ML20212R258
| ML20212R258 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 04/16/1987 |
| From: | Robert Williams PUBLIC SERVICE CO. OF COLORADO |
| To: | Calvo J NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM), Office of Nuclear Reactor Regulation |
| References | |
| P-87136, TAC-59936, NUDOCS 8704270026 | |
| Download: ML20212R258 (9) | |
Text
.
O Public Service ~
- *,: 2 L April 16, 1987 Yn $ N eo201-os40 Fort St. Vrain Unit No. 1 R.O. WILLIAMS, JR.
P-87136
$RE$'E" R OPE NS l
l U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 Attention: Mr. Jose A. Calvo l
Director, Project Directorate IV Docket No. 50-267
SUBJECT:
Actions to Mitigate Moisture Ingress Into the Primary Coolant System
REFERENCE:
- 1) PSC Letter, Walker to Gagliardo, dated April 2, 1986 (P-86265)
- 2) PSC Letter, Lee to Johnson, dated January 4, 1985 (P-85003)
Dear Mr. Calvo:
On April 2,1986, Public Service Company of Colorado (PSC) submitted a letter to the Regional Administrator, Region IV describing the actions taken by PSC to mitigate moisture ingress into the primary coolant system during the calendar year of 1985.
That letter (Reference 1) described the Fort St. Vrain Improvement Committee, the l
actions taken by PSC to mitigate moisture ingress into the primary coolant system and the actions pending to mitigate moisture ingress into the reactor vessel.
This letter and its attachments provide the NRC with an annual report (per item IV.a of the Attachment to Reference 2) of actions that have been taken by PSC or that are under consideration by PSC to mitigate moisture ingress into the primary coolant system.
The 1986 report consists of the following attachments: - Fort St. Vrain Improvement Committee -
Organization and 1986 Activities - Actions Taken to Mitigate Moisture Ingress into the Primary Coolant System - Actions Pending to Mitigate Moisture Ingress
{ f into the Primary Coolant System
\\\\
8704270026 870416 PDR ADOCK 05000267 g
P.-87136 April 16, 1987 e
. Attachment 2 has a number of actions-that were completed prior. to 1986 but not included in the first annual' report of.. Reference 1.
These actions have been included -in this attachment for record keeping purposes, that is -to identify in a single list all of the actions taken to mitigate moisture ingress ^into the primary coolant-system of Fort St. Vrain.- While some of. these -actions.may have already been~ presented to the -NRC in a variety of earlier PSC submittals, many were never ~ specifically. addressed
.in those-submittals as moisture ingress corrective actions.
Due ' to the evaluationLof Fort St. Vrain's future operation currently
~
in process,'most of the actions in Attachment 3 have been.placed on a temporary. " hold".
While the " hold" on.these actions represents a temporary delay, the progress on the actions already taken by the t
Committee indicates Public Service Company of Colorado's commitment to the dependable operation of Fort St. Vrain.
The Committee believes that its actions have resulted currently in one of the lowest levels of moisture ever maintained during an extended outage of the plant.
This will result in a shorter non-nuclear dryout period and a shorter time for the resumption of nuclear operations.
If you have any questions please contact Mr.-M.H. Holmes at (303)'
480-6960.
Very truly yours, R. O. Williams, Jr.
Vice President Nuclear Operations R0W/AW:jw Attachments cc: Regional Administrator, Region IV Attn: Mr. J.E. Gagliardo,; Chief Reactor Projects Branch Mr. R.E. Farrell Senior Resident Inspector Fort St. Vrain I
=
~ATTACIMENT 1
~
9 FortSt.VraiSImprovementCommittee Organization and 1986 Activities The 1986 Fort.St.
Vrain Improvement Comittee. consisted of the following members:
e I
Mr. R.F. Walker, President, PSC and Improvement Committee Chairman-1
.Mr. R.O..-Williams, V.P. Nuclear.0perations 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 i
4 Mr. L.W. Singleton, Manager,. Quality Assurance Division :
..Mr.'P.F. Tomlinson, Manager, Quality Assurance Division
.The p'urpose of the Fort St. Vrain Improvement Comittee.is to
-formulate and review proposed technical improvements to enhance the operation and reliability of Fort _St. Vrain.
Actions ~taken by the Fort St. Vrain Improvement Comittee may take the form of-studies, engineering evaluations, equipment tests' and
. plant modifications.
Outside companies are utilized as necessary 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-recomendation.
The Fort St. Vrain Improvement Committee held two meetings during
~
1986.
It is believed that the actions promulgated by this comittee i
have significantly contributed to the reduction in the number and severity of moisture ingress events. Of note is the current. outage i
for EQ modifications during which time unprecedented low levels of moisture have existed, such that upon the start of the non-nuclear-3 dry-out period the moisture level was less. than 100 ppm. Previous experience had been starting non-nuclear! dry-out with an order of
+
magnitude higher level of moisture.
4 6
l i
Mr. Williams became a member of the comittee in mid-year,.
following his appointment to the position of V.P.
Nuclear.
Operations.
Mr. P.F. Tomlinson became a member of the committee-i following the retirement of Mr. L. W. Singleton.
4
ATTACHMENT 2 Actions Taken to Mitigate Moisture Ingress Into the Primary Coolant System The following actions are numbered sequentially to facilitate record keeping. The first 18 action items are listed in Attachment 2 to PSC letter, Walker to Gagliardo, dated April 2, 1986 (P-86265).
(Note:
The actions marked with an
- were completed in 1986.)
- 19.
A moisture removal device (knockout pot) and moisture level alarm monitor have been installed in the purified helium supply header to detect moisture in the header and eliminate moisture in the Control Rod Drive Orifice Assembly (CRD0A) cavities.
- 20.
A knockout pot has been installed in the drain line from each helium circulator penetration interspace and in each loop drain header for the steam generator interspaces to eliminate potential moisture carryover into the helium purge piping and the CRD0A cavities.
21.
The Barton water level instruments in the recirculator containment tanks were replaced with Foxboro instruments.
The piping configuration was also revised to improve level indication of the seal water in the weirs of all recirculator containment tanks.
22.
To improve Control Room human factors and help reduce potential operator errors, various system controls were reorganized and functionally grouped on control board I-9301.
23.
Since the helium circulators' bearing water pumps in each loop are always operated in series, their discharge check valves serve no purpose, and have been removed from the system. This will preclude loss of bearing water to the helium circulators in the event of pipe blockage due to a failed check valve.
24 A drain valve has been added to the buffer helium sun 91y line to each helium circulator to permit draining moisture that could collect in this piping.
- 25.
Seals currently designed into the conceptual large HTGR circulators have been investigated for application to the existing FSV circulators. The design concept of the Large HTGR Circulator shaft seals is similar to the design of the FSV circulator seals. The Committee considered that this concept would be a negligible improvement in the performance of the FSV circulator shaft seals.
- 26.
Addition of a water slinger in the existing FSV circulator has been evaluated and has been rejected. A slinger'would require major circulator modification and would be effective only at high circulator speeds.
It would not be effective at low circulator speeds or during a circulator trip.
(Should other circulator bearing water cartridge
~
s..
i to P-87136
_Page 2
_ modifications become 4 feasible, the water slinger concept-would be' considered as a part of those modifications.)
' 27.
The possibility' _ of installing motor. driven, hermetically sealed, magnetic bearing circulators in'the'FSV plant 'was' investigated and was rejected.
_S.M.
Stoller Company?
prepared a cost benefit study. This design was discussed and ' considered too complex -and costly for incorporation into the FSV plant.
i 28.
A manual mode. of. operation has'been-installed which allows i
the operator to take direct control of the ' main drain l valve position.from the control room.
- 29.
Replacement of-the existing half-capacity bearing water pumps with full ' capacity pumps was considered.
.The engineering evaluation showed that new diesel-generator units would also be required to support the. pumps, involving significant cost.. The Comi.ttee rejected this proposed _ modification.
- 30.
The proposal to eliminate circulator _ trip's upon occurrence of a positive buffer mid-buffer (primary coolant flowing-down the shaft) _ condition was evaluated by engineering.
l The licensing associated-with this change 'and..the fact l
that this trip mechanism has a' low frequency of occurrence.
l influenced' the Committee to reject this proposal.
- 31.
The inservice operational assessment of the new electronic control system (Action'5,-Attachment 2 of P-86265) for'the four circulator drain valves and the new digital main drain valve for circulator "A" was completed.
The.new digital valve. experienced severe-in-service mechanical-problems, indicating a very short service-life.
This valve was' removed and the old main drain valve was reinstalled. The new electronic controls, when_used with l
the four original main-drain -valves, showed; improved operational performance.
The new. control. system has resulted in the best benefit possible, so that no follow-
[
on work will be undertaken.
- 32.
Extensive-training sessions on helium circulator I
construction, operation and their auxiliary systems have been provided for the Equipment Operators (EO) and Auxiliary Tenders (AT) in addition to.the ' training sessions provided for-the Reactor Operators (RO). This increased training provides' the operators-with 'an awareness of the helium circulators' involvement in'the moisture' ingress accidents and how -operator actions' can mitigate these accidents.
- 33.
Procedures were developed for use throughout the 1986-1987 l
EQ outage to prevent or minimize moisture ingress and-to e
-Attachment 2 to P-87136 Page 3 maintain low moisture levels. throughout this period. This was accomplished by:
A.
Assuring water sources to the circulators were isolated (under. mechanical clearances-to the Superintendent of Operations or the Shift Supervisor) prior to clearing out the systems for work on the circulators.
B.
Procedurally (per SMAP-19) modifying the standard clearance point form to have a check-off for.
clearances to be performed.in a specified sequence.
C.
Constant emphasis to increase the conciousness level of the entire staff of the need to maintain minimum moisture levels.
D.
Maintaining the PCRV' above atmospheric pressure whenever possible during the shutdown.
34.
In spite of various modifications that have been made to the bearing water system,. there is still some concern about the pressure build-up in the bearing water surge tanks due to sudden water level changes.
The operators had no way of correcting an overpressure condition. This situation has been corrected by the addition of a 1-inch line with a control valve and check valve from each buffer helium loop to relieve the bearing water surge tank over pressure through the purified helium line to the PCRV.
- 35. A computer analysis of the logic and ' control of systems / components related to moisture ingress was completed by the Proto-Power Corporation. The two major conclusions of this analysis for possible causes of moisture ingress were (1) the simultaneous operation of three normal bearing water pumps and (2) the inadvertent starting of normal bearing water pumps while the backup bearing water system is in operation. Occurrence of these situations is prevented by installation of circuitry interlocks.
36.
The buffer helium system was separated into two loops to minimize the interactions of the auxiliary systems upon a
component or system upset.
During this modification, significant changes were made to the buffer helium control system (e.g.,
changed from pressure control to flow control) to provide improved response to transients in the system.
ATTACHMENT 3 Actions Pending to Mitigate Moisture Ingress Into the Primary Coolant System 1.
There is a tendency for fine particles carried in the bearing water supply system to accumulate in the circulator bearing cartridge where they could adversely impact the bearings.
Installation of full-flow or by-pass filters will' be investigated with reference to system operation and pressure drops.
2.
Moisture monitors that detect the moisture level in the PCRV have required frequent maintenance and could contribute to plant unavailability.
Alternative designs of moisture monitors have been evaluated. An infrared moisture monitor, developed by the OPHIR Company, has been selected and adapted for installation testing at FSV.
3.
In late 1986 the program for conceptual design and feasibility study of a new helium circulator with magnetic bearings (see 4.A below) was modified so that only the portion of the study associated with the " Catcher Bearing" was continued.
The remainder of the program was placed on hold due to long term concerns over the future of FSV.
EPRI is funding the " Catcher Bearing" study which is beneficial to both FSV and the Modular HTGR (MHTGR) because a " Catcher Bearing" is necessary for protection of the circulator from damage when control power or magnetic power is lost.
It is anticipated that the James Howden Company will perform this study.
4.
Following Public Service Company of Colorado's decision to write-down the costs associated with the operation of FSV, the Committee met to discuss the technical issues concerning improvements in the operation of FSV.
The decision was made to place long-term technical issues temporarily on " hold" until completion of the evaluation asscciated with the long-term future of FSV.
This decision influences the direction to be taken in the near-term for the following actions:
A.
After evaluating various proposals involving major modifications to the circulators to reduce the possibil'ty of moisture ingress into the reactor vessel, Proto-Po-er Corporation, with the support of James Howden Company, a major designer of gas-cooled reactor circulators, was authorized to initiate the conceptual design and a
feasibility study for new helium circulators at FSV. The new circulators would utilize the existing single stage steam turbine and Pelton wheel drives, but the existing high-pressure, high-flow water lubrictted thrust bearings would be replaced with magnetic bearings.
This evaluation, which was being co-sponsored by Public Service Company of Colorado and EPRI, has been temporarily modified as described in Action 3 above.
B.
GA Technologies has submitted a proposal to modify the existing circulators and their auxiliaries to incorporate the following:
fixed orifice main water drain control; the use of an eductor to replace the recirculators; the
to P.87136 Page 2 addition of a scavenging jet pump to the helium / water drain; elimination of the High Pressure Separator; elimination 'of the 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 horizontal bearing water pumps with uninterruptible power supplies for each circulator and the addition of a positive water ingress detector on each circulator.- The next phase of this work is estimated at $376,000.
C.
The existing circulator design features an upper labyrinth static helium seal that can only be set after a circulator has stopped turning.
Westinghouse was authorized to develop a hydrostatic seal concept, as well as a static seal ring concept, and to perform the preliminary engineering of these concepts in terms of feasibility.
The Westinghouse report is being studied by Public Service Company of Colorado.
The preliminary feasibility study indicates the cost to continue this effort for development of a detailed design and testing program is $329,000.
D.
A passive Core Support Floor (CSF) vent system design effort, estimated at $745,000, has been connitted to the Proto-Power Corporation.
Additional work has also been done on core support floor liner tube leak detection via a contract with D0E.
E.
The current plant protective system helium circulator logic circuitry inhibits the trip of the second helium circulator in a loop on a buffer mid-buffer upset. This inhibit potentially allows continuous moisture injection into the primary system from the operating circulator. An evaluation is in progress to determine the feasibility of removing this circulator trip inhibit.
F.
The existing laminar flow elements in the buffer helium supply lines frequently become plugged with foreign matter.
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 with low flows, the new flow meter was removed for further engineering analysis and the laminar flow element was returned to service.
Engineering was evaluating a venturi type flow element witn dual range instrumentation.
G.
Although the pressure inside the reactor vessel increases when plant startup operations begin due to nuclear heat, the circulator bearing water cartridge differential
l
~
to P-87136
-l Page 3 1
pressure remains constant.- A study will be performed to determine whether varying bearing water cartridge differential pressure with the reactor vessel pressure would help to mitigate th4 moisture ingress problem.
l 4
+, - -
--