ML20039G806

Responds to 811015 Request for Commitment Re Mod to Install Common Ref Level Per NUREG-0737 II.K.3.27.Arguments Supporting Util Contention That Mod Is Unnecessary to Nuclear Safety Presented.Drawings Encl

ML20039G806
Person / Time
Site:	Cooper
Issue date:	01/11/1982
From:	Pilant J NEBRASKA PUBLIC POWER DISTRICT
To:	Ippolito T Office of Nuclear Reactor Regulation
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.K.3.27, TASK-TM LQA8200026, NUDOCS 8201190165
Download: ML20039G806 (8)

Text

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e UM M COOPER NUCLEAR STATION

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P.O. box 98, BRoWNVILLE. NEBR A$hA 68324 i

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LQA8200026 January 11, 1982

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Mr. Thomas A.

Ippolitc, Chief 1

Operating Reactors Branch #2 4

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U.S. Nuclear Regulatory Commission Washington, D.C.

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Subject:

NUREG-0737. Item II.K.3.27 Cooper Nuclear Station NRC Docket No. 50-298, DPR-46

Reference:

1) Letter from T. A. Ippolito to J. M. Pilant, Dated October 15, 1981, "NUREG-0737, Item II.K.3.27"

2) Letter from J. M. Pilant to D. G. Eisenhut, Dated June 30, 1981, " Post TMI-Requirements /NUREG-073""

3) Letter from J. M. Pilant to D. G. Eisenhut, Dated February 27, 1981, " Revised Response to NUREG-0737"

4) BWR Owners Group Evaluation of NUREG-0737, II.K.3.27

5) Letter from J. M. Pilant to D. G. Eisenhut, Dated June 9, 1981, " Emergency Response Facilities"

Dear Mr. Ippolito:

Your letter of October 15, 1981 (reference 1) requests that NPPD provide by January 15, 1982 the following:

1.

The District's commitment to install a modification that provides a common re.ference level; 2.

A description of that modification, including proposed imple-mentation schedules, and; 3.

The District's commitment to meet acceptance criteria 2 and 3 of reference 1.

0 h/ f 8201190165 820111 PDR ADOCK 05000290 i

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l Mr. Thomas A. Ippolito January 11, 1982 l

Page 2 l

l In reply, the District does not consider it appropriate to commit to acrosplishing the above requests as it is our opinion that this modi-I ficction is not necessary to assure nuclear safety and that furthermore, I

this modification is not a well thought out requirement with respect to good human factors engineering concepts and does not really consider how the operator actually utilizes level indication during a transient condition.

The District's arguments supporting this viewpoint are l

presented by the following paragraphs.

The control room operator at CNS has available nine level indicators or recorders. They are as follows:

A.

Level Instrumentation Referenced to the Bottom of the Steam Dryer Skirt There are seven level instruments that are referenced to the bottom cf the steam dryer skirt. Zero on these instruments corresponds to 165 inches above the top of active fuel (TAF).

l Operating and Transient Level Instruments l

1 1.

Three narrow range indicators (0 to 60 inches).

2.

One narrow range recorder (0 to 60 inches).

3.

Two wide range indicators (-150 to 60 inches).

Shutdown Level Instrument 1.

One wide range indicator (0 to 400 inches).

B.

Level Instrumentation Referenced to TAF LOCA or Fuel Zone Level Instruments 1.

Two wide range indicators (-100 to 200 inches).

As can be seen, seven of the nine level instruments that are available have a common reference point.

They cover the normal and shutdown level ranges and the setpoints for initiation of HPCI/RCIC, low pressure ECCS, ADS and Primary Contsinment isolation as discussed in reference 4.

Of the seven only those classified as Operating and Transient Level Instru-ments would be used to determine water level during normal operation and transients. The Shutdown Level Instrument is used for monitoring level during refueling s. hen the reactor is depressurized and flooded up.

e Mr. Thomas A. Ippolito January 11, 1982 Page 3 The remaining two of the nine level instruments are not used during normal operation or transients. They are provided to indicate reactor water level following a large break LOCA and to verify core reflood by ECCS. They do not provide meaningful indication other than when the Recirculation (RR) or Residual Heat Removal (RRR) pumps are not running and when the reactor is not pree~irized. At 0 psig, O inches on these two indicators corresponds to TaF At 1000 ps;g, -80 inches corresponds to TAF.

Thus, it can be seen that these two indicators cannot be used directly to determine reactor water level other than during very re-stricted conditions. As a result, no direct comparison can be made between the LOCA or Fuel Zone Level Instruments and the rest of the level instruments other than when these very restricted conditions are satisfied.

Therefore, the staff's argument that the operator would have to perform a mental interpolation to understand what a. reading on one water level indicator means relative to a reading on another water level indicator is not a valid argument. Those ther. would be used during normal opera-tion or transients have the same reference point.

The LOCA or Fuel Zone Level Instruments would not be used for a direct comparison to the Operating and Transient Level Instruments, not because of the difficulty of performing a mental interpolation to understand what a reading on one water level indicator means relative to a reading on another water level indicator, but because they do not read accurately other than in very restricted conditions. At reactor pressures other than atmospheric pressure, with the RR and RHR pumps not running, an adjustment must be applied to the reference point that is dependent upon the actual reactor pressure (temperature). With the RR and RHR pumps running, these two instruments cannot be used to determine level as there is no way to ascertain the variable effects of the pumps on these levsl instruments.

Based upon the above, it is the District's opinion that there is little to be gained by requiring the LOCA or Fuel Zone Level Instrumentation I

and the Operating and Transient Level Instrumentation to have the same reference point.

In the staff's letter (reference 1) to the District, it is stated that the operator should not have to perform mental interpolations to under-stand what a reading on one water level indicator means relative to a reading on another water level indicator. The staff further states that the District's modification makes information readily available that the operator needs to perform a mental interpolation, but it doca not eliminate the need for performing the interpolation. The District concurs that if the operator had to make such a mental interpolation, then our modification does not eliminate the need for performing the interpolation. However, it is the District's view that this does not reflect how an operator actually uses the water level instrumentation

i Mr. Thomas A.

Ippolito January 11, 1982 Page 4 during a transient or accident situation. The District's modificacion (reference 3) informs the operator how far above TAF the water level is at a minimum at any time.

It is the District's opinion that the operator is interested in knowing only whether water level is at least 15 inches or 165 inches above TAF and whether it is increasing or decreasing. The staff's view that the operator will have to make a mental interpolation to determine whether the water level is for example 17 inches or 172 inches above TAF is not realistic.

The operator will look at the in-dicators and only be interested in knowing whether water level is at least 15 inches or 165 inches atove TAF or whether it is increasing, decreasing or holding steady. Even in the very restricted conditions when the LOCA or Fuel Zone Level Instruments are responding correctly, this type of direct comparison can still be made. All indicators can be compared to determine whether the core is adequately covered or not and 4

l whether level is increasing or decreasing. This is consistent with the l

viewpoint of the symptom oriented Emergency Procedure Guidelines being developed by the BWR Owners Group which emphasize that the primary indication of nuclear safety during a transient or accident situation is an indication of adequate core coverage. Knowledge of the exact water level is not as important as knowledge of how tne water level is varying relative to TAF.

Based upon the above, the District is firml/ convinced that the modi-fication that we have made provides sufficient information (see enclosed phctographs) to the operator to adequately adjudge adequate core cooling during a transient or accident situation.

Regarding human factors engineering considerations for action item II.K.3.27 of NUREG-0737, the District believen there are two aspects relative to the desirability of changing to a common reference level and that the staff has focused on only one of these aspects without ade-quately determining if there is a positive benefit to be gained. These aspects are the positive side of the requirement which would permit the operator to more easily determine reactor water level and the negative l

side which must weigh the desirability of retrofitting this requirement to an operating plant versus the benefits to be gained. The District does not believe the staff has properly weighed the two aspects for an operating plant. The staff's argument in NUREG-0737 is that this modi-1 i

fication will help eliminate operator confusion regarding water level.

As stated above, the District is of the opinion that the staff has not I

correctly considered how the operator actually utilizes water level indication during a transient or accident situation and as a result, has incorrectly assessed the potential for operator confusion. Furthermore, the District is of the opinion that this modification quite probably will contribute more confusion than it will alleviate (see reference 3).

For this reason, we do not believe that modifications other than those we have already implemented are appropriate.

~~

Mr. Thomas A. Ippolito January 11, 1982 Page 5 As part of the District's plans regarding the NRC requirements of NUREG-0696, we are considering implementing a fuel zone water level monitoring package on the proposed computer system (reference 5).

This package would utilize all level sensors discussed above and would com-bine them to develop or.e composed 1.evel indication that would be pressure (temperature) compensated as necessary to provide accurate level indication under all conditions. This would provide ona indi-cation available via the SPDS, that would be validated as necessary to provide reliable indication from 100 inches below TAF to vessel top.

Enclosed is an example of the type of display that is being considered.

This display would be available on a color CRT in the Control Room and would be color coded for various operating conditions. The District believes this modification is preferable to changing existing equipment and would provide better information to the operator.

If you have any questions concerning this response, please contact me.

Sincerely, k

.i. Pilant Division Manager of Licensing 6 yuality Assurance JMP: ROP:1b Enclosures

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