ML20137E494
| ML20137E494 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 11/22/1985 |
| From: | Brey H PUBLIC SERVICE CO. OF COLORADO |
| To: | Butcher E Office of Nuclear Reactor Regulation |
| References | |
| P-85442, TAC-52634, NUDOCS 8511270265 | |
| Download: ML20137E494 (13) | |
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2420 W. 26th Avenue, Suite 1000, Denver, Colorado 80211 November 22, 1985 Fort St. Vrain Unit No. 1 P-85442 Director of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention: Mr. E.J. Butcher, Jr., Acting Chief Operating Reactors Branch No. 3 Docket No. 50-267
SUBJECT:
Revised Draft of LC0 4.1.9, Core Region Tempe*ature Rise (1) PSC Letter, Brey(P-85372)
REFERENCE:
to Butcher, dated 10/17/85, (2) PSC Letter, Lee to Collins, dated 12/15/83, (P-83403)
(3) PSC Letter, Gahm to Johnson, dated 8/14/84, (P-84223)
(4) PSC Letter, Brey to Johnson, dated 5/20/85 (P-85159)
Dear Mr. Butcher:
This letter is to submit a Draft revision of Fort St. Vrain Technical Specification LC0 4.1.9, Minimum Helium Flow / Core Region Temperature Rise, to tb NRC for review as discussed in Reference 1. This Draft Specification (Attachment 1), has been prepared based on the considerations described in Attachment 2.
This proposed specification revision has been the subject of numerous analyses, documents, and discussions between PSC,
- NRC, Oak Ridge National Laboratory, and GA Technologies since the initial submittal of a Technical Specification amendment in Reference 2.
The issues that affect this specification have been identified in References 3 and 4, and are discussed in Attachment 2 to this letter. The flow requirements contained in the Draft Specification are conservative, as confirmed by the calculations discussed in item 1 of Attachment 2.
Upon resolution of any NRC g
w2nast nagg7 U
P
.- comments regarding the croposed draft, PSC will submit a formal Technical Specification amendment request.
If you have any questions or comments, please contact Mr. M. H.
Holmes at (303) 480-6960.
H. L. Brey, Manager Nuclear Licensing and Fuels Division Attachments HLB /DJN/ paw
J
+-
Page 1 of 8 ATTACHMENT 1 DMR
-NOV22INMi REACTOR CORE AND REACTIVITY CONTROL LCO' 4.1.9 CORE INLET ORIFICE-VALVES / MINIMUM HELIUM FLOW and CORE REGION-LIMITING CONDITION FOR OPERATION The total reactor helium coolant flow or the helium coolant temperature rise for all core regions shall be maintained within the limits given in Table 4.1.9-1.
APPLICABILITYi Power levels below 25?;,
including shutdown with decay heat.*
ACTION:
a.
With any of the above limits exceeded, either:
' 1.
Increase the - region helium coolant flow or correct the out-of-limit condition, within 15 minutes, or 2.
Be in at least REACTOR SHUT 00WN within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> with the inlet orifice valves adjusted for equal region coolant flows within the following-8 hours.
SURVEILLANCE REQUIREMENTS The total reactor coolant flow or the helium coolant temperature rise through all core regions shall be determined to be within the above limits at least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
- With the calculated bulk core temperature greater than 760 degrees F.
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i Page 2 of 8 DRAprr.
Table 4.1.9-1 N041oo1985 l REGION ORIFICE. l REACTOR PRESSURE l LIMITING CONDITION FOR
.l l_
' POSITION l
HELIUM DENSITY l OPERATION 1.
I i
l-I l.All regions set l Greater than 50 l The total core helium coolant l l for equal.regioni psia with I flow shall be greater than or l l coolant flow l helium density
- l equal to the minimum' l
l-EXCEPT l greater than l allowable value shown on l
- l Up to 5 regions l 60*;.
l Figure 4.1.9-1.
l l may have their -l l
l l orifices furtherl l
.l l open.
l l
l l
l l
l l As above.
l Greater than 50 l The total core helium coolant l l
l psia with helium l flow shall be greater than or l l-l density
- less l equal to the minimum l
l' I than or equal to l allowable value shown on l
- l l 60*;.
l Figure 4.1.9-2.
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l l
l l All regions set l Less than or l The helium coolant temperature l l for equal-region l equal to-50 psia.l rise ** through any core regioni l coolant flow.
l l shall not exceed 600 degrees l
- l l
I F.
l l
l l
l l Orifice valves l Greater than l The helium coolant temperaturel l at'any position 1 50 psia.
l rise ** through any core region l l (Adjusting for l l shall not exceed the limit l
l equal region l
l shown in Figure 4.1.9-3.
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- 1. outlet tempera-l l
l l ture).
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l Orifice valves-l Less than or l The helium coolant temperature l l at-any position l equal to 50 psia.l. rise ** through any core regioni l (Adjusting for l
-l shall not exceed 350 degrees l
1 l equal region l
l F.
l l outlet tempera-l l
l s
l ture).
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l l
l l
l Percent helium density equals:
0.373 x Reactor Pressure (psia)
).
(Circulatorinlettemperature(degreesFTplus460)x0.00213 Helium coolant temperature rise equals INDIVIDUAL REFUELING REGION OUTLET TEMPERATURE minus core average inlet temperature.
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HELIUM' DENSITY. EQUALS'107.5 PERCENT 30 estIFICE SETTiteCS t0Uet POSITIoses Tsiiiii: ortT
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y 5 H CALCULATED PERCENT RATED THERMAL POWER m
(STEADY STATE - PRIMARY SIDE HEAT BALANCE)
FIGURE 4.1.9-1 MINIMUM ALLOWABLE PRIMARY COOLANT FLOW
G e
e HEtllM DENSITY EQUALS 60 PERCENT 0.3-ee n ce u m ans C
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5-10 15 20 25 CALCULATEDPIRCENTRATEDTHERMALPOWER (STEADY STATE - PRIMARY SIDE HEAT BALANCE)
FIGURE 4.1.9-3 MINIMUM ALLOWABLE PRIMARY COOLANT FLOW
800 Drifice Settings R
/
Eny Position E
G (Adjusting for I
equal region outlet temperature) 0 600--
H T
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4_
R I
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200--
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CALCULATED PERCENT RATED THEMIAL POWER (STEADY STATE - PRIMARY SIDE HEAT.8ALANCE)
FIGURE 4.1.9-3 MINIMLM ALLOWABLE REGION TEMPERATURES RISE (*F) i
Page 6 of 8 DRAFT BASIS FOR SPECIFICATION LCO 4.1.9 NOV 2 919%
The minimum reactor helium coolant flow or the maximum core region helium coolant temperature rise as a function of calculated reactor thermal power (including power from decay heat) have been specified to prevent very low helium coolant flow rates through any coolant channel.
Very low helium coolant flow rates may result in laminar flow conditions with resultant high friction factors, low heat transfer film coefficients, and potential for possible local helium flow stagnation or reverse flow, which could result in excessive fuel temperatures.
This Specification addresses minimum flow requirements for all coolant channels.
Since low coolant flows exist at lower reactor
- powers, its applicability is limited to approximately 25'4 RATED THERMAL POWER.
Since thermal power is continuously generated by decay heat even after the reactor is
- shutdown, the flow requirements are also applicable in the REACTOR SHUT 00WN mode.
In addition to this Specification, fuel integrity is ensured for power levels from 0 to 100's by limiting the INDIVIOUAL REFUELING REGION OUTLET TEMPERATURES to values given in Specification 4.1.7.
The calculated bulk core temperature is the calculated average temperature of the core, including graphite and fuel but not the reflector, that occurs following a loss of all forced circulation of primary coolant flow.
The calculation assumes that all decay heat is retained in the core with no heat transfer to the reflector, PCRV internals or primary coolant.
If the decay heat is sufficiently low, with all primary coolant flow terminated, the calculated bulk core temperature will not exceed 760 degrees F, this specification is not applicable.
Below this temperature, there is no damage to fuel or PCRV internal components.
The limits have been developed based upon a number of conservative assumptions.
For the limits in Figures 4.1.9-1 and 4.1.0-3, it was assumed that the primary system was pressurized to full inventory (107.5 percent of design helium density was used in the analysis).
At lower densities higher region temperature rises and lower core coolant flow are acceptable.
Since startup operations can proceed with lower helium densities, after the reactor has been pressurized to greater than 100 psia, which corresponds to about 30 percent helium inventory at 200 degrees F, flow requirements were calculated for 60'4 helium density and are given in Figure 4.1.9-2.
Percent helium density equals:
(Circulator inlet temjorature [deg7e(psia)es F) plus 86) x QT662 D 0.373 x Reactor Pressure
Page 7 of 8 DRAFT NOV 2 21985 The core inlet helium temperature used in the analysis cover the range of 100-400 degrees F between 0 and 5*. RATED THERMAL POWER and 100-700 degrees F between 5 and 25*.
RATED THERMAL POWER.
These are reasonable assumptions for low power operation.
In the analysis to determine the limits, the effects of heat conduction between columns in a region, or between regions, were conservatively neglected.
Envelope values of RPF/ Intra Region peaking Factors (3.0/1.25 and 1.6/1.61) were used to anticipate worst case conditions considering all future fuel cycles.
Consistently conservative nominal values and uncertainties were used for bypass flows and measured parameters throughout the analysis.
For the condition with orifice valves at any position, the allowable region delta T is based upon a region power density (P-reg /P-core) equal to 0.4.
For regions with higher power densities, higher region delta T's are acceptable.
Besides the minimum flow requirement curves with the orifices set for equal region flows in Figures 4.1.9-1 and 4.1.9-2, flow requirements are provided with a number of orifice valves positioned further open.
These curves allow for a minimum number of orifices stuck open as well as assisting in the transition between equal region flows and equal region outlet temperatures.
By monitoring the total reactor coolant flow when the orifices are adjusted for equal region coolant flows, minimum flow through each region at the appropriate power can be assured. When the orifice valves are adjusted to different positions, minimum coolant flows can be assured for each region by monitoring the helium coolant temperature rise in that region.
For depressurized operations, limits are also specified to prevent very low helium coolant flow rates through any coolant channel.
These limits have been established based upon a 50 psia reactor pressure.
To ensure that flow stagnation in a fuel column or region does not persist, an action time of only 15 minutes is allowed to correct the out of limit condition.
The requirement to be in REACTOR SHUTOOWN within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> with the orifices set for equal flows in an additional 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> is realistic because it takes from 4 - 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> to set the orifice valves from equal temperatures to equal region flows.
This is considered acceptable since there is sufficient primary coolant flow from the circulators which are driven by steam generated from residual heat.in the system following REACTOR $ HUT 00WN.
Page 8 of 8 DRAFT NOV29 #6 In performance of the surveillance, the total reactor helium coolant flow is determined by calculation based on measured circulator inlet nozzle low range delta P,
temperature and pressure.
This is consistent with the method to determine the required flow in the analysis.
Procedures require that the flow rate be monitored whenever the power level is being changed to ensure that the requirements of this Specification are satisfied, but the surveillance is required once per shif t (12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />) and is consistent with other Specifications.
ATTACHMENT 2 The attached draft of Technical Specification LC0 4.1.9 is based upon the following considerations and decisions:
1.
GA Technologies Calculated Data is Used as the Basis.
Benchmark calculations by PSC Nuclear Fuels Analysis Depeartment, using Oak Ridge National Laboratory (ORNL) nuclear codes, has confirmed the methodology and results when conductivity between fuel columns is ignored.
In addition, when performing the (benchmark) calculations using the ORECA computer code (ORNL), apparent anomalies in intra-region flow calculations were observed for the case when intra-region conduction is included. Because of these anomalies and the l
fact that including conductivity would only reduce the coolant flow requirements by about Ife at the 1*6 'ower level, conductivity effects between fuel columns has w.. ignored.
Previous apparent differences between GA Technologies and ORNL calculated minimum flow requirements has been virtually eliminated when the same assumptions are considered.
This has been confirmed by (benchmark) calculations.
- 2. Orificing Strategy The current orificing strategy of starting up with the orifice valves adjusted for equal region coolant flows is retained.
Consideration was given to starting up with the orifice valves adjusted for equal region temperature rise based on calculated RPF's, but considering the uncertainty associated with the calculated data, the changes thAt occur with core burnup, and the potential error in the initial valve settings, it was decided that the small reduction in flow requirements did not warrent this strategy. A detailed discussion regarding this alternate orificing strategy is given in item 5 of attachment 1 to Reference 3.
3.
Startup with Some Orifices Further Open In addition to the minimum requirements specified for equal regions flow, curves have been provided to allow for starting with up to 5 orifice valves further open.
This will allow for startup with some orifice valves stuck, but of more importance, this will allow for additional coolant flow to be provided to regions with a high RPF.
This will assist in the transition between equal region flows (Figures 4.1.9-1 and 4.1.9-2) and equal region outlet gas temperatures (Figure 4.1.9-3).
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- 4 '.
- Calculated Flow (Measurement Uncertainties)
The calculated. minimum coolant. flow or the allowable core region temperature rise has been determined consistent with the measurement uncertainties in core power and flow. That is,.an -allowance has been included for the.. maximum uncertainty whether' it'. is determined by instrument input to
.the-data logger or control room indicators for temperature and primary coolant flow.
A discussion of the method and instruments ' for determining the coolant flow is given in Reference 3.
S.
Calculated Thermal Power (Including Decay Heat)
.The calculated thermal power, one parameter for the minimum flow curves, is based on a primary side heat balance calculation. This is the'same primary side heat-balance used to calibrate the linear channels during power operation below
-25*4 power.
This calculation can be obtained from the data logger or can be'done using calculated core coolant flow and the average core' coolant temperature rise.
In this way, the thermal power can also be calculated for the decay heat generated during REACTOR SHUTDOWN.
6.
Flow Requirements During Transients Some analysis has been.done to evaluate the flow requirements during flow transients.
Consideration has been.given to increasing minimum flow requirements to' allow a longer corrective action time during a reduced flow transient condition.. However, this Specification does not include an allowance for this consideration.
7.
Intra Region. Reverse ' Flow No allowance is made for reverse flow in some of the columns.
The resulting reduction in required flow would be small and
.does not warrant the additional analysis to support it.
8.
Evaluation of Flow Capabilties Although tests to determine primary coolant flow capabilties during low power using various circulator motive forces has not been done, an engineering evaulation has indicated that there is sufficient auxiliary steam to complement the nuclear
-steam generated to assure the minimum flow requirements of-this specification can be satisfied.
p-i.- !
9.
Flow Requirements With Decay Heat Only i
The Specification allows for primary coolant flow termination when the calculated bulk core temperature with no flow is less than 760 degrees F during the interval of termination.
This condition can exist after an extended REACTOR ShuTCC'n:,
when the decay heat level is low.
.A consideration that is still being evaluated involves operation when decay heat is the only heat source.
In this condition, the heat source is more uniformly distributed than during operation when the power distribution is dominated by the control rod configuration and the burnup within each region.
For the more uniform distributed heat source, lower primary coolant flow requirements are acceptable.
This Draft Specification has no special provisions for this case, t
I L