ML20042B005
| ML20042B005 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 03/12/1982 |
| From: | Withers B PORTLAND GENERAL ELECTRIC CO. |
| To: | Clark R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20042B006 | List: |
| References | |
| TAC-42594, NUDOCS 8203240385 | |
| Download: ML20042B005 (6) | |
Text
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March 12, 1982 Trojan Nuclear Plant Docket 50-344 License NPF-1
,y Director of Nuclear Reactor Regulation g
ATTN:
Mr. Robert A. Clark, Chief ffggyNO g
Operating Reactors Branch No. 3 Division of Licensing
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[r!4Rg g 82 6 -3 U. S. Nuclear Regulatory Commission timMI gg Washington, DC 20555 Y
Dear Mr. Clark:
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Engineered Safety Features Actuation Signals By letter dated December 18, 1981 the NRC presented tentative conclusions regarding the acceptability of the Trojan Engineered Safety Features and the Solid-State Protection System with respect to NRC review criteria.
PCE's response to this NRC letter is contained in Attachment 1.
Sincerely,
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l Bart D. Withers
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Vice President CO Nuclear
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Mr. Lynn Frank, Director f
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Trojsn Nuc}scr Picnt Mr. Robert A. Clark Docket 50d44 March 12, 1982 License NPE -1 Page 1 of 5 Criterion 1 "In keeping with the requirements of General Design Criteria (GDC) 55 and 56, the overriding of one type of safety actuation signal (e.g., radiation) should not cause the blocking of any other type of safety actuation signal (e.g., pressure) for those valves that have no function besides containment isolation."
NRC Tentative Conclusions "In the case of the Containment Ventilation Isolation system, the ' RESET' feature of the Solid State Protection System will cause the overriding of one type of actuation signal (e.g.,
safety injection) and the block of a different type of actuation signal (e.g., containment high radiation). This design feature does not comply with Criterion No.1.
The fact that PGE is currently maintaining Containment purge supply and exhaust valves shut during plant operation does not eliminate the long-term potential for failing to re-close these valves automatically when a second isolation signal is received."
"Other ESF systems with this feature are acceptable only because a single actuation parameter is involved."
PGE Response:
The " RESET" feature of the Containment Ventilation Isolation (CVI)
System will cause the overriding of an initial safety injection (SI) or Containment high radiation actuation signal; this is its purpose.
The " RESET" feature could also block a subsequent Con-tainment high radiation or SI signal from initiating CVI should the initial actuating signal still be presant.
It should be noted that Containment high radiation is not a generating station con-dition required for actuation of Engineered Safety Feature (ESF)
Systems (see response to Criterion 5).
The " RESET" feature of CVI does not reduce the effectiveness of the Reactor Protection System for the reasons discussed below.
For the CVI portion of the SSPS, the Franklin Research Center report discusses the potential for preventing a Containment high radiation signal from initiating CVI due to resetting CVI with a safety injection (SI) signal present. Trojan Technical Specifications will require that Containment purge supply and exhaust valves be shut and inoperable during operating Modes 1 through 4 (PCE to NRC letter of February 12, 1982).
The opening of any of these valves would be a deliberate action and violation of procedural controls.
Hydrogen vent supply valves are also required to be shut during Modes 1 through 4 (until they are replaced by valves with non-resilient seats), while hydrogen vent exhaust valves are opened only when necessary. A SI signal will initiate a Containment Isolation Signal (CIS) which will also provide a signal to shut the hydrogen vent valves (see enclosed drawings).
Therefore, even if the operator reset CVI with a SI signal present and then received a high radia-tion signal, the hydrogen vent valves would already be receiving a close signal due to SI and CIS.
If the SI signal cleared and the operator then reset CVI, a subsequent high radiation signal would not be blocked and would shut the hydrogen vent valves.
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Trojsn Nuclear Plant Mr. Robzrt A. Clark
- Dock'et 50-344 March 12, 1982 License NPF-1 Page 2 of 5 It should be noted that when a SI signal is received by the SSPS, the control room operator is required to carry out his immediate actions, one of which is verifying engineered safeguard valves 1
are aligned properly (Containment purge and hydrogen vent valves are shut).
The operator's primary concern, after his immediate actions and accident diagnosis, is to regain manual control of the Plant when it is safe to do so.
To do this he is required to reset SI.
The resetting of SI removes the SI signal input to the CVI portion of the SSPS.
Should the operator then reset CVI, a subse-quent high radiation signal would not be blocked.
The po tential for preventing a SI signal from initiating CV1 due to resetting CVI with a Containment high radiation signal present is also discussed in the Franklin Research Center report. Under normal conditions for all operating modes an operator would only attempt to reset CVI if he desired to open Containment ventilation valves.
But, he would not reset CVI and open Containment ventilation valves with a high radiation condition existing in Containment. Venting is a deliberate controlled event and takes place only af ter a careful assessment of radioactive conditions inside Containment.
As is discussed in the first paragraph, the Containment purge supply and exhaust valves are inoperable during Modes 1 through 4.
Even if an operator reset CVI with a high radiation signal present, a 'subse-quent SI would still shut the hydrogen vent valves due to the CIS.
There is not a potential for blocking a true SI signal by resetting CVI in Modes 5 and 6.
A SI signal cannot activate ESF systems due to steam flow mismatch or low primary pressure because SI block is in e f fec t.
Containment high pressure and steam line differential pressure will not initiate SI in Modes 5 and 6 because primary Plant temperature is less than 200*F.
The Containment high radiation signal provides input to the CVI circuitry from 1 of 4 different channels.
Thus, resetting CVI due to a false high radiation signal present may block a subsequent real high radiation signal from another channel.
Although the control room operators would receive audible and visual alarms of a high radiation condition, PGE will modify its operating proce-dures to not allow resetting CVI with a high radiation signal present unless necessary during post-accident conditions.
Should an operator receive a false radiation signal, he would deenergize the affected channel prior to resetting CVI.
Criterion 2 " Sufficient physical features (e.g., key lock switches) are to be provided to facilitate adequate administrative controls."
l NCR Tentative Conclusions "None of the ESF systems at the Trojan plant satisfy Criterion 2.
SSPS ' RESET' push buttons act as overrides since their actuation will eliminate an output signal from their associated SAF-0UT device when an ESF initiating signal is present."
Trojan Nuclear Plant Mr. Robart A. Clark Docket 50-344 March 12, 1982 License NPF-1 Page 3 of 5 I
PGE Response:
Only personnel in the control room with a reactor operator license or under the supervision of a person with a reactor operator license are permitted to manipulate the reactor plant controls.
The con-trol room operators are allowed to actuate a " RESET" push button when permitted by operating procedures.
The criteria for proper use of push buttons are included in operating procedures and in the operator training program.
To reset an ESF system an operator is required to push two " RESET" buttons, one for train A, the other for train B.
For the CVI system, train A provides isolation of valves inside Containment and train B isolation of valves outside of Containment.
Should a CVI " RESET" button be inadvertently actuated, two additional deliberate actions (pushing the other " RESET" button and posi-tioning a valve control switch) would be required by an operator to change the position of a Containment ventilation isolation valve.
Operation of the " RESET" push buttons alone will not cause the actuation nor change the operating status of any ESF system.
The " RESET" feature only allows the control room operator to mani-pulate the Plant controls for an ESF system after the ESF system has actuated.
Accordingly, because the operation of " RESET" push buttons is con-trolled by licensed trained operators utilizing approved operating procedures, and because inadvertent operation of a " RESET" push button in itself will not affect the operational status of an ESF system, additional physical features to facilitate administrative controls for SSPS " RESET" push buttons are not necessary.
Criterion 3 "A system level annunication of the overridden status should be provided for every safety system impacted when any override is active.
(See NRC Regulatory Guide 1.47.)"
NRC Tentative Conclusions "ESF systems at the Trojan plant do not satisfy Criterion 3.
The ' RESET' of a SAF-0UT device with an input signal present performs as an override of one or more actuating parameters which should be annunciated at the system level in order to satisfy Criterion 3."
PGE Response:
The potential for the " RESET" feature of the SSPS to block a SAF-0UT input signal with another input signal present is discussed in the response to Criterion 1.
Regulatory Guide 1.47 requires annuncia-tion at a system level when the Protection System or lystems con-trolled by it are bypassed or made inoperable.
Proper utilization of the " RESET" feature does not render the SSPS inoperable, nor does it bypass or prevent any ESF system from performing its necessary function.
The " RESET" feature is only utilized by the operator af ter the SSPS has responded to an accident situation and after an ESF system has responded to the SSPS signal.
(See Response to
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i Trojan Nuclear Pltnt Mr. Robart A. Clark
- Docket 50-344 March 12, 1982 License NPF-1 Page 4 of 5 Criterion 2.)
Proper utilization of the " RESET" feature does not have an adverse impact on safety systems and should not require annunciation.
Criterion 4 " Diverse signals should be provided to initiate isolation of the containment ventilation system. Specifically, containment high radiation, safety injection actuation, and containment high pressure l
(where containment high pressure is not a portion of safety injection actuation) should automatically initiate CVI."
NRC Tentative Conclusions "ESF systems at the Trojan plant partially satisfy Criterion 4.
Containment purge and exhaust valves (54-in.) are isolated by the CVI system which is actuated by diverse signals (safety injection actuation and high radi-ation). Other ventilation valves, however, are not isolated by the CVI subsystem. Those valves (e.g., 8-in. hydrogen vent valves) are isolated by the containment isolation system. This system is activated automatically by safety injection actuation which, while providing some signal diversity, does not satisfy the requirement that isolation of ventilation valves be initiated by containment high radiation."
PGE Response:
The 8-in. hydrogen vent valves at the Trojan plant have been modi-fied so that they will close upon receipt of a Containment high radiation signal (see enclosed drawings).
Criterion 5 "The instrumentation and control systems provided to initiate the ESF should be designed and qualified as safety-grade equipment."
NRC Tentative Conclusions "ESF systems at the Trojan plant partially satisfy Criterion 5.
No information has been provided concerning the design and qualification of containment high radiation detectors and associated circuitry."
PCE Response:
The Trojan Engineered Safety Features (ESFs) sense selected Plant parameters to mitigate the consequences of a primary or secondary system boundary rupture.
Section 7.3 of the FSAR does not refer-ence Containment high radiation as a generating station conditioa required for ESF actuation.
Although not designated safety grade, the Containment High Radiation Detection System does provide for Containment ventilation isolation (CVI).
The primary means, how-ever, of actuating CVI is provided by the SI portion of the ESF system.
Section 6.2.4 of the Standard Review Plan (SRP) states that Con-tainment purge and vent lines "should be equipped with radiation monitors that are capable of isolating these lines upon a high radf ation signal"; this is the case at the Trojan plant.
The SRP also says that, "A high radiation signal should not be considered
Trojtn Nucicar Pitnt Mr. Robsrt A. Clsrk Docket 50-344 March 12, 1982 License NPF-1 Page 5 of 5 one of the diverse Containment isolation parameters".
The SRP does not require the high radiation signal to emanate from safety-grade equipment.
Branch Technical Position (BTP) CSB 6-4 requires that " instrumentation in controlled systems provided to isolate the purge system lines should be independent and actuated by diverse parameters".
The Trojan plant meets this requirement.
The BTP does not require the high radiation signal to emanate from safety-grade equipment.
Furthermore, NUREG-0737 (Section II.E.4.2) does not require the radiation monitors to be safety grade.
Criterion 6 "The overriding or resetting of the ESF actuation signal should not cause any valve or damper to change position."
NRC Tentative Conclusion "ESF systems at the Trojan plant do not satisfy Criterion 6.
Several instances were found where a solenoid operator control scheme is used that will result in valve repositioning upon ESF actuation signal override. Valves observed during this review, which must be so categorized, have been identifed in the attached table. The licensee has indicated that modifications have been completed for 23 Con-tainment isolation valve control circuits at the Trojan plant to preclude valve repositioning upon ESF reset.
No such modifications were evident on the drawings provide by PGE for review to indicate if any of the valves identified in the Table may have been so modified."
PGE Response:
Updated drawings have been provided with this letter to show which Containment isolation valve control circuits have been modified.
All valves listed on the table provided in the NRC letter of December 18, 1981 will not reposition automatically upon ESF actu-ation signal override, with the exception of the feedwater flow control and bypass flow control valves.
The feedwater flow control and bypass flow control valves return to the positions determined by their respective hand controllers when the feedwater isolation signal clears.
Modifications to these valves are not necessary since feedwater isolation is provided by the feedwater isolation i
and bypass isolation valves, which will not return to their pre-vious position automatically.
Containment isolation is also pro-vided by Seismic Category I check valves upstream of the feedwater isolation and bypass isolation valves.
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