ML20205B412
| ML20205B412 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 03/22/1987 |
| From: | Robert Williams PUBLIC SERVICE CO. OF COLORADO |
| To: | Berkow H NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation |
| References | |
| P-87113, TAC-61580, NUDOCS 8703270603 | |
| Download: ML20205B412 (6) | |
Text
,
Grubiicservice-
=v' P.O. Box 840 Denver, CO 80201- 0840 March 22, 1987 n.o. wiulAMS, JR.
Fort St. Vrain Unit No. 1 vicE PRESIDENT NUCLEAR OPERATIONS P-87113 t
U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C.
20555 Attn: Mr. H. N. Berkow, Director Standardization and Special Projects Directorate Docket No. 50-267
SUBJECT:
Status of the Reactor Building Sump In-Line Beta Monitoring System
REFERENCE:
- 1. PSC letter, Gahm to
,Berkow dated 09/18/86 (P-86559) w 2.PSCletter,GUImtb
Berkow dated.12/22/86 (P-86655)
Dear Mr. Berkow:
-s This is the second quarterly report on the status U'the Reactor Building Suno Beta Monitoring System in accordance with Public Service Compa,'y of Colorado's agreement with you.
The Reactor Building Sump Beta Monitoring System changes r,ince the last report are as follows:
A replacement metering nump that was ordered from Cole-Parmer was returned due to a defective speed control feed back loop to the motor.
The replace:mont purp arrived December 9, 19a5 and w.ss installed the following day.
1 A pressure switch was installed to the inlet side of tha metering pump of the in-line beta monitoring system. The switch is wirrJ so that when the Reactor Building Sump pumps are turned or, pressure on the inlet side of the metering pump causes the punp to start automatically. When the Reactor Building Sump pumps are turnec off, the pressure in the inlet line to the pump will bleed off and the switch will de-energize the pump.
! bI O
\\
g 32 g h $$$
(O 7
I
c I
4 P-87113' March 22, 1987 t
Use.of the automatic switching function allows a Reactor Building
- Sump release to start and stop the beta. monitor without operator interaction.
The switch is essential since running the pump q
without water ~for any length of time will seriously damage the
)
pump gears.
The switch. is wired so that the metering pump only needs to be plugged into it. This allows use.of the pump for testing and
. calibration without use of the automatic function by plugging the pump into the power strip located in the back of the unit.
A 0-100 psig pressure gauge was installed to the inlet side of the scintillation cell.
This modification allows close monitoring of the pressure applied to the cell.
The flow cell was removed from the flow path. Th'e flow rates we I
B are using (=4-7 ml/ min) are on the minimum edge of usefulness of it the cell. The flow cell was originally installed to monitor a no
[i flow condition that was inherent to.the system-due to the original pump.
When the pump was changed and the scintillation cell was redesigned,.the no flow condition disappeared.
I 1
The cells that were constructed on site with a particle size of
=250-335 microns appear to have an efficiency of slightly greater than 2% for tritium.
This cell will still tend to act as a filter media and build up back pressure. We elected to try an even larger particle size of =375-850 microns. The cells tested with this size particle, even after prolonged use and accumulation of debris, did not build up back pressure. The
,P efficiency of these cells for tritium is
=1%.
Thi.s is
'i -
approximately the same efficiency as the factory manufactured y
calcium flouride cells.
The following is a chronology of Beta Monitor history:
12/10/86 The new ISMATEC magnetic drive pump was installed. The
- 7' pressure gauge was added to the inlet side of the scintillation cell.
12/11:/86 The first Reactor Building Sump release using the new pump and scintillation cell packed with =250-335 micron 4
calcium fluoride particles was started and monitored.
s I
12/13/86 The Reactor Building Sump release was interupted to install and test the pressure switch.
i i %
3
]
)
t P-87113
, March 22, 1987
\\
.s 12/16/86 The =250-335 micron particle cell was removed-from the system.
Attempts were unsuccessful to reduce the pressure of the cell due to the buildup of debris, 12/17/86.Another scintillation cell was prepared using the
'a375-850 micron calcium fluoride particles and installed (in the unit.
A total of six Reactor Building Sump releases were monito. red using" achieved before removal for disassembly this cell.
=53.8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> of actual-operation were and cleaning was necessary.
01/12/87 A second scintillation cell was prepared using the-
=375-850 micron calcium fluoride particles. and installed in the unit.
A total of nine Reactor Building Sump releases were monitored using this cell.
=172.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> of actual operation were achieved before the cell was removed for disassembly and cleaning.
02/18/87 The second scintillation cell was removed from the monitor.
Further monitoring of the Reactor Building Sump effluent was suspended pending investigation of P
the adequacy of the filtering system.
The following is a summary of Beta Monitor in-service performance:
The magnetic drive gear metering pump appears to work well and is reliable. The only moving parts are the magnet coupler, the driver gear and the driven gear.
This pump has an inherent safety feature for our applications.
At =100 psig the pump will " decouple", that is the drive magnet and driven magnet decouple from turning in unison.
The scintillation cells made on
- site, by virtue of their construction, are capable of withstanding =125 psig under ideal conditions. Decoupling of the pump assures that cells will not exceed the maximum pressure that can be applied to the tubing.
New gears arrived from Cole-Parmer as part of a pump rebuild kit.
The gears are constructed of graphite, approximately 2/3 the size of a dime and about the same thickness. The old gears still function even with the wear they have experienced so change out will not occur immediately.
P-87113 March 22, 1987 In mid February the gears were removed and examined for wear under magnification. The gear teeth appear smoother where the j
teeth mesh.
Premature wear however appears to be occurring on the horizontal surface of the gears that contact the surface they ride on.
We attribute this wear to particles larger than the maximum size recommended by the manufacturer (5-20 microns) entering the pump cavity.
- Also, several. teeth on both gears chipped.
The scintillation cells manufactured by the Radiochemistry Laboratory are better suited to our application than those supplied by the factory. The 250-335 micron particle CaF cell has the best efficiency for tritium at slightly greater than 2%.
The one drawback of this size particle is that there was still a back pressure buildup over the course of a release.
We also attribute this to the filtration of debris which is a highly undesirable condition.
The larger particle size, 375-850 micron, when tested over a period of time appears to filter debris out of the water; however, there is no pressure buildup.
Two cells have been tested with this particle size over the course of 15 Reactor Building Sump releases and neither cell has shown any back pressure buildup.
In both cases the cells were removed and cleaned because light output to the photomultiplier tubes had been drastically degraded.
Efficiency for sulphur-35 was determined on the 375-850 micron cell and was determined to be =15%.
To date we have not been able to keep the efficiency of a cell constant over the course of a release due to the buildup of debris and oil on the crystals.
We have set up the scintillation detection unit tritium window l
for this particular calcium fluoride crystal at 0 to 310 channels l
and a sulphur-35 window at 311 to 999 channels. This was L
determined experimentally by varying the window widths for tritium and sulphur.
It appears that the spillover correction for each window will occasionally overcompensate and as a result we do not anticipate using this function at this time. Hand calculations to determine activity may be necessary in the event that high activities for both these nuclides appear at the same time.
Further testing is still required.
,l.
m P-87113 March 22, 1987
'The_
recorder has functioned well.
The output of :the scintillation detection unit has been matched to provide a linear recorder-. response for each energy window. Other channels have l
been programmed to provide data on percent spillover for each window.
~
The recorder relays can be programmed to activate an alarm _ due to a high count rate. We have elected not to use this feature until a constant sensitivity value for. a scintillation cell can-be obtained.
The pressure switch has operated reliably' for all releases monitored. The setting for the switch was adjusted to =5-7 psig and-there appears to be no problem with this component.
Problems and Resolutions:
Our main problem,.at present, is not with the Beta Monitor but with the quality of the effluent from the Reactor Building Sump filter banks. The maximum particle size from the last filter in the-bank should be less than 1 micron. Many samples taken have been filtered and indicate particles greater than 1 micron are still in the effluent.
The Nuclear Engincering Division is working on.this problem.
A second problem with the effluent is oil contamination. During backflush of the scintillation cells an oil film can be seen.
This is not as apparent as the excessive particle size. Nuclear Engineering is also working on the oil problem.
These two problems are the main cause of reduced sensitivity of the scintillation cells over the course of a release and increased wear of the pump gears.
Based. on our experience to date with this prototype monitoring system, we do not feel that we can adequately evaluate the feasibility of the system. We would like to continue the test period for another six months until September 22, 1987. We would continue to operate the Reactor Building Sump in a batch release mode during this six month period. We would also submit quarterly reports on June 22 and September 22 and a final evaluation report on October 22, 1987, rather than on April 22, 1987 as previously committed to.
P-87113.
March-22, 1987 Your prompt' response to this request is appreciated.
' Sincere.ly,.
s
'h G
R. O. Williams, Jr.
Vice President, Nuclear Operations.
Fort St. Vrain Nuclear Generating Station R0W:DPM/pbh cc:
Regional Administrator, Region IV' Attention: Mr. J. E. Gagliardo, Chief Reactor Projects Branch' Mr. R. E. Farrell Senior Resident Inspector Fort St. Vrain