ML20033F595
| ML20033F595 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 03/15/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20033F593 | List: |
| References | |
| NUDOCS 9003220134 | |
| Download: ML20033F595 (10) | |
Text
~
~
1
. /
UNITED STATES Y
g NUCLEAR REGULATORY COMMISSION
- 7,,
- j WASH 3NGTON, D C. 20555
\\....+/
i SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING j
AMENDMENT NO. 90 TO FACILITY OPERATING LICENSE NO. NPF-12 SOUTH CAROLINA ELECTRIC & GAS COMPANY SOUTH CAROLINA PUBLIC SERVICE AUTHORITYf VIRGIL C. SUMMER NUCLEAR STATION, UNIT NO.1 DOCKET NO. 50-395 N
1.0 INTRODUCTION
By letter ' dated July 21, 1989, South Carolina Electric & Gas Company (the licensee) proposed to modify the reactor coolant temperature neasurenent system for the hot and cold-legs for V.C. Sumer Nuclear Station Unit No.1, Summer) and requested changes to the Sumer Technical Specifications-TS).
osed modification would eliminate the resistance tesperature The prop (RTD) bypass manifold and replace it with fast response RTDs device located in reactor coolant hot leg and cold leg piping.
This modification would eliminate operating obstacles associated with the bypass system.
These obstacles include leakage through flgnges and valves and radiation exposure during reactor building maintenance.
In addition, the licensee proposed changes to TS 2.2.1, Reactor Trip System Instrumentation Setpoints, TS 3/4.3.1, Reactor Trip System Instrumentation, and TS 3/4.3.2 Engineered Safety Feature Actuation System (ESFAS) Instrumentation which would revise certain setpoints, allowable values, and response times as a result of the replacement of the RTD bypass manifold.
2.0 BACKGROUND
The July 21, 1989 submittal contained the proposed TS changes and the Westinghouse Proprietary (WCAP-12189) and Non-Proprietary (WCAP-12190),
reports covering the technical basis for the modification to the reactor.
coolant temperature neasurement system for the hot and cold legs. These are not topical reports but are plant specific.
The December 11, 1989 submittal contained the plant specific safety evaluation for the change.
Clarifying information in support of the anendment request was submitted on January 2,1990 and February 6,1990.
The current method of measuring the hot and cold leg reactor coolant temperature uses an RTD bypass system.
This system was designed to address temperature streaming in the hot legs and, by use of shutoff valves, to allow replacenent of the direct immersion narrow-range RTDs without draindown of the Reactor Coolant System (RCS).
For increased accuracy in measuring the hot leg tenperatures, sanpling scoops were placed in each hot leg at three locations of a cross section,120 degrees 9003220134 900315 l
PDR ADOCK 05000395 P
PDC a
9
.;* ' apart.
The flow from the scoops is piped to a nanifold where a direct-
.insnersion RTD neasures the average temperature of the flow from the three.
J scoops. This bypass flow is routed back to the RCS downstream of the i
steem generator.
The cold leg tenperature is measured in a similar manner with piping to a bypass manifold except that no scoops are used, as tenperature streaming is not a problem due to the mixing action of the RCS punp.
Both hot and cold leg manifolds enpty through a conmon header to the intermediate leg between the steam generator and reactor coolant pump.
The output from the bypass loop RTDs provides the signals necessary to calculate T and Delta T.
The T and Delta T parameters are then input to th6VEeactor protection syIUm overtemperature and overpower Delta T reactor trips.
The control system input of T provided through a separate dedicated set of bypass 18$ and Delta T are RTDs and T and Delta T calculations, avg The new method proposed for measuring the hot and cold leg temperature uses narrow-range fast response RTDs nanufactured by Weed Instruments, Inc. The RTDs are placed in thernowells to allow replacenent without draindown.
The thermowells, however, increase the response time.
The licensee proposed to measure-the hot leg tenperature on each loop with three fast response, narrow range, dual element RTDs mounted in thermowells.
One element of the RTD is considered active while the other element is heid in reserve as a spare.
To acconplish the sanpling function of the RTD bypass manifold system and the need for additional-hot leg piping penetrations, the thermowells will be placed within the existing scoops. A hole will be drilled through the end of each scoop so that water will flow through the existing holes in the leading edge of the scoop, past the RTD, and out through the hole.
This RTD arrangement accomplishes the same sanpling/tenperature averaging functiun as the bypass manifold system.
The RTD measures the temperature at one point in the new method. This is in contrast to the RTD bypass flow method which utilizes the tenperature neasurement of the average of the flow from the five sample holes from the hot leg scoops.
In the new method, the radial location of each RTD reasurement is at the same radius as the center hole of the scoop.
Therefore, it is the equivalent of the average scoop sanple if a linear radial temperature gradient exists in the pipe.
The licensee has also proposed to modify the means for measuring the cold l
leg terrperature.
Because temperature gradients in the cold leg are i
eliminated by the mixing action of the reactor coolant pumps, only one l
RTD is necessary for cold leg temperature neasurenent.
The licensee L
proposes to mount a single thermowell with one fast response, narrow range, duel-element RTD in each cold leg at the discharge of the reactor coolant pump.
One of the dual elements is a spare.
This is in place of I
the original method in which the measurement was by an external RTD in i
the cold leg bypass manifold.
As in the hot leg, the bypass manifold l
penetration nozzle will be modified to accept the RTD thermowell.
Additionally, the bypass manifold return line will be capped at the nozzle on the intermediate leg.
I
m
acted. The accidents in the FSAR, Sections 15.1 to 15.6, were examined ay the licensee and it was determined that plant operation will be maintained within the bounds of safe, analyzed conditions as established by the reanalysis performed for the current i transition core reload associated with Amendnent No. 75. Since the increased RTD response time of 8.5 seconds was used in the prior reanalysis, the staff finds the previously reviewed results remain a cceptable. In sunnary, the staff has evaluated the irsact of the RTD bypass elimination for V.C. Summer on the TSAR non-LOCA 4ccident analyses has i becn evaluated. For the events i@ acted, it was demonstrated that the conclusions presented in the transition core reload, Amendment No. 75, remain y ali d. 3.2.4 LOCA Evaluation The elimination of the RTD bypass system inpacts the uncertainties associated with RCS tenperature and flow measurenent. The information presented by the licensee in WCAP-12189 that the magnitude of the uncertainties are such that RCS inlet and outlet temperatures, thermal design flow rate and the steam generator performance data used in the LOCA analyses will not be affected. Past sensitivity studies concluded that the inlet temperature effect on peak clad temperature is dependent on brea k size. As a result of these studies, the LOCA analyses are performed at a nominal value of inlet tenperature without consideration of small uncertainties. The RCS flow rate and steam generator secondary side tenpera ture and pressure are also determined using the loop average tenperature(T ou tput. These nominal values used as inputs to the analyses are n619a)ffected due to the RTD bypass elimination. The staff has concluded that the elimination of the RTD bypass piping Will not affect the LOCA 6nalyses input and, hence, the results of the analyses remain unaffected. Therefore, the staff finds the plant design i changes due to the RTD bypass elimination are acceptable from a LOCA analysis standpoint. 3.2.5 Flow Measurement Uncertainty i The licensee stated in their January 2,1990 submittal that the flow calculation uncertainty and cold leg elbow tap flow uncertainty values are based on a prior evaluation for Summer which was submitted in a Hovenber 21, 19 86 Ictter to the NRC. This evaluation was used to establish the present TS value of 2.1 percent for RCS loop flow uncertainty. When compared to the value of 1.9 percent calculated in l WCAP-12189, the present value of 2.1 percent is judged to be sufficiently s r- L. l e' (* 7-conservative to acconnodate uncertainties associated with feed flow venturi fouling (typically 0.1 percent). Also, the licensee has previously committed to cleaning the feed flow venturies and measuring the throat diameter every refueling outage. Based upon the above, the staff has determined that the licensee's approach to retaining the value of 2.1 percent for the RCS loop flow I uncertainty is acceptable. 3.2.6 Sumnary, Accident Analyses The inpact of the RTD bypass elimination for Sunmer on the FSAR, Chapter 15, non-LOCA accident analyses has been evaluated. For the events impacted by the increase in the channel response tine, it has been demonstrated that the conclusions presented in the evaluation of the transition reload core associated with knendment No. 75 of the Summer i license remain valid. For the remaining Chapter 15 non-LOCA events,- the effect of the increased initial RCS average temperature error allowance has been ascertained by separate evaluations. In all instances, the conclusions presented in the Summer FSAR remain valid under this error allowance assumption and the DNBR limit value is met. The current LOCA analysis is based on conservative nominal input values and remains acceptable. The licensee's analysis to support an RCS flow measumment uncertainty value, which includes the new hot leg RTD tenperature accuracy, was provided in WCAP-12189, and is acceptable. 3.3 Instrurentation and Control To acconplish the hot leg tcoperature averaging function previously done by the bypass manifold system, the nodified hot leg RTD temperature signals are electronically averaged in the reactor protection system. This averaged T-hot signal will then be used with the T-cold signal to calculate reactor coolant loop Delta T and T values utilized in the reactor pmtection and contml systems. avg The present bypass system uses separate dedicated RTDs for the contml and protection systems. However, the modified system thermowell mounted RTDs will be used for both pmtection and control. This class IE to Non-IE interface will require the use of isolation devices for contml system T"Y9 and Delta T signals derived from the reactor pmtection sy stem. and Delta T signals used in the control grade logic will be a input into h analog median signal selector (MSS). This device selects the signal between the highest and lwest values of the three T and Delta T loop inputs. Sy selecting the median value, the MSS prMides the plant control system with a valid T and Delta T in the event that a spurious signal (failed sensor or dPYit error) is input to the MSS. The MSS also preserves the functional independence between separate control and protection systems that share a common sensor. To ensure proper operation of the MSS, the existing nenual switches that allow for defeating a T or Delth T signal from a single loop will be climinated. Also, the &Myersion to thernowell nounted RTDs L r' 8 will result in the elimination of the control grade RTDs and their associated control board indicators. The protection system channels will now provide inputs to the control system through isolators and the analog MSS. Existing contml board alarms, indicators T and Delta T deviation alarms will provide the means to identif)VRTD failures. A failure of a hot leg RTD may be handled in two wgys. The first puts the affected channel in trip and rescales the electronics to average the remaining two inputs. A bias is then added to the T-hot ave age signal in order to conpensate for the failed RTD and to maintain a value conparable with the previous three RTD average. As an alternate, the failed RTD elenent may be disconnected and tle spare element utilized. A cold leg RTD failure can be handled by utilizing the spare RTD elenent provided in each loop. The staff has determined that the modified RTD system is not functionally different from the unmodified system except for the use of 3 RTDs instead of one. The reactor trip or engineered safety features actuation systems will operate as before. The original staff evaluation as docunented in i Section 7 of the Safety Evaluation for Sunmer remains valid. The additional electronics for averaging the three T-hot RTD signals (7300 based) will be qualified to the same level as the existing 7300 electronics. The isolation devices are also standard 7300 series equipnent and were previously reviewed under Westinghouse Report WCAP 8892A. The RTD qualification will be to 10 CFR 50.49. To support the modifications required to eliminate the RTD bypass manifold system, changes to the Sumner TS were proposed. One of these changes is the result of the difference in response time of thermowell mountt-d RTDs as opposed to the original RTD bypass system. The staff has determined, based upon a review of calculations performed by the licensee and a review of the Sumner TS response tines for OTDT and OPDT, that the proposed changes to response times are acceptable. The remaining technical specification revisions are a result of the difference in uncertainty considerations between the therrowell mounted RTDs and the bypass manifold system, i.e., calorimetric flow, hot leg tenperature streaming and instrument uncertainties. Revised values for allowable value, Z and S for OTDT, OPDT, loss of flow T low-low along with new set point values for P12 were calculated using $Uentially the same setpoint methodology as previously appmved by the staff.
- Again, evaluations by the itcensee determined that the revised values of l
allowable value, Z and S remain valid for the proposed bypass I elimination. Based upon the staff's review of the licensee's submittals l and the Summer T5, the staff finds the proposed plant modification to replace the RTD bypass manifold system with thernowell mounted, fast response RTDs mounted directly in the reactor coolant system to be acceptable. 4.0. TECHNICAL SPECIFICATION CHANGES The licensee has proposed changes to Table 2.2-1 of TS 2.2.1, Reactor Trip System Instrunentation Setpoints, and Table 3.3-4 of TS 3/4.3.2, Engineered Safety Feature Actuation System Instrumentation to allow F .. o .g. operation of Sunener within acceptable safety limits. The changes are associated with trip setpoints for OTOT, OPDT, loss of flow, steam line isolation on low-low T In addiU8n,,and engineered safety feature interlocks on low-low T a footnote is added to Table 3.3-2, Reactor Trip SystN#.!nstrumentation Response Times of TS 3/4.3.1, Reactor Trip l System Instrunentation and a change is nede to the Bases Section 2.2.1, Reactor Trip System Instrumentation Setpoints. These changes are necessary for consistency with the revised uncertainty analysis. lhe staff finds the proposed change in values for the reactor trip setpoints along with the other proposed changes, based upon the above perforned evaluations, acceptable.
5.0 ENVIRONMENTAL CONSIDERATION
This amendnent involves a change to a requirenent with respect to the installation or use of a facility conponent located within the restricted area as defined in 10 CFR Part 20 and changes to the Surveillance Requi renent.
The staff has determined that the anendment involves no significant increase in the amunts, 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 expo sure.
The Commission has previously issued a proposed finding that this anendnent involves no significant hazards consideration and there has been no ptblic comnent on such finding.
Accordingly, this anendnent meets the eligibility criteria for categorical exclusion set forth in 10 CFR Section 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no cnvironnental inpact statenent or environnental assessment need to be prepared in connection with the issuance of this amendment.
6.0 CONCLUSION
The Consnission has issued a " Notice of Consideration of issuance of Amen &ent to facility Operating License and Propose No Significant Hazards Consideration Determination and Opportunity for Hearing" which was published in the FEDERAL REGISTER on October 18,1989 (54 FR 42864) and consulted with the State of South Carolina.
No public comments or request for hearing were received, and the State of South Carolina did not have comnents.
The additional information provided by the licensee on December 11, 1989, January 2,1990, and Fabruary 6,1990 was clarifying infonnation and did not change the substance of the Anendnent request.
l l
l l
I G
..e s ';s o.
4 =.
The staf' has concluded, based upon the considerations discussed above, I
that: (1) there is reasonable assurance that the health and safety of the p(ublic will not be endangered by operation in the proposed nanner, and2 regulations and the issuance of this amendnent will not be inimical to I
the common defense and cecurity or to the health and saf:'v of the public.
Principal Contributors C. Doutt J. Hayes M. McCoy D. Sellers Dated: March 15,1990 I
i i
i l
1.
R i
w