was held open because its actuator was misassembled 
and, furthermore, its shaft packing gland was too tight to have permitted 
closure. The RPS and PCIS initiated at +12.5 inches to terminate the event, 
but the vessel level went from +50 inches to O inch (161.5 inches above the 
top of the active fuel). 

Several corrective actions were taken by the licensee. The inoperable 
testable check valve was repaired and other testable check valves in the 
RHR, low pressure core spray, high pressure core spray, and reactor core 
isolation cooling systems were checked. Post maintenance local leak rate 
testing was performed as needed. The test procedures were modified to 
require the manual stop valve to be closed for the loop in test. 


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                                                        IN 84-81          
                                                        November 16, 1984 
                                                        Page 3 of 4       

Brunswick Unit 2 

On September 24, 1984, an integrated containment leak rate test was being 
performed on Brunswick 2. Some RPV inventory was lost during an attempt to 
lower torus water level. The RHR system was aligned in the shutdown cooling 
mode with the RPV refueled and reassembled following a 5-month refueling and
maintenance outage. An operator opened a drain path from the RHR system to 
the radwaste system thinking that RHR was in the torus cooling mode. Instead
of draining water from the torus as intended, the RPV was partially drained.
The RPS and PCIS initiated to terminate the event. The licensee altered the 
procedures for the integrated containment leak rate test to require 
additional operator monitoring during a containment test. 

Discussion: 

This information notice details five events in which RPV inventory was 
partially drained through various systems--primarily because the procedures 
focused on the system being tested without proper consideration for the 
plant as a whole.*  The RPS and PCIS functioned, as designed, to terminate 
the events.  However, the events were unnecessary challenges to safety 
systems. 

In addition, General Electric Company's SIL No. 388, "RHR Valve Misalignment
During Shutdown Cooling Operation for BWRs 3/4/5 and 6," February 1983, 
addresses possible misalignments of the RHR system that could lead to a 
reduction in RPV coolant inventory. 

The potential for partially draining the RPV exists with all water systems 
connected directly or indirectly to the RPV. Barriers exist to prevent a 
loss of RPV inventory to systems not designed or intended to receive it. In 
most cases, the system functions automatically to prevent a breach of these 
barriers, but a system that is largely manually operated, such as RHR, 
depends heavily on accurate procedures and appropriate operator actions. 
Licensees may wish to review their procedures and training programs in view 
of the events and corrective actions discussed above and the information 
provided in the General Electric SIL. 


 *   One of these events also involved an improperly maintained testable 
     check valve actuator. Several other instances of improperly maintained 
     testable check valve actuators have recently occurred at BWRs. 
     Information Notice 84-74, dated September 28, 1984, describes some of 
     these events in light of the concern with overpressurizing low-pressure
     systems connected to the primary coolant system. 


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                                                        IN 84-81          
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No specific action or written response is required by this information 
notice. If there are any questions regarding this matter, please contact the
Regional Administrator of the appropriate NRC regional office or this 
office. 



                                   Edward L. Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  M. S. Wegner, IE 
                    (301) 492-4511 

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