ML20137S009
| ML20137S009 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 02/07/1986 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20137S001 | List: |
| References | |
| NUDOCS 8602130547 | |
| Download: ML20137S009 (13) | |
Text
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Enclosura 1 ENCLOSURE
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SAFETY EVALUATION REPORT OF THE NOVEMBER ~30, 1985 DEADLINE FOR THE FORT ST. VRAIN NUCLEAR GENERATING STATION 1
CONFIRMATORY ACTIONS 7, 8, 13 AND 14 l
INTRODUCTION l
By letters dated September 25, 1985, and October 22, 1985, the Public Service CompanyofColorado(PSC)requestedthattheCommissiongrantanextension until March 31, 1986, for environmental qualification of electrical equipment at the Fort St. Vrain Nuclear Generating Station (FSV).
In a subsequent
. T, meeting with the NRC staff on November 18, 1985, the licensee agreed to modify.
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its position, and provided a revised request by letter dated November 22, 1985.
I The Commission met with the staff on November 19 to review the licensee's 4
request; at this meeting utility representatives responded to several Consission questions on equipment qualification and related matters.
l The Commission had reviewed in detail the licensee's submittals, the staff's analysis and reconenendation as set forth in SECY-85-370, and had considered all additional information provided at the November 19 meeting. Based on this review the Consnission found that the licensee had demnstrated exceptional l
circumstances warranting approval of its revised request. However, in accor-( ~,
_ dance with the staff's request, the licensee was required to provide an accept-i able confirmatory submittal with respect to the following items before plant operation would be approved.
CONFIRMATORY ACTIONS IN SUPPORT OF THE FORT ST. VRAIN 35 PERCENT POWER RESTRICTION DURING THE ENVIRONMENTAL QUALIFICATION SCHEDULE EXTENSION PERIOD i
f PSC will complete and document the following actions to confirm the accepta-j bility of a 35 percent power restriction during the Fort St. Vrain environ-mental qualification schedule extensior, period to May 31, 1986 PSC will submit 1
the results of these actions to the NRC staff for review and approval prior to resuming Fort St. Vrain plant operation at power levels up to the 35 percent power restriction.
P
f~
. 1.
Complete an evaluation which confirms that the prestressed concrete reactor vessel (PCRV) liner cooling system using firewater can be utilized to prevent significant damage to any of the fission product barriers, including fuel particle coatings, in the event of a high energy line break at power levels up to the 35 percent power restriction.
2.
Evaluate the leak tightness and structural integrity of the PCRV during the heatup which would occur following an extended loss of forced cir-i culation cooling resulting from a high energy line break from 35 percent of rated power. Consider tha cold reheat helium interspace leak, PCRV penetrations and seals, and other portions of the PCRV where leakage may be a concern. Actual PCRV leakage experience should be considered (e.g.,
the recent LER on the PCRV penetration cold reheat helium leak).
3.
Provide high energy line break temperature profiles for accidents from reactor power levels up to 35 percent demonstrating access to plant areas where operators are required to take the necessary manual actions by specified times.
Identify all assumptions made regarding operator response times to the high energy line break, Credit will be taken only for qualified systems. An evaluation will be made of the need for steam-line rupture detection isolation system for 35 percent power operation.
4.
Provide an evaluation of the estimated time and primary coolant tempera-ture beyond which the PCRV should net be depressurized during the remainder of a PCRV liner cooldown following a postulated high energy line break from the 35 percent power level.
5.
Provide an estimate of the maximum reactor power level at which it would be safe to perform a pressurized PCRV liner cooldown while protecting the integrity of the PCRV liner and liner cooling system, 6.
Submit a proposal for performing inservice inspections on seveal critical areas of the Fort St. Vrain's high energy piping to verify the current integrity of this piping prior to returning the plant to operation.
7.
Evaluate the need for actuating the Fort St. Vrain reserve shutdown system
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for postulated high energy line breaks from power levels up to 35 percent.
Determine the latest time by which manual actuation must be accomplished, I
if needed, and evaluate the feasibility of taking the required manual l
actions by this time..
1 1
8.
Confirm that procedures for taking the necessary operator actions in response to a high energy line break from 35 percent power will be in l
place prior to resuming Fort St. Vrain plant operation. Evaluate the i
need for any changes to the Fort St. Vrain Technical Specifications to accommodate Fort St. Vrain operation up to the 35 percent power level restriction, including the possible use of a pressurized PCRV liner cooldown in the event of a high energy line break.
9.
Document the extent of PCRV damage expected during a liner cooldown from 35 percent power following a high energy line break.
- 10. Evaluate the effect of a PCRV liner cooldown from the 35 percent power level on the previously analyzed PCRV hot spots.
- 11. Evaluate the impacts on the integrity of the PCRV liner cooling system of re-establishing liner cooling after prolonged periods of core heating without liner cooling or forced circulation cooling. Verify that the impacts of _re-establishing liner cooling follwing a costulated high energy line break from 35 percent power with i pressurized liner cooldown would be no worse than those for the depressrrized liner cooldown after e
30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br /> from full power previously evaluated in the Fort St. Vrain FSAR.
Compare the associated heat fluxes to the maximum acceptable heat flux to the PCRV liner cooling system assuming single loop operation.
- 12. If Fort St. Vrain operators will be required to take manual actions in environments whose temperatures exceed normal power plant operating temperatures to respond to high energy line breaks from 35 pertent power, provide the NRC with infonnation on the ability of operators to work in J
4, these higher temperature environments and the need for operators to utilize cold suits.
- 13. Provide a sunnary listing of which systems and their associatedlequipment items are considered qualified for 35 percent power operation and a con-firmation that no unqualified equipment items are needed.
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- 14. Submit an engineering evaluation that describes the systems and equipment which will be utilized to respond to high energy line break from 35 percent power operation.
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EVALUATION ThePlant,Electiical,InstrumentationandControlSystemsBranch,PhR-B,
-evaluated the Itcensee's responses to Confirmatory Actions 7, 8,13 and 14
' listed above. By letter dated December 10, 1985, the licensee provided responses to the confirmatory actions in support of 35 percent power restric-l tion during the EQ schedule extension period. Other Sefety Evaluation Reports Iover the other confirmatory actions.
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Confirmatory Action 7
- Evaluate the need for actuating the Fort St. Vrain reserve shutdown system for l~
postulatedhighenergylinebreaksfrompowerlevelsupto$5 percent. Deter'-
mine the latest time by which manual actuation must be accomplished, if needed, and evaluate the feasibility of taking the required manual actions by this time.
i PSC Evaluation
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Actuation of the Fort St. Vrain reserve shutdown system is required following aLOFC(lossofforcedcooling)at100percentpower. This inserti,on is I
necessary to provide negative reactivity insertion to counteract the large amounts of fission product poisons being driven out of the core due to fuel particle coating failure. For all of the cases analyzed in Evaluation 1 in the PSC December 10, 1985 submittal, the peak fuel temperatures are several hundred l
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_. _ _ _ _. _ _ _ _ - _ ~
s.,
degrees below the fuel temperature where fuel particle coatings exhibit significant failure. Thus, neither the pressurized nor the'depressurized situations require the reserve shutdown balls to be inserted.
However, in accordance with the defense in depth concept, the-procedures con-tain instructions to manually insert the reserve shutdown systems together with the manual initiation of depressurizatien and liner cooling with fire water.
i There are two factors which determine the time by which the reserve shutdown balls must be inserted. These two factors are:
1.
The time when the temperature of the control rod guide tubes exceed 2075 degrees Fahrenheit. Tests have been conducted on control rod tubes at this temperature and the results showed only minor deformation which posed no threat to the safety function of the guide tubes.
For the pressurized cases the control rod guide tubes never reach this temperature.
For the depressurized cases the reserve shutdown system will be inserted in the same time frame (12-15 hours) as initiation of depressurization and liner cooling. This is well before the control rod guide tube temperature reaches 2075 degrees Fahrenheit.
2.
The time when the top head cover and liner insulation fails, which could -
interfere with the insertion of the reserve shutdown balls. This time is conservatively assumed to be the time when the top heat cover plate reaches a temperature of 1500 degrees Fahrenheit. The top heat cover plate for the depressurized cases peaked at 1250 degrees Fahrenheit and thus without any possible failure.
For the worst pressurized situation, Case 3 in Evaluation 1, the top heat cover plate was calculated to reach a temperature of 1500 degrees Fahrenheit by 29.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. Therefore, for this pressurized case the reserve shutdown balls must be inserted prior to 29.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> into the event.
l (g.
Based on the staff review of the PSC evaluation, we find the licensee's response to Confirmatory Action 7 to be acceptable because neither the pres-surized nor the depressurized situations require the reserve shutdown balls to be inserted.
l Confirmatory Action 8 Confirm that procedures for taking the necessary operator actions in response to a high energy line break from 35 percent power will be in place prior to i
resuming Fort St. Vrain plant operation. Evaluate the need for any changes to the Fort St. Vrain operation up tc the 35 percent power level restriction, including a possible use of a pressurized PCRV liner cooldown in the event of a high energy line break.
PSC Evaluation Normal and abnormal operating procedures were in place to support decay heat removal with the liner cooling system, utilizing fire water as a cooling medium j
prior to the environmental issue. For purposes of providing a concis'e and explicit procedure to manually lineup the associated systems, parts of the System Operating Procedures and Safe Shutdown Cooling Under Higb y Degraded Conditions procedures were combined and issued as Operations Order No. 85-17.
The procedure contained in this Operations Order assumes that no AC power, DC power, instrument air supply, or instrumentation is available to assist in the system lineups and continued operation. Operations personnel, including licensed operators and Technical Advisors, have completed training on this mode of operation.
PSC has committed to change this procedure to accommodate the modifications to permit manual actuation of the circulator brake and seal system and to permit operator action to shutdown the electric feedwater pump and auxiliary boilers. These changes will be in place and personnel trained prior to plant restart to achieve the 35 percent power level. Also operations personnel will l
be trained in the use of cool suits and Scott Air-Paks.
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a
PSC stated that there is no need for any changes to the Fort St. Vrain Technical Specifications to accomodate plant operation at 35 percent power. Although the consequences of a pressurized PCRV liner cooldown with fire wa'ter have been analyzed, this was performed to demonstrate that, even in the unlikely event that personnel access is not possible within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, the plant could be safely i
shutdown using a pressurized cooldown with liner cooling following a high energy line break. The intent is to operate the plant at 35 percent power level in 6
accordance with the present Technical Specifications.
PSC stated that no Technical Specification changes for valve surveillances are necessary since all valve lineups are manual. operations. Technical Specifi-cation limiting conditions for operation and surveillance tests of fire water and circulating water makeup pumps assures that this equipment will be ready and operable. The two fire water pumps were surveillance tested in June, 1985 for their rated flow and discharge head.
Based upon the staff review of the PSC evaluation, we find the licensee's response to Confirmatory Action 8 to be acceptable because PSC has committed to procedural changes to permit manual actuation of the circulator brake and seal system and to shutdown the electric feedwater pump and auxiliary boilers and Technical Specification changes are not necessary to accommodate a 35 percent power level.
Confirmatory Action 13 Provide a sumary listing of which systems and their associated equipment items are considered qualified for 35 percent power operation and a confirmation that no unqualified equipment items are needed.
PSC Evaluation PSC stated that the following systems / equipment items are required for responding to a high energy line break at 35 percent power:
A.
Helium Circulator Brake and Seal System B.
PCRV Liner Cooling
A
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C.
Reserve Shutdown System D.
PCRV Depressurization Equipment E.
Fuel Storage Facility Cooling F.
Equipment to Mitigate Steam Production 4
Discussion A.
Helium Circulator Brake & Seal System 2
The primary coolant boundary isolation by this system can be accomplished manually without the need for electrical components.
B.
PCRV Liner Cooling
.The basis for taking credit for operation of this equipment is as follows:
1.
PSC does not expect that there would be.a loss of outside power coin-cident with a HELB. The reasons for this are as follows:
8 a.
'At 35 percent power Fort St. Vrain does not represent a large percentage of the total PSC grid.
b.
Fort St. Vrain has tripped several times in the past from power levels well above 35 percent without causing a loss of outside power.
c.
The Fort St. Vrain switchyard, in addition to interconnections with the PSC system, is also directly interconnected with an outside power system (Platte River Power Authority).
- 2..There are multiple circuits and power sources to the required electrical equipment as follows:
a.
With outside power available P4501, P4118 and P41185 can be powered via either the normal cables (some of which are in the turbine
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_g.
building HELB environment or via an ACM backfeed (cables are all in mild environments).
b.
If offsite power was lost, power can be supplied via the ACM Diesel Generator.
(Cables and other items are in mild environments).
If a HELB were to occur in the reactor building the emergency diesel generators (cables in turbine building) would be available to supply power via cables in a mild environment.
3.
P4501S is diesel driven and independent of offsite power.. Cables in the auto start circuitry are in the harsh environment. However, these cables cannot prevent local: manual start of this pump.
C.
Reserve Shutdown System This system may be actuated manually without the need for electrical components.
D.
PCRV Depressurization Equipment This equipment may be actuated manually without the need for electrical components.
E.
Fuel Storage Facility Cooling System Equipment This equipment may be actuated manually without the need for electrical components.
F.
Equipment To Mitigate Steam Production In order to generate a bounding set of temperature profiles, very conserva-tive assumptions were utilized in regards to termination of the high energy line break (HELB). That is, all valves regardless of location (reactor building.or turbine building) were assumed to fail open.
In reality, with
the HELB occurring in only one building or the other, many circuits (even though unqualified at this time) that are in the building that did i
not have the HELB would be expected to be functional.
The conservative method utilized for terminating the HELB in the profile scenarios is to trip various pumps and allow the entire steam system inventory to blow down. The basis for tripping these pumps is as follows:
1 1.
Equipment items, electric power cables and electric control cables h-are all. located in the harsh environmment.
It is highly unlikely that a discriminatory cmanon mode failure would occur. That is, it' is not reasonable to expect that electrical equipment items and their associated power cables survive the HELB while at the same time all
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control cables fail. Therefore, any equipment that is still operating l
following a HELB is assumed to be controllable from a trip standpoint.
2.-
Multiple methods exist for tripping equipment, such as tripping the equipment breaker, a 480V bus, or a 4160V bus.
3 3.
In a worst case scenario, all 4Ky buses can be de-energized from controls, cables and circuit breakers not in a harsh environment.
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Based upon the staff review of the PSC evaluation, we find the licensee's response to Confirmatory Action 13.to be acceptable because the systems / equip-ment items listed above perform functions that can be accomplished manually
. 'thout reliance on unq1alified electrical equipment.
wi Confirmatory Action 14 4
Submit an engineering evaluation that describes the systems and equipment which will be utilized to respond to high energy line break from 35 percent power operation.
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i T
1 PSC Evaluation l
The PSC analysis has shown that if the Fort St. Vrain reactor has not been operated at power levels in excess of 35 percent of rated power, a permanent Loss of Forced Circulation _(LOFC) can be tolerated without fuel damage resulting. This analysis also shows that depressurization of the PCRV is net necessary to limit heat transport from the active core and that liner cooling will still effectively and safely remove core decay heat.
Furthermore, this analysis concludes that actuation of the reserve shutdown system is not required to ensure reactivity shutdown margin.
For the purposes of this PSC evaluation, no credit is taken for any of the multiple and redundant methods of removing core decay heat utilizing forced circulation.
This PSC evaluation also presumes that the reactor has not operated at greater than 35 percent rated power since 1984. This latter condition ensures that a total loss of forced circulation can be tolerated with no fuel damage to the Fort St. Vrain reactor core. Following a high energy line break, the. fire. water system, in lieu of the normally operating reactor plant cooling water system, would be utilized for cooling the PCRV liner. Utilizing the fire water system eliminates reliance on electrical equipment in a harsh environment and also ensures that the intent of 10 CFR 50.49 is satisfied during the interim. This method also provides full redundancy as only one of two fire water pumps, and PCRV liner cooling ' loops, are required for core cooling. Also, operating pro-cedures are currently in place at Fort St. Vrain for PCRV liner cooling utilizing fire water (Section III, Option C of " Safe Shutdown Cooling Under Highly Degraded Conditions" and Section 5.3 of 50P 46 " Reactor Plant Cooling Water System").
The flow paths for liner cooling are established by positioning of manually operated valves or by utilizing manual overrides of air and motor operated l
valves. A Change Notice is currently being implemented to provide for setting the helium circulator brake and seal without reliance on electrical equipment items. Systems that are required to be operable to perform these two functions and to accomplish safe shutdown cooling are:
i Brake and Seal System Provide Path for High Pressure Helium to Actuate Circulator Brake and Seal Fire Water' System Cooling for PCRV Liner Reactor Plant Cooling Provide Flow Path fcr Fire Water Water System Circulating Water System Provide Inventory of Cooling Water Including Make-up Electric Power Power for Electric Motor Driven Fire Water Pump Power for Circulating Water Make-up Pumps Electrical equipment items that are required to function are not located in the harsh environment (e.g., circulating water make-up pumps and associated instrumentation). Although these two functions (liner cooling with fire water and setting of the helium circulator seals) do not rely on the operability of electrical equipment items in a harsh environment, some cables that are required to remain functional are located in a harsh environment.
Based upon the staff review of the PSC evaluation, we find the licensee's response to Confirmatory Action 14 to be acceptable because following a HELB, the fire water system would be utilized for cooling the PCRV liner and at power levels of 35 percent or less, a permanent LOFC can be tolerated without fuel damage resulting.
. Conclusion The licensee's response dated December 10, 1985, to the November 27, 1985, Memorandum and Order was reviewed by the Plant, Electrical, Instrumentation and Control Systems Branch (PWR-B). Specifically, Confimatory Actions, 7, 8 13 and 14 were reviewed by the staff and found to be acceptable in support of the Fort St. Vrain thirty-five percent power restriction during the environ-mental qualification schedule extension period.
i Reviewer:
P. Shemanski 1
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