ML20112G495

Responds to 850220-22 Requests for Addl Info Re Improvement Committee & Plant Mods Concerning Reduction of Primary Sys Moisture.Historical Background,Review Committee Responsibilities & Description of Helium Issues Encl

ML20112G495
Person / Time
Site:	Fort Saint Vrain
Issue date:	03/12/1985
From:	Lee O PUBLIC SERVICE CO. OF COLORADO
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20112G501	List: ML20112G495 ML20112G517
References
P-85082, TAC-59936, NUDOCS 8504010140
Download: ML20112G495 (13)

Text

g.,--w, y

c.

'9:

PUBLIC SERVICE COMPANY OF COLORADO P.

O. BOX 540 DENVER.

COLORADO 80200 2420 W. 26th Avenue, Suite 1000, Denver, CO 80211 OSCAR R. LEE -

VICE PRESIDENT March 12, 1985 Fort St. Vrain Unit No. 1 P-85082

%B@M0WM %

Regional Administrator s

= Region IV MAR 2 21985 U. S Nuclear Regulatory Coninission

'y 611.Ryan Plaza Drive, Suite 1000 Arlington, Texas 76011

SUBJECT:

Actions Taken to Mitigate Moisture Ingress

REFERENCES:

1) P-85022, 0.R. Lee to E.H. Johnson, 1/24/85, Fort St. Vrain Improvement Committee Actions

2) H.R. Denton to R. F. Walker 10/16/84, Audit of Fort St.

Vrain Operations

Dear Mr. Johnson:

Public Service Company (PSC) recently submitted, as Reference 1, a brief. description of the Fort St.

Vrain Improvement Coninittee including a listing of issues under consideration and circulator auxiliary system modifications in process or anticipated which have the potential of reducing moisture _ ingress into the Fort St. Vrain Primary Coolant System. Subsequently, at the PSC/NRC meeting of

. February 20-22, 1985, further information was requested concerning this committee and plant modifications associated with the reduction Lof primary system moisture. Amplification of these items is included g

in the following three at'achments:

,7U.. Historical Background and Fort St. Vrain Review Committee Responsibilities.. Description of Major Helium Circulator Issues Under Consideration by the Improvement Committee i

_ g 40 g j 850 g67 REO PDR Z Q

p.

9 b ~P-85Gd2 Pags 2

'n

' ' ' i Attachment' 3.. Modifications Concerning Moisture Ingress Either.

Completed During the Current Shutdown or to be Completed Prior to Startup Provided ' Material Availability _and Schedule Permits

.The information in Reference 1 is important.in providing a complete overview of " this. subject and,. as such,Jis. included herein as Attachment-~4.

Please contact Mr. H.L. Brey.at (303) 571-8404 if you desire further clarification of this issue.

Very truly yours,

, +

0. R. Lee, Vice President Electric Production

.0RL/ HLB:pa Attachment v

f FkE -

p _ '

(

7 8

-e f

.w.

+p y

&w-

,n-g

,4 7r--+

y

,-v--

9 sew,wy-9.e, y

9

--99

y [; -

?'

.Attachmeht 1 jf N _

Page 1 to P-85082

:? :'

a I

SHISTORICALBACKGROUND'ANDFORTST.VRAIN'

-REVIEW C0lWITTEE RESPONSIBILITIES

~

,The. Fort,St.-: Vrain plant has had.a'significant history'of problems:

l associated..'with moisture _in thei; primary coolant:: system.

.This

moisture, has almort exclusively'been the result of helium circulator.

~

H

bearing Ewater flowing ?up sthe ? shaft L.of the _ circulators during

l transient or upset conditions. ::Numerousimodifications of the helium:

-; circulator : auxiliary -system have been performed -in :an-attempt.to -

~

Lprecludee'or minimize moisture upsets.. These included modificationsJ

. performed by Gulf General' Atomic prior to acceptance of the plant by PSC 'in ~1979' and; subsequent technical evaluations'of the system and

modifications by PSC thereafter.

y

~ A raajor plante outage took place in 1981[1982 to isolate the buffer systems of the circulators of loop 11 (from loop: 2.

Although the primary purpose of this modification _was to prevent circulator upsets-

in one: loop from reflecting into the ' econd, a significant goal of s

the imodification 3was to,. reduce moisture; ingress by minimizing the-lnumberiof circulators responding:to a' system upset.- ' Comparison} of

~

. the.recordsl:of-circulator Ltrips:before"and after splitting:of'the' -

buffer loops { indicate a substantial reduction in circulator ' trips

!which? should result.in "a lowering offmoistur'e.ingresssevents..

"However,

. moisture jingress events continued 'and in 1982 PSC Eestablished the.~ Moisture-Ingress. Committee.

This Comittee was ci comprised _of-key PSC management and technical personnel and selected The actions of this y

consultants with expertise in Fort St. Vrain.

Committee; resulted 11n the evaluation of.many possible modifications

'to the helium circulator auxiliaries,. evaluations of ' instrumentation h

Shardware. 'and L software, evaluation of procedures, and evaluation of

~

-various methods:for; improving transient analyses.

~ Many ' ' activities were

' evaluated-and-R dispositioned to include' initiation of modifications which showed promise for the reduction of the frequency

<and severity of moistureiingress into the primary system.

-InI0ctob'er1Mr. R.F. Walker, President and Chief Executive Officer of

~ PSC', formulated the Fort St.lVrain Improvement Comittee. Under his s.

-Chainnanship this. comittee' has' a's.its primary purpose to evaluate

~1nnovativ'e and substantialLideas which would' resolve Fort St. Vrain's

~

tdeficienciesLandisignificantly. improve its capacity factor. Although 3;, ~

-primary coolant: system' moisture is.the predominant contributor to FortT St. iVrain's_-poor' operation, the Improvement Committee is also

evalu~ating other major issues which have the L*

plant.availabilityt potential of-limiting

+

[

T bL.

g L.

p

to P-85082 Pag 2 The membership of this Comittee as presently constituted-and in keeping with. the current PSC Nuclear organization includes the

~following:

Mr. R. F. Walker, President and Chief Executive Officer, PSC, Chairman Mr. O. R. Lee, Vice President, Electric Production Mr. H. L. Brey, Manager, Nuclear Licensing and Fuel Division Mr. J. W. Gahm, Manager, Nuclear Production Division Mr. D. W. Warembourg, Manager, Nuclear Engineering Division Although the membership is currently as indicated, augmentation with personnel with expertise in.the nuclear power industry has not been precluded and ~will take place as specifically required.

The

-Executive membership of this Comittee assures leadership with the ability and resolution to commit resources as necessary to achieve the goal'of seeing that Fort St. Vrain operates efficiently and economically.

As a first step in its fonnulation in October,1984, the Committee undertook the task of reviewing actions of the Moisture Ingress Committee.

To provide an appropriate base from which to function, this' review included all actions previously taken by the Moisture Ingress Comittee as well as ongoing issues under consideration at that time.. Issues and actions under consideration by the Moisture Ingress Comittee were then absorbed by the Improvement Comittee and the Ingress'Comittee was subsequently dissolved. Attachment 3 herein provides a brief description of current modification work on the

' helium circulator auxiliaries which was primarily originated through

the Moisture Ingress Comittee.

The Fort St. Vrain Improvement Comittee has embarked on a review of innovative helium circulator design. changes to ' improve Fort St.

Vrain's performance. herein is a brief description of tasks currently under consideration.

A review of. Attachment 2 indicates that the issues under consideration have been expanded from the category of pipe and valve changes to the evaluation of major modifications or complete replacement of the existing helium circulators.

.The

~ President

-and Chief Executive Officers' Chairmanship assures the highest involvement of PSC in this endeavor.

r

'to P-85082 Page 1 DESCRIPTION OF MAJOR HELIUM CIRCULATOR ISSUES

.UNDER CONSIDERATION BY:THE IMPROVEMENT COMMITTEE This is. an update of what has transpired concerning major helium circulator issues currently under consideration by the Fort St. Vrain

. Improvement _ Consnittee.

Many of these are.new and the investigation of their feasibility for Fort-St. Vrain is in the initial formulation

stage.

Public Service: Company has undertaken an investigation-of a new circulator' concept.

This concept is a motor driven helium circulator utilizing' magnetic bearings.

PSC is working with Proto-Power Corporation -in addressing this new circulator.

Proto-Power -has formulated a consortium of international experts including the J. Howden Company from Scottland, the worldwide principle manufacturer of circulators having built over 100 circulators for the_ European Gas-Cooled Reactor programs; i

Magnetic Bearings Inc.,

the United States representative of Societe de Mecanique Magnetique, with extensive experience in the

-application of magnetic: bearings to machinery including the

-. helium circulator rated at 840 degrees F for a test facility in the Federal Republic of Germany; and General Electric Corporation for the design of a 5000 hp/9000 rpm synchronous motor.

lIn-. December,1984'PSCcontradtedwithProt'o-PowerCorporationto perform a qualitative engineering and licensing assessment of the suitability of hermetically sealed,_ motor driven, magnetic

-bearing, helium circulators for Fort St. Vrain.

The primary

. purpose ~ of this contract !was to assess major engineeringLand

-licensing issues to determine if there are any which may preclude r

l

'the use of this type of. circulator within Fort St. Vrain. This evaluation is still. in. process, but to date no: significant impediment has been identified which would preclude this circulator type.

On January 29, 1985, PSC met with key representatives from Proto-Power, J. Howden Company, Magnetic Bearings Inc. and General Electric to discuss the feasibility of this concept. We were informed that preliminary investigations' show this concept to have:~ considerable merit and PSC is awaiting a proposal from Proto-Power Corporation to provide a preliminary design study for

' Fort St. Vrain.

PSC recognizes this circulator concept will require extensive evaluation prior to its physical' application.

Before undertaking a modification-of this magnitude PSC must closely evaluate this design in light of other possibilities for the plant including the-extensive capitalization and plant outage which would be required. Preliminary cost and schedule estimates are to be submitted to~PSC by Proto-Power Corporation in the near future.

L

1 m

to P-85082 Page 2 j

J Public Service Company is also investigating the possibility and feasibility of making major modifications to the existing Fort 4

St. Vrain Helium Circulators. Some of the areas currently under O

investigation include the following:

f N

The addition of a water slinger on the existing circulato'r shaft R

The addition of a helium / water drain forced scavenging jet pump Replacement of the buffer helium recirculator with an eductor Plugging of the lower helium / water drain ports 7

in the existing circulator housing

~R Replacement of the main bearing water drain control s

3 valve with a fixed orifice These issues were a major subject of the PSC/GA Technologies management meeting held in San Diego December 13-14, 1984.

Many of g

these items are incorporated in the standard design for the large HTGR helium circulators, but their incorporation into Fort St. Vrain as a backfit to rur existing circulators would be a substantial undertaking whose cost / benefit has -yet to be detennined.

Also, i

incorporated into the design of the conceptual large HTGR circulators

-3 is a significantly modified seal arrangement compared to Fort St.

Vrain.

The practicality of redesigning the existing labyrinth seals al 7

has yet to be addressed.

'E The possibility of installing hydrostatic seals onto the existing a

Fort St. Vrain circulators is also under consideration.

PSC has discussed this issue with Westinghouse and is currently reviewing a

]

proposal for an engineering evaluation to make this modification.

g A modification to the plant protective system which was under d

consideration by the Moisture Ingress Committee and continues to be

]

addressed is to remove the interlock inhibit which would prevent a second helium circulator in a coolant loop froit tripping under Ti certain conditions if the first circulator has already tripped. This 3

change in the plant protective system has some potential for reducing i"

moisture ingress events.

A detailed analysis will be required to p6nnit evaluation of all aspects of this modification.

i 2

The Imptovement Committee has also evaluated a number of other 4

possible concepts including a motor driven, oil bearing circulator 3

unit utilizing magnetic bearings with high pressure helium as

]

and a the main power source.

In actions taken at the March 8, 1985 meeting i

of the Improvement Committee, the decision was made to initially i

concentrate on evaluating three possible circulator options

}

l i

~'

'=

d y

L.

m'-

m l

g g all

91 to P-85082 jj Page 3 gg W

including:

1 The motor driven circulat'or utilizing magnetic bearings Performing some or all of the significant modifications ir to the existing circulators discussed on page 2 of this

]i attachment Installation of hydrostatic seals on the existing Fort St. Vrain circulators.

32 d

3 9

2R

-E a

5 5

i

?

~

1 5

E 1

]a 1

i M

i i2

?

I 9i i

i

to P-85082 Page 1

. MODIFICATIONS CONCERNING MOISTURE' INGRESS EITHER COMPLETED DURING THE CURRENT SHUTDOWN OR TO BE 4

COMPLETED. PRIOR TO STARTUP PROVIDED MATERIAL AVAILABILITY AND SCHEDULE PERMITS Then following includes a 'brief description 'of individual helium circulator auxiliary system modifications which have the reduction of

. moisture' ingress -into the primary coolant as their major basis for

.impiementation.

~It -has been determined that a high percentage of helium circulator' transients, resulting in ' water ingress to ~the

.PCRV are related to inability to drain water from the bearing cartridge.

Several aspects of the system

contributed to these water ingress problems. A loop seal existed between the circulator and the high pressure separator.

During transients wherein water _ levels in the high pressure. separator were changing rapidly, water from the loop seal was forced back _into the circulator, resulting-in an upset of the - pressure relationships of buffer and bearing water-within the circulator bearing water _ cartridge.

. During the: current outage, this piping has been modified to-eliminate the. loop-seals.

- The high pressure: separator previously drained into the r.ain drain line. ; During plant. transients, this drain path had considerable resistance _and ineffect acted as a loop seal in the drain from the high pressure separator.

Fluctuations in the. bearing water; surge tank < levels often times resulted in flooding of the high' pressure separator. ~During this outage we have re-routed the high pressure separator drain directly to the~ gas side ofLthe bearing water. surge tank.

This l

. change should_

provide' proper high pressure separator draining during circulator transient conditions.

Another proble'm related. to flooding of theihigh pressure

' separator was the -insufficient piping flow capacity of the system.

The old. system had a capacity of approximately 5 gallons per minute. We.-have-increased this capacity to 20 gallons per'. minute, which should ' help to eliminate high pressure separator flooding during transients.

e -

.~

to P-85082 Page 2 The ' original main drain control system was pneumatic with a

- pneumatic operated ~ valve. There is an inherent system lag 1

in. this type'of system due to the characteristics of an air control system.~

It-has been determined from. computer model studies that if_.the main drain valve responds fast enough, the circulator can go through severe plant transients

- without water ingress.

In order to speed up the response of the main drain valve, pneumatic boosters were added.

Plant transients that were experienced after-insta'llation of these

. boosters did not result in water. ingress events.

While the booster improved the main drain performance, they also--introduced control. instability problems.

When we attempted to slow down the: system to eliminate this instability, th' effectiveness of the boosters was. reduced.

An.investiprtion into better main drain control showed that converting the pneumatic system to ' electronic controls

- should make significant improvements. During the current outage, we will convert the main drain control for all four

- circulators to an electronic system.

We have also' located an unconventional type of valve known

^

as a Digital valve. This valve provides full open to full close-stroke -time in. 100 milliseconds.

The. pneumatic valves' stroke time was.on'the order'of 12 seconds. We are installing one 'of these digital valves on the A circulator and sending a second Digital valve out for seismic and environmental qualifications.

Tests will be performed to

. verify valve performance, and we plan to operate with a Digital valve in the-A circulator main. drain when we. restart the plant.'

The~ electronic main drain controls for-the'other three circulators-may: enhance the performance of' the existing

. valves to where: they provide satisfactory response. The installation of the Digital valves is an effort to take steps in parallel in case the electronic control does not completely. solve the main drain problems.

With the installation of electronic control for the main drain system, we are giving the operator more control options.

- The high pressure separator level control now provides a feed forward signal to the main drain set point.

With the

- higher response speed of the electronic control system, this may not be necessary.' We are providing an option where the main drain is' controlled strictly from main drain to buffer differential pressure.

Computer model studies performed by GA indicate that this is L

a more effective mode of control.

The increase in high l

pressure separator drain capacity from 5 gpm to 20 gpm will l

enable the control system to function properly with this L

. mode of control.

L.

~

' ;r

~'

to P-85082 e

3 Page 3 We are. also prov_iding a manual mode of operation where the operator can take direct control of the' main' drain ; valve position from the Control Room.

In-the~ past there have.. been circulator trips in which analysis of the transient could not satisfactorily identify the cause of the. trip'or the

cause of the resulting moisture ingress. -In order to. pursue _ a more intense effort to resolve':these moisture ingress events, a transient review -

consnittee.was-formed. This committee performs an in-depth

~

analysis of all plant transients such as circulator trips, loop = shutdowns, and reactor-scrams.

-One of the items identified by. this transient review committee was the need

- for. additional data points at a higher - sampling frequency

-than' the' plant. data. logger could provide. A dedicated system has been installed to provide this infomation and additional inputs have been added as the need has been

. identified. :The system 'still has considerable.

spare capacity for new inputs if they are found to be necessary.

Another item identified by' the committee _ as a possible source of circulator trips was the possibility of spurious

- trips induced into the system. The committee identified that the signal cables for the bearing water and buffer,.

mid-buffer _ pressure differential switches were not shielded.

- We will install shielded cables during this outage. The'new.

shielded ' cables will be connected to the buffer, mid-buffer

- switches and many system 21 computer data signals during this shutdown.

It is-our intent to replace the bearing water _ pressure differential switches in the future and the new shielded cables will-be connected to these switches at that time.

Y r

y m

j< - :

\\

s.;:

"4

~

to'P-85082-w

Page 4-d

• 4 Another.Elong-standing jinstrumentation _ and control problem -

~

zinvolvesTthe-laminar flow elements'for providing indication of.. buffers helium supply:Jand.Ereturn flows. The existing _

laminar typeLelements are extremely sensitive to particulate

' 7

contamination ~ Lor. to any moisture that might get into these

-sensing. lines.

It has-been determined that under certain-s conditions,- the - Control _. Room indication for buffer aelium d

supply, and : return flows are n'ot: correct. 'If the circulator is foperated with : improper buffer flow, the circulator is t

~

vulnerable toLtrips during a plant transient.

In - order - to 1

provide the operator with better indication of actual buffer

flows,Lwe intend to investigate alternative instrumentation

. that may be available. : This: instrumentation must operate in helium at-a very. low differential pressure.

As soon as possible,; we intend-to replace the buffer helium supply _and return laminar flow elements on D circulator with Thermal

-Dispersion type' flow elements.

In P-85022, the replacement

. type of, flowmeter was~1ndicated to be of a subsonic Venturi design.

. Subsequent 1 engineering analysis indicated the R

-thermal dispersion type to be superior for our application.

.If this. type.~of flow element _provides.more reliable flow indication,.then the. flow elements on the other circulators will-be changed out in the future.

In.the ~ past, it has been difficult-to determine whether or

'not a bearing water accumulator has1 fired.

An emergency Laccumulator is provided to prevent circulator damage on loss of bearing water. This accumulator is fired on sensing low n

l

= cartridge differential pressure in order to provide bearing

^

i

. water during the. coast-down of the circulator. The' operator

~did 'not _'have. positive : indication that an accumulator had

- been-fired, and accumulator firing has been associated with

suspected. water. ingress.

Indicators have been provided in the Control ~ Room to show the operator when an accumulator M

has been fired. The accumulator control system has valves which are programmed to provide proper bearing water flow l based on ~ any given PCRV pressure.

We have completed a 0

review of these programmed valve. positions and the program L-

~has been :found to be' satisfactory.

The calibration frequency of all helium circulator auxiliary instrumentation l

has been evaluated and necessary modifications were made to 4

these procedures.

g During normal; circulator operation, bearing water for the

~

circulators is provided from the bearing water pumps.

If a h

- pump:.is: lost, the back up bearing water automatically comes in to provide adequate 1 water,to 'the circulators bearings.

If -the pump was restarted, a surge of bearing water to the

[.

circulator bearing'cartr,idge occurred until the automatic p

control _on' the-back up bearing water could act to reduce this flow.

l.

j b

L g

r t

_~

3

'k

C 3_

dttachment'3 to P-85082.

. b~

Page 5

" - 4

~

.' water, itLis;necessaryifor the' operator to return to the

After the helium circulatorsfare operated on back-up bearing

~i norma 1 7 earing 7 water; supply. from bearing water pumps.

A-b a;t - E.L

-severeitransient was.sometimes' induced'if the bearing water

' i~

-pumps (were brought on1 11nein-addition to the back'~up bearing waterLsource. The operator had no control: over the y'

~'

ratef ats which the-normal. bearing water was pumped into the system.;; Controls)are beingLadded to allow the operator to bring ; inormal J bearing ~. L water supply ~ in gradually,1 and this

'~

supply will back;out the back-up bearing ; water.. system so that -this-transition 1 can. be :made :in a more controlled manner.

-During overhaul o'f 'the control rod drives, we observed

-indication that moisture may -.be coming into the drive mechanism through the purified helium header. A bearing

,N

.waterLleak from the A circulator into: the penetration interspace: has been identified, and this is the probable source of moisture into the purified helium header.

In

. order:' to detect and. eliminate moisture from any source in

~

ithe purified helium header, we plan to ' install moisture removal devices and moisture monitors in the~ purified helium-header. The moisture removal devices and instrumentation are not available :for installation during: this outage, however, piping revisions will be made to allow-installation of these devices when they become available.

GA developed a moisture ingress / removal manual several years

• =

ago.. We have asked GA to update.this manual to reflect current' plant configuration. The manual has been reviewed and-approved by various-plant organizations:and will be used for operator training, as well as 'being a source of reference information for operators during and after any-moisture ingress events.

.The ' positioners on the High Pressure Separator drain valves are being replaced during this outage. The old positioners

-required frequent-maintenance to match controller output to the pneumatic valve operator. The new positioners match the

-controller output to the pneumatic operator range and should give,better valve performance with less maintenance.

In the.past we have had difficulty obtaining reliable

. indication of the water level in the buffer.

helium recirculators.

During -this

-outage the Barton level instruments are being replaced with Foxboro instruments.

The piping-- configuration is also being revised to enhance a.

igood level indication on all recirculators.

i

)

5 l-

Y G

Attachm:nt 3 to P-85082.

Page 6 We-havel contracted with.Proto Power Corp. to perform a

• computer analysis.of the logic and control-systems for most of the helium circulator isystems.

-It is our intent to verify trip and control-logic to assure.that there are no unidentified improper': modes of logic or control that could cause circulator or loop ~ trips;and -lead. to water ingress events.

We have received final lists of System Error Definitions, and we expect to receive preliminary,results of this~ analysis' by April.1,1985.

~

~

Prior 'to startup, 'we -have scheduled a five-day training session for the-- Reactor -Operators.

-This training will include. two days where' circulator startup,' operation, and theory will be stressed with the intent of making operators more aware of-moisture ingress problems associated with circulator operation.

'