ML18010A938
| ML18010A938 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 11/27/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18010A937 | List: |
| References | |
| NUDOCS 9212080158 | |
| Download: ML18010A938 (6) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20665 SA A U T ON 8 TH OFF C
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PO GHT COMP SH ARON HARRIS NUC E
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U DOC NO. 50-400 l.
~IA UOOUOTIO At a meeting on October 7, 1992, the Carolina Power and Light Company (CPLL)-
described a modification to the high-head safety injection (HHSI) alternate mini-flow (AMF) system for its Shearon Harris Nuclear Power Plant (SHNPP).
The licensee supplemented this description in its Shearon Harris HHSI's AMF system modification package and related information, which was submitted as,:-.-
enclosures to the October 9, and October 12, 1992, letters.
The licensee submitted additional clarification in letters of October 28 and November 5, 1992.
The proposed modification removes the AMF relief valves and installs restricting orifices upstream of isolation valves.lCS-752 5 1CS-746.
The restricting orifices are installed to allow 60 gallons per minute (GPM) flow back to the refueling water storage tank (RWST) in the event that reactor coolant system (RCS) pressure exceeds the design shutoff head of the pumps during safety injection.
Isolation valve logic is also revised to modify the opening and closing of existing motor-operated valves
U.
~UTAFF UAT O 2.1 Modified Alternate HHSI Mini-flow System Design The design intent of the original relief valves had been to permit flow through the mini-flow lines to the RWST at 2300 psig in order to protect the HHSI pumps from damage when attempting to pump against high discharge pressures exceeding their shutoff head.
For other situations the relief valves were. intended to close and remain closed to enhance the injected flow rate and avoid the return of contaminated water to the RWST.
The intent of the modified design is to functionally emulate the originally-installed pressure relief valves.
In the modified design, newly installed orifices limit AMF line flow to 60 GPM, and control logic is added to automatically open (normally closed) isolation valves in the AMF lines in response to a high RCS pressure (about 2300 psi) signal coincident with a safety injection signal.
The logic will reclose the valves when the pressure drops to about 1750 psi.
The modified AMF system will be safety grade.
The licensee indicated that the modified AMF system design will assure adequate HHSI alternate mini-flow to protect the HHSI pumps, and will assure adequate HHSI injected flow to meet licensing basis analysis injected flow assumptions.
The staff reviewed the information provided at the October 7, 1992, meeting and as supplemented in the submfttals of October 9, 12, 28, and November 5, 1992.
The staff review consisted of the evaluation of (1) the modified isolation logic to control the motor-operated valves (MOVs), (2) the capability of existing MOVs in the modified configuration, (3) the piping and support modification, (4) surveillance/maintenance
- testing, and (5) procedures and training.
Oetails of the staff evaluation are as follows:
- 2. 1. 1 Evaluation Of Isolation Valves'odified Logic The operating logic for the AMF valves currently initiates on a safety injection (SI) signal.
The proposed modification revises this logic to include a permissive on high reactor pressure.
Should RCS pressure reach the shutoff head of the HHSI pumps, the AMF isolation valves will open providing the required AMF for pump protection during SI.
Once the RCS dept essurfzes, the isolation valves will close allowing full SI flow.
\\
The revised logic is accomplished by the addition of components to the 7300-';
racks (RCS wide range pressure loops),
and additional relays in series with'I relay K740 to provide automatic valve control.
The automatfc valve control
'ogic essentially mimics the previous function of the AMF safety relief valves.
The additional K711 relays that provide the coincident logic are Potter Brumfield relays.
The licensee reviewed these relays to applicable information notices for this application and found them acceptable.
The additional relays are wired in series with the SI slave relay to provide the coincident logic.
The setpoint as specified by the licensee is 2300 psig for valve opening and 1750 psig for valve reset/closure with a total channel uncertainty of 109 psig.
The licensee determined that the setpoint is low enough to protect the charging
- pumps, and the valve reset (closure) setpoint will ensure that SI flow is established in accordance with the safety analysis for events not requirf.og AMF.
The cable additions/modifications continue to maintafn separation, and the proposed ahk44fonal instrumentation is powered from safety-related busses.
The fncreasef electrical loads resulting from the proposed modifications have been evaluaeik'by the licensee and found to be acceptable.
r The desfge package setpoint and accuracy calculations for the AMF modification were also reviewed.
The licensee followed the guidance as outlined fn Regulatory Guide (RG) 1. 105, Rev.
1, as committed to in SHNPP Final Safety Analysis Report Section 1.8.
It should be noted that RG 1.105, Rev.
1, does not include the additional criteria of Instrument Society of America (ISA) standard ISA-S67.04-1982 as endorsed by RG 1. 105, Rev. 2.
However, the setpoint methodology employed reflects that described in the ISA standard.
The uncertainties employed in the setpoint calculations are consistent with RG 1.105, Rev.
1, and applicable standards.
One inconsistency was noted in the calculation of drift for the pressure transmitters in that square root-sum of squares (SRSS) techniques were employed for a Tobar model 32PA2 and algebraic techniques were employed for an ITT Barton transmitter.
Either technique is considered acceptable practice.
By employing the SRSS methodology for the Tobar transmitter the licensee assumes that the drift term is random and independent where as the drift term for the Barton transmitter is considered linear with respect to time.
The setpoint calculation for AHF did not reference an allowable value.
The licensee states that the surveillance procedures utilize calibration tolerance criteria to establish instrument operability in lieu of an allowable value.
Should an instrument be found outside the calibration tolerance a review is performed to determine instrument operability.
The licensee also stated that listed uncertainties incorporate the response time of the AHF isolation valves and provide adequate pump protection based on the highest rate of RCS pressure increase.
Based on the above review, the staff finds that the modified design to the MOVs'ontrol logic meets the applicable regulatory criteria and the uncertainties and methodology employed are consistent with RG 1. 105, Rev.
1, and industry practice for setpoints.
- 2. 1.2 Evaluation Of Capability Of Motor Operated Valves In The Modified Alternate Mini-Flow System Configuration In the modification of the AHF system for the HHSI pumps at Unit 1 of the
- SHNPP, the licensee relies on an MOV in each of two lines to open to allow minimum flow for the HHSI pumps.
Those two MOVs and an additional MOV in each line are also designed to isolate flow when necessary.
With respect to these HOVs (1CS-745,
- 746, 752 and 753), the staff reviewed the licensee's determination of the thrust and torque required to open and close their globe valves and the capability of the HOVs to deliver. the required torque and thrust.
The licensee has tested 1CS-752 under a differential pressure of 2730 psid with flow, and the valve opened and closed successfully.
The licensee has made a commitment to test all four MOVs under approximately design-basis differential pressure and flow conditions as part of post-modification testing.
The four globe valves are installed such that differential pressure will assist the valves in opening.
The licensee assumed the differential pressure would be zero in the opening direction.
The licensee calculated the differentiaE: pressure in the closing direction as the shutoff head of the pumps plus tha static head of the refueling water storage tank at its maximum level.
The. licensee used the standard industry equation for predicting the thrust required to open or close a globe valve with flow under the seat.
The licensee assumed a 0.2 stem friction coefficient in converting the predicted thrust to torque requirements.
The licensee determined the capability of the motor actuator from the Limitorque equation using degraded motor torque, overall actuator ratio, actuator efficiency (pullout efficiency for opening and running efficiency for closing),
and a 0.9 application factor:
The licensee determined the degraded motor torque based on the rated motor starting torque and the calculated minimum voltage available at the motor assuming approximately 80 percent voltage at the motor control center (MCC)
and a 0.4 power factor.
With these assumptions, the licensee asserts that the four MOVs would. be capable of performing their safety functions in the AHF system for the HHSI pumps.
In determining the maximum allowable thrust for the four MOVs, the licensee determined that the weak link of the MOVs was the valve structural limit.
(Although the licensee's calculations indicate the actuator thrust rating as the weak link, Limitorque is approving thrust allowable limits beyond the actuator rating.)
With the small margin between required thrust and the maximum allowable thrust, it will be difficult to set the actuator to provide the required thrust without the inertia of the actuator causing the weak-link thrust limit to be exceeded.
Therefore, the licensee decided to use required thrust"data from the dynamic test of 1CS-752 in establishing the torque switch settings for the four HOVs because the test data indicated a smaller thrust requirement than predicted by the standard industry equation.
The staff considered this use of the 1CS-752 test data acceptable for that HOV, but the licensee had not demonstrated the applicability of the test data for the other three HOVs at the time of the staff review.
The licensee stated that it would confirm the adequacy of the torque switch settings of 1CS-745,
- 746, and 753 during their post-maintenance testing near design-basis differential pressure and flow conditions.
The licensee assumed a 0.2 stem friction coefficient as conservative in converting the thrust required to open or close the valve to torque requirements.
Although this stem friction coefficient is typically conservative, the licensee will verify its assumption during the post-maintenance testing of the four HOVs under differential pressure and flow conditions.
In its calculation of a degraded motor torque, the licensee assumed a power factor of 0.4 in its calculations.
As discussed in NRC Inspection Report 50-400/92-06, Limitorque has notified licensees that the use of a 0.4 power factor is not appropriate for HOVs in nuclear power plants.
In the inspection report, the staff noted the licensee's use of a 0.4 power factor as a concern and requested that the licensee resolve this issue.
In response to staff questions on the HHSI miniflow modification, the licensee stated that it had requested, but had not received, guidance from Limitorque on the appropriate power factor to use in its degraded motor torque calculations.
The licensee considered. the effect of assuming a higher power factor (such as 0.8) in response te the.staff questions and believed that sufficient margin existed to accomaodate;ttte.higher power factor.
The staff did not identify any immediate concern with-the capability of the HOVs when the higher power factor is assumed.
lfevertheless, the staff expects the licensee to incorporate the guidance to be provided by Limitorque on the appropriate power factor assumption when received and to take any action found necessary by the new calcul'ations.
The licensee should evaluate and incorporate Limitorque's guidance on the assumption of an appropriate power factor and document the actions taken in an auditable form for possible future staff audit.
In the
- meantime, the NRC staff will accept the licensee's determination that the HOVs can perform their safety functions provided the licensee verifies its assumptions as part of the post-modification testing of the HOVs.
Among the assumptions that the licensee should verify during the post-modification
testing are (1) the thrust and torque required to open and close the valves under design-basis conditions, (2) the amount that load sensitive behavior (rate of loading) reduces the actuator output under dynamic load conditions from output under static conditions, and (3) the valve and stem factors.
Using the data from the post-modification testing, the licensee should confirm the capability of each MOV to deliver the required torque and thrust to open and close its valve.
Since the assumption of a minimum voltage of 80 percent at the HCC will likely not be verified during the post-maintenance testing of the HOVs, the licensee will need to provide continuing assurance that this assumption remains valid.
- 2. 1.3 Evaluation Of System Piping And Supports Modification The originally-installed AHF system employed pressure relief valves (RVs) to control the HHSI pump mini-flow.
However, the HHSI AHF system had no air
- vent, and when the entrapped air was discharged by the RVs during periodic pump testing, severe air and water slug formation resulted.
Four waterhammer-type transient events caused by this testing occurred between 1986 and 1991.
To eliminate the concern of air entrapment and water slug formation, -CPKL first implemented a procedure change to keep the inlet side of the RVs filled with water.
- However, excessive vibration that was detected during the subsequent system test revealed that the procedure chahge did not resolve the problem.
CPSL's modification to the SHNPP HHSI NF system generally retain+
the original system configuration.
However, certain. piping sections and components were revised.
To provide adequate supports for the new elements such as orifices and strainers, anchors had to be relocated and redesigned.
The modified AHF system is to be constructed in accordance with Equations 8,
9 and 10 for loading determination as embodied in the ASHE Boiler 8 Pressure Vessel
- Code,Section III, Subsection NC, Class 2 requirements (the Code).
The staff reviewed the results of the licensee's piping analysis with respect to the ANF system modification and found that the maximum calculated stresses caused by normal, upset, emergency and faulted loading conditions, together with anticipated valve accelerations, are well within the allowable limits established by the Code, and are, therefore, acceptable.
The maximum stress determined by Equation 8 was 8000 psi, by Equation 9 were 11600 psi for upset conditions and 13000 psi for emergency conditions, and by Equation 10 was 11500 psi.
Based on the above review, the staff concludes that the proposed piping and support changes. are acceptable.
2.1.4 Surveillance And Maintenance Testing Because proper operation of the HHSI ANF system is necessary for the HHSI system to perform its safety function, the staff considers the licensee's surveillance and maintenance activities for the modified NF system as part of the HHSI system.
The modification of the AHF line results in new setpoints and protection logic for the HHSI pumps.
The added instrumentation and setpoints will, therefore, be considered as part of the Engineered Safety Features Actuation System Instrumentation (functional Unit 1, Sl) by the licensee.
The surveillance requirements verify that each automatic isolation
valve actuates to ihe correct position on safety injection actuation and safety injection. coincident with high RCS pressure.
Although the action of the automatic valve control for AHF actuation is functionally the same as the previous relief valve arrangement, additional testing requirements are warranted.
The testing of the isolation valves and logic is to be associated with the surveillance testing of SI.
This will be accomplished by revising the-applicable SI surveillance tests to include the revised ANF logic and instrumentation.
The testing of the ANF logic and instrumentation is associated with SI based on the fact that if ANF is inoperable then HHSI is considered inoperable.
An evaluation of the failure of the ANF isolation valves and required procedures has been considered by the licensee.
In its October 28, and November 5, 1992, letters, the licensee stated that emergency operating procedures (EOPs) confirm valve alignment upon SI initiation and committed that the SHNPP HHSI AMF system TESTING will be covered by TS governing the HHSI system.
The staff finds this acceptable.
- 2. 1.5 Procedures And Training The staff considers proper operation of HHSI miniflow systems as integral to the safety function of the HHSI system and should be governed by normal and emergency operating procedures.
Ouring the meeting on October 7, 1992, the licensee stated that SHNPP operators are trained in the execution of these procedures, and, in its October 28, and November 5, 1992, letters, the licensee committed to update procedures and training to reflect the modifications to the HHSI ANF.
The staff. finds this acceptable.
3.0 STAFF CONCLUSIONS The staff finds the SHNPP's modified HHSI AMF system acceptable, contingent upon the satisfactory completion of post-modification testing of the four NOVs and verification of the following assumptions during the past modification testing:
(I) the thrust and torque required to open and close the valves under design-basis conditions, (2) the amount that load sensitive behavior (rate od loading) reduces the actuator output under dynamic load conditions from output under static conditions, and (3) the valve and stem factors.
Using the data from the post-modification testing, the licensee should confirm the capability of each HOV to deliver the required torque and thrust to open and close its valve.
Since the assumption of a minimum voltage of 80 percent at the HCC will; likely not be verified during the post-maintenance testing of the HOVs, the licensee will need to provide continuing assurance that this assumptioo-remins valid.
This finding is based on the above review of the licensee's ctestgs justification as presented at the October 7, 1992,. meeting, and design detatls provided in licensee submittals dated October 9 and 12, as supplemented:
on-October 28, and November 5, 1992.
Principal Contributors:
F. Orr C. Ooutt T. Scarbrough H. Shaw Date: go<a~~
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