ML19098B417

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Letter Response to Request for Further Analysis of Refueling Accident Inside Containment
ML19098B417
Person / Time
Site: Surry  Dominion icon.png
Issue date: 03/21/1977
From: Stallings C
Virginia Electric & Power Co (VEPCO)
To: Reid R, Rusche B
Office of Nuclear Reactor Regulation
References
Download: ML19098B417 (15)
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VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 Ma:tch.21., 1977 otr.~;~ ~lOR¥ Oil~itti ;~;~, COPJ Mr. B~~Jl*'cf.'Rusche Ditector of Nuclear Reactor Regulation U. s. Nuclear Regulatory Connnission Washington, D. C.

20555 Attn: Mr. Robert W. Reid, Chief Operating Reactors Brnach 4 License Nos. DPR-32 DPR-37

Dear Mr. Rusche:

This is in response to your letter of January 17, 1977, in which you requested a further analysis of a refueling accident inside containment. A previous brief analysis of the postulated accident was conducted and forwarded at your request, on January 11, 1977. That analysis indicated the result would be zero off-site radiation dose. A further analysis has been conducted and is attached.

Briefly, the results of this analysis, including single failures, show that the potential site boundary radiation exposures would be well below the exposure guidelines of 10CFRlOO. You requested a twd part evaluation which has been done with the following principle assumptions and conclusions:

follows:

1. Your part (1) requested, "a conservative analysis using parame 1ters (e.g., maximum allowable valve closu~e times)
  • as limited by the technical specifications." As our Technical Specifications do not contain any valve closing time re-quirements, we did this part of the analysis with the valves not closing and the filters at 70% efficiency. This was Case 3 resulting in a worst case possible dose at the site boundary to the whole body of 8.9 rem and to the thyroid of 149 rem.
2. Your part (2) requested, "an analysis using parameters associated with current known facility operating conditions (e.g.,

actual valve closure times). This was done as cases 1 and 2 with co1nservatisms being fully incorporJted and resulting in a possible dose at the site boundary for Case 1 of zero and for Case 2 of 2.6 rem to the whole body and 43 rem to the thyroid.

The environment for which the equipment is qualified is as 1 ?lJ 8") ()// /)

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e VIRGINIA ELECTRIC AND POWER COMPANY TO Mr. Benard C. Rusche Page No. 2 The containment purge supply and exhaust valves are seismically qualified.

The manipulator crane area monitor, the containment gas and particulate monitors and the ventilation filter banks are non-seismic.

A review of our Technical Specifications, related to this postulated accident, reveals that the radiation monitors and the automatic isolation of the purge system on high radiation signals is proved operable irmnediately prior to refueling. This equipment is sufficient to limit a potential release to zero. The only additional equipment required to be operable, to provide assurance that potential off-site exposures are low, is the ventilation filter banks. In order to provide assurance of this equipment's operability, it is proposed that the ventilation filters be tested and verified operable immediately prior to refueling operations. No other equipment is necessary to provide added assurance that potential offsite exposures are low, as this equipment will satisfy single failure criteria and stfll maintain offsite radiation exposures to well within the guidelines of 10CFRlOO.

The single failure analysis failed the following components:

1. The manipulator crane monitor (Case 2)
2. The valve closing circuitry (Case 3)
3. The filters and the manipulator crane radiation monitor-*

(Case 4)

As previously stated, Part 100 guidelines are not exceeded for any single failure and no change to facility equipment is necessary.

Attachments cc: Mr. Norman C. Moseley Very truly yours,

~.m.Jaai~~

C. M. Stallings Vice President-Power Supply and Production Operations

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  • ATTACHMENT ANALYSIS OF REFUELING ACCIDENT IN CONTAINMENT Page l of 11*

During refueling the contain~ent purge* system is set up to exhaust through "the ventilation filters in the Auxiliary Building. Both filter banks will*

. be on line because the Fuel Building is also exhausting through the filters.

The total flow rate for both systems is 66,000 cfm while the design flow

  • rate for each filter is 36,000 cfm.

While the purge system is in operation, the air flow in the containment is as follows. Air enters the containment through two 15000 cfm fans (FS-;

F-4A & B), through two 36 inch butterfly supply valves (MOV-VS-100 A &

B) and is dispersed through the ring header outside the crane wall at EL-3'6.". The air is continuously recirculated inside the containment by three 75,0GO cfm recirc fans (VS-F-1 A,B,C). The air is purged from.the containment through the ring header at EL-20' outside the crane wall.

The air discharges through two 36 inch butterfly valves in series (MOV-VS-100-C,D). The air then passes through the Auxiliary Building Filter Banks (VS-FL-3 A & B) and the two 15000 cfm Purge Exhaust Fans (VS-P-5 A,B).

The*worst single failure would be loss ot the valve closing circuit which closes the valves and secures the purge fans r.n an alarm from either the crane monitor or the containment gas and particulate monitors. The two output relays are sufficiently redundant to secure purge flow; however, a loss of power to this circuit would cause them not to function. This would cause a total release through the filters with a boundary dose as calculated for _case 3 of the dose calculations. This dose is still within the allowable limits, but our worst case.

Locations The sample line ties into 30" recirc. duct in c;~mtainment at EL-9' 10"

  • The monitors are located in the Auxiliary Building at EL 45' 10" along the west wall.

Sample line 1" ARC-2-21B Length from 11448-FK-10 A & B System floN from 11448-SN-207

. 214 ft~

10 cfm Volume o. 870 ID Tube*= 1526. 6., in3 Response Time

  • ,3 3

. 3 Flow== 10 Ft3/min X mi~/60 sec X 1728in /Ft = 288 in /sec Time= 1526.6 in3

  • 288 in3/sec =

5.3 seconds

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. Page 2 of 11 To be conservative because we can not determine the pump efficency or calculate the volumes in fittings or sampling components use 53 seconds Air Flow Rate 30,000 cfm Duct Area Duct Lengths Velocity Inlet to exhaust valve 130' Exhaust valve to filters 130' V_Q.Ve = 30,000. Ft3/min X min/60"sec X "Ft/9.,62 Ft3 Y = 51.9 Ft/sec Peak centerline velocity Umax

  • -=

6 (Re=l.096Xl0 = Turb~lant Flow)

Umax 0.8 Umax = 51.9-:-

0.8 = 64.9 Ft/sec Transit Times

=

130 "T 64.9 = 2 seconds

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Use l._4 seconds to be conservative This analysis assumes that the air flow path in the containment is continuous from the surface of the reactor cavity to EL-27. This is very conservative as there is no velocity profile across the reactor cavity. Also,it is assumed that 50% of the area outside the crane wall is blocked with stnuctures and equipment. This is a conservative assumption based on figures used _in the LOCA analysis.

Determine the open area outside the crane wall Containment diameter 126 1 Diameter inside crane wall 106 1 Air Velocity Recirc air flow 22~000 cfm Purge air flow 3QOOO cfm Total 255.000 cfm

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e Page 3 of 11 V = 255000 Ft3 /min' X 1/1822 Ft2 X. 1 min/60 sec = 2.33 Ft/sec Air Transit Time Shortest distance from cavity surface to purge duct suction 70 Ft.

Time= 70 Ft T" 2.33 Ft/sec= 30 sec This is one-half the time assumed in our initial analysis.

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Page 4 of 11

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CASE ANALYSIS PROBLEM BASIS of Supposed Refueling Accident inside of Containment

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Case 1:

The manipulator crane monitor is functional and actuates the containment*

isolation valves and s_ecures the purge fans'!...

Case 2:

The manipulator crane area monitor is not functional requiring the containment gas or the containment particulate m~nitor to actuate.

the isolation valves and secure the purge fansm

  • Case 3:

Neither the manipulator crane area monitor or the containment gas

.and particulate monitors are.operational resulting in a:total release.

Case 4:

Assume worst case isolation (i~e. Case 2) and the filters are not available or the exhaust duct outside of containment and downstream of the isolation valves fails.

Physical Characteristics of Systems and Assumptions Item 1) Assume a puff release of radioactivity from a ruptured fuel assembly in the reactor fuel cavity. This puff release is as close to the nearest purge exhaust grill as is physically possible.

Item. 2)

The response of the area monitor is gamma radiation sensitive so that

!:: !.:; ~c:: ::.::~::::::::::::~:T £')!: ; t-rn hP immersed in a radioactive cloud to detect.radioactivity~ It's position (i.e. approx. 10 feet) above the fuel cavity, unshielded from direct /'-rays from the pool reaffirms its capability to detect an accident release immediately.

\\,:C-Item 3)

The travel time* of a radioactive cloud from a puff release at a point on the pool surface to the purge duct suction and recirculation suction is 30 seconds which is twice as conservative as the initial analysis.

item 4)

The closure time of the isolation valves (including all electrical impulses and processes) is 20 seconds.

(Worst Case at Site 19.4 sec.

for valves alone)

Item 5)

The response time from the recirculation suction to the gas and particulate

. Item 6)

Item 7)

Item 8)

Item 9) monitors detection is assumed at.54 seconds

  • The purge rate is 30000 cubic feet per minute.

Filtration of containment purge exhaust during refueling is assumed to be conservatively 70% efficient.

The assumed volume of containment air with which the radioactive release is mixed: during the 30 second transit t.ime from the reactor cavity to the purge duct equals 127,500 cubic feet.

The time for air to travel through the purge duct to. the inboard isolation valves is assumed to be 1.4 seconds.

Item 10) The delay time from reactor shutdown to initiation of fuel assembly transfer operations is at least 100 hrs (Tech. Spec.)*

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Item 11) The.radial peaking factor is assumed to be 1.65, Item 12) The number of fuel assemblies in the CORE is 157.

Page 5. of 11

  • rtem 13) Ten percent of the Iodine fuel assembly activities are assumed to be released into the reactor cavity water with 99.75% being inorganic and.25% in the organic form. The fuel pool D.Fe for inorganic iodine is 133 while the DF for organic iodine is 1.

Item 14) Ten percent of the Noble Gases present in the fuel assembly are released to the reactor cavity pool with the exception of Kr 85; 30% of Kr 85 is released. The DF of the Fuel Pool water for Noble Gases is 1.

Item 15) Dose calculational method from R.. P. 13, section "Dose Conversion Factors and Equations" (includes average gamma and beta energies for each isotope and thyroid dose conversion factors)

Item 16) 'X./Q = 2.. 1 X 10-3 sec/m 3 (Latest meteorology)

17) h

-- 3 *. 47 X 10-4 m*.

3/sec Item Breat _ing rate Item 18) SiLe boundary distance= 1650 ft Item 19) Surry 1 & 2 CORE activities

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CASE 1 When a puff release results in airborne and direct gamma irradiation of the Manipulator Crane area monitor so that a prefixed dose rate setpoint is surpassed, activation of the isolation valves occurs instantaneously. It takes 20 seconds to isolate the containment.*Thirty seconds i's required for gaseous transit time to the purge duct. An additional le4 seconds is required from the purge duct grill to the isolation valve. Therefore, if the Manipulator Crane Area Monitor is operational following a Fuel Handling Accident, zero release of radioactivity from the containment is expected.

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Isotope CASE 2 If _the manipulator crane area monitor is not functional, following a fuel handling accident, the containment gas and particulate monitors will be used to actuate the containment isolation valves. The valves and site doses are as follows:

Activity for hottest

  • fuel element (ptc:.)

Activity Released Whole Body(1) Whole Body(§)

Thyroid Inorganic I 131 4.46 + 11 6.33 - 02 5.38 + 10 6.93 - 23 4.35 + 07 2~90 + 01 4.02 - 12 3.50 + 00 4.5i - 33 3.13 + 01 1.57 -

13 1.02.+.oo 8.22 - 35 2.56.. 04 132 133 134 135 Orgariic

. :I 131 132 133 134 135 I 131 132 133 134 135 Kr 83m 85m 85 87 88 89 Xe 131m 133m 133 135m 135 137

. 138 Total

  • 2.83 - 03 4.46 + 11
9. 71 + 00 6.33 - 02 1.38 - 12 5.38 + 10 1.17 + 00 6.93 - 23 1~51 - 33 4.35 + 07 9.47 - 04

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1.85 - 05 5.37 13 4.07 + 04 1.18 - 03 6.06 + 09 5.27 + 02 4.03 - 12 1.17 - 19 1.25 + 01 3.63 - 07 4.51 + 08 1.31 + 01 9.99 + 09 2.90 + 02 8.54 + 11 2.48 + 04 8.96 + 07 2.60 + 00.

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  • 7.62 - 03 6.49 - 15 1.56 - 03 7.93 36 2.90 06 9.18 - 03 rem 1.41 18 9.67 - 08 5.80 04 5.27 - 23 3.80- - 10 1.51 04 3.63 03 9.60 01 3.40 + 04 3.Yl - 03 1.10 15 9.09 04 1.62 36 8.67 07
4. 82 - 03 8.80 18 5.77 - 08 5.80 02 5.70 23 5.40 11 8.53 - 04 2.68"- 02 1.51 + 00 3.80 - 04 rem 9.63 01 rem 1.59 + 00 rem 32.32 + 00-1.05 + 01 5.38.

14 3.41 - 01 2.75 - 35 8.56 - 05 1.08 + 01 9.72 - 01 rem 1.59 + 00 rem 43.12 rem

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Case 2: Total Whole Body dose is 2.56 rem Total Thyroid dose is 43.12 rem e

  • Page 8 of 11 Case 2 assumes a 30 second transit time from the reactor cavity fuel pool to the purge duct during which time a certain amount of mixing occurs, as specified by suction off of the recirculation and purge fans. An additional t.4 seconds. is consumed in the purge duct p:rior t_o _ the isolation valve. The containment will be isolated 74 seconds after the radioactivity reaches the purge duct, result:ing in a 73 second release of the concentrations present at the purge duct grill one minute following the fuel handling accident.

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  • CASE 3 If none of the radiation monitors capable of the containment isolation is functionai or if a selective power failure occurs at the semi-vital bus, all of the radioactivity released from the reactor cavity fuel pool is assumed to be.released to the environment through_the filters. This assumes no manual securing of the purge system. The releases and site.doses are.as follows:

. Isotope Activity Released Inorganic I 131 1.00 + 02 132 1.42 - 11 133 1.21 + 01 134 1.56 - 32.

135 9e 76 - 03 Organic

  • I 131 3.35 + 01 132 4.75 -12 133 4.04 + 00 134 5.20- 33 135 3.26 - 03 n"I*..

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85m 4.07 - 03 85 1.82 + 03 87 4.03 - 19 88 1.25 - 06 89 Xe 131m 4.50 + 01 133m 1.00 + 03 133 8.53 + 04 135m 135

.8.97 + 00 137 138 I 131 132 133 134 135 Total Whole Body(f)

Whole Bodyyt} Thyroid

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1.98 - 06 2.00 - 03 2.00 - 01 1.81 - 22 1.97 - 22 1.31 - 09 1.85 - 10 5.20 - 04

2. 93 - 03 1.25 - 02 9.23 - 02 3.31 + 00

.5.20+00 1.17 - 03 1.31 - 03 3.33 rem 5.50 rem 2.64 - 02 1.35 - 02 2.28 - 14 3.86 - 15 5.38 - 03 3.13 - 03 2.74 - 35 5.61 - 36 9.96 - 06 2.98 - 06 3.18 - 02 rem 1.66 - 02 rem 8.88 rem 1.08 + 02

. 5.54 *- 13 3.53 + 00 2.84.- 34 8.82 - 04 111.5 rem

. 3.61 + 01

1. 85 - 13 1.18 + 00 9.47 - 35 2.95 - 04 37.28 rem 148.8 rem
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-. Case 4 It is assumed that the worst case purge isolation exists (i.e., Case 2) and the filters have zero percent efficiency or the exhaust duct down stream of the isolation valves fails and the purge rate remains constant. The releases

.would be Case 2 modified by:

.The contribution by Kr and Xe would remain unchanged with *a whole body 'f"

. of*9.63 - 01 rem and a4 l.~9 + 00 rem. The Iodine contribution to whole body would be:

9.18 - 03 rem T

= 3.06 - 02 r2m 0.3 4.82 - 03 rem 0.3

= 1.61 - *02 rem ~

Totals 1 = 9.936 - 01 Total Thyroid Dose

,d = 1.61 43.12 rem= 143.7 rem 0.3 Whole body= 2.60 rem

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Conclusion Case 1 (Manipulator Crane monitor triggers isolation)

  • Case 2 (Containment gas or containment particulate triggers isolation)

Case 3 (No containment isolation but 70% filter)

Case 4

  • (Worst case containment isolation and 0% filter) 10CFRlOO Guidelines e

Dose at Site Boundary Rem Whole Body 0

2.,56 B.BB 2.60 25 Thyroid 0

43.12 148.8 300 I

RECEf \\!ED DOCUHFNT PROC[S:SIHG U/./fr' 19{( M/t.R 25 PM 2 46 e

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