United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 73-02: Malfunction of Containment Purge Supply Valve Switch

                                                             IEB 73-02

                                 UNITED STATES
                           ATOMIC ENERGY COMMISSION
                             REGION II - SUITE 818
                        230 PEACHTREE STREET, NORTHWEST
                            ATLANTA, GEORGIA 30303

                                        July 13, 1973


The attached Directorate of Regulatory Operations Bulletin No. 73-2,

"Malfunction of Containment Purge Supply Valve Switch," is sent to you to 

provide you with information we received from the Wisconsin Electric Power 

Company concerning the Point Beach 2 pressurized water reactor facility.

This information may relate to the design and performance of certain equipment

at your facility.  Action requested on your part is identified in Section B of

the bulletin.

                                          Very truly yours,

                                          Norman C. Moseley

RO Bulletin 73-2


                                                             July 15, 1973

                               RO Bulletin 73-2


We recently received information from the Wisconsin Electric Power Company
concerning a problem found during functional testing following maintenance at
the Point Beach 2 pressurized water reactor which may relate to the design and
operation of the control circuit for containment purge valves at your
facility.  Pertinent details relating to this problem are contained in Section
A below.  Action requested by this Bulletin is contained in Section B.

A.  Description of Circumstances

During the performance of functional testing of one of the Unit 2 containment
purge valves following maintenance, the valve opened when the manual control
switch was moved to the open position but failed to close when the switch was
placed in the closed position.  In the Point Beach facility design, the
redundant pneumatic operated, air to open containment purge supply valves are
manually controlled by a signal switch.  For testing purposes during facility
operation, instrument air is secured to one valve that remains closed to
maintain containment integrity while the other valve is being tested.

Subsequent investigation by the licensee revealed that a small screw which
secures the contact closing cam to the manual portion of the switch had
loosened.  This permitted the cam to stay in the "Contacts Closed" position
and prevented further manual operation of the switch from opening the contacts
and closing the valve.  A followup review of electrical drawings also revealed
that in the event of a similar switch failure open redundant purge valves
would not close on receipt of a containment isolation signal.

The corrective action for this apparent design deficiency consisted of
modifying the control circuit such that each individual valve is operated by a
separate switch.  Thereby, a malfunction of a single switch can result in one
valve failing to close with containment integrity maintained by the redundant

B.  Action Requested of the Licensee

It is requested that you review the design of the control circuit for the
containment ventilation system isolation valves installed at your facility to
determine whether the failure of a single 


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control switch could result in the simultaneous failure of the redundant
supply valves or redundant exhaust valves and provide this office with your
findings.  If the results of your review indicate that the simultaneous
failure of the redundant containment purge valves could exist under the
conditions described above, please include in your response a description of
the corrective action taken or planned and the date of scheduled completion of
your corrective actions.  This information should be provided to this office,
in writing, within 45 days of your receipt of this letter.

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