ML19259C060
| ML19259C060 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 05/04/1979 |
| From: | Johnson W Maine Yankee |
| To: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| WMY-79-45, NUDOCS 7906120282 | |
| Download: ML19259C060 (8) | |
Text
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$Mh ENGINEERING OFFICE WESTBORO, MASSACHUSETTS 01581 617-366-9011 w. u x:2 0 B.4.11 WMY 79-45 May 4, 1979 United States Nuclear Regulatory Commission Region 1 631 Park Avenue King of Prussia, Pennsylvania 19406 Attention: Office of Inspection and Enforcement Mr. Boyce H. Grier, Director
References:
(a) License No. DPR-36 (Docket No. 50-309)
(b)
I&E letter to MYAPC dated April 14, 1979, (I&E Bulletin No.79-06B)
(c) MYAPC letter to I&E dated April 25, 1979
Dear Sir:
Subject:
Supplemental Information in Response to I&E Bulletin 79-06B In response to Reference (b), the Maine Yankee Atomic Power Company hereby submits as Att.achment A, supplemental information relative to the review of operational errors and system misalignments identified during the Three Mile Island incident. For your convenience, we have delineated our supplemental responses in the same sequence as each item listed in your bulletin.
We wish to point out that we had several justifiable reasons for not immediately addressing your Bulletin 79-06B. The bulletin assumed design configuration not applicable to Maine Yankee (MY) and we become concerned that to quickly comply with the bulletin could lead to difficulties.
Therefore, many of our initial responses were incomplete at the time of our response, Reference (c).
During subsequent discussions with members of your staff, previous confusion and design misconceptions were eliminated. We were able to satisfactorily address all items of the bulletin and present arguments in support of securing the reactor coolant pumps if their continued operation will result in degradation of core safety.
7906120232.
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United States Nuclear Regulatory Commission Page 2 Attention: Office of Inspection and Enforcement May 4,
1979 We trust this information adequately addressed your concerns and is acceptable to you. Should you have any questions with regard to this matter, please contact us.
Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY
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W. P.' Johnson Vice' President RHG/smv Enclosure 2284 206
ATTACHMENT A MAINE YANKEE SUPPLEMENTAL RESPONSE TO ISE BULLETIN No.79-06B RESPONSE TO ITEM NO. 2 2.
a.
The a pplicable operating procedures have been revised to require operator verification of conditions which could lead to voiding.
Parac4 cers checked are pressurizer pressure and hot leg temperature to determine the amount of reactor coolant system subcooling.
b.
To prevent void generation within the reactor coolant system, pressurizer pressure must be maintained above the saturation pressure of the reactor coolant.
During normal operation, pressurizer temperature is maintained at least 500F above reactor coolant system temperature by proper operation of the chemical and volume control system, pressurizer heaters and pressurizer spray.
The automatic operation of these systems, with anticipatory control room alarms of of f-normal conditions, provides assurance of proper pressurizer pressure and inventory control.
During non-routine operations, when pressurizer pressure and level cannot be maintained by the above mentioned sys tems, the high pressure safety injection system will provide a coarse pressure control dependent upon the status of reactor coolant system integrity.
c.
The applicable emergency procedures have been revised to provide specific guidance if voiding is indicated by the verifications described in section (a) of this item.
The major effort will be to restore pressurizer pressure and level control and reinstate reactor coolant system cooling using the steam generators.
Included in this effort will be the isolation of any indicated reactor coolant system leak path.
Dependent on the status of reactor coolant system integrity, pressurizer pressure and level control will be reestablished using the chemical and volume control system or the high pressure safety injection system and pressure increased to collapse any condensible voids.
In addition, the steam generators will be used to cool the reactor coolant to aid in condensible void collapse.
The use of reactor ecolant pumps to provide forced flow is discussed in item 6.c.
RESPONSE TO ITEM No. 3 In addition to the information previously provided, the following a tions c
have been taken which will not adversely affect existing plant safety features or cooling capabilities.
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ATTACHMENT A (continued) 1.
The containment sump pump has been removed from automatic operation by electrically disconnecting the automatic signal.
The sump level alarm remains to warn operators and allow for manual starting of sump pumps when existing conditions permit.
2.
Operators have been instructed to manually isolate the following systems upon initi.ation of safety injection:
a.
Primary Drain Header to PDT b.
Primary Vent Header c.
Pressurizer Sample d.
Pressurizer Interf ace e.
Loop's Sample f.
Purge Exhaust Duct g.
Containment APD and Gas Monitor h.
Continuous SG Blowdown Lines i.
Containment Sump Our previous response to Item 3 indicated that a design review of containment isolation design and associated procedures would be completed by June 1, 1979.
As a result of subsequent discussions with members of your staff, the completion date for this design review is now revised to May 15, 1979.
Should this review indicate that problems exist with any of our above listed actions, discussion will be immediately initiated with appropriate members of NRC staff.
RESPONSE TO ITEM NO. 5 A review of appropriate plant procedures has been performed and a.
additional emphasis has been incorporated into these procedures to assure operators are aware of the various indications which are available to determine that the pressurizer power operated relief (POR) valve (s) are open.
b.
Additionally, steps have been incorporated into the appropriate procedures which direct the operators to close the POR motor-operated isolation valves when the RCS pressure has been reduced below the POR setpoint if the POR remains stuck open.
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ATTACHMENT A (continued)
RESPONSE TO ITEM NO. 6a The operating procedures and training instructions have been reviewed, revised and implemented where necessary to ensure that automatic actions of engineered safety features. will not be overridden by operator action, unless continued operation will result in unsafe plant conditions or until the plant is in a safe and stable condition.
RESPONSE TO ITEM NO. 6b Operating procedures have been reviewed, revised and implemented to ensure that the HPI system either automatically or manually actuated, will remain in operation until the functions it is intended to perform are provided for by other systems as detailed in the bulletin, item 6.b(1) and (2).
These actions were further reviewed and found acceptable to I&E Inspector W. J. Lazarus.
The established criteria for termination of safety injection includes overpressure requirements, RCP operating conditions, and considerations for degrading plant safety.
RESPONSE TO ITEM NO. 6c The reactor coolant system at Maine Yankee has three loops with one reactor coolant pump in each loop.
This item of the bulletin requires that one pump in each loop be operated during HPSI initiation as long as the pump is providing necessary forced flow. At Maine Yankee this would require a corsitment to run all reactor coolant pumps, which in our judgment may not be in the direction of improved safety for most events.
This concern for=ed part of the basis for our relur.tance to comply fully to the bulletin without further evaluation, Referenne (c).
Our concern was expressed in a phone conversation with your staff on May 3.
The staff response was that the bulletin sent to Maine Yankee was intended for plants of the 2 loop /2 pump per loop configuration.
Since Maine Yankee has a 3 loop /1 pump per loop configuration, the staff verbally amended its requirement to reflect the IE Bulletin sent to Westinghouse plants, i.e., operate only two of the three main coolant pumps.
In our judgment, it would be more conservative to operate only one reactor coolant pump under conditions which =sy be conducive to pump f ailure, keeping two pumps in reserve for longer term accident recovery and cooldown.
This judgment is based on the unfavorable environmental conditions in the reactor containment and the severe service conditions which are likely to be present during an event calling for RPSI operation, and in recognition that a safe shutdown condition can be reached more promptly if at least one reactor coolant pump is operable past the point of core stability.
However, in the interest of complying with the staff's concern, Maine Yankee agrees to operate two reactor coolant pu=ps under the conditions discussed in this le t te r.
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4 ATTACHMENT A (continued)
Maine Yankee has a concern with the requirements of Bulletin 79-06B, question 6c:
to operate the reactor coolant pump as long as the pump is providing forced flow. We appreciate and share the staff's concern that the operator should not hesitate to run a pu=p to destruction if in doing so he avoids or limits damage to the reactor core.
However, in our judgment, reactor coolant pump operation should be secured if it is clear to the operator that while the core is being adequately cooled, indications show the operator that continued pump operation would probably result in destruction of the pump seals of both pumps and two additional small LOCA's.
An example of such an event may be postulated as follows:
(a) A small loss of coolant accident followed by a safety injection actuation.
(b)
EPSI restores overpressure and decay heat is removed via s team generato rs as indicated by SG AT.
(c) Any number of occurrences such as CIS trip, valve closure, impingement forces generated from a LOCA itself, loss of instrument air, etc. results in or may result in a loss of component cooling flow to the rede ar r
coolant pu=ps.
(d) An operator follows IE Bulletin No.79-06B and continues to operate two reactor coolant pumps because they are providing forced flow.
The pump manuf acturer has provided his best guess that seals will being fatling 30 minutes af ter the loss of cooling, rapidly progressing to gross f ailure.
(e) The conditions of (b) above degrade to a loss of coolant f rom two loops at the pump seals in addition to the original event.
Pressure drops to saturation.
Cold leg injection begins to flow toward the pump seals and away from the core in two loops.
Maine Yankee has no knowledge nor assurance f rom the NRC staff that the above scenario has been evaluated or that the bulletin, as written, may not involve an unreviewed safety question.
This again, serves to illustrate why, in our response of April 26, we were reluctant to make the bulletin changes to our operating instructions.
Maine Yankee, without further evaluation, has changed its operating procedures to provide for the operation of two reactor coolant pumps in the event of a safety injection actuation.
The pumps shall remain operating as long as they are providing forced flows unless continued pump operation will result in degradation of core safety.
We believe that this meets the intent of the bulletin and precludes degrading an easily recoverable small LOCA to a much more serious event.
RESPONSE TO ITEM NO. 6d Revisions to plant emergency procedures have been implemented to instruct the operators not to rely on pressurizer level alone to evaluate plant 2284 210
ATTACHMENT A (continued) conditions.
The instructions specify the utilization of a combination of RCS pressure, Th temperature, RCS water inventory, contain=ent sump levels, and other plant parameters to assure a positive overpressure is being maintained.
_RE_SPONSE TO ITEM NO. 7 Maine Yankee has reviewed its Safeguards Locked Valve Lists which specifies the position requirements and positive controls which assure that these valves and controls remain in the proper position to ensure proper operation of the engineered safety systems.
This review indicated
- hat additional valves, related to the Auxiliary Feedwater System and its controls, needed to be inco rpo rated.
These valves and controls have now been added to the Safeguards Locked Valve List and the revised procedurer have been issued.
During plant startup and prior to exceeding 2100F and 400 psig in the Reactor Coolant Sys tems, the Safeguards Loc ked Valve List is performed in its entirety to verify proper valve and control position.
Additionally, this list is performed on a monthly basis as required by our Technical Specifications.
The Safeguards Locked Valve List and its implementing procedure, including the additions specified above, were reviewed by an on-site IE Inspector during the last 3 days and was found to be acceptable with regard to the concerns expressed in IE Bulletin No.79-06B.
RESPONSE TO ITEM NO. 8 In addition to the information provided in the original response to this item, the following actions have been taken to preclude the inadvertant pumping, venting or other release of radioactive liquids and gases:
1.
Manual isolation of those systems listed in the response to Item 3 upon safety injection actuation.
2.
To ensure that such an occurrence will not be caused by the retesting of engineered saf ety f eatures instrumentation, the isolation valve control switches for all the systems listed in the original response will be placed in the closed position prior to resetting engineered safety features.
This action prevents these valves f rom opening following resetting of engineered safety instrumentation.
The operators have been instructed to evaluate the situation prior to manually re-opening these isolation valves.
RESPONSE TO ITEM NO. 9 Maine Yankee has reviewed its Maintenance Requests and Tagging Rules forms and procedures to ensure the concerns of Item 9.a, b., and c have been addressed.
Although existing policies and procedures have always addressed these areas, it was determined that documentation of certain steps had not been provided on the appropriate forms.
To correct this apparent discrepancy, the forms have been modified to add the following:
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ATTACHMENT A (continued) 1.
a sign-off by a Senior Reactor Operator for the release of any safeguards equipment.
This sign-off will indicate that the appropriate redundant piece of safeguards equipment is available snd operable.
2.
a sign-off by a SRO verifying that a retest of the applicable piece of safeguards equipment has been performed following the completion of maintenance.
3.
a sign-off by a SRO verifying that the applicable piece of safeguards equipment has been returned to service following the completion of testing.
The Maintenance Request and Tagging Rules forms have been revised and are presently being reproduced by a local contractor.
Implementation of these new forms is anticipated within the next week. Until such time as implementation of these forms is possible (i.e., the forms are received back from the printer) a temporary sign-off sheet will be utilized to document the areas addressed above.
Procedures specifying the proper methods of watch relief require the review of the Maintenance Reques t, Tagging, and Yellow Tag Jumper Logs.
This review ensures on-coming personnel are fully aware of any safeguards equipment which has been removed from se rvice prior to their assuming the watch.
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