ML20059D093
| ML20059D093 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/30/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20059D091 | List: |
| References | |
| RTR-REGGD-01.097, RTR-REGGD-1.097 NUDOCS 9401060418 | |
| Download: ML20059D093 (7) | |
Text
e
. e> nam
.7 UNITED STATES E
'N E
NUCLEAR REGULATORY COMMISSION WASHINCToN D.C. 20555-0001
\\,
[
SUPPLEMENTAL SAFETY EVALUAIl0N BY THE OFFICE OF NUCLEAR REACTOR REGULATION CONFORMANCE TO REGULATORY GUIDE 1.97 NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION. UNIT 1 DOCKET NO. 50-245
1.0 INTRODUCTION
The staff's safety evaluation (SE), dated April 24, 1991 (Reference 1),
identified several parameters in Hillstone Unit 1 post-accident monitoring instrumentation that did not conform to Regulatory Guide (RG) 1.97, Revision 2 requirements.
These variables are:
reactor coolant level, reactor coolant system pressure, primary containment isolation valve position, containment and drywell hydrogen concentration, containment and drywell oxygen concentration, suppression chamber spray flow, drywell spray flow, and neutron flux.
Northeast Nuclear Energy Company (NNECO), submitted additional information regarding these variables in letters dated September 11, 1991 (Reference 2),
November 15, 1991 (Reference 3), March 31, 1992 (Reference 4), and June 10, 1992 (Reference 5). Also in a letter dated September 8,1992 (Reference 6),
NNEC0 submitted an updated matrix of the post-accident instrumentation at the plant, which listed the status of compliance with the requirements of RG 1.97, Revision 2.
The NRC staff's review of these submittals, especially the matrix where all the parameters were listed, identified several items (ten items in addition to the eight unresolved items of the staff's April 24, 1991, SE) which needed some clarification or were deviations from the RG 1.97 requirements.
NNECO's letter dated July 21, 1993 (Reference 7) provided resolution to some and committed to perform further analysis for the remaining unresolved items.
In NNECO's subsequent submittals dated October 6,1993, November 12, 1993, and December 16, 1993 (References 8, 9, and 10 respectively), NNEC0 provided additional information to resolve the remaining items. The staff performed a detail review of those submittals and the following is the result of that review.
2.0 EVALUATION The staff review of the matrix in Reference 6 identified several variables where the accident monitoring instrumentation was not in compliance with the requirements of RG 1.97.
The staff has characterized th'ese into the following three areas:
(1 qualification category, (2) instrumentation not provided, and (3) power sup) ply redundancy and qualification.
This supplemental SE addresses these three areas and the NNEC0 submittals to resolve them, as well as NNECO's response to the staff's April 1,1993, letter pertaining to neutron flux monitoring.
i 9401060418 931230 PDR ADDCK 05000245 P
q i l 2.1 Oualification Cateaory a
Six variables (A-2, A-4, A-5, A-6, A-9 and C-5) were identified in the matrix whose control room recorders were evaluated by NNEC0 for compliance with the RG 1.97 requirements for qualification category.
l NNECO determined that three of the six variables have their individual recorders isolated by an output transformer in a Class IE module while the remaining three-recorders are qualified to the Class IE requirements and, therefore, do no need isolation from their respective instrument. loop. Thus, the qualification for these six variables is acceptable.
2.2 Instrumentation not Provided Three variables (D-3, D-8, and D-9) were identified in the matrix for which no instrumentation is provided as follows:
Torus and drywell sorav flow (D 3. D-8)
The Millstone Unit I design does not provide instrumentation exclusively for torus and drywell spray flow indication (D-3 and D-8 respectively). The total spray flow (combined torus and drywell flow) can be determined by subtracting the low pressure core injection (LPCI) flow directed to the reactor vessel from the total LPCI flow. NNEC0 stated that spray flow indication is not needed by the operator to carry out the instructions of the emergency operating procedures (EOPs).
NNEC0 further stated that the E0Ps direct the operator to use torus (suppression chamber) and drywell sprays _ only when the drywell pressure exceeds 9 psig.
If the drywell bulk temperature is less than 281*F, the torus, sprays are initiated first. When the torus water level increases such that-torus bottom pressure exceeds 15 psig, then.the drywell sprays are initiated.
If the drywell bulk temperature exceeds 281*F, the drywell sprays ~ are initiated to control drywell temperature.
In all _ cases, spray flow is terminated when drywell pressure decreases to 9 psig.
The operation of torus and drywell spray only requires the operator to initiate or:to. terminate spray flow tv,ed upon the above parameters.
~
The operator is not required to throttle spray flow,-and can determine the operability of both sprays by. monitoring the drywell and torus air space pressures, drywell bulk temperature, and torus bottom pressure.
Instrumentation to monitor both~ drywell and torus spray flows is, therefore,.
not necessary.
The three instruments mentioned by'NNECO as an alternate to the'drywell and torus spray flow (drywell pressure, drywell bulk temperature, and torus bottom pressure) are reliable instruments qualified to Category I requirements.
Therefore, based on the above, the staff finds this alternate instrumentation acceptable.
~
[ "
Main Steam Line Isolation Valve-(MSLIV) Leakaae Control System Pressure (D-9)
The Millstone' Unit I design does not include monitoring or control of. MSLIV leakage as part of its accident design basis. Consequently, there is no MSLIV -
leakage control system installed and hence no instrumentation is provided to measure pressure of MSLIV leakage control system as required by RG 1.97.
NNEC0 maintained that the MSLIVs are tested for leak tightness as part of the Millstone Unit 1 Appendix J program, and that a fully qualified MSLIV position indication is available in the control room for post-accident monitoring.
In addition, the Millstone Unit 1 Technical Specification (TS) limit on leakage from an MSLIV can be determined to be met indirectly from the drywell sump level indication. The staff finds this deviation acceptable.
2.3 Power Supply Redundancy and Oualification Eight variables (A-1, A-2, A-7, A 8, A-10, B-10, C-11, and C-12) were identified in the matrix whose instrumentation did not meet the power supply redundancy and qualification crit via of RG 1.97 as follows:
Reactor Pressure Vessel (RPV) Pressure (A-1) and RPV Level (A-2)
The staff SE (Reference 1) found this instrumentation lacking Category 1 power supply redundancy and equipment-qualification. NNEC0's subsequent submittals (References 2 and 10) stated the the RPV level (A-2) instrumentation channels were upgraded to meet Category 1 equipment qualification requirements and to provide a redundant power supply. NNECO further stated that the RPV pressure (A-1) instrumentation receives its power supply from redundant DC buses and does not need to be qualified to Category 1 qualification criteria because it is located in a mild environment. The staff finds NNEC0's response acceptable.
LPCI Flow (A-7). Core Sorav (CS) Flow (A-8) and Emeraency Service Water (ESW) to LPCI Differential Pressure (A-10)
Three variables were identified in the matrix (Reference 6) that were included
- as Type A, but were listed as Category 2 variables.
NNECO indicated that this instrumentation does not meet the Category 1 criteria with regard to cable separation, power supply, and instrument redundancy.
In subsequent
- submittals, however, NNECO:
(1) proposed design modifications for both LPCI and CS regarding power supply, (2) provided additional justification for the lack of instrument redundancy and cable separation, and (3) changed the ESW-to LPCI differential pressure instrumentation type classification.
These are described in more detail below.
A new redundant Category 1 CS flow (A-8) indicator will be installed during the Cycle 15 refueling outage and its power supply will be from a different source. One indicator will be powered from a vital AC source while the redundant indicator will be powered from instrument AC - both of which are Class IE power sources.
Similarly, the total LPCI flow and the LPCI injection flow (A-7) instrumentation will be reconnected to redundant power supplies j
)
I
. during the Cycle 14 refueling outage. NNECO stated that the proposed modifications will bring both LPCI and CS flow instrumentation in conformance with RG 1.97 Category I criteria with the exception of cable separation ir both variables and redundancy for only the LPCI flow.
The LPCI flow indication is credited for oserator action to control LPCI pump flow within the required net positive suction head following a loss of coolant accident (LOCA). As the torus water hds up, the operator reduces pump flow to avoid pump cavitation. The LPCI injection flow instrumentation provides complete redundancy to the LPCI total flow instrumentation except when the drywell or torus sprays are on (the spray flow bypasses the LPCI injection flow instrumentation).
In this case, the LPCI injection flow instrumentation does not represent the actual pump flow when the spray is on. However, the torus and/or drywell sprays are on only intermittently and remain on for a short period of time because the high setting of the drywell pressure interlock automatically terminates both drywell and torus spray when the drywell pressure drops to 9 psig.
If the operator has to rely on the LPCI injection flow indication for adjusting the LPCI pump flow to avoid pump cavitation (for a single failure of total LPCI flow instrumentation) the adjustment can be made when the spray is terminated. The LPCI pump cavitation is a concern only when the torus water is at an elevated temperature and the operator can not wait for the termination of spray before adjusting the LPCI injection flow. NNECO's pump cavitation test on an identical pump showed no damage to the pump with cavitation for up to 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />. Therefore, the potential for LPCI pump damage from cavitation is not a concern because the torus or drywell spray is on for a much shorter period of time. The staff, therefore, finds the exception to the LPCI flow instrumentation-redundancy, to be acceptable.
NNEC0 stated that to. both the LPCI and CS instrumentation loop modifications, the existing field cables will be used. These cables run in common trays and conduit.
NNECO provided an exception for cable separation based on the following:
The instrument cable is rated for 600 to 1000 volts, while the maximum signal potential is 120 volts ac, or 125 volts dc.
The only event for which cable separation is an issue is fire.
LPCI and CS are not required to ensure safe shutdown in the event of a fire in any area where cables from both trains could be affected.
The staff, therefore, finds NNECO's exception for LPCI and CS instrumentation loop cable separation, to be acceptable.
NNECO's evaluation of ESW to LPCI Differential Pressure (A-10)' concluded that this variable does not require Type A classification because it does not provide primary information to the control room operator to take specified
. manually controlled actions for which no automatic control is provided.
Therefore, NNECO removed this variable from the Type A list and added it to the Type D variables 1 St (D-30).
Although nat listed in RG 1.97, NNECO indicated that this is an important variable to indicate operating status of the LPCI system, and_as such, the instrumentation is designed to qualification criteria of Category 2.
The staff finds the design of the ESW to LPCI differential pressure instrumentation acceptable.
Primary Containment Isolation Valve (PCIV) Position Indication (B-10)
The staff SE (Reference 1) noted that the PCIV Category 1 position indication instrumentation (B-10) loops were not supplied by redundant Class IE power sources, as required.
NNECO's response to this SE open item (Reference 2) stated that a high reliability of the PCIV position indication power supply was achieved by a combination of redundancy and diversity. The power supply arrangement to both valve motor and position indicator of a typical pair of motor-operated valves with their associated limit switches consists of one source from a 480 volt ac Class IE bus and the other source from a 125 volt dc Class IE bus. An exception to this design is a valve combination where one out of the two valves is a check valve which does not have position indication.
The other exception to this design is the manually actuated motor operated valves or the air operated valves whose pilot solenoid valve and its limit switch circuits share a common power source (separately fused feeds from 120 volt ac instrument power (IAC) or a high-reliability non-Class IE power source) and the power supply cables are not separated. The valves may be designed to remain open or closed during normal operation. However, these valves are designed to fail to the closed position on a loss of control power.
A problem in either valve's indication circuit might cause its fuse to open, but this would not affect the operation of the redundant valve's indication.
In the unlikely event of loss of IAC, both sets of indication w ild be lost.
However, in this scenario, control power to both the redundant valves would also be lost, and the valves would assume their fail-safe position (" fail-closed"). A single failure of either valve or of the power source would not preclude the valve pair from performing its isolation function.
NNECO in a subsequent submittal (Reference 6), changed the qualification for the PCIV position indication instrumentation to Category 2 and accordingly requested exception to the Class IE criteria for redundant power supply, equipment qualification, and instrument redundancy. However, in response to staff concerns, NNECO reexamined the issue and the review determined that, with exceptions from recommended design and qualification criteria for selected valves, this variable can be reclassified as Category 1.
NNECO submitted a detailed analysis (Reference 8) to justify deviations for valves associated with 45 containment penetrations. NNECO further indicated that the subject PCIVs are listed in the plant TS and the deviations are only for the valve position indication. As such, they do not affect any containment
- integrity requirements of the valves. Additionally, the need for position indication for certain valves is still being evaluated under the Integrated Safety Assessment Program (ISAP), Topic 1.09, and consideration of the valve position indication deviation is part of the review under ISAP Topic 2.116.
The staff has reviewed the justification for the deviations provided for valve -
position and finds them acceptable. Any need for change to this acceptance-will be part of the resolution of the ISAP topics.
Drywell Hydroaen (C-11) and Drvwell 0xvaen Concentration C-12)
The staff SE (Reference 1) identified that both drywell hydrogen and oxygen concentration do not meet the redundancy aspect of the Category 1 qualification criteria. NNECO's justification for this exception was that the back-up Post-Accident Sampling System (PASS) and the TS limit on the oxygen concentration are adequate to satisfy the requirement for monitoring and maintaining acceptable protection against containment hydrogen burning.
However, the back-up system (PASS) is incapable of providing the information regarding hydrogen concentration during the first few hours after.on accident.
The staff, therefore, requested that NNEC0 provide redundant instrumentation for these two variables.
Item II.F.1.6 of the THI Action Plan, NUREG-0737 also requires post-accident hydrogen monitoring instrumentation and refers to RG 1.97 for the instrunantation qualification.
In response to the staff's SE, NNEC0 submitted additional information on this issue.
In a letter dated September 7, 1993 (Reference 11), the staff found a combined (single) post-accident hydrogen / oxygen analyzer to be acceptable. The staff's acceptance was based on plant specific deterministic and probabilistic analyses performed by NNECO on this issue.
The staff considers the RG 1.97 issue for drywell hydrogen and oxygen concentration monitoring to be resolved.
2.4 Neutron Flux Monitorina By letter dated July 30, 1993, NNEC0 responded to the staff's generic evaluation regarding relaxation of the need for Category I neutron flux monitoring instrumentation as documented in the staff's April 1, 1993, letter to NNECO. The staff has reviewed the July 30, 1993, letter and finds NNECO's te;ponse consistent with the staff's position, and therefore, acceptable.
3.s L0yCLUMON Oued on review of NNEC0's submit'tals, the staff finds the Millstone Nuclear Power Station, Unit I design in conformance with the criteria of RG 1.97, Revision 2 for 'pust-accident monitoring inst.rumentation for reactor coolant level, reactor coolant system pressure, primary containment isolation valve l
- position, primary containment hydrogen and oxygen concentration, torus spray flow, drywell spray flow, neutron flux, LPCI flow, core spray flow, and emergency service water to LPCI differential pressure. The staff, therefore, concludes that RG 1.97 capability for Millstone Unit 1, is acceptable.
4.0 REFERENCES
1.
NRC letter (M. Boyle) to NNECO (E.J. Mzoczka) dated April 24, 1991 2.
NNECO letter (W.D. Romberg) to NRC (Document Control Desk) dated September 11, 1991 3.
NNEC0 letter (J.F. Opeka) to NRC (Document Control Desk) dated November 15, 1991 4.
NNECO letter (J.F. Opeka) to NRC (Document Control Desk) dated March 31, 1992 5.
NNECO letter (J.F. Opeka) to NRC (Occument Control Desk) dated June 10, 1992 6.
NNECO letter (J.F. Opeka) to NRC (Document Control Desk) dated September 8, 1992 7.
NNEC0 letter (W.D. Romberg) to NRC (Document Control Desk) dated July 21, 1993 8.
NNEC0 letter (J.F. Opeka) to NRC (Document Control Desk) dated October 6, 1993 9.
NNEC0 letter (J.F. Opeka) to NRC (Document Control Desk) dated November 12, 1993 10.
NNECO letter (E.A. DeBarba) to NRC (Document Control Desk) dated December 16, 1993 11.
NRC letter (J.W. Andersen) to NNECO (J.F. Opeka) dated September 7, 1993 12.
NNECO letter (J.F. Opeka) to NRC (Document Control Desk (dated July 30, 1993 Principal Contributor:
- 1. Ahmed Date: December 30, 1993 1
i r