ML20212B758

Forwards Cycle 10 Startup Test 5,Stability Comparison Between Dual Loop Operation & Single Loop Operation, Completing Startup Test Rept Summary Initially Transmitted on 861126

ML20212B758
Person / Time
Site:	Dresden
Issue date:	02/23/1987
From:	Johnson I COMMONWEALTH EDISON CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
2753K, NUDOCS 8703030636
Download: ML20212B758 (11)

Text

.-

-m Conunone EsNeon y

One First Nabonal Plaza, Chica00, Illinois

\\v'2 Mdrosa Floply to: Post Office Box 767 Checa0o. Ilkncis 00690 0767 February 23, 1987 Mr. Harold R. Denton U.S. Nuclear Regulatory Conunission Office of Nuclear Reactor Regulation Washington, DC. 20555

Subject:

Dresden Station Unit 3 Summary Startup Test Report - Cycle 10 NRC Docket No. 50-249

Reference:

(a) Letter from I.M. Johnson to H.R. Denton dated November 26, 1986

Dear Mr. Denton:

In the above referenced letter, we provided you with the Dresden Station Unit 3 Cycle 10 Startup Test Report Sunurary. This was provided in order to fulfill the requirements of Section 6.6 of the Technical Specifications.

At the time of the transmittal of the Startup Test Report Summary, the single loop operatien stability test had not been performed, and hence was not included ihour original submittal. We are now transmitting the results of this test for your review. This transmittal completes all actions required of Ceco, pertaining to this matter.

Please address any questions concerning this matter to this office.

Very truly yours,

{ {-

N I. M. Jo son Nuclear Licensing Administrator

/klj att.

cc J. Stang/M. Grotenhuis NRC Resident Inspector-Dresden f6N Attachment (A): Dresden Unit 3 Cycle 10 Startup Test l

l No. 5 Stability Comparison Between Dual i

Loop and Single Loop Operation 2753K 0703030636 G70203 PDH ADOCK 05000249 P

PDR 1

ATTACHMENT A DRESDEN UNIT 3 o

CYCLE 10 STARTUP TEST No. 5 STABILITY COMPARISON BETWEEN DUAL LOOP OPERATION AND SINGLE LOOP OPERATION PURPOSE The intent of this test is twofold:

1) to examine Local Power Range Monitor (LPRM) and Average Power Range Monitor (APRM) noise levels (peak-to-peak oscillations) in Region II of Figure 5.1 during Dual Loop Operation (DLO) and Single Loop Operation (SLO).

Region II is defined as the operating region above 80% Flow Control Line (FCL) between 39% and 45% total core flow.

2) To collect baseline LPRM and APRM noise levels while in SLO outside of Region II for use in stability surveillances should SLO become necessary during D3C10.

BACKGROUND In early 1984, General Electric released Service Information Letter No. 380, rev.1, which discussed BWR Core Thermal Hydraulic Stability. This was followed by, in 1986, a NRC Generic Letter titled " Technical Resolution of Generic Issue B-19-Thermal Hydraulic Stability (Generic Letter No. 86-02)."

Both these documents stress the fact that BWR's exhibit less margin to thermal hydraulic stability when operating in the low flow /high power region of the allowed operating map.

This is generally not a concern, however, with low power density plants such as Dresden Units 2 and 3.

This type of instability is not considered a safety concern because it is easily detectable and readily suppressed by control rod insertions or core flow increases.

Furthermore, analyses have shown that should instability occur and go undetected, violation of applicable safety limits will not occur.

The parameter used to measure reactor stability is called the decay ratio which yields information on how effectively small power excursions are dampened by reactor feedback mechanisms (the smaller the decay ratio the more effective the damping; a decay ratio greater than 1.00 indicates an unstable condition).

Because of the uncertaintles inherent in Exxon's method for predicting reactor decay ration, the NRC specified in Generic Letter 86-02 that plants with calculated decay ratios exceeding 0.75 must establish operating provisions which provide for the detection and suppression of flux oscillations in operating regions of potential instability.

Although Exxon's calculated decay ratio for Dresden 3 Cycle 10, 0.53, was well below this value, the NRC raised concern over the fact that Dresden 3 was receiving 9x9 fuel, a non-conventional fuel design typically less stable than 8x8 fuel.

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M 4

For this reason, Dresden submitted stabi'lity monitoring Technical Specifications for SLO,.and was further regaested to perform a i

Dresden 3, Cycle 10 startup test to measure and compare peak-to-peak noise levels in SLO and DLO_while operating in the low flow /high power region of the operating map (see Reference 1).

The results of this test are included herein.

It should be noted that'this test does not attempt to measure the s

l reactor decay ratio.

However, a measurement of local and core wide noise levels can provide valuable stabilit9 information. Tests-4 performed at Brown's Ferry, see Reference 2, indicate that SLO will exhibit higher noise levels primarily due to increased turbulence in the downcommer region.

The increase in turbule0ce is a result of crossflow between the active and inactive jet pumps. For plants with ample margin to stability, these noise levels will increase with core flow. This information will be used to evaluate the data collected during this test.

4 LIMITATIONS AND ACTIONS 1

a)

The A and C levels of nine LPRM strings representing each octant of the core and the center of the core shall be operable prior i

to performing this test.

b)

During SLO, reactor operation above 80% FCL below 39% total core flow (Region I of Figure 5.1) is not permitted per Technical 4

Specification 3.6.H.3.b.

The low flow /high power region of the

)

operating map typically exhibits less margin to stability than other regions.

Instabilities may result in LPRM and APRM oscillations significantly greater than normal noise levels.

c)

During SLO, reactor operation in Region II without LPRM and APRM baseline data is not permitted per Technical Specification.

3.6.H.3.c.li.

l d)

If LPRM and APRM noise levels are three times greater than their baseline values, stable operation must be restored within two hours per Technical Speelficatica 3.6 H.3.c.iv.

i l

e)

If the reactor remains in SLO for an extended period (more than 24 houes), the following restrictions required per Technical Specification 3.6.H.3.f. must be implemented within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> j

after shutting down one recirculation pump:

1)

Reduce the APRM scram and rod block setpoints by 3.5%.

{

2)

Reduce the Rod Block Monitor (RBM) rod block setpoint by l

4.0%.

3)

Increase the Minimum Critical Power Ratio (MCPR) Safety Limits and Operating Limits by 0.03.

4)

Reduce the Maximum Average Planar Linear Hect Generation Rate (MAPLHCR) Operating Limits by 30%.

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CRITERIA a)

During SLO in Region II, the measured LPEN and APRM noise levels should remain below the Technical Specification limit of three times their baseline values (collected outside of Region II).

b)

The LPRM and APRM noise levels measured in Region II during DLO should be significantly lest than those measured during SLO at approximately the same power / flow conditions.

c)

SLO noise levels should increase proportionally with core flow 1

while oporating on a constant rod line.

ERSULTS AND DISCUSSION On December 3, 1986, LPRM and APRM noise levels were measured during DLO and SLO in accordance with Special Procedure 86-6-102,

" Acquisition of APRM/LPRM Noise Levels During Dual Loop and Single Loop Operation." The power maneuvers performed to accumulate the necessary data are depicted in Figure 5.2.

Although no specific criteria has been established for comparing noise levels during DLO and SLO in Region II, DLO should certainly exhibit noise levels less E

than SLO.

Although the noise levels ace expected to be greater in i

SLO, thay should not increase such that measuring reactor local and core wide power becomes difficult.

Initially, noise levels uere noenured during DLO (at various flows) at approximately 100% FCL in Region II.

Following this phase of the test, SLO was commenced by first tripping the A recirculation pump.

Prior to operating in Region II, LPRM and APRP noise levels for each j

active recirculation loop were measured below 80% FCL between 39% and 45% total core flow and reduced to baseline data (see Table 5.1).

Then at approximately 100% FCL in Region II, LPRM and APRM noise levels for each active recirculation loop were me asut ed again and comparett to their baseline values. The average of these noise levels was less than the Technical Specification requirement of three times their baseline values, exhibiting adequate margin to instabilities in I'

the low flow /high power region of the operating map.

The results are summarized in Table 5.1.

l It should be noted that the measured neutron noise levels with the A Loop active were greater than those with the B Loop active. This was attributed to an increase of 5% of rated core thermal power with the A Loop active (see Figure 5.3).

Durirg SLO, the APRM noise levels increased as core flow increased (see Figure 5.3 and Table 5.2).

The increase in APRM noise was associated to the increase in core flow noise related to turbulence in the downcomer region which is produced by crossflow between the inactive and active jet pumps. The LPRM t.oise levels in Table 5.2 follow the same trend as the APRM noise levels. This indicates that the observed increase in neutron noise levels was not due to core-wide or local instability phenomona.

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Tha sv:rrg9 LPRM cad APRM noiso Isvals during SLO end DLO in R!gica II woro also comp;r.ed. As expected, naiss 10vsla obssry;d during SLO were found to be greater than those during DLO.

This demonstrates that DLO in the low flow /high power region of the operating map exhibits more operating margin to instabilities than SLO, Yb furthermore, SLO in Region II should not present any operational

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difficulties since noise levels were not excessive. The resultir -are summarized in Table 5.3.

Based on.'the'results of this testing, it can be concluded that Region II of the operating map exhibits adequate margin to power / flow instabilities in SLO and DLO.

As expected, DLO was significantly more stable than SLO, demonstrating that stability monitoring Technical Specifications are not required during DLO.

Furthermore, the current SLO. stability surveillances required by Technical Specifications are adequate for detecting any core wide or local instabilities.

REFERENCE 1.

J. Wojnatowski letter to H. Denton, "Dresden Station Unit 3 Supplement to Proposed License Amendment - Cycle 10 Reload NRC Docket No. 50-249," dated April 18, 1986.

.s 2.

Becwns Ferry Nuclear Power Plant Unit 1 Stability Tests, February 9, 1985.

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TABLE'5.1 NOISE LEVELS DURING SINGLE LOOP OPERATION i APRM APRM Baseline Value (%)

Average APRM Noise Levels in Region II (%)

Noise / Baseline **

Channel A Loop Active

• B Loop Active A Loop Active

• B Loop Active A Lcop*

B Loop 'j 1

2.33 1.50 3.33 2.00 1.43 1.33 2

2.10 1.25 3.50 1.67 1.67 1.34 3

2.00 1.00 3.67 1.83 1.84 1.83 4

2.33 1.50 3.50 2.00 1.50 1.33 5

2.33 1.17 3.67 1.67 1.53 1.43 6

2.27 1.17 3.33 2.10 1.47 1.78 2

LPRM Baseline Value (CM2)

Average LPRM Noise Levels in Region II(CH2)

Noiso / Baseline **

LPRM Location A Loop Active

• B Loop Active A Loop Active

• B Locp Active A Loop

• B Loop i

16-41-A/C 1.10 / 1.00 0.58 / 0.42 1.33 / 1.10 0.92 / 1.17 1.21/1.10 1.59/2.79 24-49-A/C 0.83 / 1.10 0.50 / 0.50 1.17 / 1.17 0.75 / 0.50 1.41/1.06 1.50/1.00 40-49-A/C 0.93 / 1.23 0.83 / 0.67 1.40 / 1.33 0.83 / 0.92 1.50/1.08 1.00/1.37 56-33-A/C 0.50 / 0.73 0.58 / 0.42 0.83 / 1.10 0.58 / 1.00 1.66/1.51 1.00/2.38 48-25-A/C 0.87 / 1.00 0.58 / 0.67 1.23 / 1.23 0.83 / 0.92 1.41/1.23 1.43/1.37 40-09-A/C 0.93 / 1.00 0.50 / 0.50 1.07 / 1.17 0.92 / 0.50 1.15/1.17 1.84/1.00 24-09-A/C 0.83 / 1.00 0.58 / 0.75 1.50 / 1.33 0.83 / 0.83 1.81/1.33 1.43/1.11 16-25-A/C 1.00 / 1.00 0.83 / 0.92 1.33 / 1.67 1.00 / 1.17 1.33/1.67 1.20/1.27 32-33-A/C 0.70 / 1.00 0.50 / 0.58 0.87 / 1.07 0.67 / 0.83 1.24/1.07 1.34/1.43 t

All noise levels are measured, peak-to-peak values. For APRM data, all values are in units of % power, 2

while LPRM data is expressed in units of W/CM.

O Noise levels for A Loop were measured at a higher core thermal power than those for B Loop.

00 These values must be below 3.00 in accordance with Technical Specifications 4

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TABLE 5.2 NOISE LEVELS IN REGION II DURING SINGLE LOOP OPERATION i A LOOP ACTIVE

• CORE APRM NOISE LEVELS (%)

A/C LPRM NOISE LEVELS (

FCL

(%)

CHANNELS LOCATION 1

2 3

4 5

6 10-41 24-49 40-49 56-33 48-25 40-09 24-09 16-25 32-33 97.9 39.5 3.0 3.0 3.0 2.5 3.0 2.0 1.0/1.0 1.0/1.0 1.0/1.0 0.5/1.0 1.5/1.0

' 0/1.0 1.0/1.0 1.0/1.0 1.0/1.0 98.2 43.7 3.0 3.5 3.0 3.0 3.0 4.0 1.0/1.5 1.0/1.0 2.0/1.5 1.0/1.0 1.0/1.5 1.0/1.5 2.0/2.0 1.5/2.0 0.8/1.0 100.7 45.3 4.0 4.0 5.0 5.0 5.0 4.0 2.0/0.8 1.5/1.5 1.2/1.5 1.0/1.3 1.2/1.2 1.2/1.0 1.5/1.0 1.5/2.0 0.8/1.2 B LOOP ACTIVE CORE APRM NOISE LEVELS (%)

A/C LPRM NOISE LEVELS (k)

FCL CM4 (1)

CHANNELS LOCATION 1

2 3

4 5

6 16-41 24-49 40-49 56-33 48-25 40-09 24-09 16-25 32-33 93.0 39.0 2.0 1.0 1.5 1.0 1.0 1.8 0.75/1.0 1.0/0.3 0.75/1.0 0.5/1.0 0.75/0.75 0.75/0.5 0.75/1.0 1.0/1.5 0.5/0.5 97.0 42.5 1.5 2.0 1.5 2.0 2.0 1.5 0.5/1.5 0.5/0.25 0.75/0.75 0.5/1.0 0.75/1.0 1.0/0.5 0.75/0.5 1.0/1.0 1.0/1.0 99.1 44.1 2.5 2.0 2.5 3.0 2.0 3.0 1.5/1.0 0.75/1.0 1.0/1.0 0.75/1.0 1.0/1.0 1.0/0.5 1.0/1.0 1.0/1.0 0.5/1.0 t All noise levels are measured, peak-to-peak values. For APRM data, all values are in units of % power, 2

while LPRM data is expressed in units of W/CM,

o Noise levels for A Loop were measured at a higher core thennal power than those for B Loop.

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TABLE 5.3 COMPARISON OF SINGLE LOOP CPERATION AND DUAL LOOP i OPERATION NOISE LEVELS IJ REGION II APRM Average APRM Noise Levels (%)

A Loop /

B Loop /

Chennel A Loop Active

• B Loop Active Dual Loop Operation Dual Loop

• Dual Loop 1

3.33 2.00 1.00 3.33 2.00 2

3.50 1.67 1.33 2.63 1.26 3

3.67 1.83 1.17 3.14 1.56 4

3.50 2.00 1.17 2.99 1.71 5

3.67 1.67 1.27 2.89 1.31 6

3.33 2.10 1.27 2.62 1.65 Average LPRM Noise Levels (CM2)

A Loop /.

B Loop /

LPRM Location A Loop Active

• B Loop Active Dual Loop Operation Dual Loop

• Dual Loop 16-41 A/C 1.33 / 1.10 0.92 / 1.17 0.50 / 0.67 2.66 / 1.64 1.84 / 1.75 24-49 A/C 1.17 / 1.17 0.75 / 0.50 0.67 / 0.55 1.75 / 2.13 1.12 / 0.91 40-49 A/C 1.40 / 1.33 0.83 / 0.92 0.83 / 0.58 1.69 / 2.29 1.00 / 1.59 56-33 A/C 0.83 / 1.10 0.58 / 1.00 0.42 / 0.43 1.98 / 2.56 1.38 / 2.32 48-25 A/C 1.23 / 1.23 0.83 / 0.92 0.50 / 0.75 2.46 />1.64 1.66 / 1.23 40-09 A/C 1.07 / 1.17 0.92 / 0.50 0.55 / 0.50 1.94 / 2.34' 1.67 / 1.00 24-09 A/C 1.50 / 1.33 0.83 / 0.83 0.50 / 0.75 3.00 / 1.77 1.66 / 1.11 16-25 A/C 1.33 / 1.67 1.00 / 1.17 0.68 / 0.67 1.96 / 2.49 1.47 / 1.75 32-33 A/C 0.87 / 1.07 0.67 / 0.83 0.50 / 0.50 1.74 / 2.14 1.34 / 1.66 i

All noise levels are measured, peak-to-peak values.

For APRM data, all values are in units of % power, 2

while LPRM data is expressed in units of W/CM.

Noise levels for A Loop were measured at a higher core theenal power than.those for B. Loop.

n 0044n