ML20125D587
| ML20125D587 | |
| Person / Time | |
|---|---|
| Site: | 05000130 |
| Issue date: | 05/11/1966 |
| From: | Boyd R US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML20125A538 | List:
|
| References | |
| FOIA-85-54 NUDOCS 8506120411 | |
| Download: ML20125D587 (6) | |
Text
.
r,
. ].
(
(
f SAFETY EVALUATION BY THE RESEARCH 6: POWER REACTOR SAFETY BRANCH DIVISION OF REACTOR LICENSING i
IN THE MATTER'0F
/
NORTHERN STATES POWER COMPANY PATHFINDER ATCHIC POWER PIANT
)
'~
I DOCKET No. 50-130
)
PROPOSED CHANGE NO. 9 Introduction By application dated April 4,1%6, the Northern States Power Company (NSP) requested o change in the Technical Specifications of License No. DPR-11. The request would cllow a number of changes to the Pathfinder reactor facility which are discussed ccparately as Items (1) - (8) in the following evaluation. We have designated th:se requests Proposed Change No. 9.
Evaluation 3
(1) The Technical Specifications presently require that the total rate of reactor coolant flow increase limited by the udtterfly valves on the discharge side of the rceirculation pumps shall not exceed 455 spa /second, and that this rate shall cor-l
,rospond to a reactivity addition rate of less than 5 cents /second. Recent calculations cad measurements indicate that, at the specified rate of flow increase, the l
carresponding reactivity addition rates could exceed 5 cents /second for some condi-ticas of flow rate and power. For this reason NSP is requesting that the reactivity rate limit in Section 4.2.1.2 be deleted. The governing rate of reactivity addition would then be 12 cents /second specified in the second paragraph of Section 5.13 cuthorized by a subsequent section of this change and discussed under Item (5) of this evaluation.
S:ction 4.2.1.2 also specifies that reactivity addition by recirculation flow control ch511 not be continued for more than 10 seconds in any one 20 second interval. In modifying the valves to meet the flow increase limit discussed later, the valve ep:ning time was necessarily increased. Since the valves automatically open to the 45% position upon pump startup (their travel cannot be stopped unless the pump is turned off), NSP proposes to delete the time restriction of this section. This daletion would essentially make it possible to continuously add reactivity at the
~
maximum rate which NSP calculates to be 9.2 cents /second. In support of this change -
NSP has run a series of transients on its analog simulator. An analysis starting at i
tho worst case o'f power and flow and assuming that flow rate is continuously increased I
< k.
8506120411 850214 PDR FOIA PAY 85-54 PDR 8
---~--.----,,,_,,-,,__,,,,,ww,,,w.
.,,_-_m.
-,,,,,~--,,.-,,,_--_-,,,_n,,-
_,,,,--n.,.
. 't -
(
(
.n at twice the maximum possible rate up to 100% flow, resulted in no scram (trip points ware not reached), and temperature rises of 380F for bulk exit steam, and 100*F f:r the superheater fuel. In our opinion, these calculations are conservative and the results indicate that the request is acceptable from a safety standpoint.
(2) The maximum steam temperature is specified to be 750*F in the Techgical Specifications. However, the trip point is presently authorized at 775 F to allow
. far sufficient operating margin above the expected operating temperature of 7250F.
NSF is requesting that the maximum limit of 750*F specified in Section 5.6.1(b) be changed to 7750F to conform with the trip point allowed in the second table of S:ction 6.1.4.
Since NSP assumes a set point of 775*F in performing accident cualyses, we believe that the maximum steam temperature may be specified to be the cces as the trip set-point temperature as requested without' compromising operational cafety of the reactor.
(3) During the core shutdown margin demonstrations, Section 5.8.2 now requires that tha core remain suberitical after the most worthy rod is fully withdrawn, and a rod i
cr rod group of known worth greater than 0.003 k,gg is withdrawn. NSP sta.tes that tha worth of the rod group cannot always be known before it is withdrawn and is th:refore proposing a different procedure which allows a demonstration that the p:rtially withdrawn rod group is worth more then 0.003 k,gg after criticality is cchieved. We do not believe that this new procedure is significantly different from that now allowed with the possible exception that the worth of the rod group could c
However, under the old procedure a precise measurement of
.I b3lessthan0.003k,bilywithdrawnrodgroupbeforewithdrawingthemostworthy tha worth of the part red is difficult due to the reacitvity interaction effects between rods adjacent to tha most worthy rods while it is still in the core. The new procedure requires a more conservative approach to critical since some rods will be cocked before the worthy rod is removed.
In our opinion, the proposed procedure allows for a more prccise measurement of shutdown margin and is acceptable from a safety viewpoint.
(4) To add further automatic protection during the shutdown margin verification, discussed in Item (3) above, the applicant proposes to procedurally limit the range cwitch positions on the intermediate level channels 5 and 6 such that a scram will cecur if the power level exceeds 600 Kw.
This would serve as a backup to the source rcnge period protection and has the additional advantage of preventing excessive power peaking in either side of the core (near the fully withdrawn rod) since scram will not require coincident signals from each channel. The adequacy of a set point of 600 Kw in an accident case is discussed in Item (5) below. We believe.this chinge will further enhance safety and is therefore acceptable.
(5) The licensee states that the maximum reactivity insertion rate specified in Section 5.13 to be less than 5 :ents/second when the core k,ff is greater than
(
0.997 cannot be met under certain conditions. These conditions are:
(1) differential red worth measurements indicate that reactivity insertion may exceed 5 cents /second l
I i
- F p
i
. t-far some rods during a portion of their travel, (2) rate of recirculation flow increase could cause more rapid insertion rates as discussed in Item (1) above, cid (3) the shutdown margin verification procedures allowed by this change and diccussed in Item (3) above result in reactivity additions in excess of 5 cents /
ccc:nd due to depletion effects and altered procedures. Thus, NSP proposes that I
th3 reactivity insertion rate be limited to 12 cents /second for all conditions where th3 core k is above 0.997 except during the zero-power shutdown margin verifica-
)
.titawhere,Nelimitisrequestedtobe,approximately34 cents /second.
The staff believes that the time requirement in Section 5.13 which specifies that the reactivity insertion shall not last longer than 10 seconds in and 20 second inttrval can appropriately be deleted since it is more important for an operator to cbetrve the response of the nuclear instrumentation rather than time. Also the worst c:ro accident evaluations assume continuous reactivity addition to the maximus j
j cbecinable amount and the safety evaluation is made on.this basis, not on the cp:rators termination of reactivity addition after 10 seconds.
l In support of these proposed increases in rate of reactivity insertion,<the licensee has performed a number of calculations using its analog simulator. We have been l
inf:rmed that the most recent data measured at the facility have been used in these l
l l
sismlation studies. The evaluations assume scram takes place when any one of the cet points for a icram condition is exceeded since redundancy of instrumentation is provided for each of these conditions. The temperature of the core superheater section is the most critical during a power excursion due to assumed inadequate cooling of
- h3 superheater which is conservatively assumed to be stean-filled during all but i
th3 34 cents /second reactivity insertion accidents when the reactor will be at zero-power and the superheater dry. The applicant reports that the most serious accidents would occur for initial conditions between 20% and 100% of full power and accordingly i
cn:1ysed several different reactivity addition rates up to 25 cents /second starting from power levels in this range. Additional cases assuming the teactor was in the scrs-power condition and cold were run assuming ramp reactivity insertion rates up to 68 cents /second, which is twice the requested limit of 34 cents /second necessary during shutdown margin verification. Only level scram at 600 Kw (required by this ch:nge and discussed in Item (4)) was assumed, even though period scram protection is in ef fect in the three startup channels. In all cases it was found that maximum sup rheater temperatures were below the level at which damage could occur. NSP I
}
ciso reports that the burnout limits of Section 5.6.1(b) are not affected by this change.
On the basis of the evaluations reported and our review of the simulation technique, w3 believe the requested changes are acceptable and that safe operation of the fcsility will not be compromised.
(6) The licensee proposes to modify the pushb'utton which initiates operation of l.
tha emergency condenser to make it incapable of starting operation of the condenser en the basis that inadvertent operation could result in addition of cold water to th3 reactor. NSP has proposed to delete the reference to this pushbutton in S:ction 6.1.1 since operation of the cendenser can also be manually initiated through tha use of the manual reactor isolation scram pushbutton. Inadvertent use of the isolation button would not result in a reactivi'y ex-ursion since the reactor would
(
l
. J.
ceram prior to introduction of cold water from the condenser. Operation of the emergency condtaser can still be terminated by the modified pushbutton. We believe this change is acceptable and will in no way limit proper function of the emergency condenser.
(7)
Section 6.1.7 of the Technical Specifications now requires a rod runback upon locs of all three recirculation pumps. This makes it impossible to latch or unistch rods or perform shutdown margin verifications unless the breaker circuit is bypassed with a jumper. NSF proposes to install a key switch bypass to provide more stringent cdministrative control during manipulation of rods when pump operation is not required cr desired during certain test programs and core manipulations at sero-power. In ccr' opinion the bypass key switch can be installed and safely used as proposed.
(8)
NSF requests that Table 2 of Section 6.1.9.6, " Nuclear System Annunciator Points,"
b3 updated to reflect small modifications made to the annunciator system. We have reviewed the proposed new Table 2 and have concluded that the annunciators listed th rein are adequate to direct operators attention to abnormal conditions important to safe operation of the plant.
3 Technical Specifications In view of the foregoing, we believe that the Technical Specifications (Appendix A) l
.of License No. DPR-11 should be changed as follows:
i t
(1) Delete the last sentences from the first and third paragraphs of Section 4.2.1.2 which read:
"(This shall correrpond to a maximum reactivity addition rate of less than 5 cents /sec)," and i
" Reactivity addition by recirculation flow control shall not be 1
continued for more than 10 seconds in any one 20 second interval."
{
I (2)
Change the maximum steam temperature in the table of Section 5.6.1(b) from "7500F" to "775 F."
i (3) Delete the first sentence of the second paragraph of Section 5.8.2 and substitute the following:
"The core shutdown margin shell be verified by a demonstration that l
the reactor is suberitical with the superheater in its most reactive condition, the most. valuable reactivity-worth rod fully withdrawn, and other rods partially withdrawn. Innsediately, subsequent to the i
withdrawal of the most valuable reactivity-north rod, it shall be
-demonstrated that the rods partially withdrawn contribute 0.003 k,gg or more to the effective multiplication."
j I
k I
l
e-(
(4) Add the following to the last sentence of the second paragraph of Section 5.8.2:
... and with the range switch of c'hannels 5 and 6 set at positions such that scram level shall not exceed 600 Kw for the duration of the demonstration."
(5) Change the second paragraph of Section 5.13 to read:
"The maximan reactivity insertion rate when the k,gg of the core is greater than 0.997 shall be 12 cents /see except during the core shutdown margin verification of Section 5.8.2, when it shall be approximately 34 cents /sec."
(6) Delete the words "and operation of the emergency condenser." from the second paragraph of Section 6.1.1.
(7)
Change the wording in the first table of Section 6.1.7 to read:
" Condition Setpoint (1)
Loss of all three Breaker Operation (may be bypassed recirculation pumps through use of a key switch during rod latching and unistching and during verification of core Wbut-down margin)"
(8) Replace Table 2, " Nuclear System Annunciator Points" in Section 6.1.9.6 with an updated Table 2 (attached) dated 3/1/66.
Conclusion i
8: sed on our review, we have concluded that the changes previously discussed do not present significant hazards considerations not described or implicit in the Final Hazards Summary Report, and that there is reasonable assurance that the health cud safety of the public will not be endangered.
d ! pied by:
.. S. B:yd Roger S. Boyd, Chief Research & Power Reactor Safety Branch Division of Reactor Licensing Date:
MAY 1 1 EEo
(
s-(
~
3/1/66 TABLE 2 e
i NUCLEAR SYSTEM A?UUNCIATOR POINTS Superheater outlet t ;,erature - High Reactor feedwater temperature - Low Superheater outlet pressure - High l
Reactor ' pressure - High j
Turbine 102% overspeed - Tripped -
Turbine trip-stop valves - Tripped Reactor Control - Runback Reactor Control - Scram Nuclear instrumentation reactor period - Short Main steam isolation valve by-pass flow - Low Main steam isolation valve - Tripped - Closed Main s' an isolation valve - Loss of Power I
Super!.ater outlet temperature - Low Superheater outlet pressure - Low Main steam safety valves - Open l
Reactor rpcirculating pump motors bearing temperature - High Reactor recirculating pump motors - Overload Reactor recirculating pump motor temperatures - High Reactor recirculating discharge valves - Loss of Power Reactor water level - High Reactor water level - Low Reactor feedwater temperature - High Reactor recirculating water temperature - Low Reactor feedwater temperature control set point - Low Reactor building shield pool seals - Leaking Reactor building air lock doors - Open Reactor building pressure - High l
Reactor vent temperature - High Radiation - High, Isolation - Trip Reactor control rod drive motors - Overload Reactor control rod drive motors - Loss of Power Reactor control rod drive motors - Reverse Phase Reactor control rod drive seals leakage flow - High Main steam isolation valve interlock switch - Out-of-Position Nuclear instrumentation power range flux channels 7 & 8 - High Differential Nuclear ins'trumentation - Trouble Reactor pressure control pressure error - High - Low Nuclear instrumentation short period - Runback Trip Nuclear instrumentation channels, 5, 6, 7, & 8 - 2 of 4 Runback trip Reactor control loss of feedwater - Runback Trip Reactor control ejector exhaust high activity - Isolate - Scram Reactor control main steam dump valva - Low oil pressure Nuclear instrumentation channels 5, 6, 7, & 8 - Scram logic trip l
(
i 9