ML20006E698
| ML20006E698 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 02/15/1990 |
| From: | Boyle M Office of Nuclear Reactor Regulation |
| To: | Mroczka E CONNECTICUT YANKEE ATOMIC POWER CO., NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| TAC-75185, NUDOCS 9002260236 | |
| Download: ML20006E698 (7) | |
Text
_ _ _.
[hh February 15, 1990 l
Docket'No. 50 245-I m.[
hr. Edward J. Mroczka y
' Senior.Vice President y
-Nuclear Engineering and Operations J.
Connecticut-Yankee Atomic Power Company-Northeast Nuclear Energy Company l
P. O. Box 270 Hartford, Connecticut 06141 0270
Dear Mr.-Mroczka:
SUBJECT:
EVALUATION OF E0P DEVIATION REQUEST. MILLSTONE NUCLEAR POWER STATION, UNIT NO. 1 (TAC NO. 75185) 1 During the week of October 23-27, 1989, the NRC conducted an inspection of the.
Millstone Unit 1 Emergency Operating Procedures (EOPs). As discussed with your staff at the exit meeting on October 27, 1989, the inspectors identified 6
~
significant deviations between the Millstone 1 E0Ps and the BWR Owner Group 1
Generic Emergency Procedure Guidelines Revision 4.
The staff is currently-evaluating'information supporting the deviations provided in letters dated July 25, 0ctober 19, and December 27, 1989.
Enclosed is an interim evaluation and request for additional information.
This informatioW is necessary so that we can resolve the issues identified in the evaluation.
In order to expedite our review of the Millstone' Unit 1 E0P deviations, we would like to meet with NNECO in late February to discuss the enclosure to this letter. You.will.be contacted about'this proposed meeting by a representative from our Region I office.- A forma; response to the request
_t for additional information~will_not be required until efter the meeting has taken place.
The reporting and/or recordkeeping requirements contained in this letter affect
)
. fewer than 10 respondents; therefore, OMB clearance is not required under P.L.96-511.
s Sincerely,
/s/
Michael L. Boyle, Senior Project Manager o
D e ora u I-4 9002260236 900215 PDR ADOCK 05000245 Division of Reactor Projects - I/II i
G PNU E Office of Nuclear Reactor P.egulation 1
Enclosure:
- As stated cc w/ enclosure:
\\,
see next page
{
wDo: w,tFilew NRC & Local PDRs Plant File S Varga (14E4).
DISTRIBUTION cket B.Boger(14A2)
S7Norris M. Boyle OGC-E. Jordan (MNBB3302)
ACRS (10)
G. Thomas (8E23)
.0FC. :LA:PDI-4
- PM:PDI 4
- PD. DI-4
.....:-__... 2._-:............:..
.__\\.g :-_....___...:__...___--.:.-_-----____:_.... __.
,NAME:SNbMs
- MBoyle:1m
- JSt
- M h2//$/90', _
- h/fj/90,
Q//f/90,
. urr icinc nr.cunu cun ggj Document Name: IIILLSTONE 1.1/31
}
?\\\\
- 3.. -
..a
'Mr. Edward J. Mroczka Millstone Nuclear Power Station
= Northeast Nuclear Energy Company-Unit No. 1 Cc:
Gerald Garfield, Esquire R. M. Kacich, Manager Day, Berry and Howard Generation Facilities Licensing Counselors at Law Northeast Utilities Service Company City Place Post Office Box 270 Hartford, Connecticut 06103-3499 Hartford, Connecticut 06141-0270 W. D. Romberg, Vice President D. O. Nordquist Nuclear Operations Manager of Quality Assurance.
Northeast Utilities Service Company Northeast Nuclear Energy Company Post Office Box 270 Post Office Box 270 Hartford, Connecticut 06141-0270 Hartford, Connecticut 06141-0270' Kevin McCarthy, Director Regional Administrator Radietion Control Unit Region I Department of Environn' ental Protection U. S. Nuclear Regulatory Comission State Office Building 475 Allendale Road Hartford, Connecticut 06106 King of Prussia, Pennsylvania 19406 Bradford S. Chase, Under Secretary First Selectmen Energy Division Town of Waterford L
Office of Policy and Management Hall of Records
- 80. Washington Street.
200 Boston Post Road' l,
Hartford, Connecticut 06106 Waterford, Connecticut 06385 L
S. E.:Scace, Station Superintendent W. J. Raymond, Resident Inspector Millstone Nuclear Power Station Millstone Nuclear Power Station-Northeast Nuclear Energy Company.
c/o U. S. Nuclear Regulatory Comission
. Post Office Box.128 Post Office Box 811 Waterford, Connecticut 06385 Niantic, Connecticut 06357 J. P..Stetz, Unit Superintendent
. Millstone Unit No. 1 Northeast Nuclear Energy Company Post Office Box 128 t
Waterford, Connecticut 06385
~!
l
p -.
L 9
l
- /
UNITED STATES NUCLEAR REGULATORY COMMISSION I
_ {
.f wAssiwovow, p. c. ro666 l
(,
J
\\....+./
3 V
l INTERIM. EVALUATION AWD RE00EST FOR. ADDITIONAL INFORMATION l
SY.THE OFFICE OF WUCLEAR. REACTOR.REGULA710N RELATING TO EMERGENCY OPERATIN
G. PROCEDURE
S
[
NORTHEAST.WUCLEAR EWERGY.CONPANY l
HILLSTONE WUCL EAR POWER.SYAT10W.. UNIT.WO.1 DOCKET.WO. 50 245
1.0 BACKGROUND
i L
t As a result of an Emergency Operating Procedure (EOP) inspection at Millstone r
Unit 1, conducted the week of October 23, 1989, significant deviations were c
identified between Millstone 1 E0Ps and the BWR Owner Group Generic Emergency l
ProcedureGuidelines(EPG),Rev-4 The licensee Northeast Nuclear Energy Company (NNECO), provided information justifying the deviations in letters dated July 25, October 19 and December 27, 1989.
I Even though NNECO took many deviations from the EPG, only the major deviations l
are addressed in this evaluation. The major deviations are:
r (1)
IfthereisnoinjectionsystemoperatingandtheIsolationCondenser(10) is not available, emergency reactor pressure vessel (RPV) depressurization is not initiated until RPV level reaches 2/3 of the core height. The EPGs require initiation of Emergency RPV Depressurization when RPV level i
reachesthetopoftheactivefuel(TAF).
o l
(2) If one core spray pump is operating, primary containment flooding is performed only when RPV level reaches 1/2 of the core. The EPGs require primary containment flooding when RPV level reaches TAF.
(3)'Ifnoinjectionsystemisavailable,thereactorisnotdepressurizedto protect the containment even if the containment parameters exceeds the set limits. The EPGs require emergency RPV depressurization irrespective of systems availability.
2.0 EVALUATION i
2.1 Emeroency.RPV.Depressurtration.for.RPV. Level. Control and Primary t
containment noodtog Operator actions for different conditions required by the EPG, Rev-4 and Millstone Unit 1 E0Ps are given in Table 1.
RPV pressure is considered high if it is higher than any available low pressure injection system. As noted in the Table, when the reactor is at high pressure and if the RPV water level drops to TAF with only one pump running, both the EPG and Millstone Unit 1 E0Ps require emergency RPY depressurization to allow use of low pressure injection systems.
e l
y Emergency RPV depressurization is performed regardless of the operational status of the IC. When the RPV level reaches 2/3 core height without any core injection, both the EPG and Millstone Unit 1 E0P require steam cooling. Both the EPG and E0P use the IC as reactor pressure and temperature conditions permit.
For RPV low pressure conditions, operator actions in Millstone Unit 1 mainly depend on Core Spray pump availability. The RPV level is allowed to decrease to 1/2 core height with at least one core spray injecting. When the RPV level reaches 1/2 core height, RPV is depressurized in anticipation of containment flooding.
In the EPG, when the level reaches TAF, emergency RPY depressurization is performed, irrespective of core spray running in anticipation of the need for the containment flooding. At reactor pressures below about 100 psig IC is no longer effective and hence the reactor is depressurized in anticipation of primary containment flooding. This recognizes that all efforts to maintain the RPV level have failed and submergence of the core through the primary containment flooding is necessary as a last resort.
In the Millstone Unit 1 E0P, primary containment flooding is delayed if one Core Spray pump is running. Primary enntainment flooding is performed only under the following three conditions:
(1) RPV level cannot be maintained above 1/2 core height (2) only one Core Spray pump is injecting imo the vessel and (3)
RPV is depressurized.
If both Core Spray pumps are inoperable, containment ficoding is initiated at TAF.
If one Core Spray pump is operating and it cannot maintain level, it is very likely there is a "large break" and primary containment flooding will be required to assure core cooling. Waiting until core level reaches the mid 1
plane may not provide adequate time.
The delayed primary containment flooding during one Core Spray pump operation is a significant deviation from the EPG, where flooding is initiated if RPV water level cannot be restored and maintained above TAF. The impact of the delayed containment flooding on total risk to the plant needs to be evaluated.
The licensee in their submittals, did not address the impact of either the delayed or elimination of containment flooding at TAF on total risk to the plant. The licensee needs to submit additional analyses to justify that there is no significant increase in risk to the plant due to these deviations.
2.2 Emergency Depressurization.for. containment-Control
(
The EPG requires Emergency RPV depressurization if the containment parameters
/
exceeds the set limits. The safe limits are set to protect the containment and the equipment necessary for safe shutdown. EmergencyDepressurization(DP) is required due to one or more of the following reasons:
(1)Establishor maintainadequatecorecooling;or(2)Terminateorminimizethedischargeof reactor coolant from unisolable primary system breaks; or (3) Reduce the energy within the RPV before reaching plant conditions for which the pressure suppression system may not be able to safely accommodate an SRV opening or a loss of coolant accident; or (4) Minimize radioactivity release from the RPV to the primary containment and secondary cor.tainment, or to areas external to the primary containnent and secondary containment.
n
<e-
1 3
In the EPG, DP is performed irrespective of the core injection systems availability. The assumption is that once the RPV is depressurized, it is in a safer condition, taking advantage of the pressure suppression system before it exceeds the safe limits.
But in Millstone Unit 1 E0Ps, when containment parameters exceed the safe limit. DP is performed only if a core-injection system is available.
If no core injection systems are available and IC is running the Millstone Unit 1 E0Ps require no action to depressurize the RPV when a containment parameter exceeds a safe 11mit. However, if the core water level has decreased to 2/3 of the core height and the IC is not running, steam cooling is done by opening the SRVs.
According to EPG guidance, all the limits used in the EPG should be based on "best estimate" analyses and not " conservative analyses." Therefore if a containment parameter exceeds the limit, the situation is perceived to be grave and future actions requiring use of the suppression pool may be required. The EPG philosophy is to take necessary actions to protect the availability of the suppression pool for future operator use.
l In Millstone Unit 1 E0Ps, Emergency RPV Depresst.rization for containment control depends upon the availability of injection systems. This restriction can take the containnent to a degraded condition and it may not be available for its safety function. The operator may lose the option of using the containment sitould it be needed for future recovery actions. The EPG requires emergency RPV depressurization irrespective of the availability of systems if the containment limits are exceeded. This assures containment availability throughout the sequence of events. The licensee's approach of putting conditions or restrictions for keeping the containment available for its safety function is not acceptable.
Containrent availability is critical to minimize the radioactivity release to outside environment. The BWR Owners Group and the staff position is conservative. NNEC0's philosophy of depending only on the IC for all eventualities is inconsistent with the EPG. We require additional information about the efficiency of IC during low reactor pressure conditions. We require 1
more clarifications and explanations from the licensee to justify its deviation from the approach approved by the staff in the EPGs.
3.0 CONCLUSION
The delayed containment flooding during one Core Spray pump operation is a s
significant deviation from the EPG and the impact of the delayed containment
/
flooding on total risk to the plant needs to be evaluated.
Emergency RPV depressurization for containment control is performed only if one injection system is available.
If no injection system is available, j
4
. emergency RPV depressurization for containment control is performed only when the RPV level reaches 2/3 core height.
It seer.s that the Millstone Unit 1 E0Ps give core protection precedence over containment protection during these scenerios. Since the Millstone Unit I containment control method may result in an ineffective containment to support possible future operator actions, the actions are considered to be a significant deviation.
Principal Contributor:
G. Thomas Dated: February 15, 1990 4
)
~
TAJLE 1 COMPARISON BETWEEN.EPG..REV-4.AWD. MILLSTONE-UNIT 1 t-
ITIONS OPERATOR ACTIONS Rx PR b Level No: of IC EPG MILLSTONE-1 SYSTEM OP:
HIGH TAF 1
Y 2/3 0
Y 2/3 0
N SC SC LOW TAF No Core Spray N*
DEP,CF DEP,CF TAF Core Spray N*
DEP,CF 2/3 Core Spray N*
DEP,CF 1/2 Core Spray N*
DEP,CF DEP CF Y - YES, N - NO CF Containmer.t Flood i
TAF Top of the Active Fuel DEP Emergency RPV Depressurization
.IC Isolation Condenser SC Steam Cooling 2/3 - 2/3 of the Core Height (Approx:)
1/2 of the Core Height (Approx:)
1/2 l
i
- At Low Reactor Pressure Conditions, IC is assumed to be not functional