ML20081L725
| ML20081L725 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee  |
| Issue date: | 07/01/1991 |
| From: | Murphy W VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BVY-91-64, NUDOCS 9107080030 | |
| Download: ML20081L725 (22) | |
Text
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. VERMONT YANKEE NU. CLEAR POWER CORPORATION y ~.
. ": - f Ferry hood, Brattleboro, V105301-7002 BVY 9I-64 r f Grd EH:tKi OF r icr.
pp.) gg";
July 1,1991 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Document Control Desk Referencos: a) License No. DPR 28 (Docket No. 50-271) b) Letter, USNRC to VYNPC (NVY 9170), Requallfication Program Evaluation and Operational Evaluations, Report No. 50/271/91-02 (OL), dated April 19, 1991 c) Letter, USNRC to VYNPC (NVY 90 230), inspection Report 50-271/90 16, dated December 27, 1990 d) Letter, VYNPC to USNRC (BVY 90-082), Status of Vermont Yankee Procedure Generation Package and Corresponding Emergency Operating Procedures, dated July 24, 1990 e) Letter, USNRC to VYNPC (NVY 90118), Safety Evaluation for Vermont Yankee Nuclear Power Station Procedures Generation Package (TAC No. 44347), dated June 7,1990 f) NRC Safety Evaluation Report - BRWOG Emergency Procedures Guidelines, Revision 4, dated June 7,1990 g) Letter, USNRC to VYNPC (NVY 88160), Emergency Operating Procedure (EOP) Inspection (50 271/88-200), dated August 10, 1988
Dear Sir:
Subject:
Vermont Yankee Response to Report No. 50 271/91 02, Additional Information Regarding Emergency Operating Procedures (EOPs)
As a result of the Emergency Operating Procedure (EOP) review conducted as part of the Licensed Operator Requalification Program Evaluation performed at our facility during the period of February 25 to March 1,1991, Reference b) requested that we provide you with additional Information regarding our technical justifications for the items discussed in Attachment 7 of Reference b) This request is based on an unresolved item relating to the adequacy of ses al of our justifications for departing from the accident mitigation strategy of Revision 4 of the BWR Owners Group Emergency Procedures Guldelines (EPGs). The attachment to this letter provides detailed responses to the concerns raised in Attachment 7 to Reference b).
9107080o30 910701 PDR 0 ADOCK 0500o271 PDR q
. VERMONT YANKEE NUCLE Ar4 POWER CORPOR ATION U.S. Nuclear Regulatory Commission July 1,1991 Page 2 i
To address the issue in an efficient and effective manner, we are presently in the pro, uss of performing a complete review, verification, and validation of our Procedure Generation Package (PGP) and EOPs. The PGP which include our !
Writer's Guide and our Plant Specific Technical Guldelines (PSTGs), the technical i justifications for differences from Revision 4 of the EPGs. It is our plan to resolve all issues related both to our Internal review and the NRC inspection and include the appropriate revisions within an updated PGP and EOPs. In order to ensure that our EOPs properly implement the EPG accident mitigation strategies and provide our operators with the best possible guidance, the verification will be performed by an independent consultant expert in the area of EPGs. If our verification and validation effort identifies any deviations from l
positions presented in this letter, they will be submitted for your review.
We expect to incor) orate the updates to the PGP and the EOPs so that they may be used for tra ning beginning October 1,1991. The Writer's Guida included within the updated PGP will also address the issues presented in Reference e). Following the updates, documentation will be maintained at our facility and will be available for inspection.
We trust that the above information is satisfactory; however, chould you have any questions or desire any additional information on this issue, please do not hesitate to contact us.
Very truly yours, Vermont Yankee, Nuclear Power Corporation g/ 'Y Warren P. Murphy Senior Vice President, Operations cc: USNRC Regional Administrator, Region I
I
ATTACHMENT 1 Response to NRC Concerns Vermont Yankee PSTG/EPG Revision 4 Differences ,
I Summary:
Our technical justifications for deviations from the BWR Owners Group Emergency Procedures Guidelines (EPGs) result from our method of implementing the Plant S ecific Technical Guidelines (PSTGs). Specifically, the PSTGs provide the overall uldance for implementation of the EPGs at Vermont Yankee. Where other speci e Vermont Yankee operating and emergency procedures implement 1 the guidance provided by the EPGs, this is recogn' zed as a deviation from the '
EPGs and suitable justillcation is provided for not including the action in the i core EOPs (i.e., OE 3101 through OE 3106). Vermont Yankee fully endorses the implementation of the accident mitigation strategies contained in the EPGs.
To document this hilosophy, we are currently in the process of updating our PGP, and specificall the PSTGs, to ensure they more accurately reflect this concept. We will also d velop a " linkage document" which will reflect the inter-relationships between the Vermont Yankee implementing procedures and the PSTGS.
Supplement 1 to NUREG-0737 requires that plant specific technical significant differences "guidelines include rom the generic plant specific technical information guidelines. justifying safetyin this context, is not Safety significance, defined. Per NUREG-1358, the technical guidelines should be sufficiently documented to show the flow of information from the analytical basis to the guideline. Therefore, in order to demonstrate adequate justification for a specific deviation, the analytical basis for the generic guideline must first be known.
In isolated cases, an analytical basis does not exist. Rather, the bases presented in the EPGs result from industry consensus drawn from operational experience of the various BWR types and systems, with differing organizational structures and operating philosophies.
Since some of the NRC identified inadequacies of our technical justifications for deviations from the EPGs lie in the area of insufficient analysis supporting the deviation, part of the above described revision workscope will include a more thorough presentation of both the generic technical basis and our reasoning supporting the deviation and its relationship to Vermont Yankee's BWR type and s as our organizational structure and operating l
philosophy. ystems, as well l
1 L
- 1) EPG Statement: j RPV Control Guideline Entry Condition - RPV pressure above [1045 psig (high RPV pressure scram setpoint)).
PSTG, Revision 6 Statement:
N/A Basis for NRC Concern:
"The VY PSTG does not describe unique desb,,i features or provide 1 analysis that would justify deleting this symptom as an entry condition into j symptom based emergency operating procedures."
Response
In the case of a high RPV pressure condition, the symptom based, i flowchart formatted procedure OE 3100, " Scram Procedure," is entered whenever a condition exists where RPV pressure is above the scram setpoint, i.e., a scram condition exists. The operator is then directed to control RPV water level and pressure, monitor SRV actuations, initiate Torus cooling as required, and commence RPV depressurization and cooldown in a manner consistent with the PSTGs. If an ATWS or low RPV water level condition exists, the operator is directed to execute OE.
3101, "RPV Control Procedure," concurrently, where the additional RPV pressure control actions described in the PSTGs are performed.
The Vermont Yankee PSTGs wili be revised to include the above RPV Control Guideline Entry Condition.
The addition of this entry condition to the PSTGs will not affect the actions directed by the Vermont Yankee EOPs. The PSTGs RPV Control Guideline is implernented via OE-3100 and OE-3101, as described above. .
This ensures a consistent accident mitigation strategy should an event subsecluently degrade and prevents concurrent, conflicting instructions regarding the control of RPV parameters. As discussed in the Summary section of this Attachment, the imalementation of the PSTG guidance in this manner is considered a deviat on from the EPGs and justification will be included in our " linkage document" which will reflect the inter.
relationships betwoon the Vermont Yankee implementing procndures and the PSTGs.
- 2) EPG Statement:
RPV Control Guideline Entry Condition Drywell pressure above [2.0 psig (high drywell pressure scram setpoint)].
2
PSTG, Revision 6 Statement:
N/A i Basis for NRC Concern:
"The VY PSTG does not describe unique design features or provide analysis that would justify deleting this symptom as an entry condition into symptom based emergency operating procedures."
Response
In the case of a high drywell pressure condition, the sym flowchart formatted procedure OE 3100, " Scram Procedure,"ptom-based, is entered whenever a condition exists where drywell pressure is above the scram setpoint, i.e., a scram condition exists. The operator is then directed to control RPV water level and pressure, monitor SRV actuations, initiate Torus cooling as required, and commence RPV depressurization and cooldown in e manner consistent with the PSTGs. If the high drywell pressure Is caused by an ATWS or low RPV water level condition exists, the operator is directed to execute OE-3101, "RPV Control Procedure,"
concurrently, where the additional reactor aower control and RPV water level and pressure control actions describec in the PSTGs are performed.
The Vermont Ysnkee PSTGs will be revised to include the above RPV Control Guideline Entry Condition.
The additior, of this entry condition to the PSTGs will not affect the actions directed by the Vermont Yankee EOPs. The PSTGs RPV Control Guideline is implemented via OE-3100 and OE 3101, as described above.
This ensures a consistent accident mitigation strategy should an event subsequently degrade and prevents concurrent, conflicting instructions regard ng the control of Rr'V parameters. As discussed in the Summary section of this Attachment, the implementation of the PSTG guidance in this manner is considered a deviat on from the EPGs and Justification will be included in our " linkage document" which will reflect the inter-relationships between the Vermont Yankee implementing procedures and the PSTGs.
- 3) EPG Statement:
RPV Control Guideline, Step RC/P-3 When either:
- All control rods are inserted to or beyond position [02 (Maximum Suberitical Banked Withdrawal Position)], or 3
i It has been determined that the reactor will remain shutdown under all conditions without boron, or
- 700 pounds (Cold Shutdown Boron Weight)] of boron have been njected into the RPV, or
- The reactor is shutdown and no boron has been injected into the RPV, depressurize the RPV and maintain a cooldown rate below (100 'F/hr (RPV cooldown rate LCO)).
PSTG, Rovlslon 6 Statement:
RPV Control Guideline, Step RC/P 4 - When:
- All control rods are inserted to or beyond position 02 (Maximum Suberitical Banked Withdrawal Position), or
- 465 pounds (Cold Shutdown Boron Weight) of boron have been injected into the RPV, and RPV level has been restored between 127 inches (Low reactor water level scram setpoint) and 177 inches (High reactor water level trip setpoint),
Proceed to cold shutdown in accordance with Plant Restoration procedure OP-0109.
Basis for NRC Concern:
"The VY PSTG does not consider the deviation in the context of the overall EPG RPV pressure control strategy as it relates to RPV Control, Primary Containment Control, Secondary Containment Control, Radiation Release Control, and the Contingencies. These procedures depend on the reactor pressure reduction as a part of the overall accident mitigation strategy. The EPG considerations for beginning a pressure reduction are that the reactor will remain shutdown during the cooldown and an emergency situation still exists (page 1-4 of EPG). There is no consideration provided in the EPG for RPV level to be restored before a pressurs reduction is initiated. Inclusion of the RPV level in the direction to begin normal depressurization unnecessarily delays actions that could also mitigate the symptoms in other procedures.
"It is appropriate to include the statement 'It has been determined that the reactor will remain shutdown under all conditions without boron.' The VY PSTG does not describe any unique features that would justify not 4
r Including this statement. The statement does not direct operators to make this judgement, and other BWRs do not require operators to make this determination. If this information is available from either the reactor engineer or the Technical Support Center, then it can be used as part of the accident mitigation strategy."
Response
The Vermont Yankee PSTGs and EOPs will be revised to perform an RPV pressure reduction when it is assured that the reactor will remain shutdown during the depressurization, irrespective of RPV water level considerations.
The phrases "It has been determined that the reactor will remain shutdown under all conditions without boron" and "The reactor Is shutdown and no boron has been Injected into the RPV" were added to Revision 4 of the EPGs in an effort to provide additional flexibility in responding to an ATWS event. The EPGs also leave it up to the individual utility to determine what the acceptance criteria should be. Based on concerns with the format of the EPG statements and shift staffing requirements, Vermont Yankee established the criteria as "all control rods are inserted to or beyond position 02". The justification for this decision is as follows:
- 1. For a given set of reactivitv coefficients, the reactor can be shutdown by any of the follow [ng methods:
I a) Control rod insertion alone, or b) Boron injection alone, or l c) A combination of control rod insertion and boron injection.
The EPG conditions, as written, exclude the third method. They aertain to the current shutdown state of the reactor and all possible "uture states of core reactivity, hence the use of the future tense l'1 the EPG phrase "... will remain shutdown under all conditions ...".
Actions that follow the EPG conditions are not allowed to proceed unless sufficient control rod density exists to assure reactor shutdown under all possible subsequent reactivity states.
- 2. The determination that the reactor will remain shutdown for control '
rod insertion configurations other than:
a) All control rods inserted to or beyond position 02 (Maximum Suberitical Banked Withdrawal Position), or b) The existence of the Technical Specifications requirement for shutdown margin (i.e., all control rods inserted to position 0 5
l except one rod), is beyond the capability of the control room crew. All other control rod configurations would not be considered until the Technical Sup? ort Center response team is assembled to evaluate the shutcown state of the reactor.
Upon review, our overall accident mitigation strategy may be enhanced by
-providing clear, concise direction through revision of the PSTGs as follows:
"When:
All control rods are inserted to or bevond position 02 (Maximum L Suberitical Banked Withdrawal Position), or All control rods are inserted to position 00 except one rod (Technical Specifications requirement for shutdown margin), or 1
Technical Support Center or Reactor Engineering has determined that sufficient control rod density exists, or 465 pounds -(Cold Shutdown Boron Weight) of boron have been I
injected into the RPV, ..."
l -The Vermont Yankee PSTGs and EOPs will be revised to include the above conditions, i
- 4) EPG Statement:-
RPV Control Guideline - Step' RC/P 1 Override - If while executing the following steps:-
- . Boron injection is required, and
- The main' condenser is available, and L
L
-- There has - been' no indication of gross fuel failure or steam line 1 break, l .:- open MSIVs, bypassing pneumatic system and low RPV water level p isolation interlocks if necessary, to reestablish the niain condenser as a heat sink.- - -
L PSTG, Revision 6 Statement: l l RPV Control- Guideline, Step RC/P If:
1
-: MSIV isolation occurred,
- Theimain condenser is available, and 6
..- . -. -. .- . - - . . - - . . . . . - . - . _._--=.-.-..-----.-.:.-----.
i
)
- No indication of gross fuel failure or steam line break exists, Open MSIVs, bypassing Low Low RPV water lovel (82.5 inches) and High Steam Flow Not in Run (40%) isolation interlocks, if necessary, to re-establish the main condenser as a heat sink.
Basis for NRC Concern:
"VY has a design feature of a 105% bypass valvo capability and its uso should be factored into the accident mitigation strategy. The EPGs support the use of the main condenser as a heat sink. The EPGs also are clear on those conditions which authorizo use of defeatirg isolation interlocks to be able to use the main condenser as a heat sink. For the
) articular stop in question, the EPGs do not allow defeating the MSIV solation interlocks unless boron injection is required. This occurs when the reactor cannot be shutdown and the suppression pool temperature reaches the boron injection inillation temperature (BilT). The BilT is established to assure that the heat capacity temperature limit will not be exceeded when the hot shutdown borca weight is injected into the vessel during an ATWS, the MSIVs are clossd, and no torus cooling is available.
The VY PSTG defeats an isolation provision without analysis of the consequence of the actions. This may represent an unreviewed safety issue."
Response
The Vermont Yankee PSTGs and EOPs will be revised to permit defeating the MSIV isolation interlocks only if boron injection is required.
Analysis for the present PSTG and EOP actions clearly demonstrates that an unreviewed safety issue does not exist. Assurance that the uso cf the MSIVs will not result in adverse radiological consequences is provided by the PCIS Group 1 Isolation signals, which will close the MSIVs should adverse conditions develop. Vermont Yankee Technical Specifications Bases Section 3.2 states 11at the function of the PCIS Grou) 1 isolation signal for low low RPV water level is to assure that tio limits of 10CFR100 will not be violated. However, the following PCIS Group 1 isolation signals, which are not bypassed in PSTG Step RC/P-1, provido equivalent protection:
- High Main Steam Line Radiation Levels. The setting of 3 times normal background levels, coupled with the MSIV closure time requirements, assure that ficslon product release is limited so that 10CFR100 limits are not exceeded for the control rod dro) accident, and 10CFR20 limits are not exceeded for gross fuel fai uro during reactor operations.
- High Steam Tunnel Area Temperatures. The cetting of ambient plus 95 F is low enough to detect leaks of the order of 5 to 10 gpm; 7
thus, it is capable of coverin0 the entito spectrum of breaks and gives isolation before the limits of 10CFR100 are exceeded.
- Low Condenser Vacuum. The purpose of this isolation signal is to prevent the release of radioactive gases from the primary containment through the main condenser. The setting of 12 inches of mercury absolute provides sufficient margin to assure retention capability in the condenser when gas flow is stopped and sufficient margin below operating values.
- 5) EPG Statement:
N/A PSTG, Revision 6 Statement:
Torus Control Guldeline, Step T/T 3 If torus water temperature is above 120 'F (Technical Specifications torus temperature LCO, during reactor isolation conditions, requiring reactor depressurization to <200 psig) and the RPV is isolated from the main ccndenser, commence depressurizing the RPV at normal cooldown rates to <200 psl 0, unless Emergency RPV Depressurization is required.
Basis for NRC Concern:
"The licensee steps severely complicate the actions for responding to an ATWS event with the MSIVs closed and a relief valve operating. The licensee actions to depressurize the RPV are in direct confilet with the overall EPG strategy to combat ATWS scenarios. During the ATWS, the EPGs do not depressurize the RPV based on torus temperature considerations unless the torus temperature is im3 acting the heat capacity temperature lim!t (HCTL), Based on the VY HCT L curve, this temperature is approximately 195 'F. The VY PSTG does not describe unicue faatures regarding the VY torus which would justify ATWS actions di forent than that contained in the EPGs in addition had the licensee implemented the pressure control portion of the RPV control in accordance with the EPG guidelines, the procedure would require beginning a cooldown when reactor power is under control which would address the actions covered in the VY technical specifications. The operators are trained not to depressurize the RPV with an ATWS condition, which directly conflictc with tne direction given in the suppression pool temperature control procedure."
Response
Page 49 of the NRC Safety Evaluation Report [ Reference f) for Revision 4 of the EPGs states that "each BWR licensee should verif if the EPGs are consistent with its licensing based analysis. That is, B R plants 8
4 should implomont appropriato plant specific procedures consistent with its safety analysis or provide the staff with additional information to remedy such deviations."
The addition of PSTG Stop T/T 3 was performed to maintain compliance with Vermont Yankee Technical Specifications Section 3.7.A.1.d for those EOP actions which may be performed during design basis events and so meet the intent of the above SER statomont. Continued NRC/NRR and BWROG discussions are in progress on the design basis issue. Program enhancements may be maco based on how the results effect Vermont Yankee.
Technical Specifications Section 3.7.A.1.d states that during reactor isolation conditions, the RPV thall bo depressurized to less than 200 psig at normal cooldown rates if sup,vession pool temperature exceeds 120 F.
The basis for this Technical Specification is formed by experimental data which Indicates that excessive steam condensing loads can be avoided if the peak temperature of the suppression pool is maintained below 160 F during any period of relief valve operation with sonic conditions at the dischargo exit. Therefore, this specification has been placed on the envelope of reactor operating conditions so that the reactor can be depressurized in a timely manner to avoid the regimo of potentially high suppression pool loadings. This condition is not addressed by the EPG Heat Capacity Temperature Limit (HCTL). The HCTL is defined to be the highest supprossion pool tem perature at which initiation of RPV depressurization will not result in either (1) exceeding the suppression chamber design temperature or (2) exceeding the Primary Containment Pressure Limit before the rato of energy transfer from the RPV to the containment is within the capacity of the containment vent.
Both PSTG Step TIT-3 and Technical Specifications Section 3.7.A.1.d direct the operator to commenco RPV depressurization at normal cooldown rates to below 200 psig. Technical Specifications Section 3.6.A.2 specifies a maximum heatup or cooldown rate of 100 *F averaged over any one hour period.
No minimum cooldown rate is specified and the operators are properly trained to prioritize actions and control the cooldown rate to prevent an inadvertent reactor power level increase during the level / power control actions of PSTG Contingency #5. No conflicting actions have been identified with the present procedural steps during previous EOP validations and continuing Licerised Operator Requalification Training.
- 6) EPG Statement:
Secondary Containment Control Guideline Entry Condition - Differential pressure at or above 0 inches of water.
PSTG, Revision 6 Statement:
9
i Basis for NRC Concorn:
"The EPG ontry conditions are symptomatic of both emergonclos and events which may degrado into emergenclos. The EPGs specify actions appropriato for_ both. Entry into procedures dovoloped from tho guidelinos is not conclusive that an omorgency has occurred. Differential pressure at or abovo 0 Inches of water, is symptomatic of a condition which may degrado into an omorgency. The VY PSTG does not describo unique featuros or provido analysis that justiflos doloting this entry condition."
4
Response
it is the Vermont Yankoo position that the EOPs are bui a part of the overall omorgency responso strategy. For cortain events, omorgency responso and recovery are optiml:ed through the combined uso of the symptom based, flowchart format EOPs and supplomontal proceduros. This is true for this caso.
For the condition of Secondary Containment differential pressure at or above 0 inches of water, the EPG basis states that a high Secondary Containment differential pressure is indicativo of a potential loss of Secondary Containment integrity and could result in uncontrolled release of radioactivity to the environment. However, the root cause of the high diffo.ontial pressure may be either a condition symptomatic of an omorgency, one which could degrade into an omorgency, or a non-omergency condition such as shutdown of the Secondary Containment HVAC or high wind conditions.
At Vermont Yankee, the Secondary Containment arossure with respect to the outsido atmosphoto is measured on each of 110 four (4) outsido walls of the reactor building. Two separato sets of instruments exist which independently moar,uro all four (4) sides of the building and read out in the control room. The results of testing indicate that under high wind conditions, the pressure at the looward side of the building may Decome positive with respect to the outside almosphoro. Therefore, the existence of Secondary Containment differential pressure greator than zero is not conclusivo indication of a loss of reactor building structural Integrity.
Further, the radiological consequences of the reactor building pressure becoming positivo under high wind conditions has been previously evaluated. (
Reference:
Memo, E.C. Tarnuzzer to A.M. Shepard,
" Evaluation of Reactor Building Leakage," dated January 18, 1972)
In all cases, the EPG Secondary Containment Control Guldolino directs the following initial operator actions for area temperature, radiation levels, or water lovels exceeding the maximum safe operating limits:
- Monitor and control Secondary Containment tem 3eratures, radiation lovels and water levels. (EPG Steps SCfr, SC/A and SC/L) 10 I
- Operate available area coolers. (EPG Step SC/T 1)
- If Secondary Containment HVAC exhaust radiation level is below the Secondmy Containment HVAC isolation setpoint, operate available secondary containment HVAC. (EPG Step SC/T-2)
In order to ensure a consistent accident mitigation strategy should an event subsec,uently degrade, and to prevent concurrent, conflicting Instructions regard:ng the control of secondary containment HVAC and eliminato needless entry into an EOP when it is not required, the above initial actions common to both non emergency and emergency conditions are contained within procedures, OP 2116, " Secondary Containment Integrity Control", ON 3153, " Excessive Radiation Levels," and ON 3158, " Reactor Building High Area Temperature / Water Level". OP 2116 directs the operator to place area coolers in operation and start the Standby Gas Treatment System for Secondary Containment HVAC. ON 3153 and ON.
3158, which are entered for area temperatures, radiation levels or water levels at or below to PSTG entry condition values, direct the operator to monitor area temperatures, radiation levels and water levels.
For conditions which are symptomatic of an emergency or those which could degrade into an emergency, pressurization of the Secondary Containment to or above atmospheric pressure would be accompanied by either high area temperatures, radiation levels, er water levels due to a high energy line brea <. Each of these conditions is an entry condition into OE 3105, " Secondary Containment Control," which includes both the above initial actions and the required subsequent actions.
The Vermont Yankso PSTGs will be revised to include the above Secondary Containment Control Guideline Entry Condition.
The addition of this entry condition will not affect the actions directed by the Vermont Yankee EOPs. The PSTGs Secondary Containment Control Guideline is implemented via OP 2116, ON-3153, ON 3158 and OE-3105, as described above. As discussed in the Summary section of this Attachment, the implementation of the PSTG guidance in this manner is considered a devlation from the EPGs and Justification will be included in our " linkage document" which will reflect the inter relationships between the Vermont Yankee implementing procedures and the PSTGs.
- 7) EPG Statement:
Secondary Containment Control Guideline, Stop SC/T-4.2 - When an area temperature exceeds its maximum safe operating temperature in more than one area, Emergency RPV Depresse Ization is required.
PSTG, Revision 6 Statement:
Secondary Containment Control Guideline, Step SCTT-3.2 - When a maximum safe operating temperature for a limiting combination is 11
o exceeded, Emergency RPV Depressurization is required, enter Contingency
- 2 and execute it concurrently with this procedure.
Basis for NRC Concern:
"The VY distinction of limiting combination rather than more than one area does not address the consideration of a wide spread problem which may pose a direct and immediate threat to seconcary containment integrity.
The VY PSTG can allow more than one area above the maximum safe temperature without requiring omergency depressurization. The VY PSTG does not address unique design features that would justify not implementing revision 4 of the EPGs. The PSTG justification also does not address temperature limitations due to personnel access requirements."
Response
Step SCR4.2 of the EPG Secondary Containment Control Guideline directs the operator to perform an Emergency RPV Depressuritation when an area temperature exceeds its maximum safe operating temperature in more than one area. The basis provided for this step stains:
"The criteria of 'more than one area'speelfled in this step identifies the rise in secondary containment temperature as a wido-spread probloni which may pose a direct and immediate threat to secondary containment Integrity, equipment located in the secondary containment, and continued safe operation of the plant."
The EPGs do not explicit!y define the term " area" to mean physical area.
As such, Vermont Yankee has defined " area" to mean functional area, which may be made up of one or more physical volumes. The physical volumes, in turn, are obtained from the Vermont Yankee specific Reactor Building model developed for the Vermont Yankee Environmental Qualification Program. This model is used in the RELAP/ MODS computer application code to predict high energy line break mass, energy release and subsequent Reactor Building response.
In establishing the Vermont Yankee area temperature limits and functional areas, critical plant physical volumes and equipment were determined and the environmental tolerance levels for this equipment obtained. Critical equipment was defined as that equipment needed for chutdown and decay heat removal. Only those functional areas which could result in the potential loss of both redundant trains of a required safety, or critical, 9 unction were considered. This addresses preservation of reactivity control, ECCS initiation and cooling, RPV level and pressure control, decay heat removal, and post accident monitoring functions. Focus on these functions j prioritizes actions necessary to address core cooling and primary
! containment integrity concerns relative to secondary containment concerns and so assures that radioactive releases to the environment are minimized.
As such, an Emergency RPV Depressurization, with the resulting transient on the RPV and potential complications, is performed only as required.
12 l
O i .
It is the Vermont Yankee position that this in-depth study provides a greater degree of safety than that provided by the EPGs.
Concerning temperature limitations due to personnel access requirements a review of the above area temperature limits indicates that personnel access considerations are adequately addressed through present Vermont Yankee administrative procedures.
- 8) EPG Statement:
Secondary Containment Control Guideline, Stop SC/R 2.2 When an area radiation level exceeds its maximum safe operating radiation level in more than one area, Emergency RPV Depressurization :s required.
PSTG, Revision 6 Statement:
N/A Basis for NRC Concern:
" Radiation levels above the maximum safe o]erating in more than one area is a symptom that there is a widespreacl problem which may pose a direct and immediate threat to plant equipment and to personnel t,oth on and off site. Rellance on actions within the temperature leg, which do not require emergency depressurization unless a I miting combination is exceeded does not assure that the personnel on or off s te are protected.
If a limiting temperature combination is not exceeded and there is more than one area above the maximum safe radiation operating level during an unisolated primary system discharge to the secondary containment, emergency depressurization will not be performed to minim ze the release of radloactivity to secondary containment. The licensee justification does not address the threat to personnel both on and off site from radiation releases. The licensee justification is based on a high energy line break with no substantial radiological source term. The licensee is using event based information to restrict symptom based procedures."
Response
The EPG Secondary Containment Control Guideline directs the operator to operate secondary ventilation systems, isolate system discharges and control RPV pressure through sequentially executed steps as required to:
l Protect equipment in the secondary containment, Limit radioactivity release to the secondary containment, and either:
l l 13 1
l
- l. _. _
. - - _= ._ - _ _ _ . - _ _ - . . .
l 3
Maintain secondary containment intogrity, or Limit radioactivity release from the secondary containment. )
1 The Vermont Yankee position, as discussed in the above NRC concern, was based upon an engineering evaluation performed in 1986 In support of the implementation of Revision 3 of the EPGs. That evaluation concluded that, in the case of Vermont Yankee, the requirement to aerform an Emergency RPV Depressurization due to high area radiation evels within the secondary containment was redundant to actions already contained within the area temperature and water level sections of the PSTG Secondary Containment Control Guideline and that no credible svent sequence could be identified for utilization of the remaining EPG Guideline Steps. This position was carried forward to Revision 4 of the PSTGs as the EPG Secondary Containment Control Guideline remained essentially unchanged.
Further review in this area has been performed using expanded criteria and improved analytical techniques. This updated evaluation concludet that event scenarios exist where secondary containment area radiation levels may exceed the Maximum Safe Operating Level without the corresponding area temperatures or water levels.
Based on this updated evaluation, our overall accident mitigation strategy may be enhanced through the inclusion of the EPG Secondary Containment Control Guideline Step SC/R 2.2 within the Vermont Yankee ,
PSTGs. The Vermont Yankee PSTGs will be revised to reflect this.
The Mazimum Safe Operating Radiation Levels will be defined based on a) ecluipment qualification doses, b) onsite habitability requirements, and c) olisite dose potential.
- 9) EPG Statement:
Radioactivity Release Control Guideline.
PSTG, Revision 6 Statement:
N/A Basis for NRC Concern:
"Not all scenarios for primary systems discharging outside 3rimary and secondary containments were addressed since the licensee Just fication only considers a high energy line break without a significant radiological source term. The radioactive release control procedure is intended to limit radioactivity releases to areas outside of primary and secondary containments. The VY PSTG does not describe unique features which 14 l
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would justify deleting this emergency operating procedure. Technical specification 6.5 A.4 also requires procedures 1or emergency conditions involving potential or actua* ialease of radioactivity. The licensee is using event based information tt :estrict symptom based procodures."
Response
The EPG Radioactivity Release Control Guideline directs the operator to isolato primary system discharges and control RPV pressure through sequentially executed steps as required to minimize the offsite release of radioactivity during emergency response conditions.
The Vermont Yankee position, as discussed in the above NRC concern, was based upon an engineering evaluation performed in 1986 in support of the implementation of Revision 3 of the EPGs. That evaluation concluded that, in the case of Vermont Yankee, the actions prescribed in the EPG Guideline were redundant to actions already contained within existing plant procedures and other sections of the PSTGs and that no credibis event sequence could be found for utilization of the remaining EPG Guideline Steps. This position was carried forward to Revision 4 of the PSTGs as the EPG Radioactivity Release Control Guideline remained essentially unchanged.
Further review in this area has been aerformed using expanded critoria and improved analytical techniques. '~his updated evaluation concludes that:
a; The 3 resent EPG actions relating to Turbine Building HVAC and isolat on of primary systems discharging into areas outside of primary and secondary containments are adequately contained within procedure ON-3153, " Excessive Radiation Levels",
b) An event scenario exists where offsite radioactivity release rates may exceed the value which requires a General Emergency prior the initiation of an Emergency RPV Depressurization from guidance already contained within the PSTGs Thic scenario involves a liquid ground release resulting from a small break LOCA in which neither cooling nor filtering of the discharge occurs.
Based on this updated evaluation, our overall accident mitigation strategy may be enhanced through the implementation of the EPG Radioactiv.ty Release Control Guideline. The Vermont Yankee PSTGs will be revised to include the EPG Radioactivity Release Control Guideline with the following exceptions:
- 1) EPG: "Offsite radioactivity release rate sbove the offsite release rate which requires an Alert" PSTG: "An Alert Radiological Conditions Emergency Action Level exists in accordance with AP 3125" 15 i
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- 2) EPG: "When offsite radioactivity release rate approaches or exceeds the offsite release rate which requires a General Emergency but ... "
PSTG: "When a General Emergency Radiological Conditions Emergency Action Level exists in accordance with AP 3125, but ... "
These revised statements will provide clear concise direction to the operators in carrying out the required actions and will improve coordination with our Emergency Plan implementing procedures through reference to AP-3125, " Emergency Plan Classification and Action Level Scheme". The Emergency Plan implementing procedures satisfy the requirements of Tecnnical Specifications Section 6.5.A 4.
The PSTGs Radioactivity Release Control Guideline will be implemented via ON 3153, as described above, and a new EOP, OE 3106, " Radioactivity Release Control Procedure". As discussed in the Summary section of this Attachment, the implementation of the PSTG guidance in this manner is considered a deviation from the EPGs and justification will be included in our " linkage document" which will reflect the inter-relationships between the Vermont Yankee implementing procedures and the PSTGs.
- 10) EPG Statement:
Contingency #1, A) ternate Level Control, Step C13.2 When RPV water level drops to [164 in. (top of active fuel)]:
- If any system, injection subsystem or alternate injection subsystem is lined up with at least one pump running, Emergency RPV Depressurization is required.
PSTG, Revision 6 Statement:
Contingency #1, Alternate Level Control, Step C1-4 If any system, injection subsystem or alternate injection subsystem is lined up with a pump running, Emergency RPV Depressurization is required; enter Contingancy t!2 and execute it concurrently with this procedure.
Basis for NRC Concern:
"The licensee argument is not based on technical arguments but on
' prudence.' As long as the core is covered adequate core cooling is assured. In addition the RPV control strategy if implemented in accordance with the EPG guidelines will require the operator to begin a normal cooldown if reactor power is under control. The licensee actions are not a conservative or required action to take under all circumstances.
The additional time obtained by delaying emergency depressurization until 16 l
o RPV water level is at the top of activo fuel permits recovery actions for other sources of water to avoid an unnecessary emergency depressurization. The VY PSTG does not describe unique features which would justify adding this to the emergency operating procedure."
Response
As discussed in the Summary section of this Attachment, in some cases the bases presented in the EPGs are based on Industry consensus drawn from operational experience of the various BWR types and systems, with differing organizational strucures and operating philosophies, rather than on detailed analytical review. This is true for this case.
The basis for the EPG position for not initiating an Emergency RPV Depressurization until RPV water level has dropped to the Top of Active Fuel is as follows:
- " Adequate core cooling exists so long as RPV water level remains above the Top of Active Fuel.
- "The time required for RPV water level to decrease to the Top of Active Fuel can best be used to line up and start pumps, attempting to reverse the decreasing RPV water level trend before RPV depressurization is required to assure adequate core cooling."
The Vermont Yankee position stated that an Emergency RPV 1 Depressurization should be performed if any system, injection subsystem '
cr alternate injection subsystem is lined up with at least one pump runnin drops to the Top of Active Fuel. g,The without basiswaiting for thisuntil RPV is posillon water level as follows:
Entry into Contingency #1 is made when it has been concluded that RPV water level cannot be maintained above the Top of Active Fuel.
This determination may be reached either before or when RPV water level has reached the Top of Active Fuel. As such, sufficient time may or may not exist to line up and start additional injection sources.
When at least one system, injection subsystem or alternate injection subsystem is lined up with at least one pump running, conditions have been established whereby injection will occur as soon as RPV
- pressure drops below the system shutoff head.
The preferred method of adequate core cooling is by core submergence. By delaying Emergency RPV Depressurization until the Top of Active Fuel is reached, core submergence may not be maintained during the subsequent depressurization and initial low-pressure system injection.
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e Each of the above positions presents positive and negative aspects.
However, because neither position can be analytically determined to be superior and in order to provide consistency with the EPGs, the Vermont Yankee PSTGs will be revised to perform an Emergency RPV Depressurization when RPV water level drops to the Top of Active Fuel and any system, injection subsystem or alternate injection subsystem is i lined up with a pump running. !
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- 11) EPG Statement: )
N/A PSTG, Revision 6 Statement:
Contingency #2, Emergency RPV Depressurization, Step C2 3 If the MGIV's are open and the main condenser is available:
Open a minimum of 3 turbine bypass valves (Minimum number of bypass valves required for emergency depressurization).
Basis for NRC Concern:
"The 105% turbine byaass capability is a VY feature that should be considered in the deve opment of the VY EOPs. The EPGs utilize the SRVs as the prime method to RPV emergency depressurize when the arocedures indicate that it is required. The EPGs also indicate that, if 3PV emergency depressurization is anticipated and if the bypass valves are available, the bypass valves should be used. The justification does not address why it is acceptable to utilize the turbine bypass valves as the pr!me method versus the SRVs when emergency depressurization is requ red. There is no analysis referenced that ind cates that the depressurization rate using the BPVs is equivalent to or greater than the capability of the SRVs. Using the bypass valves versus the SRVs for RPV emergency depressurization las an influence on other portions of the procedures (i.e., when establishing the minimum alternate flooding pressure). Use of the BPVs for emergency depressurization in place of the SRVs was not accounted for in the other portions of the PSTG and EOPs."
Response
Use of the turbine bypass valves (BPVs) as the prime method for Emergency RPV Depressurization is consistent with the overall Vermont Yankee strategy concerning containment venting. Discharging of heat energy from the RPV to the main condenser, while it is safe to do so, preserves the heat capacity of the suppression pool and may delay, or arovent, the need for containment venting due to high containment energy evels.
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4 The above position is also consistent with the NRC aosition on primary containment venting, as presented on page 12 o' the NRC Safety Evaluation Report for Revision 4 of the EPGs [ Reference f)]:
"The staff's basic concern was (and remains) that venting, even if it results in some radiological consequences, should only be undertaken as an extreme means to prevent core melt or as a last resort measure to prevent the irreversible and unpredictable rupture of the containment which could otherwise lead to a larger release.
The underlying strategy of containment venting is to prevent core melt and in extremel rare cases the choice of limit ng potential release of radioactivlt to avoid uncontrolled release."
The PSTG conditional statement requiring the MSIVs to be open provides assurance that the use of the BPVs will not result in adverse radiological consequences. The PCIS Grou) 1 Isolation signals will close the MSIVs should adverse conditions c evelop. Vermont Yankee Technical Specifications Bases Section 3.2 states that the function of the PCIS Group 1 isolation signal for low low RPV water level is to assure that the limits of 10CFR100 will not be violated. As this isolation interlock may have been previously bypassed in accordance with the PSTGs 4 above),11e followir:g PCIS Group 1 Isolation signals, which(See item are not bypassed, provide equivalent protection:
- High Main Steam Line Radiation Levels. The setting of 3 times normal background levels, coupled with the MSIV closure time requirements, assure that fission product release is limited so that 10CFR100 limits are not exceeded for the control rod dro) accident, and 10CFR20 limits are not exceeded for gross fuel fai ure during reactor operations.
High Steam Tunnel Area Temperatures. The setting of ambient plus 95 'F is low enough to detect leaks of the order of 5 to 10 gpm; thus, it is capable of covering the entire spectrum of breaks and gives isolction before the limits of 10CFR100 are exceeded.
t Low Condenser Vacuum. The purpose of this isolation signal is to prevent the release of radioactive from the primary containment through the main condenser.gasesThe setting of 12 inches of mercury atesolute provides sufficient margin to assure retention capability it' the condenser when gas flow is stopped and sufficient margin below operating values.
Although not referenced in the technical justification for this deviation, Vermont Yankee Calculation Number OPS 43, " Minimum Number of Bypass Valves Required for Emergency Depressurization for EPG, Rev. 4," dated January 9, 1990, provides the analysis that concludes that the depressurization rato using the BPVs is equivalent to that when using the SRVs.
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The PSTG conditional statement requirin the main condenser to be available pre-supposes that the Advanced Off Gas system is functional and can be villized for gas processing prior to release.
To ensure consistency with other portions of the Vermont Yankee PSTGs and EOPs, the use of the BPVs will be included in the other applicable sections. Values for the Minimum Alternate RPV Flooding Pressure and the Minimum Core Flooding Interval have been calculated considering the use of BPVs. These calculations were performed in a manner cons, stent with the EPG calculations.
- 12) EPG Statement:
RPV Control Guldsline, RC/P Override Statement If while executing the following steps:
- RPV water level cannot be determined and less than [7 (number of SRVs dedicated to ADS)] SRVs are open, enter [ procedure developed from Contingency #2).
PSTG, Revision 6 Statement:
N/A Basis for NRC Concern:
"The VY PSTG does not direct the operator to enter emergency deoressurization if RPV water level cannot be determined and less than 4 SRVs are opened. The RPV flooding procedure does not roculre the operator to enter emergency depressurization if less than 4 SRVs are opened. The PSTG actions will not allow RPV flooding to take place if emergency depressurization is not performed when RPV water level cannot be determinecl. The justification does not address why RPV emergency depressurization is not required."
Response
The RPV Flooding Cont!ngency of the Vermont Yankee PSTGs and EOPs will be revised to require an Emergency RPV Depressurization if less than 4 SRVs, or an equivalent number of turbine bypass valves (BPVs) are open, consistent with the EPGs. The use of BPVs is discussed in item 11 above.
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