ML17158B063
| ML17158B063 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 01/03/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17158B062 | List: |
| References | |
| NUDOCS 9601160185 | |
| Download: ML17158B063 (9) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMtSSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TQ AMENDMENT N0.156TO FACILITY OPERATING LICENSE NO. NPF-14 AMENDMENT NO. 127 TO FACILITY OPERATING LICENSE NO. NPF-22 PENNSYLVANIA POWER 5 LIGHT COMPANY ALLEGHENY ELECTRIC COOPERATIVE INC.
SUS UEHANNA STEAM ELECTRIC STATION UNITS 1
AND 2 DOCKET NOS.
50-387 AND 388
1.0 INTRODUCTION
By letter dated March 31, 1995, the Pennsylvania Power and Light Company (th' licensee) submitted a request to change Surveillance Requirement 4.4.4.b.3.a; Reactor Coolant System Chemistry, in the Technical Specifications (TSs) for Susquehanna Steam Electric Station, Units 1 and 2 (the Station).
The licensee requested that the current surveillance requirement, to measure the pH of the reactor coolant every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for all reactor modes of operation (i.e., at all times),
be amended.
The licensee proposed to add the clarifi.cation that the pH measurement will be performed only when the coolant conductivity (or specific conductance) is greater than 1.0 pmho/cm at 25'C (77'F).
The measurements for chlorides in and conductivity of the reactor coolant, and the channel check for the recording conductivity monitor in the other surveillance requirements for the reactor coolant chemistry are not being changed by this request.
- 2. 0 EVALUATION
- 2. 1
Background
The periodic measurement of the pH and conductivity of the reactor coolant is part of the maintenance of the water quality in the reactor coolant by the licensee to minimize the probability of corrosion-induced failure of the reactor coolant pressure boundary.
For boiling water reactor (BWR) plants, the staff has issued Regulatory Guide (RG) 1.56, "Maintenance of Water Purity in Boiling Water Reactors,"
dated July 1978, to provide guidance on acceptable water quality for BWRs.
It applies to the Station.
The RG provides a table of acceptable reactor water chemistry limits for BWRs.
The range of acceptable pH values for BWR reactor coolant in the table is the following:
'I 960iih0185 'MOi03 13 PDR ADQCK 05000387 P
. 'DR,
Steaming rates greater than IX of rated steam flow pH not less than 5.6 nor greater than 8.6 Reactor is not ~ressurized (i.e.,
pH not less than 5.3 nor greater at or below 212 F 100'C than 8.6 The above range of pH values are for the minimum pH and maximum pH around a
pH value of 7, of a neutral solution (i.e., neither acidic or basic).
The limits for the maximum conductivity of the reactor coolant in the table are from 1.0 to 10 pmho/cm at 25'C (77 F).
The pH and conductivity limits in Table 3.4.4-1 of the Station TSs are the same as the values above and in the table of acceptable values in the RG.
The TS 3.6.B.c for Peach Bottom Atomic Power Station, also a
BWR plant, for the measurement of the pH of the reactor coolant states that the pH shall be measured during power operation oily if the conductivity is greater than 1.0, pmho/cm at 25'C (77'F).
Therefore, the staff has previously approved the same restriction for when the pH would be measured that the licensee has proposed for the Station.
The basis for the restricted surveillance on pH measurements for Peach Bottom is stated in the Peach Bottom TSs.
The basis of these TSs indicate that when conductivity is in its proper range the pH of the reactor coolant must also be within its normal range.
In BWRs, where no additives are used and where neutral pH is maintained, the conductivity provides a very good indicator of the quality of the reactor coolant.
Conductivity measurements are required on a continual basis because changes in this parameter are an indication of abnormal conditions in the reactor coolant.
- 2. 1 Evaluation The conductivity, or specific conductance, of a solution, in this case the reactor coolant, is a measure of the ability of the solution to conduct electric charge.
The greater the ability or higher the conductivity, the more ions in the solution.
Because both the negative and positive ionic species in the solution will conduct, the specific conductance of the solution is the sum of the equivalent conductance for each ionic species in the solution times the concentration of that species:
C - Sum (G(i) x Con(i))/1000 where C
specific conductance in pmho/cm at 25'C (77'F)
Sum ()
=
Sum of all the ionic species i
G(i)
=
equivalent conductance in pmho-cm at 25'C (77'F) of ionic species i in solution Con(i) -
Concentration in equivalents/liter of ionic species i.
The units for the concentrations is equivalents/liter which is moles/liter times the number of units of charge of the ionic species (e.g., Cl-is one unit and S04 is two units).
Because the solution is always neutral in charge, the sum of positive charged ionic species is equal to the sum of the negative charged ionic species:
Sum (Con(+i))
Sum (Con(-i)).
(2)
One of the positive charged ionic species in the solution is the hydrogen ion (H+), which is related to the pH by the following equation:
pH - - log(Con(H+)).
(3)
The pH is also measured at 25'C.
The hydrogen ion concentration is related to the hydroxyl ion (OH-) concentration by the following equation:
Con(H+) x Con(OH-)
Kw
=
10 '4 at 25'C, and the concentrations for the hydrogen and hydroxyl ions are in moles, or equivalents, per liter because both ions have single charges.,
(4)
Therefore, the pH of the reactor coolant is related to the conductivity of the coolant.
Figure 2 of RG 1.56 shows the conductivity and pH of simple aqueous solutions containing different amounts of hydrochloric acid (HCl) and sodium hydroxide (NaOH), which are commonly in the reactor coolant.
This figure is attached to this safety evaluation report.
The figure represents the following equations for conductivity and pH:
1000xC G(H+)xCon(H+) + G(Na+)xCon(Na+)
+ G(OH-)xCon(OH-) +
G(Cl-)xCon(Cl-)
(5) and pH
-log(Con(H+)).
(3)
As the.congentrat4ons ofI the chlorine and sodium ions are varied, the specific conductance;and the pH of, the solution follows the solid V-shaped curve in the attached figUre.
y e'hen the, coolant pH is close to the limits of the range of acceptable pH values recommended in RG 1.56, the coolant ion concentration will be essentially the hydrogen and chlorine ions if the pH is close to 5.6:
1000xC
=
G(H+)xCon(H+) + G(Cl-)xCon(Cl-)
and essentially the hydroxyl and sodium ions if the pH is close to 8.6:
1000xC G(H+)xKw/Con(H+) + G(Na+)xCon(Na+).
(6)
through the application of equations (3) and (4).
For example, at a
pH value of 5.6, the hydroxyl ion concentration is less than 1 percent of the hydrogen ion concentration and the solution is essentially only the hydrogen and chlorine ions.
Using the conservation of charge in equation (2), the equations for the conductivity and hydrogen ion concentration are the following:
1000xC
=
[G(H+) + G(Cl-)]xCon(H+)]
for pH about 5.6 (8) 1000xC
=
[G(H+)xKw/Con(H+) + G(Na+)xCon(H+)] for pH about 8.6.
(9)
Therefore, the pH, or hydrogen ion concentration, can be easily determined from the conductivity of the solution.
The curve of conductivity versus pH is V-shaped because the conductivity increases with increasing concentrations of either the hydrogen or hydroxyl ion concentration, but the pH decreases with increasing hydrogen ion concentration and increases with increasing concentrations of hydroxyl ion concentration.
Therefore, for pH less than 7, the pH decreases and conductivity increases with the hydrogen ion concentration.
For a
pH greater than 7, both the pH and the conductivity increase with the hydroxyl ion concentration.
The minimum conductivity versus pH is at approximately
- 7. 1 because of the difference in equivalent conductance for the hydrogen and hydroxyl ions.
The equivalent conductance for the hydrogen ion is about twice that for the hydroxyl ion.
If a horizontal line is drawn on the attached figure for a measured specific conductance at 25'C (77'F), the line will cross the pH-conductance curve at two pH values.
These two values are the maximum and minimum pH values for that conductivity and mark the ranges of possible pH values for that conductivity of the HCl/NaOH solution'.
The possible pH values will lie between the maximum and minimum pH values based on the different HCl/NaOH solutions that have the same measured specific conductance.
Because the reactor coolant is not a simple HCl/NaOH solution, the coolant conductivity would have additional terms for the additional ion species in the coolant solution.
However, if these other ion species are disregarded (or assumed to be included in the hydrogen ion concentration),
the attached figure for HCl/NaOH specific conductance will provide the range of maximum and minimum values of pH for the coolant sample that is greater than is actually tr'ue for the coolant.
This is to say that the range of possible pH values from the attached figure for the measured conductivity will be greater than the true pH values for actual coolant samples.
However, the attached figure does not'epresent the greatest range of pH values for the conductivity of a reactor coolant sample because the chlorine and sodium ions do not have the 1'owest equivalent conductance values for
possible ion species in"the coolant.
For example, if the sulfate ion is present instead of the chlorine ion, the range of pH values would be slightly greater because the sulfate ion equivalent conductance is lower than the chlorine ion equivalent conductance.
The licensee has proposed to use the attached figure to determine from the coolant conductivity if it is necessary to measure the pH of the sample.
To do this, the measured conductivity must indicate the maximum range of pH for the sample (i.e., the actual pH can not be outside the range indicated by the conductivity and the attached figure). If the range of'H indicated by the conductivity is within acceptable values for the reactor coolant, then the pH does not have to be separately measured.
Therefore, the conductivity would have indicated that all the possible pH values for the coolant are within acceptable values and the pH of the coolant does not have to be separately measured.
The error in using the V-shaped curve in the attached HC1/NaOH figure for the maximum range of pH values in the coolant is from the following:
(I) the equivalent conductance for the chlorine and sodium ions are not the lowest values for possible ionic species in the coolant and (2) the error in the conductivity measurement for the coolant sample is not being taken into consideration.
The error in equivalent conductance values is less than 80/350 (equivalent conductance of chlorine ions to hydrogen ions) for acidic solutions (pH about 5.6) and less than 50/200 (equivalent conductance of sodium ions to hydroxyl ions) for basic solutions (pH about 8.6).
The 80 and 50 are the equivalent conductance values for chlorine and sodium ions, respectively.
This is an error of about 25 percent.
The error in the conductivity measurement is about 5 percent.
The total error would be about 30 percent.
An error of 30 percent in hydrogen ion concentration is about an error of 0. ll units in the pH.
This is about the error in the measurement of pH.
The attached curve is not sufficiently detailed to show differences as small as
- 0. I pH units.
Therefore, the error in using the V-shaped curve in the attached figure to determine the maximum range of pH values in the coolant is not significant.
I The licensee has proposed to use a conductivity value of 1.0 pmho/cm at 25'C (77'F) as the limit a't 'or below which the pH measurement of the reactor coolant does not.hav'e-to be performed.
From the attached figure, the range of pH values"of the co'olant""would be between 5.6 and 8.6 (i.e., 5.6 < pH > 8.6).
This range of pK'values for the reactor coolant is in accordance with the table of allowable values in RG 1.56 and the pH measurement of the coolant would not be necessary.
As discussed
- above, the error in the pH values at this limit will be about 0. I units and this error is sufficiently small to not be significant.
Therefore, the conductivity limit of 1.0 pmho/cm at 25'C (77'F) proposed by the licensee is acceptable to determine if pH measurements of the reactor
coolant need to be made.
This conductivity limit is the same value as the conductivity limit for performing pH measurements for the reactor coolant in the Peach Bottom TSs.
2.3 Trip to Susquehanna Plant Site In its application; the licensee stated that it had difficulty in measuring pH values of the coolant when the conductivity was below 1.0 pmho/cm and that large errors occurred in grab samples because of the adsorption of carbon dioxide from the atmosphere into the sample.
On October 4,
- 1995, the staff visited the site to discuss the methods used by the licensee to measure the pH of the reactor coolant and the difficulties encountered in these measurements.
The staff also observed the measurement of pH.
The representatives of the licensee that participated in the visit were the following:
Drew Maron, Bruce
- Roads, Patrick Treier, and Ray Dulton.
During the visit, the licensee stated that the error in measuring the conductivity of the reactor coolant was 5
percent.
2.4 Conclusion Based on its evaluation, the staff concludes that the proposed qualification on the surveillance requirement in TS 4.4.4.b.3.a, to limit pH measurements of the reactor coolant to when the measured conductivity values of the coolant are greater than 1.0 pmho/cm at 25'C (77'F), is acceptable.
It should be noted that the surveillance requirement in TS 4.4.4.3.b, which is not being changed by these amendments, requires that the pH is measured every 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> whenever the conductivity is greater than the conductivity limit in TS Table 3.4.4-1.
For Operational Condition 1, the limit in TS Table 3.4.4-1 is also 1.0 pmho/cm and the TS 4.4.4.b.3.b would tak'e precedent over TS 4.4.4.b.3.a (i.e., at a conductivity greater than 1.0 pmho/cm at 25'C the pH would be measured at 8-hour intervals, not 72-hour intervals, until the conductivity was reduced below the limit).
For other operational conditions, the conductivity limit in TS Table 3.4.4-1 is above 1.0 pmho/cm and the two surveillance requirements would not conflict.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Pennsylvania State official was notified of the proposed issuance of the amendments.
The State official had no comments.
4,0 ENVIRONMENTAL CONSIDERATION The amendments change a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change surveillance requirements.
The NRC staff has determined
that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released
- offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a
proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (60 FR 20522).
Accordingly, the amendments meet eligibility criterih for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
- 5. 0 CONCLUSION The Commission has concluded, based on the considerations discussed
- above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed
- manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Attachment:
Figure Principal Contributor:
Jack Donohew Date:
January 3,
1996
SODIUM CHLORIDE (NaCI) 10 HYDROCHLORIC ACID (HCI)
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10 pH Figures CONDUCTIVITY,pH, AND CHLORIDE CONCENTRATION OF AQUEOUS SOLUTIONS AT77 F (25 C)
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