ML20155G018

Forwards Info Re Fort St Vrain Improvement Committee & Actions Taken & Under Consideration to Mitigate Moisture Ingress Into Primary Coolant Sys,Per Util 850312 Commitment

ML20155G018
Person / Time
Site:	Fort Saint Vrain
Issue date:	04/02/1986
From:	Walker R PUBLIC SERVICE CO. OF COLORADO
To:	Gagliardo J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
P-86265, TAC-59936, NUDOCS 8604300077
Download: ML20155G018 (7)

Text

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R. F. WALKER PftESIDENT April 2, 1986 Fort St. Vrain Unit No. 1 P-86265 .-

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Regional Administrator Region IV \! g l 4% I i

U. S. Nuclear Regulatory Comission 611 Ryan Plaza Drive, Suite 1000

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ATTN: Mr. J. E. Gagliardo, Chief Reactor Projects Branch Docket No. 50-267

SUBJECT:

Actions To Mitigate Moisture Ingress Into the Primary Coolant System

REFERENCE:

1) PSC Letter, Lee to Johnson dated March 12, 1985 (P-85082)

2) NRC Letter, Heitner to Walker, dated March 14, 1986(G-86130)

Dear Mr. Gagliardo:

On March 12, 1985, Public Service Company of Colorado (PSC) addressed a letter to the Regional Administrator, Region IV describing the actions undertaken by PSC to mitigate moisture ingress into the primary coolant system. That letter (Reference 1) provided the historical background and responsibilities of the Fort St. Vrain Review Comittee and its successor comittee, the Fort St. Vrain Improvement Ccmittee. The letter also described the major helium circulator issues under consideration by the Fort St. Vrain Improvement Comittee and plant modifications related to moisture ingress either completed or to be completed prior to startup.

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,, . P-86265 April 2, 1986' The NRC responded in a letter dated March 16, 1986 (Reference 2) stating that PSC's plans for modifications to. Fort St. Vrain in order to reduce moisture ingress into the reactor vessel had been reviewed and that the NRC had concluded (based on a_ safety evaluation enclosed with the letter) that these modifications should reduce the likelihood of moisture ingress into the reactor _ vessel. The letter also noted that PSC had committed to further studies and plant design modifications to mitigate moisture ingress into the reactor.

This letter and attachments constitute PSC's commitment to provide the NRC with an annual report.of actions that have been taken by PSC or that are under consideration in order to mitigate moisture ingress into the primary coolant system.

The current report consists of the following attachments:

Attachment 1 - Information Concerning the Fort St. Vrain Improvement Committee.

Attachment 2 - Actions Taken to Mitigate Moisture Ingress Into the Primary Coolant. System Attachment 3 - Actions Under Consideration to Mitigate Moisture Ingress Into the Primary Coolant System Public Service Company of Colorado wishes to reemphasize its total commitment to the dependable operation of Fort St. Vrain and to assure the NRC that this commitment is-being translated into plant improvements to attain this goal.

Very truly yours, R. Y waLAa-R. F. Walker RFW/GG:kb Enclosures

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,, '. P-86265 ' April _2, 1986 ATTACHMENT'1 Information Concerning the Fort St. Vrain Improvement Committee The Fort St. Vrain Improvement' Committee consists of the following members:

Mr. R. F. Walker, President, PSC and Improvement Committee Chairman-Mr. H. L. Brey, Manager, Nuclear Licensing and Fuels Division-Mr. J. W. Gahm, Manager, Nuclear Production Division Mr. D. W. Warembourg, Manager, Nuclear Engineering Division Mr. L. W. Singleton, Manager, Quality Assurance Division The purpose of the Fort _ St. Vrain Improvement Committee is to formulate and review proposed technical improvements t) enhance.-the operation and reliability of Fort St. Vrain.

Actions .taken by the rort St. Vrain Improvement Committee may take the form of studies, engineering evaluations, equipment, tests -and plant . modifications. Outside . companies are utilized as necessary' 2 when specialized technical competence is required. . Each issue considered by the Fort St. Vrain Improvement Committee is assigned to a specific member of the Committee for investigation and recommendation.

The Fort St. Vrain Improvement Canmittee held six meetings during 1985. Another meeting of the Fort St. Vrain Improvement Committee took place on February 14, 1986.

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;P-86265 April.2, 1986.'

ATTACHMENT'2' Actions Taken To Mitigate Moisture Ingress Into the Primary Coolant System

.1. Piping modifications. were made-to eliminate the loop seal-between the circulator and the high pressure. separator.

2. The water drain line from the high pressure separator was rerouted into the bearing water surge tank instead of the main drain line.

3. The . size .of the high pressure l separator drain .line-was '

increased to ensure adequate . drainage during. transienti conditions.

4. Pneumatic valve-opening boosters were added .to the main-drain valves to speed up.their response.

5. Electronic controls for the main drain: valves were installed to improve the stability of the system.

6. A control option under which the main drain is controlled ~

from the main drain-to-buffer differential pressure was provided.

7. A computerized System 21 data acquisition system was placed--

in service to facilitate the analysis ~of plant transients.

8. Differential pressure instrument cables'were replaced with shielded cables to minimize spurious' circulator trips induced into the system..

9. Controls to allow the operator to bring the normal bearing water supply in gradually-after operating on back-up bearing water were installed.

10. A moisture- ingress / removal manual . for; use -in- operator training and-guidance was prepared and issued.

11. An alarm function for the differential pressure between. . -

reactor vessel and b aring water surgc- ta'nk was provided..

12. An uninterruptible power. supply for critical;: System 21 (Primary Coolant) components.was provided.-

13. Indicating lights were installed in the control room-to.show; the operator when an accumulator has fired.

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' P-86265 April 2, 1986 14.- The accumulator firing program'was evaluated and found to be.

satisfactory.

15. The calibration. frequency for System 21 instruments was evaluated and the procedures modified.

16. A Transient- Improvement Committee was established to investigate all serious plant transients and to . recommend plant modifications which might prevent future transients from similar conditions'- .

17. New positioners- were installed on the high pressure

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separator drain valves.

18. Portions of the helium circulator auxiliaries were put into a simulator . in order to improve operator training capabilities.

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, - P-86265 ' April 2, 1986 ATTACHMENT 3 Actions Pending to Mitigate Moisture

Ingress Into the Reactor Vessel.

1. Moisture removal devices- (knockout pots) and moisture monitors have been' installed in the purified helium header to eliminate and detect,mois'ture. Piping ~ changes were made during the current outage to accommodate.these devices.

2. An unconventional type of valve (known as a digital valve) is being evaluated for possible use.as a main drain valve.

When a digital valve, which has a' full open to full.close stroke time of 100 milliseconds, was tested, it developed-mechanical- problems indicating a relatively short service life. The valve is undergoing engineering evaluations by the manufacturer.

3. Although the pressure inside the reactor vessel increases-when plant startup operations begin due to nuclear heat, the circulator bearing water pressure remains constant.- A study._

will be performed to determine whether floating the bearing.

water pressure with the reactor vessel pressure would help '

to mitigate the moisture ingress problem. )

4. The buffer-midbuffer system. is designed to maintain equilibrium between the circulator bearing water and the primary coolant in the reactor vessel.- If- a positive buffer-midbuffer condition occurs, the circulator _ i. tripped ,

to prevent primary coolant from flowing down the, shaft.

Evaluations are in progress to determine the feasibility of.

continuing circulatbr operation even though it could result in primary coolant being released.

5. There is a tendency for fine particles carried in the bearing water supply system to accumulate.in the circulator .

bearing cartridge where chey could adversely impact the bearings. Installation of full-flow.or by-pass filters will be investigated with reference to ~ system -operation and pressure drops.

6. The existing laminar flow - elements in the _ buffer helium supply lines tended to become plugged with foreign matter with resulting infrequent system ' maintenance' and calibration. A new flow meter utilizing a resistance type of detector was installed in "D" circulator auxiliary system on a trial basis. Due to inadequate response low flows, the new flow meter was removed for further engineering analysis' and the laminar flow element was returned to service.

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7. The ' existing circulatorIdesign features an upper labyrinth s static helium Seal thatican only be set _ after a . circulator has stopped turning. Westinghouse ~was authorized.to develop:

> a hydrostatic seal concept and to _ perform the preliminary- -

engineering of: a 1 hydrostatic seal- that will set when pressure transients occur in the bearing water system. The

' Westinghouse report is being studied .by Public Service

.F Company of Colorado.

8. The circulators have. dual h'elium/ water drains. A report  :

received from GA : Technologies indicated: that- the._ lower helium / water drain _of the circulators could be plugged which

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I would reduce the amount of bearing water..to be handled. '

This modification will t considered as the circulators are.

removed for refurbishmen .

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9. GA Technologies has submitted a proposal currently _under .

review by the Fort St. Vrain Improvement Committee to modify' '

the existing circulators and their auxiliaries, to l incorporate the following: fixed orifice . main water drain control, the use of an eductor to replace the recirculators,  ;

the addition of a scavenging jet pump _ to the helium / water i drain, elimination 'of the H.P._ Separator, backup'. bearing water and accumulator systems, complete separation' of the .

bearing water and buffer helium systems so each circulator '

is independent of all other circulators, .. installation of  :

three bearing water pumps with uninterruptable power supplies for each circulator and the. addition of a positive water ingress detector on each circulator, p i 10. The current plant protective system helium circulator logic -

inhibits the trip of the second helium circulator in a . loop 1 on a buffer mid-buffer upset. This inhibit provides the .

potential of continually injecting moisture.into the. primary-  ;

system from the operating circulator. An evaluation ~is in progress to determine the feasibility of removing this j

4 1 circulator trip inhibit.

i i 11. After evaluating. various . proposals- involving . major I i modifications to the circulators to reduces thet-possibility of moisture. ingress into the reactor vessel,_Proto-Power

) Corporation, with-the support of James 'Howden. Company, a

major designer of gas-cooled ' reactor circulators =was L authorized' to initiate the conceptual. design ~and.~ a F feasibility study for new helium circulators :at Fort-St. '

i Vrain. The circulators would util.ize the'Lexisting . single -

' - stage steam turbine and Pelton ' wheel drives but would-replace the existing- :high-pressure, high-flow water-

lubricated thrust bearings 'with ; magnetic. bearings. This-

) - evaluation is being co-sponsored by Public Service Company 1

{ of Colorado and the Electric Power Research Institute'.-

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