ML20137G793

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Ro:On 711022,during Startup of Reactor,Period Limiting Signal Unavailable for Servo Sys Which Continued to Raise Rod Causing Rapid Rise of Power.While Reactor Manually Scrammed,Reactor Period Less than Min Allowed in Tech Specs
ML20137G793
Person / Time
Site: Dow Chemical Company, 05000000
Issue date: 11/22/1971
From: Boer F
DOW CHEMICAL CO.
To:
US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20136D183 List: ... further results
References
FOIA-85-256, FOIA-85-258, FOIA-85-259, FOIA-85-261 5176, NUDOCS 8508270386
Download: ML20137G793 (2)
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THE DOW CHEMICAL CO M PANY MIDLAND. MICHIG AN 45640 November 22, 1971 9 '

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U. S. Atomic Energy Commission Division of Reactor Licensing '

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We would like to describe an experience related to the opera-tion of our Dow Triga Reactor '(Docket 50-264, License R-108) which occurred on October 22, 1971.

This occurred during startup of the reactor af ter all safety and control channels had been checked and calibrated. The operator removed the safety rod and part of the shim and regulating rods as during normal startup. While the reactor was still. subcritical and with the linear channel indicating 0.05 watt, and while the log channel was not yet in its operating range, the operator s)vitched to the automatic mode.

The demand had been set to 95% of the range of 0.03 watts, so that the transfer to the automatic mode caused immediate with-drawal of the regulating rod by the servo system. Since the. .

log channel was not yet in its operating range no period limit-ing signal was available for the servo system which continued to raise rod and caused a rapid rise of the power as indicated by the linear channel. When the operator realized that there was no period indication and the power increased at an unusu-ally rapid rate he manually scrammed the reactor,at the 0.2 watt level. It appears from the record tha t. during this short time interval the' reactor period might have been less than the 7 sec. minimum period set point for the log N channel given in Table I of the Technical Specifications. Thus, at low power levels the safety circuit associated with the log N channel may not be effective in limiting the reactor period.

No safety problem was involved in this occurrence, since Triga reactors with our fuel have been licensed for pulsing and operate without period limita tions. Two automatic scram cir-cuits were available to terminate the run, the first, if the power had reached 0.33 watts and the second if the power had risen beyond 110 kw. Moreover, there exists a high likelihood that neither scram would have been required since the flux controller would have rapidly reinserted the regulating rod when the power had exceeded the demand set point, so that the power would have levelled out at 95% of the 0.3 watt range without reaching the 0.33 watt scram level.

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U. S. Atomic Energy Commission November 22,-1971 Page 2

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The Reactor Operations Committee has reviewed the startup procedures and specified that startup of the reactor must be done in thepower the desired manual mode level until the has been reactor is critical and reached. Only then may the operation be transferred to the automatic mode. A notice to this effect is now posted on the mode switch of the console.

Very truly yours U W F. Peter Boer Chairma n , Reactor Operations Committee 1602 Building mb 4

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THE DOW CHEMICAL COM ANY u.auana, unemenu <.. a December 30, 197]

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Mr. Donald J. Skovholt Assistant Director for

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?.4 U. S. Atomic Energy Commission Washington, D. C. 20545 M;j~.qf ~

Dear Mr. Skovholt:

This letter is in response to your letter dated October 5, 1971, requesting detailed information concerning radio-activity effluents from our reactor. The Dow TRIGA Reactor, AEC license No. R-108, Docket No. 50264, has been in operation since July 6, 1967. It is used primarily for activation analysis studies.

The radioactivity released to unrectricted areas on an annual basis results from the disposal of spent activated samples and the release of argon-41 stemming from the air contained in the " sample" rack and the pneumatic sample transfer system.

Most of the activated samples contain only short-lived isotopes. In 1970 and 1971, a minimum hold-up time of seventeen days was maintained between the time of activation and the time of disposal. From this procedure less than 0.0006 curies were released to unrestricted areas ennually.

The production of argon-41 accounted for an additional release of less than 0.0004 curies to unrestricted areas annually.

It has been the practice during this period to incinerate the radioactive waste in Dow's main incinerator. This unit is operated at approximately 1100 C with an air flow of 50,000 cubic feet per minute. The effluent temperature is approximately 200 C, and the effluent stack height is 200 feet. The incinerator is equipped with a triple spray wash system. The effluent water goes to Dow's water waste treatment facility. The amount of water effluent from this treatment facility is approximately 50 million gallons per day.

We assume that the 0.0006 curies of activated samples, when burned, were all released in the gaseous effluent from the incinerator. For this case, the concentration at the TjoW d 4 y' ( b

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.a D.-J. Skovholt December 30, 1971 L

Several monitoring systems are used to determine radiation exposures to both staff and non-staff. In the reactor room itself, are located two area monitors. One is a Nuclear Measurement Corporation continuous air monitor and which through. pumps airpaper.

a filter into a chamber (~2 liter 1/4 Approximately, capacity) inch f rom the filter paper is a thin end window Geiger-Mueller tube, shielded by about 2 inches of lead. The background of this monitor, stemming from radon daughters, is 1.7 x 10-11 p C1/cc of air. The second area m6nitor is a G-M tube located 13 feet from the top of the reactor. It is connected to a ratemeter and is sensitive to approximately 0.1 mr/hr.

Located in the water tre.atment system of the reactor is another G-M tube monitor, which continuously monitors the pool water and has a sensitivity of approximately 0.01 Ci/ml of water. All water in contact with the reactor core is cleaned up by means of demineralizers and recycled.

The demineralizer bed is periodically changed, with the old one being first monitor.ed and then incinerated. Its release of isotopes is included in the above calculations.

In addition to these area monitors, several " laboratory monitors" (mica-window G-M tubes connected to ratemeters) are continuously operated within the labcratory building housing the reactor. One of these is operated in the hood to which is connected the exhaust from the pneumatic sample transfer system of tae reactor. The others are operated in adjacent laboratories. These monitors have a background of approximately 100 counts per minute. Many other portable, standard, health physics monitoring instruments are used in the building for routine surveys. These instruments are used for alpha, beta, gamma, and neutron l:

radiation measurements. Several multi-channel analyzers, liquid scintillation, and proportional counters are also used for evaluating gaseous, liquid, and solid samples.

'. The lower detection limit of these instruments are generally 1 x 10-7 C1.

, Film badges for beta, gamma, and neutron dose measurements -

are used to evaluate radiation exposures of individuals present in the facility. The film badges are supplied by R. S. Landauer, Jr. and Company and are sensitive to 10

. milli-rems of X- and gamma radiation, 40 milli-rems of hard beta, 20 milli-rems fast neutron, or 10 milli-rems thermal

, neutron. Pocket dosimeters are also used to evaluate radia-tion exposures, and are sensitive to approximately 2 mr of X- or gamma radiation.

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m D. J. Skovholt December 30, 1971 point of release to an unrestricted area (the top of the stack) would be approximately 8 x 10-13 Ci/cc of air averaged over 1 year. Incinerations have been carried out

, only during favorable weather conditions to provide for maximum dispersion. -

If we assume, on the other hand, that all the activity were washed down and released in the water effluent from the plant, the averaged concentration would have been 9 x 10-12 Ci/cc of water at the point of discharge.

The isotopes released in this manner consisted of the following:

Isotope Amount (C1)

Br - 82 <0.000010 Na - 24 <0.000001 Cr - 51 <0.000025 Fe - 59 <0.000070 Sb -124 <0.000060 P - 32 <0.000250 Sc - 46 <0.000050 Zn - 65 <0.000005 Co - 66 <0.000003 Hg -203 <0.000010 Ag -110m <0.000020 Ba -131 <0.000005 Cd -115 <0.000025 S - 35 <0.000010 Se - 75 <0.000010 Ni - 63 <0.000001 Total Mixed <0.000555 The argon-41 is released through a vent to the outside l of the reactor building. The air flow through this vent

( is 1000 cfm. The concentration of the argon-41 at the j point of release is then less than 3 x 10-11 Ci/cc of l . air.

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  • The direct radiation levels to the unrestricted area from this facility is undetectable (less than 0.01 mr/hr and less than 10 milli-rem / month). The direct radiation level

'from the facility effluents is also undetectable f<1 x 10 -

C1/cc of air of long lived isotopes, < 2 x 10-11 Ci/cc of air of short lived isotopes, and < 1 x 10-* p Ci/ml of water for all isotopes).

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D. J. Skovholt December 30, 1971 In addition, air samples are taken on top of nearby buildings on filters which are counted by gamma spectro-

, scopy and by beta spectroscopy.

There are ten sampling locations in the reactor room, the building housing the reactor, and adjacent buildings.

The personnel film badges, changed once per month, have indicated that personnel are exposed to less than 100 milli-rem per year of X , gamma, or beta radiation at our facility, and to less than detectable amounts of neutron radiation. Area film badges have indicated less than detectable amounts of all radiation. .

. Air samples in the reactor room have indicated that airborne concentrations of radioactivity $o be at the background level of the monitor (1.7 x 10-11 p Ci/cc of air) except during periods immediately following atmospheric testing of nuclear weapons. This has been confirmed by gamma spectroscopy and other routine measurements around the reactor.

Air samples taken daily on nearby buildings indicated no releaseofactivitydirectlyattributab{gtotheoperation of the reactor. Some activity (1 x 10- p Ci/cc) of long g lived isotopes, mainly radium,, thorium, and their decay

products, with some fission products following atmospheric

! testing of nuclear devices were, however, identified in >

! these samples.

l We hope that the above information will suffice your need.

I In case additional discussion of any of the above items appears desirable, please do not hesitate to contact us again.

Very truly yours, LuNfdlfu hairman HErold Hoyle, l Radiation Safety Committee 1701 Building HRH:dda 4

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