Mobile unit and its role in the case of nuclear emergencies

Zdenko FRANIĆ

Institute for Medical Research and Occupational Health

Ksaverska cesta 2, PO Box 291, HR-10001 Zagreb, Croatia

E-mail: franic@imi.hr

Abstract

Emergency response mobile units play a significant role in the case of nuclear emergencies. The functioning and practice of such teams depend on the nature and phase of the nuclear emergency. In the acute phase, several teams with good navigational and communication abilities performing simple measurements can provide essential data for characterization of plume location and its magnitude. Therefore, such activities are complemental with the network of telemetric radiation monitors. However, in the late phase of an accident, in order to gather reliable data needed for utilization of remedial and recovery measures, a better equipped mobile units are necessary.

Introduction

Although the overall nuclear industry has an excellent safety record, Chernobyl demonstrated that accidents can and do happen. During and after a nuclear accident, accurate data and effective communications are essential to enable authorities to take prompt measures and to provide reliable information to the public at large. Such measures can address the consequences of a nuclear accident, save lives, and protect the environment. The Republic of Croatia is in a unique situation in that it has several power plants in two neighbouring states not far from its border. Although it is recognized that the probability of major a nuclear accident which could affect Croatia is small, according to common international practice Croatia has to set up a proper emergency organization. A significant role in the emergency infrastructure plays mobile teams.

Potential sources of nuclear emergencies

Although NPP Krško is generally identified as a major potential source of nuclear emergency situations in the Republic of Croatia, several more sources should be considered /Asculai 1993/.

These include:

a)	Paks NP station in Hungary, housing three VVER-440 nuclear power plants, some 40-50 km from the Croatian border,

b)	Transport accidents, involving sealed and unsealed sources being transported by air and overland,

c)	Accidents involving damaged or lost radiation sources, including lightening rods and

d)	Crash down of a nuclear satellite

Although above scenarios vary from relatively simple to very complex situations, mobile units are sometimes the only way to gather reliable data.

Acute Phase of Nuclear Accident

In the acute phase of a nuclear accident information provided by emergency response mobile units are essential for dose estimates needed for the application of protective measures. However, the measurements performed by such teams should include only the vital ones for characterization of plume location and its magnitude. It should be noted that such activities are complemental with the network of telemetric radiation monitors currently being established in the Republic of Croatia /Lulić 1997 and Lulić 1998/. Even in the countries that are excellently covered with fixed telemetric monitoring stations mobile units capable of transferring in real time external dose-rate data together with corresponding locality data are useful for mapping radiation levels in locations not covered by fixed monitoring network /Toivonen 1998/. An additional requirement on field measurements performed by the mobile units is that they should consume as little time as possible in order to cover maximal number of locations in a given time while samples should be taken only when there is enough time. Therefore, the number of mobile monitoring teams should be optimized from geographical time/motion studies. Good navigation abilities of the mobile teams and rapid reporting through good communications systems are essential. A typical mobile team should consist of a personal car manned by two persons. Crews can consist of previously well trained technicians from specialized institutions, fire brigades or civil defense units. Equipment should include, in accordance with international practice /Widner 1990/, dose meters, satellite-based navigation system (global positioning system - GPS), communication equipment as well as protective equipment. The crude accuracy of GPS system of approximately 100 m that is available for all users is satisfying for emergency environmental monitoring. The good practice is the use of predetermined measurement locations /IAEA 1981/. The same locations can also be used for TLD monitors as a part of the emergency TLD network. In the case of an accident, one of the functions of the mobile teams should be to collect exposed TLDs and replace them by the new ones. Readings from those monitors provide further valuable information on a cumulative dose from the very beginning of accident. Surveys with open-window vs. a closed window with the dose-rate meters could provide the immediate information about the plume location. If the open- window reading is higher than the closed window reading, the conclusion is that the team is in the plume. If the readings are the same, the team is not in the plume, i.e. the plume is above them or they are significantly off the plume centerline. Dose-rate measurements with open vs. a closed window near the ground and on 1m above ground (waist) would provide even further information (Figure 1). Such data can be used (by the technique of "backward" calculations) for "calibration" of simple plume-dispersion models. Such models like RASCAL /Sjoreen 1995/ are readily available. A source term can be estimated from available data or could be assumed to be 0.1% - 1% of the core inventory. By utilization of such data through a communication channel with the Technical support center (TSC) mobile teams could be navigated in order to efficiently locate the plume boundaries.

Late Phase of Nuclear Accident

In the late phase of a nuclear accident, when the plume has passed, in order to gather reliable data needed for utilization of remedial and recovery measures, a better equipped mobile unit is necessary. Contrary to the acute phase of the nuclear accident, in-situ gamma-spectrometry should play a significant role in the late phase. A functioning and practice of the mobile unit in the Institute for Medical Research and Occupational Health have been described previously /Franić 1991/. However, it should be revised and improved according to the future emergency plans. In addition, due to Croatian geographical shape, it would be wise to have more than one such unit. The equipment should include four-wheel-drive van, radiological monitors, air samplers, in-situ gamma- spectrometry system with PC notebook, navigation and communication equipment and various appliances and laboratory equipment. It should be noted that such units could be utilized not only in nuclear but also in radiological emergencies. A good example of such multitasking unit is Slovenian Ecological Laboratory with Mobile Unit (ELMU) /Glavič-Cindro 1995/.

Training and drills

Like each individual serving in any capacity in the emergency organization, mobile unit team members should have basic training. This training should consist of "general knowledge" training and training specific to the role that the individual plays during the emergency. Following the basic training for the members of specific teams, they shall be trained and exercised as a unit. Training and drills of monitoring teams according to the existing practice will continue to be carried out on a regular basis. The drills should be carried out as a part of a regular monitoring programme and emergency preparedness in the country and be arranged at least two times per year. They should be used to test the adequacy of the emergency response plan, procedures and equipment in field conditions and communications. Critiques are valuable as a means of improving plans, procedures and coordinated work.

Standby

The final stage in the training and exercise of the mobile unit teams as a part of the emergency system, is some sort of the certification and after that going on the permanent standby status. The standby condition of team members should be organized in such a manner to allow immediate mobilization of teams and facilities. This could easily be accomplished through pager system. For the team members is essential the familiarity with instruments, i.e. the use of instruments on day-to- day basis even during standby conditions.

Problems

The problem areas identified so far, by evaluating the practice of a mobile unit in the Institute for Medical Research and Occupational Health are similar with ones that are encountered by similar units in other countries. The extensive list given by Widner /1990/ include:

1. Communications

2. Vehicles

3. Familiarity with area and monitoring locations

4. Inexperience with instruments used

5. How to tackle air samples

6. Getting teams out in a timely manner

7. "Overproceduralization"

8. Definition of functions and expectations of teams

9. Accurate determination of team position

10. Contamination control

11. Labelling samples

12. "Giving the right people the right jobs"

13. Improper environmental sampling techniques

Conclusions

Mobile units are the useful tool in emergency preparedness to produce reliable and accurate measurements immediately after the nuclear accident. Considerable number of problems seem to be universal in the field of mobile emergency monitoring units. Therefore, some solutions might be studied from the existing practice and functioning of other teams. However, some problems appear be unique for Croatia, with no ready "textbook" solutions. To establish and maintain mobile units for the acute and the late phase of a nuclear accident, as a part of efficient emergency response system, a considerable effort is yet to be done. Prior to that, some strategic decisions should be taken, including the organization matters as well as financing.

Legend

BKG	Background radiation

GO	Ground, shield open

GC	Ground, shield closed

WO	Waist, shield open

WC	Waist, shield closed

In Plume

WO > WC > BKG

Readings

GO:	+

GC:

WO:	+

WC:

Under Plume

GO = WO > BKG

Readings

GO:

GC:

WO:

WC:

Plume has passed

GO > WO > BKG

Readings

GO:	+

GC:

WO:

WC:

Literature

Asculai E.

End of Mission Report

(Emergency Planning and Preparedness - CRO/9/002-04)

IAEA, Department of Technical Co-operation,

RU-NUMBER 4827, IAEA, Vienna, 1994.

Franić Z., Ambrošić D. i Bauman A.

Terenska ekipa za mjeridbu radioaktivnosti u slučaju nuklearne nesreće

Sigurnost 1992;34:151-7.

Glavič-Cindro D.

Ecological Laboratory with a Mobile Unit - ELMU,

1995 October 17

<http://rubin.ijs.si/elme/elmu.html>

(URL checked 1998 March 25)

International Atomic Energy Agency

Planning for Off-Site Response to Radiation Accident in Nuclear Facilities, Safety Series No. 55, IAEA, Vienna, 1981.

Lulić S.

Monitoring sustav. Informativni seminar o zaštiti u slučaju nuklearne nesreće. Ministarsvo gospodarstva, Odjel za nuklearnu sigurnost, Zagreb 1998.

Lulić S.

Prirodna doza zračenja na Puntijarki

1997 April 24

<http://www.tel.hr/dhmz/pgr.html>

(URL checked 1998 March 26)

Sjoreen A.L.

Radiological Accident Modelling for Emergency Response

1995 July 5

<http://www.cad.ornl.gov/cad_cp/text/als.html>

(URL checked 1998 March 26)

Toivonen H., Ilander T., Honkamaa T. and Lahtinen J.

Mobile dose-rate measuring & data transfer in nuclear accidents

Nuclear Europe Worldscan, 1998;3-4:48.

Widner T.E.

Power Reactor Emergency Response Field Monitoring Practices in the United States

Health Physics, 1990;58:753-8.