ML20085L767
| ML20085L767 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 04/08/1975 |
| From: | Brey H PUBLIC SERVICE CO. OF COLORADO |
| To: | Howard E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| Shared Package | |
| ML20085L744 | List: |
| References | |
| AO-50-267-75-3A, NUDOCS 8311020444 | |
| Download: ML20085L767 (10) | |
Text
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\ je public service company ce conende
/ '- P. O. Box 361, Platteville, Colorado 80651 u
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i APR. 'E/93 April 8, 1975 ;.'.'
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Mr. E. Morris Howard, Director Nuclear Regulatory Commission Region IV Office of Inspection and Enforcement 611 Ryan Plaza Drive ~
Suite 1000
- Arlington, Texas 76012 REF: Facility Operating License No. DPR-34 Docket No. 50-267
Dear Mr. Howard:
Enclosed please find a copy of Abnormal Occurrence Report No. 50-267/75/3A, (additional information to the final), submitted per the requirements of the Technical Specifications.
Very truly yours,
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- H. Larry Bre Superintendent-Operations Fort St. Vrain Nuclear Generating Station HLB:il cc: Mr. Angelo Ciambusso -
26 p ,pnY,7 8311020444 760513
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REPORT DATE:- 4-07-75 ABNORMAL OCCURRENCE OCCURRENCE DATE: 1/23/_75 O FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO P. O. BOX 361 PLATTEVILLE, COI.0RADO 80651 REPORT No. 50-267/75/ 3A
.- Final ADDITIONAL INFORMATION IDENTIFICATION OF OCCURRENCE: ,
Failure of the Dew Point Moisture Monitors to initiate a reactor scram when moisture content of the primary coolant exceeded the trip setpoint.
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This is identified as an Abnorncl occurrence per definition 2.lb of the Technical Specifications and a violation of Limiting Condition for Operation, LCO 4.2.11, Loop Impurity Levels, Low Temperatures.
CONDITIONS PRIOR TO OCCURRENCE: Steady State Power Routine Shutdown 4
llot Shutdown ' Routine Load Change Cold Shutdown X Other (specify)
Refueling Shutdown Reactor critical at.approximately
+ Routine Startup 10-5,%.of. Rated Thereni Power s' for training purposes._
The major plant parameters at the time of the event were as follows:
Power PTR 0 MWth ELECT. O MWe Secondary Coolant Pressure -1250 :psig Temperature 182 *F.
F]ow 349,000 f/hr.
Primary Coolant Pressure 234 . psig ,
Temperature -182 _ 'F. Core Inlet it s 193 'F Core Outlet Flow 2 x 105 '#/hr.
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DESCRIPTION Page 2 OF OCCURRENCE:
On January 23, 19'75, preparations were made to take the reactor critical for training purposes.
Two helium circulators, A and B, were accelerated to approximately 2300 rpm at approximately 0130.
Moisture Icvels in the of primary coolant at this time were< 1000 ppmv, well within the limit 5000 ppmv stated in LCO 4.2.11. An increase in moisture concent ration was noted on the panametrics moisture monitors shortly following accelerat ion This was considered normal from our past experience of the helium circulators.
, under similiar circ 6mstances.
T'h c reactor was taken critical at approximately 0630 hours0.00729 days <br />0.175 hours <br />0.00104 weeks <br />2.39715e-4 months <br /> and power raised to 10-5 %. It was noted that the moisture Icvel was continuing to rise in the primary coolant but the trace on the chart indicated an approach to an equilibrium condition of about 1500 ppmv, still within the limits of LCO 4.2.11.
It should be noted that the panametric monitor on 1-05 had alarmed at 500 ppm.
As the morning progressed, the indicated moisture Icvel in the primary coolant stabilized at approximately 1500-2000 ppmv. At the same time it was noted that it was necessary to continuously adjust the control rods into the core to maintain the desired power 1cvel. This initial control rod movement was, at the As core time, thought to be due to overcooling of the core with helium flow. immediately reactivity continued to change the mechanism causing it was not obvious. The reactor was scrammed when the core reactivity reached .008AK greater than expected.
As a part of the investigation into the noted reactivity change, the two high icvel moisture monitors were switched to the indicate mode and both indicated 4500-4600 ppm moisture.
Eccause of the discrepancy noted between the dew point and panametric moisture monitors, sampics of primary coolant were drawn and analyzed for moisture in the gas chromatograph. These analyses indicated moisture levels in excess of c 10,000 ppm.
APPARENT CAUSE Unusual Service Cond.
X Design OF OCCURRENCE: Including Environ.
Manufacture . Component Failure Installation /Const. X Other'(Specify)
Operator X Procedurc A check of the dowpoint moisture monitor mirror temperature setting indicated it was set at 105'F which corresponds to a moisturc*Icvel of 5000 ppm at 220 psia.
In reality, the primary coolant pressure was at 246 psia and at this pressure, This still did not the 105'F dcwpoint temperature corresponds to 4800 ppm.
explain the .dif ference between the chromatograph reading and the dcwpoint moisture monitor readings.
Apparently a. representative sampic of primary coolant was not reaching the moisture monitors.
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k Page 3 ANALYSIS OF OCCURRENCE:
At the time of the incident in question, the PCRV cooling water system was maintaining the concrete temperature at approximately 105*F. The sample lines to the dew point moisture monitors from the helium circulator outlets nust come through the concrete and therefore, the sample line temperature is controlled by the PCRV concrete temperature.
- Assuming the concretc/ sample line temperature to be 100-105*F, condensation of moisture would take place in the sample line at moisture concentrations of 4100-4800 ppm in the primary coolant. With this in mind, it is reasonable to assume the sample being received by the moisture monitors was saturated at some temperature between 100-105*F and that the monitor would never have indicated a moisture level higher than 4600 ppm until such time as the sample line condensation accumulated to the point'that a drop of liquid water reached the monitor and caused it to trip.
The sample line for the Panametric moisture monitors also comes through the PCRV wall and runs for a number of hundreds of feet through areas of the plant whose temperature is less than.100-105'F.
If we assume a minimum sacple line temperature of 80*F, the maximum moisture concentration that could be indicated at 246 psia would be approximately 2000 ppm.
It should be noted that after a number of hours, liquid water was seen flowing from the sample lines at both the dew point and panametric moisture monitors.
In conclusion, it can be said that the dew point moisture monitors were functioning properly and were correctly indicating the moisture concentration in the sample delivered to them. The limiting factor on the ability of the moisture monitors to see the correct concentration is the sample line temperature.
CORRECTIVE ACTION:
Summary In summary, a review of the moisture monitoring system has indicated its acceptability for , normal reactor operating conditions.
To facilitate determination of moisture concentrations in the primary coolant system beyond those that can be determined directly by the moisture monitors, a new procedure has been developed and incorporated into the plant procedures that uses information available from instrumentation already installed as a part of the helium purification system.
Discussion
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Because of the. problems experienced which pointed out the moisture monitor sample line temperature limitations, a review of the adequacy of the moisture monitoring system, as it relates to both normal and abnormal operating conditions, was instigated. A review of possible corrective measures was made to climinate the sample line limitations.
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g - O (j Page 4 Based upon the normal operating pressure of the primary coolant system of 700 psia and a PCRV (sample line) temperature of 100-105*F, the maximum moisture concentration of the primary coolant that can be determined is 1400-1600 ppmv. Insofar as normal operating moisture concentrations are required to be in the 0 - 10 ppmv range and the reactor scram is adjusted to take place at 500 ppav (67*F at 700 psia) It is concluded that the moisture sampling and analysis system as a whole is adequate for normal reactor operation.
In reviewing the operation of the sampling system and possibic modificat.ons that could be incorporated to extend the moisture concentrations that could be measured at normal primary coolant system pressures, two basic corrective actions were considered:
- 1. Reduce the sample pressure before it is subjected to the cooler sample line temperatures.
- 2. Heat the sample line to climinate the influence or the PCRV wall temperature.
Based upon a review of past testing and operating experience, it was concluded that the moisture monitor c1cments, both Dewpoint and Panametrics, determine with acceptabic accuracy the moisture content in the gas sample supplied to them. This review again pointed out that the sample lines, not the detectors, are the limiting component of the system.
Because of the basic design of the sampling system and its location, cast into the 9' thick wall of the PCRV, no way could'be determined to modify the present installation or to install a new heated sample probe.
The moisture monitor sample lines that samples the primary coolant system and supplies ga's samples to the Panametrics Moisture Monitors of the Analytical
, Instrument System is ' subject to cold spot temperatures that are less than the temperature of the PCRV sidewall. To assure that these instruments will not be limited further in their ability to determine dew point temperatures at least as high as 90*F to 100*F, the sampic lines are being heat traced. This will assure the " cold spot" in the sample line will be within the PCRV sidewall.
The Panametrics Moisture Monitors, although giving acceptably accurate moisture measurements, tend to respond slowly to decreases in moisture and because of their characteristics, arc difficult to read at the very low,10-25 ppmy, and very high, > 1000 ppmy, moisture levels.
For the above reasons, Public Service Company is purchasing two EG & C Model 440 Dewpoint Moisture with which to determine primary coolant moisture IcVels.
These instruments have a dewpoint temperature range of -110*F to +140*F at 350 psia and have a very fast response time for both increasing and decreasing moisture concentrations. .
Because of the sample line temperature limitations, the determination of primary coolant moisture IcVels, > 1300-1500 ppmy, cannot be made by the installed instrumentation if the primary coolant system is at normal operating pressure. At atmospheric pressure in the PCRV, the installed instrumentation can determine moisture concentrations up to approximately 85,000 ppmv (corresponds to approximately 90*F dcwpoint temperature)
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- To facilitate determination of very high moisture concentrations with the system at pressure, a method of analytically determining the moiscure concentration in the primary coolant system using information availabic from i the Helium Purification System has been dev.cloped and is to be incorporated into the plant operating procedures. The procedure is included at: Attachment 1.
Because of discrepancies in LCO 4.4.1, LCO 4.2.11, and LSSS 3.3 of the f
Technical Specifications which all concern allowabic primary coolant moisture levels, a proposed revision for.the Technical Specifications had been developed i and submitted to the NRC for considcation.
l This proposed Technical Specification revision takes into account the sample I line temperature effects to assure a dew point monitor temperature trip setting of < 90*F.
It should be noted that following removal of moisture from the primary coolant system and the reserve shutdown material from region one-(1) of the core, the
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reactor was taken critical on 3/21/75. Critical rod height was determined to be within one-half inch of the predicted position indicating the anomoly has been corrected. .
FAILURE DATA /
! SIMILIAR REPORTED OCCURRENCES:
Unusual Occurrences 50-267/74/7 and 8 dealt with spurious trips of thesc l
moisture monitors.
PROGRAMMATIC IMPACT:
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The programmatic impact of this moisture monitor failure to initiate a scram is not significant; however, removal of moisture from the primary coolant is delaying continuation of the plant testing program.
CODE IMPACT:
Nonc
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- Recommdended :
Approved: ,
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N.6 l % 1 llc o i u <.. .. .-:A err.y h H. Larry Breyl / f.rederic
.U E. Swart-
/ Superintendent Nuc1 car Production Superintendent-Operations Fort St. Vrain Nuclear Public Service Company
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- Cencrating Station of Colorado
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PCRV MOISTURE DETERMINATION BASED ON HELIUM PURIFICATION j SYSTEM WATER REMOVAL RATES i
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Attachment 1
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PROCEDURE FOR PCRV MOISTURE DETEPJIINATION 11ASED ON SYSTD123 WATER REMOVAI, RATES .
Iligh moisture concentrations in the PCRV can be estimated if the helium flow through System 23, the Primary System, the temperature of the outlet of the System 23 front end coolers, and the water removed by thes'e coolers are known. The.1 four variables should be recorded approximately every hour during a dryout procedure. The first three may be recorded directly from existing plant instrumentation, and the fourth may A beone calculated inch changef rominthe this level change in the front end cooler drain tank.
level corresponds to a 1.1 gallon change in the water collected.
Fore specifically, if 2 is the helium flow through System 23 in ACFM, P_ is the primary system pressure in psia, and 2[ is the volumetric fraction of water vapor in the PCRV, then the total waterDeviation collectedof bythis theequation helium purification is system, G, in gph, is given by equation (1) .
shown in Appendix A.
X (1)
G = .0216 P Q 1-X The total water collected by the helium purification syste, G, is composed of the water removed by the front end cooler, G1,, plus the water collected by the dryer,{g[. As indicated above, the first can be obtained by multiplying the rate of increase of the water level in the cooler drain tank in inches per hour by the constant 1.1.
G1 can be estimated by assuming that the flow leaving the front end cooler and entering the dryer is saturated with moisture. Thus, the moisture concentration of this gas, Xsat, is approximately given by:
" Psat at T (2)
. Xsat ,
P s
where P s at at T_,is the saturation pressure of water vapor at the front end cooler iiuflet temperature T.
Xsat can be substituted into }i in equation (1), along with P and R, to obtain the water removed by the dryer G2. Then, one can calculate the total amount of water removed, C, by adding G1 and G2, as indicated above:
G = G1 + G2 (3)
Finally, substituting G, P, and Q into equation (1) and solving for X,
- one can obtain the desired vessel moisture in per unit.
Consider the following example:
PCRV pressurc = 153 psia ++++ P = 153 psia Front end cooler outlet temperaturc = .2*F ++++ T = 72*F liclium flow through System 23 - 29 ACn! -++++ Q = 29 ACFM .
Level change in drain tanks = 2.6 inches / hour ++++ G1 = 2.6 x 1.1 = 2.86 gph
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' Page 2 Solution:
From the steam tables: Psat at 72*F = .388 psia Then, equation (2) yicids Xsat = .388 = 2.53 x 10-3, 153 which substituted in equation (1) yicids:
G2 = .0216 x 153 x 29 x 2.53 x 10-3 = .24 gph 1 - 2.53 x.10-J a
substituting G1 and G2 into (3) Icads to: !
G = 2.86 + ' . 24 - 3.1 gph Finally, using equation (1) ag'ain with G = 3.1 and solvin'g for X 1 cads to the desired PCRV moisture icvc1:
3.1 = .0216 x 153 x 29 X 1-X X = .0313 volumetric fraction, or 3.13%, or 31,300 ppm.
The primary system pressure may be obtained.from the data logger or from the control room instrumentation.
The System 23 helium flow may be obtained from FR-23112 on I-01. .
The front end cooler outlet temperature is availabic at.TI-2319 or TI-2320 on I-01.
Finally, the icyc1 in the front end cooler drain is availabic at LI-2377 or .
LI-2378 on I,-01.
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' * * APPENDIX A Deviation of the total water removal rate by System 23 (equation 1)
Let g be the total helium flow (purified-helium) through System 23, and Then, let X_ be the volumetric concentratio~n of water vapor in the PCRV.
the total flow at the inlet to the front end cooler is Ft =
Q 1 ACR!.
1-X
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and the partial volumetric flow of water vapor is (4)
Fw =
Q 1 ACRI = 60 Q 1 ACFil 1-X 'l-X From the ideal law of gases, which normally applies for vapor at the low partial pressures involved here, one obtains:
m = PVM (5)
RT where p,is mass flow of water vapor in Ibs/ hour, P_ is total pressure in psia, 7
V_ is partial volumetric flow of water vapor, M is the molecule weight of water, R_ is the idea) gas constant, and T_ is the absolute temperature of the water vapor.
Substituting equation (4), into (5), and assuming an approximate PCRV temperature J
of 90*F during a dryout procedure leads to:
Water mass removed = 60 Q X P x 18 144 = 0.18.PQ X lbs.
1-X 1544 (460 + 90). 1-X F;aally, converting mass of water removed to gallons of water ' removed Icads to:
G = 0.18 QP X lbs/hr x 016 x'7.48 gallons' 1-X -
Ge .0216 PQ X , which is the desired equation (1).
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