ML20127G669
| ML20127G669 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 10/18/1973 |
| From: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Mayer L NORTHERN STATES POWER CO. |
| Shared Package | |
| ML20127G674 | List: |
| References | |
| NUDOCS 9211170404 | |
| Download: ML20127G669 (3) | |
Text
_ _ _ _
fl f
' o\\
1 007 1 8 1973 Docket No. 50-263 Northern States Power Company ATIN: Mr. L. o. Mayer, nareetor of Nuclear Support Services 414 Nicollet Man Mir:neapolis, Minnesota 55401 License No. DPR-22 Gentlemen:
Approval of EOC-2 Operation We have reviewed your request dated October 10, 1973, to remove the 1200 MWD /STU control rod inventory restriction which has resulted in reduced electric power output from the Monticello Nuclear Power Plant.
Based on your revised calculations using the increased safety valve set points (1240 psig) approved by our letter dated October 2,1973, and 0.4-second relief valve response times based ou modifications to the relief valves during the September--28, 1973, Monticano plant shutdowg and response times based on GE test measurements, you have determined that normal reactor operation can continue at rated power level or less to a 2680 MWD /T fuel exposure threshold in Cycle 2.
As shown in Figure 2 of your submittal, further withdrawal of control rods must be prohibited at that exposure threshold until power level has decreased to 91% or less with the fixed control rod inventory for 2680 MWD /T at rated power. Reactor operation may continue thereafter, according to your calculations, at a anzimum power level of 91% by-continuing to withdraw control rods until all rods are completely withdrawn.
We have reviewed your analysis and the revised EOC-2, C-2, Scram Reac-tivity Curve as shown in Figure 1 of your submittal and have concluded that the changes in calculational assumptions should be identified and
~
justified, e.g., the combination of relief / safety and saiety valves assumed to open, the pressure set' points, and pump conditions.
The design and operational conservatism factors (DCF-and OCP) snould be quantified and justified. The basis for the Generic 72 B curve improved exposure threshold and the shift from C1 to C2 curve should be provided-as well as the measures to be taken by NSP to assure that scram reac-tivity effects considering actual operating history fall within the C2 curve. This supportive information should be submitted to the Directorate of Licensing prior to reaching the 2680 MWD /T esposure threshold where your August 1973 calculations result in a scram reac-tivity curve equivalent to the Generic 72 B scram reactivity curve.
9211170404 731018-PDR ADOCK 05000263 P
OCI i #
~
Northern States Power Company.
However, we have concluded that in the interim period, as shown in Table 2 of your submittal, (1) the margin between peak transient pressure following a turbine trip without stesa bypass and the safety valve set point of 1240 psig will be greater than the CE design margin of 25 psi and (2) the 1375 psig design (code) overpressure limit will not be exceeded.
On this basis, we agree that a turbine trip without steam bypass will not cause primary coolant ateam to be released into the containment drywell and the worst pressure transients (following simultaneous closure of all four MSIVs with delayed scram) will not damage the primary coolant boundary.
Ifjafter attaining the Generic 72 B Curve Reactivity Scram Shape at 100% power level or equivalent fuel depletion in Monticello Cycle 2 core, the control rod inventory is maintained (i.e., no further with-drawal of control rods) until power level decreases to 91::, we further agree that control rod withdrawal can be resumed v1th maximum power level limited to 91% for the remaindet of Cycle 2 operation (i.e.,
control rods are completely withdrawn) provided the additional infor-mation you are to submit is supportive.
j On this basis, we have concluded that reactor operation to the end of fuel Cycle 2 does not present a significant hazards consideration and there la reasonable assurance that the health and safety of the public will not be endangered by operation of the reactor in the manner you have described.
i i
Accordingly, the 1200 MWD /STU fixed control rod inventory rastriction l
for cperation of the Monticello Nuclear Power Plant is hereby removed I
and you are authorized to resume reactor operation at conditions up l
to and including rated power level until the " Generic 72" scram reac-i civity curve "B" is achieved (at 2680 MWD /T according to your cal-j' __
culations) at which time the control rod inventory will be fixed until i
l l
l I
l
---n
---_w.-w--._
. - - - ~ ~ ~
-..,..n
- =.. -
e--s e,
e s
a OCT 181973 Northern States Power Company
-3 reactor power level has dropped to 91%. At this time, control rods may be withdrawn until all rods are completely withdrawn but the maw =um reactor power level must remain below 91%.
Our Safety Evaluation is included for your information.
Sincerely, oriaal siq=ed br D. J. skoeou Donald J. Skovholt Assistant Director for Operating Reactors Directorate of Licensing
Enclosure:
Safety Evaluation Distribution d cket File cc w/ enclosure AEC PDR 1
Donald E. Nelson. Esquire Local PDR VP and GC RP Reading Northern States Power Company Branch Reading JRBuchanan, ORNL Gerald Charnoff DJSkovholt, L:0R Shaw. Pittman. Potts, Trowbridge & Hadden TJCarter, L:0R ACRS (16)
Howard J. Vogel, Esquire R0 (3)
Knittle & Vogel OGC DLZiemann, L:0RB #2 l
Steve Gadler, P. E.
JJShea, L:0RB #2 RMDiggs, L:0RB #2
(
Harriett Lansing, Esquire MJinks, DR.\\ (4)
Assistant City Attorney 4
City of St. Paul Kan Dzugan Minnesota Pollution Control Agency Warren R. I4woon, M. D.
Secretary & Executive Officer State Department of Health Environmental Library of Minnesota
..L;0RB.,f/&,,,.,.].. L:0.RB #2 L:0RB /
L: 0R,,a, ]...
L:R omer >
X740 M 4
.dy
'd
),
L
.JJ S he a.; sj h b..m...RMDiggs.f DLZie nn DJSko olt VS1 sunnwe >
Form AEC-518 (Rev.9-53) AECM 0240 I*o.19/6/...R.
.10./jkl3......... 10/gD.3......
om >.10/.MD.3..
....10//.fD3._..
i
- 4 a-to-s t ees-i
.4 pets i
e r-wn r
-w'
+-