United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-74: Reduction of Reactor Coolant Inventory Because of Misalignment of RHR Valves

                                                            SSINS No.: 6835 
                                                            IN 86-74       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                            WASHINGTON, DC 20555

                               August 20, 1986

Information Notice No. 86 74:   REDUCTION OF REACTOR COOLANT INVENTORY 
                                   BECAUSE OF MISALIGNMENT OF RHR VALVES 

Addressees: 

All boiling water reactor facilities holding an operating license or a 
construction permit. 

Purpose: 

This notice is provided to inform recipients of NRC's continuing concern 
with the potential for draining the reactor coolant system because of 
residual heat removal system (RHR) valve misalignment. This is a recurring 
situation previously addressed in Information Notice (IN) 84-81 and General 
Electric Company's (GE's) Service Information Letter (SIL) 388. This notice 
is considered an interim action pending further review of this problem. 

Suggestions contained in this notice do not constitute NRC requirements 
therefore, no specific action or written response is required. It is 
expected, however, that recipients will carefully review the information for
applicability to their facilities and consider actions to preclude similar 
problems from occurring at their facilities. 

Description of Circumstances: 

A number of events involving reduction of reactor coolant inventory because 
of RHR valve misalignment have occurred since the issuance of IN 84-81. Six 
events that occurred in 1985 have been selected for inclusion in this 
notice. A seventh case was included since RHR was intentionally used to 
drain water from the reactor cavity, (Refer to Attachment 1 for diagram and 
definition of pathways.) 

SUSQUEHANNA 2, 04/27/85 

     While attempting to align B-loop RHR in the shutdown cooling mode, a 
     portion of the RHR, piping was inadvertently drained to the main 
     condenser during the warmup process. When the operator opened the heat 
     exchanger bypass valve F048B, water drained rapidly from the vessel, 
     refilling the RHR piping, and waterhammer occurred. The reactor vessel 
     level decreased 35 inches. Reactor scram and primary containment 
     isolation system (PCIS) actuation occurred on the reactor 
     low-level signal. (Pathway 5) 


      Typical scram and PCIS actuation set point is +12.5 inches or 162
     inches above active fuel. 

8608180091 
.

                                                           IN 86-74       
                                                           August 20, 1986 
                                                           Page 2 of 4    

WNP-2, 05/07/85 

While shifting from shutdown cooling to low pressure coolant injection 
(LPCI) lineup, suppression pool suction valve F004 was opened before 
shutdown cooling suction valve F006 was shut (valves F008 & F009 were open). 
The operator did not allow for the stroke times of the valves. Water level 
rapidly fell to the scram and PCIS actuation set point. The final water 
level was +5 inches. (Pathway 1) 

SUSQUEHANNA 1, 05/16/85 

The minimum flow bypass valve F064A failed open while starting C-pump for 
shutdown cooling with valves F008A and F009A open. (Pathway 3) 

SUSQUEHANNA 1, 05/20/85 

The minimum flow bypass valve F064A failed open while starting A-pump for 
shutdown cooling with valves F008A and F009A open. (Pathway 3) 

SHOREHAM, 07/26/85 

While shifting from shutdown cooling to LPCI lineup, the F004 valve was 
opened before the F006 valve shut (valves F008 & F009 were open). 
Approximately 7500 gallons of reactor inventory was drained to the 
suppression pool. The incident was terminated by PCIS actuation on the low 
reactor water level signal. The final water level was -10 inches as opposed 
to the normal level of about +39 inches. (Pathway 1) 

PEACH BOTTOM 2, 09/24/85 

The 2A RHR pump was being realigned from shutdown cooling to the full flow 
test mode. With valves F008A, F009A and F006C open, the discharge valve to 
the suppression pool F024A was opened in the 2A line, allowing reactor water
to flow to the torus. On reaching the reactor water low-level set point, the
reactor scrammed and PCIS actuated to terminate the event. The final water 
level was -10 inches. (Pathway 2) 

VERMONT YANKEE, 05/22/86 

During refueling operations, the equipment pool, cavity and reactor, and 
spent fuel pool were communicating. With no one on the refueling floor to 
observe level and less control room attention than necessary to prevent the 
event, water level increased to the point that water was flowing into the 
ventilation ducts. To lower water level, operators aligned shutdown cooling 
to the torus. Although effective in this case to stop the overflow, use of 
the RHR pump and valves to drain the cavity is not recommended in GE SIL 
388. 
.

                                                           IN 86-74       
                                                           August 20, 1986 
                                                           Page 3 of 4    

Discussion: 

The RHR system has several modes of operation including the shutdown cooling
mode. Shutdown cooling makes use of the same piping, valves, pumps, and heat
exchangers that the LPCI function uses. The misalignment of shutdown cooling
valves with its potential for RHR system damage and draining of the reactor 
coolant system is of regulatory concern. 

Generic Letter 83-28, dated July 8, 1983, Required Action 2.2: "Equipment 
Qualification and Vendor Interface," paragraph 2, states that "licensees and
applicants shall establish, implement and maintain a continuing program to 
ensure that vendor information for safety-related components is complete, 
current and controlled throughout the life of their plants, and 
appropriately referenced or incorporated in plant instructions and 
procedures." A relevant vendor communication is GE SIL 388 which states that 
shutdown cooling "is entirely controlled by manual operator actions and is, 
therefore, subject to operator error, which could result in hydraulic and 
thermal conditions not specifically considered in the design process." It 
recommends review and upgrading of operating procedures and operator 
training programs to minimize operator error during operation of the 
shutdown cooling mode of RHR. 

Possible operator errors identified in SIL 388 include the opening of the 
F004 valve before the F006 valve is shut, intentional use of shutdown 
cooling for vessel level reduction, opening of the minimum flow bypass line, 
use of the test return line, and opening of the upper containment pool 
return line (BWR/6). This latter possibility is designated pathway 4 in 
Attachment 1. Also, GE cautions against, the use of RHR shutdown cooling to 
drain the cavity because of possible thermal and hydraulic conditions not 
explicitly considered in the design process and possible equipment damage. 

Since the RHR pumps each have a capacity of 10,000 gpm, two operating pumps 
can transfer 20,000 gpm (that is, more than 1,000,000 gallons per hour) from
the vessel to the suppression pool. Also, the paths involving gravity flow 
are through large diameter piping systems with a considerable differential 
height between the vessel and the suppression pool. The reactor and cavity, 
the equipment pool, and the spent fuel pool above the bottom of the fuel 
transfer slot contain around 800,000 gallons of water. Quantities of 5000 to
50,000 gallons have been rapidly drained in previous incidents, usually 
terminated by the operation of PCIS. PCIS has mitigated several of the 
events, although technical specifications generally do not require PCIS to 
be operable in modes where shutdown cooling is required. 

Because the problems of draining the vessel through misalignment of the RHR 
valves continue to occur in spite of GE and NRC communications alerting 
licensees to them, the NRC is considering what further action should be 
taken. 
.

                                                           IN 86-74       
                                                           August 20, 1986 
                                                           Page 4 of 4    

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office 




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

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

Attachments:
1.   Reactor Coolant Inventory Pathways Created by RHR Valve Misalignment
2.   List of Recently Issued IE Information Notices
Page Last Reviewed/Updated Tuesday, November 12, 2013