ML20238C843
| ML20238C843 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 08/31/1987 |
| From: | Andrews R OMAHA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-3.D.3.4, TASK-TM LIC-87-496, NUDOCS 8709100406 | |
| Download: ML20238C843 (12) | |
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Omaha Public Power District 1623 Harney Omaha. Nebraska 68102 402/536-4000 August 31, 1987 LIC-87-496 Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555 References 1.
Docket No. 50-285 2.
Letter NRC (W. A. Paulson) to OPPD (R. L. Andrews) dated May 28, 1987 Gentlemen:
SUBJECT:
Response to NRC Survey of Fort Calhoun Station Control Room Ventilation Reference 2 requested the Omaha Public Power District (0 PPD) review the observations noted and provide confirmation that OPPD analyses and regulatory commitments regarding the Fort Calhoun Station Control Room Ventilation System are still valid or otherwise indicate those changes OPPD proposes and the schedule for their implementation.
The responses to the observations given in Reference 2 are addressed in the attachment to this letter.
To better understand the sequence of events relating to these observations, the following information is provided.
OPPD has Technical Specifications that address the control room ventilation system.
A summary of Technical Specifications requirements is as follows:
1.
Control room temperature is maintained below 120*F and the control room air treatment system is operable (T.S. 2.12).
2.
The toxic gas monitors are operable (T.S. 2.22).
3.
Each refueling outage the control room thermometer is tested for accuracy (Table 3-3, item 13).
4.
Each refueling outage surveillance tests are performed per T.S. Table 3-3, item 10 that; a.
check damper operation for DBA mode, b.
check control room for positive pressure. (Table 3-3, item 10) gRo91oo406 870831 p
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U. S. Nuclear Regulatory Commission LIC-87-496 Page 2 5.
The following tests of charcoal and HEPA filters for the control room HVAC are performed per Table 3-5, item 10a:
a.
in place removal efficiency, b.
laboratory testing of removal efficiency, i
c.
Overall system operation including measurement of pressure drop across the combined HEPA filter and charcoal adsorber banks and fan operation shall be shown to operate within 110% of design flow, d.
automatic and manual' initiation of the system shall be demonstrated.
Test ports were installed in the duct work as required to ensure the capability to perform the Technical Specifications tests.
The surveillance tests performed over the years have been satisfactory, although the flow measurement for the charcoal and HEPA filters has occasionally required damper adjustment to achieve the 10% criteria.
As required by NUREG-0737, Item III.D.3.4, analyses were performed and submitted.
The data for control room characteristics were supplied based on
" current facility design".
Since successful surveillance testing was being performed, there was no consideration given to performing confirmatory testing of overall system performance.
In 1986, OPPD was asked to participate in the NRC survey on Control Room Habitability.
Prior to the survey, additional test ports were installed under a modification to accommodate the type of measurements requested by the NRC.
In November 1986, an NRC team conducted a one-week visit at Fort Calhoun Station. Measurements performed by the survey team indicated an inleakage problem. The Technical Specifications previously discussed did not and do not require measurements similar to those performed by the team nor did the test port configuration prior to being modified support such testing methods.
At the conclusion of the survey team's testing, a copy of the data was given to OPPD.
Data reduction, adding margin for measurement error, provided a worst case estimate for inleakage of 4000 cfm.
Based on this estimate of unfiltered air along with 1000 cfm of filtered air, the post-LOCA control room doses were recalculated based on several non-conservative, but justifiable assumptions.
The dose to the control room operators for beta and gamma were within SRP 6.4 limits. However, the thyroid dose was above SRP 6.4 limits. The thyroid dose resulted because of the use of conservative source terms and methodology that are currently being revised by the NRC.
Changes were made to Fort Calhoun post-accident implementing procedures to ensure that if an iodine monitor alarm is received, protective actions will be taken. The revised analysis was used as a justification for continued operation until the start of the 1987 outage.
Prior to the refueling outage, the concerns of the survey team were discussed.
A decision was made during the outage by OPPD to ensure that unfiltered inleakage be reduced and to ensure that a positive pressure as required by the Technical Specifications is maintained.
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U. S. Nuclear Regulatory Commission LIC-87-496 i
Page 3 During the outage OPPD:
i 1.
Reduced air flow to and from adjacent areas (stair / elevator, turbine building, cable spreading room and room 81) by sealing penetrations and adding door weather stripping and sweeps.
2.
Sealed joint.s on air handling units and room 81 ducts.
3.
Removed damper PCV-846 and sealed dampers PCV-8407, and PCV-841A closed. These dampers were associated with a 100% fresh air mode which was restricted from use during power ope ation.
4.
Replaced fresh air inlet damper PCV-860B and filtered air inlet damper PCV-860C with bubble-tight dampers and all-welded duct.
These actions resulted in:
1.
Reducing the unfiltered leakage to an approximate value of 1650 cfm, 2.
Regulating the charcoal filter flow to within its design value, and 3.
Stopping air flow through the charcoal filter when not in use.
Although significant improvements in system operation have been realized, some design assumptions used in the analysis (such as infiltration rates) are not achievable with the system as presently constructed. The analysis used for the justification for continued operation prior to the outage was reviewed. The determination was made that adequate protection was afforded to the operators to justify return to power and continued operation. OPPD plans additional testing to attempt to locate sources of air infiltration.
On June 1,1987, approximately 6 days prior to the scheduled date for return to power, Reference 2 was received.
Besides observations relative to system operation, several de;ign issues were raised. OPPD believes these concerns may be outside of the original system design bases. As part of the commitments resulting from the Safety System Outage Modification Inspection (SS0MI), OPPD has committed to the reconstitution of the design basis documentation.
OPPD plans to ensure adequate III.D.3.4 compliance without reliance upon compensatory measures and non conservative assumptions by:
Determination of the requirements for the control room heating, m
ventilating, and air conditioning system design basis Scheduled completion date - February 1988,
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1 U.'S. Nuclear ^ Regulatory Commission.
LIC-87-496 Page 4 Development of design enhancements m
Scheduled completion date - July 1988, and s'
Installation and testing of any modifications required and. verification of
' data used in the revision of the NUREG-0737, Item III.D.3.4 analyses l
Scheduled' completion date - April.1989.
OPPD will-submit the revised III.D.3.4 analysis based on the completed modification (s).
If you should have any questions,; do not hesitate to contact us.
I Sincerel,
A
'R. L. Andrews Division Manager.
Nuclear Production RLA/me LeBoeuf, Lamb, Leiby & Macr'ae c:
1333 New Hampshire Ave., N.W.
Washington, DC 20036 l
R. D. Martin, NRC Regional Administrator P. H. Harrell, NRC Senior Resident Inspector A. Bournia, NRC Project Manager I
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ATTACHMENT i
The NRC letter dated May 28, 1987 provided several observations.
The following discussion provides OPPD's response to each of the listed observations.
A.
General 0 observations A(1)
Data gathered by the survey team showed that portions of the control room envelope were at a negative pressure when the ventilation systems were operating in the emergency mode of operation associated with a radiological challenge. This is contrary to plant technical specifications and the design basis for the facility which require it to be positive.
Resnonse
. Permanently installed plant instrumentation to measure control room pressure is currently such that measurements are made relative to the outside pressure only.
Past tests conducted to demonstrate technical specification compliance have been successful.
Action was taken to seal the control room envelope penetrations and the air handling units to increase this pressure.
Recent tests indicate that this effort was successful in that readings indicate a more positive pressure relative to the outside under a wide range of conditions.
A(2)
There appears to be a significant amount of leakage from the air handling units such that under certain operating conditions a considerable amount of unfiltered inleakage into the air handling unit may occur. Since you assumed no unfiltered inleakage into the envelope in your revised III.D.3.4 analysis of September 23, 1985, the inleakage associated with these units appears contrary to your assumption.
Response
The III.D.3.4 analysis, as required by NUREG-0737, was based on design information.
As noted in Campe and Murphy, evaluation of control room infiltration is difficult.
For example, wind direction, building geometry, internal building pressure distribution, air columns, etc., can combine in a number of ways, resulting in different infiltration rates.
An alternate calculation based upon a gross assumption of an unfiltered inleakage rate of 4000 cfm was performed.
The purpose of the calculation was to determine the doses to the control room operators during the 30 days i
following a LOCA. The results of this calculation were used to modify l
existing post-accident procedures to protect the operators from airborne i
radiation in the control room as a result of the unfiltered inleakage.
1 Based on these actions, plant operation continued until the scheduled refueling shutdown in March 1987.
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l Attachment (Continued) l i
During the outage the control room envelope and air handling units were 1
sealed, two bubble tight dampers were installed, and unused duct / dampers were removed or sealed shut. Using the ICC method of subtracting flows to determine inleakage, these efforts greatly reduced the unfiltered j
inleakage.
The maximum unfiltered leakage calculated by this method is approximately 1650 cfm, considerably less than the 4000 cfm used in the revised analysis.
A(3)
There is a considerable amount of i; leakage into the control room envelope when the control room ventilation system is operating in its emergency modes of operation.
In the case of radiological challenge, inleakage measured by the survey team includes 740-1100 cfm of flow through the outside air normal makeup damper; 500 cfm of inleakage into the air handling unit VA-468, and 2000-3800 cfm in the return duct work from the control room.
For the toxic gas challenge, inleakage includes 600-1500 cfm through the normal and emergency outside air intakes, 4700 cfm into the air handling units when VA-468 is operating, 3900 cfm into the return duct work from the control room when VA-46B is operating, and 2100 cfm in the control room supply ductworks when VA-46A is operating.
Because of these large inleakage rates and the fact that portions of the control room are at a negative pressure during the radiological mode of operation, you should perform a reanalysis to determine whether the conclusions previously presented in your TMI Action Plan Item III.D.3.4 analysis are still valid.
Response
A.
Radiological Challenge - See A(2) Response to General Observations.
The validity of the III D.3.4 analysis will be confirmed after modifications to the control room HVAC system have been installed and actual data is taken.
B.
Toxic Gas Challenge - The mode of operation described is not the Fort Calhoun Station's toxic gas mode.
In the event of a toxic gas alarm, the control room HVAC system isolates the control room and all air handling units shut down to preclude the infiltration of hazardous toxic vapors.
Therefore, the observations concerning inleakage rates in the toxic gas mode are not applicable to Fort Calhoun Station operation.
B.
Observations Involvina Plant Operation Include:
B(1)
The members of the plant staff responsible for the ventilation system need to be familiar with the licensing basis for the plant I
so that they understand the impact of changes to design conditions l
involving the control room ventilation equipment and its envelope.
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Attachment (Continued) l Response-Control room HVAC training programs are being reviewed to ensure they address the licensing basis for radiation and ' toxic gas protection of control room personnel.
B(2).
The control room envelope should be at a positive pressure of 1/8 inch w.g. with respect to all adjacent areas under the emergency l
mode of operation for a radiological incident. Areas where improve-ments can be made include the sealing of doors, dampers, integrity, and the controlling of leaks in the air handling units.
L
Response
Since the NRC survey in October 1986, several improvements have been made to the control room ventilation system as discussed in the cover letter.
B(3)
Additional attention should be given to maintaining the air handling units.
flesoonse Since the visit from the NRC Control Room Ventilation survey team, OPPD has devoted considerable effort to the areas of system maintenance and modifications.
B(4)
Significant flow occurs between the idle. control room air handling unit and the operating units. There seems to be recirculation through dampers which do not isolate.
Response
The situation was investigated to determine the cause.
Damper blade edge seals have been installed and dampers adjusted which did reduce this flow to some extent.
New tighter dampers are being considered to further reduce the recirculation which was observed.
B(5)
Control room temperature is the most evenly distributed of any control room the survey team has seen to date.
Response
None.
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Attachment (Continued)
C.
Observations Involvina System Desian include:
C(1)
The control room ventilation system is susceptible to single failure (e.g., normal intake damper, PCV-860C, emergency intake damper PCV-860A, the toilet exhaust damper, and the control room exhaust damper PCV-846).
Response
This susceptibility to single failure will be considered for applicability during the review of the design criteria.
Additionally, please note that exhaust damper PCV-846 has been removed and the duct was sealed.
C(2)
The control room envelope pressure should be measured relative to all adjacent areas not just to atmosphere.
Response
Surveillance test ST-CRV-1-F.3 was updated to ta h differential pressure readings between the control room and adjacent areas.
C(3)
The location of the control room ventilation system equipment may make it susceptible to a high energy line break and to steam intru-sion into the control room.
Response
The location of the HVAC units relative to the main steam and feedwater lines is the same as was originally licensed.
Cables around the mainsteam and feedwater lines have been determined to preclude pipe whip effects.
Blow out panels in Room 81 keep the differential pressure below 1.5 psig.
This observation will be investigated as a part of the final design configuration.
The low probability of this failure provides justification for continued operation.
C(4)
The location of the diesel generator exhaust is at the same elevation as the control room intake. A concern is the drawing of CO into the control room envelope through the control room 2
emergency intake.
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Attachment (Continued)
Resoonse This concern will be addressed during OPPD's evaluation of the location of the control room filtered air intake.
If C0p becomes a potential problem, this will be considered and evaluated in the selection of a new filtered air intake location.
C(5)
The licensee should verify whether the capacity of the HEPA filter utilized in the control room emergency ventilation system is 1000 cfm or 1200 cfm.
Flow appears to be outside the technical specification limit of design i 10%. The design value should be noted in the technical specification.
Response
The design capacity of the HEPA filter utilized in the control room emergency ventilation system is 1200 cfm. The surveillance test requirement (ST-VA-4) is 1000 1 10% cfm.
OPPD has noted during the performance of ST-VA-4 that the as-found condition has been high and as a 1
result the manual damper has been readjusted as required.
The Technical Specifications will be reviewed for inclusion of design values.
C(6)
The toilet exhaust damper seals the tightest of any the staff has seen to date.
Response
None C(7)
The modification to one of the auxiliary building fans to allow it to operate at a variable speed should be considered for two fans so that redundancy is provided. With such a change, credit could be taken for the ECCS charcoal adsorber units in the LOCA dose analysis and the control room operator dose analysis.
Response
At present, the dose contribution from the ECCS pump rooms is assumed to be negligible.
C(8)
The adequacy of system cooling capability is questionable because i
both air handling units (AHU) must be operated during the summer to maintain the control room comfortable.
Response
j Tests will be conducted to determine if flow modifications can be made which would result in single AHU operation during the summer. These results will determine whether the existing systems are usable as a baseline for filtered air mode improvements.
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- Attachment (Continued) i D.
Observations on Technical Specifications Included:
D(1)
The present technical specifications do not track with the licensee's assumptions utilized in their analyses and accepted by the NRC staff. in their SER. Technical Specifications should reflect licensing basis assumptions.. Proposed changes were discussed with the OPPD staff and include acceptance criteria' to which positive pressure is to be maintained in the control room envelope.
Response
The Technical Specifications and improvements will be reviewed by 0 PPD.
Consideration of the Commission's policy statement on Technical Specification Improvements will be included in this review.
D(2)
The equipment qualification temperature should be measured in cabinets and not on the control room wall or in the operator station area.
Response
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A test is planned to measure cabinet air temperature during normal and accident modes as part of the design documentation effort.
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D(3)
Other comments were provided to the OPPD staff and included accept-ance criteria for in-place tests of HEPA filters and charcoal adsor-bers, control room equipment and instrumentation qualification temperature.
Response
See response to D(1).
E.
Observations on Procedures Include:
E(1)
Procedures need to address operation of both air handling units simultaneously as is done in the summer.
Response
01-VA-3 contains an option to go to dual operation.
This will be expanded
-and clarified. Modifications to eliminate the need for dual operation are now in the planning stage.
If dual operation cannot be eliminated and this fnode of operation is accepted as the baseline design, then it will be retained in the procedures.
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l Attachment (Continued)
E(2)
Clarification should be provided to the procedure which addresses
)
operation with the control room at high temperature so that it includes instructions which restore control room integrity in the event of a toxic gas challenge.
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Response
Clarification to the procedures will be provided by February 1988.
P.
E(3)
The proposed loss of ventilation test should incorporate a temper-ature criteria such that the tests is halted when either steady state temperature is reached and the control room temperature remains constant or the temperature rise is such that the instru-mentation and the equipment in the control room are threatened.
Resoonse The test, when conducted, will include criteria under which the test will be terminated.
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