ML20096H196
| ML20096H196 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 05/19/1992 |
| From: | PUBLIC SERVICE CO. OF COLORADO |
| To: | |
| Shared Package | |
| ML20096H192 | List: |
| References | |
| P-92196, NUDOCS 9205270131 | |
| Download: ML20096H196 (12) | |
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ATI'ACHMENT 1 TO P-92196 I
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9205270131 920519 PDR ADDCK 05000267 P
LIST OF PROPOSED CHANGES SECTION PROPOSED CH ANGE 4.2.15 Delete this Specification in its entirety, l.:
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Fort St. Vrain #1 Technical Specif.Leations Amendment No.
Page 4.2-17 top casing.
In this casa, the local temperature in the concrete would be less than 250'F, an allowable and acceptable concrete temperature.
(FSAR Section 5.4.5.3).
Specification LCO 4.2.15 - PCPV Coolino Water System Temperatures, Limitino conditions fer Operation l
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Fort St. Vrain #1 Technical Specifications Amendment No.
Page 4.2-18 l
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Fort St. Vrain #1 Technical Specifications Amendment No.
Pago 4.2-19 l
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4 Fort St. Vrain #1 Technical Specifications Amendment No.
Page 4.2-19a DELETE THIS SPECIFICATICH IN 2TF ENTIRETY l
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safety Analysis for_ Deletion of specification LCO 4.2.15 Backetround Specification LCO 4. 2.17, "PCRV Cooling Water System Temperatures, Limiting Conditions for Operation",
specifies allowable temperatures associatec with the PCRV and the PCRV cooling water.,
PSC has submitted a prcposed amendmen; to the FSV Facility License and Technical Specifications (PSC letter, Crawford to Weiss, dated March 19, 1992, P-92115) which would delete LCO 4.2.15.
The basis for its deletion is that once the fuel elements are permanently removed from the PCRV, PCRV temperatures no longer need to be controlled by-the Te chnical Specifications since the PCRV is no longer relied upon to provide the primary coolant pressure boundary and contain fission products which could potentially be released into the primary coolant from the active core.
This analysis demonstraten that the early implementation of deletion of LCO 4.2.15, now that all fuel elements have been permanently _ removed from the PCRV, does not adversely af fect p'2blic health and safety.
As discussed in the basis of LCO 4.2.15 and in the FSAR, the PCRV temperature limits provided assurance of the following:
1)
The maximum PCRV liner cooling water outlet temperature limit is sufficiently low so that concrete temperature between cooling tubes will not exceed 150*
F.
2)
By maintaining external concrete temperature, averaged over 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, within 50* F of the PCRV liner cooling water outlet temperature (representative of liner temperature), concrete stresses resulting from the temperature gradient across the concrete will be within allowables.
3)
The weekly average outlet temperature of the PCRV liner cooling water system is nct allowed to vary by mcre than 14*
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F per week. This assures that significant changes in the bulk concrete temperature occur slowly.
4)
The 85* -F minimum temperature requirement assures that the temperature of the active core will not decrease below 80* F, which was the core temper."ure assumed in the core shutdown margin assessments
. (3 O/SR 3/4.1.4 and 3 / 4.1. 6 )
for determining the reactivity contribution due to the fuel's negative temperature coefficient of reactivity.
5)
In order to prevent possible brittle fracture of the carbon steel liner, the temperature of the PCRV liner is maintained above the fracture trancition elastic (FTE) temperature, which j
is approximately equal to the nil ductility transition (NDT) temperature plus 60* F. __
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It has been necessary to periodically provide t, team from aa auxiliary boiler to heating coils in PCR/ liner cooling water surge
-tanks to meet the minimum average cooling water temperature requirements.
Once LCO 4.2.15 is deleted, PSC will isolate the supply of water to tne PCRV liner cooling tubes (including the core i
support floor cooling tubes) and will no longer provide steam to heat water in the surge tanks.
With cooling water flow to the PCRV liner cooling tubes isolated, the PCRV bulk tesaperature will
-gradually equilibrate with the Reactor Building ambient temperature. The safety analysis which follows reviews the effects of no PCRV liner cooling on PCRV structural integrity, addressing concerns discussed in the above paragraphs.
safety halvsis As described in Technical Specification Design Feature DF 6.2.1, the PCRV functioned as the primary coolant pressure boundary, while helium served to cool the ativc core.
The PCRV provided the secondary containment boundary of the iarge quantity of fission products in the fuel particles of the core, with the fuel particle coatings providing the primary boundary for fission product containment.
The PCRV provided defense-in-depth protection since it was designed to retain primary coolant, and fission products in the primary coolant, in the postulated event of fuel particle coating failure under extreine conditions of primary coolant temperature and pressure resulting from accident scenarios.
With all the fuel elements permanently removed from the PCRV and the PCRV depressurized, the PCRV no longer performs this primary coolant and fission product containment safety function.
- Instead, it serven to store and contain activity generated during previous reactor operation, and shields personnel from radioactive internal components.
PSC intends to assure maintenance of the continued structural integrity of the PCRJ up to the time when dismantling of
'the PCRV begins, during decommissioning.
However, with all fuel elements removed fram the PCRV and the PCRV depressurized, the requirements of LCO 4.2 15 are no longer necessary to protect the i
hea'th and safety of the public, as justified in the following paragraphs.
Concrete _ begins to lose some of its structural strength at temperatures above approximately 200' F.
The. thermal barrier --nd the PCRV liner cooling system were designed to protect the-PCRV-and
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core support floor (CSF) liners and concrete from high primary coolant temperatures and to maintain the concrete adjacent to the liners.within its maximum allowable temperature of 150 F between tubes.
With-al?.~ fuel elements permanently removed from the PCRV, the core haat source no longer exists, and the threat of concrete damage from high internal temperatures is eliminated.
The specification requirement which limits the maximum PCRV liner cooling water temperatura is no longer required to protect the concrete from e.:cessive temperatures.
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I The PCRV liner cooling system served to cool the lim r and inner concrete surfaces during normal operation,- which prevented high
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internal temperatures and resulting high differential temperature through the concrete, minimizing thermal stresses.
With the reactor core heat source permanently removed from the PCRV, the potential for high dif ferential temperatures across the PCRV is greatly reduced.
~If all cooling water flow to the PCRV liner cooling tubes here isolated, the PCRV temperatures would eventually equilibrate with Reactor building temperatures, with no significant tamperature difference between the inner and outer concrete surfaces.
Rapid heating or cooling of the PCRV bulk concrete, f aster than 14 '
F per week, was not permitted since significant thermal stresses could arise during-the transition from one equilibrium temperature to another.
The PCRV liner cooling system tubes, which surround the PCRV and CSF liners, have the potential for causing rapid temperature transitions, if hot or cold water (relative to PCRV temperatures) is s m iled to this system.
This potential is removed with the PCRV liner cooling tubes isolated.
It is anticipated that the PCRV will gradually decrease to equilibrium temperatures lower than those at which it is presently maintained, with PCRV liner cooling water flow isolated.
Under steady _ state conditions at a 1over bulk concrete temperature, PCRV liner and concrete stresses will be somewhat reuuced due to thermal contraction of steel and concrete at the lower temperature.
Since these matr. rials are maintained in a state of net compression by the prestressing tendons, the thermal contraction will result in a slight _ relaxation of stresses.
Since all fuel elements have bean permanently removed from the PCRV, the concern with core reazivity increases caused by fuel temperature reduction is eliminated.
There is no longer the need for a minimum PCRV liner cooling water temperature limitation, from the standpoint of reactivity _and core shutdown margins.
I The erd-of-life FTE temperatures are calculated to be less than 15*
F for both the liner and weldment materials, at the most highly irradiated portion of the liner (top head).
It is not considered credible that the PCRV liner could reach these low temperatures.
4 Even if Reactor Building heating were lost in the winter, it is estimated to take weeks before the inside of the PCRV would be l
j reduced to low temperatures, due to the 9 ft. minimum thickness of i
the PCRV concrete.
The building heating system would be repaired before _the interior of the PCRV could decrease to extremely low temperatures approaching the FTE temperature.
Deletion of LCO 1.2.15 would not' increase the probability of brittle tracture of the PCRV liner.
l Based on the above discussions, PSC does not consider cracking of i.
the liner or concrete to be crerlible with deletion of LCO 4.2.15 and with no PCRV liner cooling water flow.
Even if it were hypothesized that the PCRV or CSF liner were to crack, this would not represent a - health or safety threat to either occupational l
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workers in the Reactor Building or to members of the general public since the PCRV would be-depressurized and there would be no driving force to cause the release of significant quantities of activity from the PCRV.
The PCRV concrete, maintained under consi cable compressive stresses,_would coatinue to shield personnel ><sm the activated components within the PCRV.
j Conc! lion Based on the above infor: nation, it is concluded that deletion of LCO 4.2.15 would not increase the probability or consequences of accidents or malfur. tions of equipment important to safety previously evaluated.n the FSAR.
The source terms of accidents involving the PCRV and aaalyzed in the FSAR are effectively removed with no fuel elements in the PCRV and with the PCRV depressurized to approximately atmospher t.c pressure.
The probability of failure of the PCRV is not increasud with deletion of LCO 4.2.15 requirements.; In fact, with the primary heat source (active core) removed from the PCRV, the probability of challenging the integrity of the liner or concrete is reduced.
Brittle fracture of the PCRV liner is not considered credible with no PCRV liner cooling, since this would require the top head liner to decrease to temperatures below 15 ' -
F.
Deletion of LCO 4.2.15 does not create the possibility of new-accidents or malfunctions not previously evaluated-in the FSAR.
Even in the event of postulated crac'<ing of the PCRV concrete and/or liner due to high stresses, which is not considered credible, release of significant quantities of activity from the PORV would not occur since the PCRV ill not be pressurized.
Since the absence of PCRV liner cool would not pose a threat to PCRV integrity, and lower PCEV tempe'._ cures could i
rot cause an increase in reactivity, there is no reduction - in safety margins identified in the basis of LCO 4.2.15.
Therefore, deletion of LCO 4.2.15 does not involve an unreviewed safety question.
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