ML19263E283

Responds to IE Bulletin 79-06B, Operational Errors & Sys Misalignments Identified During TMI Incident.Emergency Procedures Have Been Revised to Provide Specific Guidance,If Voiding Is Indicated by Check of Reactor Coolant Sys Flow

ML19263E283
Person / Time
Site:	Millstone
Issue date:	04/24/1979
From:	Counsil W NORTHEAST UTILITIES
To:	Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
IEB-79-06B, IEB-79-6B, TAC-30199, NUDOCS 7906080076
Download: ML19263E283 (8)

Text

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, ..-~~.~.cc. p.o. gox 27o MM Es n S I- $ s N Ec5..m HARTFORD. CONNECTICUT 06101 L t T; SI3!:idi3,65 ::l April 24, 1979 Docket No. 50-336 Mr. Boyce H. Grier Director, Region I Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406

Dear Sir:

This responds to IE Bulletin 79-06B regarding review of operational errors and system misalignments identified during the Three Mile Island incident. Th.e paragraph numbers correspond to the bulletin's action items.

1. The actions reouested by this item are complete as of today for the majority of operational personnel. This was accomplished by preparation of a lesson plan which covered the points specified in la and lb. The lesson was presented by the Operations Supervisor to licensed operators and plant management and supervisors with operational responsibilities. Documentation of who participated has been retained. Ar.yone who missed today's lectures will be individually trained prior to plant startup in May.

Similar presentations were also made to the operators and plant management by the NRC on Friday, April 20 and Saturday, April 21.

2. a. The applicable operating procedures have been revised to require operator verification of conditions which could lead to voiding. Paremeters checked are pressurizer pressure and hot leg temperature to determine the amount of reactor coolant system subcooling and core delta-temperature, steans generator delta-pressure and reactor coolant pump motor current and vibration to determine the status of reactor coolant system flow.

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Mr. Boyce H. Grier .

In addition, if system integrity can be verified, a mass balance can be performed by charging a known quantity of water to the reactor coolant system and verifying an expected change in pressurizee level.

b. To prevent void generation within the reactor coolant system, pressurizer pressure must be maintained abcve the saturation pressure of the reactor coolant. During normal operation, pressurizer temperature is maintained at least 50 F0 above reactor coolant system temperature by proper operation of the chemical and volume control system, pressurizer heaters and prassurizer spray. The automatic operation of these systems, with anticipatory control room alarms of off-normal conditions, provides.

assurance of proper pressurizer pressure and inventory control. Routine operations involving pressurizer spray, vent and degas operations were reviewed and procedure controls deemed adequate. The applicable emergency procedures have been revised to caution against over-feeding steam generators during water level recovery so as to

. prevent loss of pressurizer pressure and level control.

During non-routine operations, when pressurizer pressure and level cannot be maintained by the above mentioned systems, 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 voidin is indicated by the verification described in section (g) 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 coolant pumps to provide forced flow is discussed in item 6. Once the condensible voids are removed, the non-condensible gases may be removed as described in item 11. If void removal is not complete, the high pressure safety injection pumps and reactor coolant pumps will be used to minimize void formation and the effect of voids on core cooling.

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Mr. Boyce H. Grier .

3. Automatic initiation of safety injection also results in initiation of the containment isolation actuation signal (CIAS).

The CIAS isolates all penetrations which are not required for engineered safety features operation or core cooling, and which are not isolated by locked closed containment isolation valves.

4. NNECo does not believe that it is necessary or desirable to implement this item on Millstone 2.

Millstone 2 by design has manual initiation of auxiliary feedwater. The operators have always been and are presently aware of this; thus, on any transient (not only a reactor trip) involving the condensate /feedwater system, the operators have always immediately verified the status of the feed system /

steam generator level. The procedure for reactor trip requires the operator to immediately verify the status of feedwater flow to the steam generators. Additionally, the same procedure specifically instructs him to initiate auxiliary feed if the main feed pumps are not available.

The bulletin seems to imply (by the words "in direct and continuous communication with the control room") that the major intent is to continuously man a previously unmanned station. At Millstone 2, the auxiliary feedwater system is started and controlled from exactly the same panel (C05) as the main feedwater system. (See FSAR Figures 7.6-1 and 7.6-5.) Stationing an operator at this panel in addition'to the reactor operator and supervising control room operator-does not enhance the Unit's ability to quickly initiate auxiliary feed. In fact, he may impede the movement of others when timely action is required for this or other events.

In the event of a complete loss of feedwater incident, the operator has in excess of fifteen minutes in which to initiate auxiliary feed before the steam generators are boiled dry (see W. G. Counsil to Robert Reid letter dated February 12, 1979 regarding cycle 3 specific analyses at 2700 MWt.) This is more than ample time for the operator to initiate auxiliary feed and is sufficient time for him to recognize an unusual situation (abnormal auxiliary feed response, for example) and respond to the situation. It is also noted tht initiation of auxiliary feed within fifteen minutes has been shown to preclude opening of either PORV's or pressurizer safety valves.

For the reasons stated above, NNECo does not feel it is necessary to station the individual described in your bulletin. If we have not been able to establish a mutually acceptab'.e position by the time the auxiliary feedwater system is required (during the plant startup in May), we will station the operator as requested.

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Mr. Boyce H. Grier .

5. a. Indications, which can be utilized to identify an open power operated relief valve (PORV), are a discharge temperature indicator on the discharge header common to both PORV's and quench tank level, temperature and pressure.

All four instruments provide control room indication and anrJnciation.

b. The emergency procedure for reactor trip has been revised to direct the operator to maintain closed the isolation valve of a stuck open PORV.

6. a. As a result of Reportable Occurrence 50-336/78-16, Override of Purge Valve High Radiation Signal, the engineered safety features systea procedures and emergency procedures were reviewed and subsequently revised to include cautions against using equipment overrides. The cautions only allow override if directed by approved procedures, for equipment or personnel protection, or when equipment is not needed for the operating mode. The licensed operators reviewed these procedure changes / revisions. The actions taken for the reportable occurrence have been reviewed in light of the Three Mile Island incident and found adequate.

The operating procedures which require override have been reviewed and it has been detemined that the overrides are required to prevent unsafe plant conditions.

Particular emphasis is placed on the decision for continued operation of containment spray pumps. The resultant water spray can damage non-essential equipment such as reactor coolant pumps which could be used to mitigate the effects of a transient condition as described in other responses. Thus, the pumps nomally would be secured if containment pressure is satisfactory. It should also be noted that the containment air recirculation units are redundant to the spray pumps and are sized to handle cooling requirenents,

b. The applicable energency procedures have been revised to prcvide the specific instructions provided by the bulletin and the NSSS supplier concerning the conditions required before a high pressure safety injection pump or a charging pump can be secured. This situation applies after an automatic initiation based on low reactor coolant system pressure or high containment pressure.

c. The applicable emergency procedures have been revised to require continued operation of at least one reactor coolant pump per loop in the event of automatic initiation of high pressure safety injection pumps.

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Mr. Boyce H. Grier .

The reactor coolant pumps will remain operating or will be Qced in operation as long as the pump is providing forced flow as detemined by pump amperage, steam generator delta-pressure, steam generator delta-temperature and pump speed.

If monitoring instrumentation and reactor coolant pump procedures dictate that the pump should be secured, all RCP's may be secured if the hot leg temperature is greater than 20*F subcooled and the Loss of Flow emergency procedure implemented .

d. The applicable emergency procedures have been revised to further minimize operator dependency on pressurizer level by referring to changes in level regardless of direction of the change. In addition, the only action in the applicable emergency procedures which was based on pressurizer level has been revised to require monitoring other parameters as well as level .

7. All safety related valve positions, positioning requirements and procedural controls, which ensure that the valves remain properly positioned, have been reviewed and are adequate to ensure proper operation of engineered safety features. The review of surveillance, test and plant and equipment startup procedures verified restoration steps existed for all instances where valves were positioned in an off-nomal manner in order to complete the procedure requiranents. The administrative procedures for control of maintenance on safety related equipment have been revised to specifically assure correct positioning of valves which were worked on or were used for isolation pu rposes.

8. Systems designed to transfer potentially radioactive gases and liquids out of primary containment are the chemical and volume control system (CVCS), the safety injection systems (during shutdown cooling and sump recirculation operations), the containment spray system (during sump recirculation), the aerated liquid, clean liquid and gaseous radwaste systems, the sampling system, the containment purge system and the hydrogen purge systens. All systems, which are not part of the engineered safety features, are isolated, as discussed in item 3, by the containment isolation actuation signal (CIAS). In addition, the containment purge system is isolated on high containment gaseous or particulate activity in Modes 5 or 6. In Modes 1 through 4, the purge system is maintained isolated at all times.

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Mr. Boyce H. Grier .

i,uring routine operations, the CVCS, the aerated liquid, clean liquid and gaseous radwaste systems and the hydrogen purge system are used to process potentially radioactive fluids.

The only potential for undesirable pumping, venting or other release would result from an automatic start of the containment sump pump. Although the pump is usually selected to MANUAL, a plant design change has eliminated the AUTO feature. During non-routine evolutions, these systems will isolate by closure of at least two isolation valves any time reactor coolant system pressure decreases to below 1600 psia or containment pressure exceeds 5 psig. While these parameters remain in an alann condition, the CIAS cannot be reset. The individual valves could be opened by using the CIAS override. However, administrative procedures restrict the use of this override to planned evolutions, thus the potential for undesired pumping, venting er releases is minimal. When the parameters clear their alarm concition, the actuation channels for CIAS may be reset. However, the act of resetting does not reposition any valves, therefore releases would not occur.

The engineered safety features system which processes potentially radioactive water during the recirculation phase of the post-incident operations merely recirculates the water from the containment sump back to the reactor. This operation would not result in any ugnificant release.

In the event of a steam generator tube leak, the steam generator blowdown system will process radioactive water from the steam generators to the environment or aerated liquid radwaste.

A CIAS or high radiadon signal from the blowdown or the steam jet air ejectors will isolate blowdown, preventing an undesired release. This high radiation signal has the same override / reset features as CIAS.

9. a. The administrative procedures have been revised to specify that prior to removal of safety related systems from service the redundant system will be verified operable.

The verification will consist of completing surveillance requirements required during operation before the system is disabled. For those equipments which Technical Specifications require specific surveillance, that testing will be completed prior to removing the system from service.

b. Procedures for maintenance and testing of safety related systems have been reviewed and changes have been made to strengthen the requirement to verify operability of safety related systems prior to taking credit for the systems (s) to satisfy Technical Specification requirements.

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Mr. Boyce H. Grier .

c. A licensed operator is required to authorize all maintenance, tests, or surveillance which affect plant systems. Prior to releasing the controlling document, the operator ensures he is aware of the effect of the activity on the system or equipment. Upon completion of the item, the document is returned to the operator for acceptance or for the purpose of returning the system to service. The administrative procedures which control these evolutions provide the required explicit notification of operational personnel whenever a safety related system is removed from and returned to service.

10. A revision to the administrative procedure on communications and outside assistance has been approved. This revision incorporates the required notifications and establishment of communication channels requested in the bulleti:

The wording of the reason for immediate notification ("The reactor is not in a controlled or expected condition of operation")

is general in th't many different circumstances may or may not fit the definition, depending on who is interpreting the s ituation. We request more specific guidance on this point in order to provide more explicit instructies to our operators and duty officers.

11. Hydrogen gas generated during a transient and remaining in the reactor coolant system would be removed by using the clean liquid radwaste degasifier to degas the reactor coolant. The gas stripped from the coolant would be stared in the gaseous radwaste decay tanks. A second method consists of a nomally utilized pressurizer steam space vent which uses the sample connection and discharges to the clean liquid radwaste system. In addition, the volume control tank gas space can be purged using nitrogen and water level changes. The discharged gas would also be processed to a caseous radwaste decay tank. These tanks could subsequently be released via the Unit 1 stack (elevated release) if the activity of the gas allows.

Hydrogen gas generated during a transient and released to the containment would be recombined in one of two 100 SCFM hydrogen recombiners located inside the containment and remotely operated, or removed from the containment using one of two 50 SCFM hydrogen purge systems, which would discharge to the Unit 1 stack. The recombiners and purge systems are required per Technical Specifications.

Procedures are implemented for the referenced operations.

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Mr. Boyce H. Grier .

The reactor coolant degasification, pressurizer venting, and volume control tank purge are routine operations, while the recombiner and purge paths are verified operable by surveillance.

Any required Technical Specification changes required as a result of the inplementation of the above items will be forwarded within thirty days as requested.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY f $$L W. G. Counsil Vice President WGC/ECF/jj cc: Director, Office of Inspection and Enforcement, Division of Reactor Operations Inspection, Washi.ngton, D.C. 20555 2357 008